Effects of the Ketogenic Diet in the Treatment of Gliomas: A Systematic Review

Abstract

The ketogenic diet (KD) is a restrictive therapeutic diet, distinguished by being hyperlipidic, normoproteic, and hypoglucidic. This diet simulates biochemical changes related to fasting periods to achieve systemic ketosis. The metabolic particularities of glioma tumors motivated the rise in investigations and nutritional strategies, such as KD, to modulate the glycemic response as a treatment. This systematic review followed the PRISMA recommendations and was published in PROSPERO, with the identification CRD42021264173. The databases used were EMBASE, PubMed/Medline, Scopus, and Web of Science, and the studies were analyzed using the web-based application Rayyan. To analyze the risk of bias, Cochrane RevMan 5 software was used. For the analysis and treatment of statistical data, Microsoft® Excel® was used. A total of nine original articles were included. Data on survival, symptomology, and quality of life were collected. Mean overall survival was 15.9 months. Constipation and fatigue were the most reported symptoms. In 44.4% of the studies, an improvement in the quality of life was found. The KD is supported by most published studies as an effective therapy in the treatment of malignant gliomas due to its positive effects on patient survival. It was not possible to conclude the effectiveness of KD on quality of life.

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Citation: Sargaço, B.; Oliveira, P.A.;
Antunes, M.L.; Moreira, A.C. Effects
of the Ketogenic Diet in the
Treatment of Gliomas: A Systematic
Review. Nutrients 2022,14, 1007.
https://doi.org/10.3390/
nu14051007
Academic Editor: Keisuke Hagihara
Received: 9 February 2022
Accepted: 25 February 2022
Published: 27 February 2022
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nutrients
Systematic Review
Effects of the Ketogenic Diet in the Treatment of Gliomas:
A Systematic Review
Beatriz Sargaço 1, 2, * , Patrícia Almeida Oliveira 2, Maria Luz Antunes 2,3 and Ana Catarina Moreira 2,4
1Faculdade de Medicina, Universidade de Lisboa, 1649-028 Lisboa, Portugal
2ESTeSL-Escola Superior de Tecnologia da Saúde de Lisboa, Instituto Politécnico de Lisboa,
1990-096 Lisboa, Portugal; patricia.aao@gmail.com (P.A.O.); mluz.antunes@estesl.ipl.pt (M.L.A.);
ana.moreira@estesl.ipl.pt (A.C.M.)
3APPsyCI–Applied Psychology Research Center Capabilities & Inclusion, ISPA–Instituto Universitário,
1149-041 Lisboa, Portugal
4H&TRC-Health & Technology Research Center, 1990-096 Lisboa, Portugal
*Correspondence: beatrizsargaconutri@gmail.com
Abstract:
The ketogenic diet (KD) is a restrictive therapeutic diet, distinguished by being hyperlipidic,
normoproteic, and hypoglucidic. This diet simulates biochemical changes related to fasting periods
to achieve systemic ketosis. The metabolic particularities of glioma tumors motivated the rise in
investigations and nutritional strategies, such as KD, to modulate the glycemic response as a treatment.
This systematic review followed the PRISMA recommendations and was published in PROSPERO,
with the identification CRD42021264173. The databases used were EMBASE, PubMed/Medline,
Scopus, and Web of Science, and the studies were analyzed using the web-based application Rayyan.
To analyze the risk of bias, Cochrane RevMan 5 software was used. For the analysis and treatment of
statistical data, Microsoft
®
Excel
®
was used. A total of nine original articles were included. Data on
survival, symptomology, and quality of life were collected. Mean overall survival was 15.9 months.
Constipation and fatigue were the most reported symptoms. In 44.4% of the studies, an improvement
in the quality of life was found. The KD is supported by most published studies as an effective
therapy in the treatment of malignant gliomas due to its positive effects on patient survival. It was
not possible to conclude the effectiveness of KD on quality of life.
Keywords: ketogenic diet; glioma; glioblastoma; survival
1. Introduction
The ketogenic diet (KD) is a restrictive therapeutic diet distinguished by being high-fat,
normoproteic, and hypoglucidic, and is considered a non-pharmacological therapeutic
method [
1
–
3
]. There are various types of KD according to the proportion of macronutrients.
The four major types of KD are the Classic Ketogenic Diet (CKD), the Ketogenic Diet
with Medium-Chain Triglycerides (MCT), the Modified Atkins Diet (MAD), and the Low
Glycemic Index Diet (LGID). The classical type is classified by a ratio of 3:1 to 4:1, that is, 3
to 4 grams of lipids for every 1 gram of carbohydrate and protein [
4
,
5
]. The utilization of
MCT as an energy source is due to the greater production of ketone bodies compared to
long-chain fatty acids.
Generally, the KD provides a high amount of lipids (60–90% of total energy value
(TEV)), a low carbohydrate content (4–19% TEV), and is adequate in protein, minerals, and
vitamins [6,7].
All of these diets have lipid restrictions, but in the CKD, the restriction is more severe.
Metabolically, carbohydrates break down into glucose. However, in the absence of this
energy source, the liver converts fat reserves into fatty acids and ketone bodies, allowing
the utilization of these as alternative sources of energy. Ketone bodies, such as acetone,
Nutrients 2022,14, 1007. https://doi.org/10.3390/nu14051007 https://www.mdpi.com/journal/nutrients

Nutrients 2022,14, 1007 2 of 17
acetoacetate, and ß-hydroxybutyrate, overcome the blood–brain barrier and replace glucose
usage [1,8,9].
KD simulates fasting periods by increasing ketones and lowering blood glucose, which
leads to increased oxidation of fatty acids and production of acetyl-CoA [10,11].
When acetyl-CoA production exceeds the capacity that can be used on the tricarboxylic acid
cycle, there is an increase in the production of ketone bodies, particularly
β
-hydroxybutyrate
and acetoacetate, that will be used as energy sources in the brain [1,8,11,12].
Gliomas are primary, heterogeneous, invasive, and aggressive malignancies, which
encompass most central nervous system tumors [
1
,
5
,
13
]. They originate from glial cells or
stem cells, and after neoplastic transformation, acquire glial cell characteristics [14].
The survival prognosis for patients with malignant gliomas is around 12 to 15 months,
with a survival rate of 5 years below 5% [
13
,
15
–
17
]. Thus, it is of high importance to develop
new therapeutic strategies for these patients, especially those that can improve quality of
life and/or survival [18,19].
The most frequent types of gliomas are glioblastomas, around 60–70% of all diagnosed
cases, followed by anaplastic astrocytomas with 10–15% of cases and, finally, anaplastic
oligodendrogliomas and anaplastic oligoastrocytomas with 10% of cases. The remainder
includes gliomas such as anaplastic ependymomas and anaplastic gangliogliomas [20,21].
The metabolic particularities of cancer have motivated increased research on nutri-
tional strategies to modulate the glycemic response during treatment. These nutritional
strategies include the use of diets with high lipidic content and low carbohydrate content
(such as KD), energy-restricted diets, or intermittent fasting [
22
]. The purpose of these diets
is to induce a state of systemic ketosis to compensate for the decrease in glucose, originated
from the lack of substrate [19].
In tumors, there are changes in the metabolism of cancer cells. These changes can be
explained by the "Warburg effect", also known as aerobic glycolysis [
18
]. Otto Warburg,
in 1924, observed that tumors had a metabolic phenotype with high rates of aerobic
glycolysis [3].
Tumor cells depend on mitochondrial oxidative phosphorylation to generate adenosine
triphosphate (ATP). Thus, when exposed to hypoxia, they switch to the less favorable
anaerobic pathway of glycolysis. However, there are cancer cells that survive and proliferate
generating ATP via glycolysis instead of oxidative phosphorylation, even in the presence
of oxygen [1,8,15,18].
Cancer cells differ from other cells in their inability to use ketones as metabolic fuel.
Tumor cells are very glucose-dependent for their growth and survival, while the remaining
cells have the flexibility to alter their energy source from glucose to ketone bodies. With
KD, tumor cells would no longer have an energy source for their growth [1,8,15,18].
By reducing glucose availability and providing ketone bodies as an alternative energy
source, KD can offer a therapeutic approach directing the Warburg effect on glycolytic
tumors such as malignant gliomas. Nutritional strategies aimed at glycemic modula-
tion to explore tumor cells’ dependence on glucose have not yet been fully studied and
investigated, so the existing clinical data are limited [19,22].
There have been several studies with the inclusion of this type of diet in the therapeutic
intervention of diagnosed gliomas. Although systematic reviews addressing the impact
of KD on the survival of patients with gliomas have been published in the past, this
area of research has been intensively studied further, with some relevant original studies
published since the latest review. The systematic analysis of the effect of this nutritional
intervention covering the different types of diets, side effects, and quality of life is not yet
well established. KD implementation raises the risk of many side effects, so it is essential to
analyze this strand and all relevant studies published to date in a systematic review.
2. Materials and Methods
This systematic review followed the recommendations of PRISMA (Preferred Report-
ing Items for Systematic Reviews and Metanalyses), which is intended for systematic

Nutrients 2022,14, 1007 3 of 17
reviews and meta-analyses of clinical intervention studies [
23
]. This systematic review was
published on the platform PROSPERO, the International Prospective Register of Systematic
Reviews [24], on 17 July 2021 with the registration number CRD42021264173.
The used databases were EMBASE, PubMed/Medline, Scopus, and Web of Science,
with the following keyword strategies:
•
[(glioma) OR (glial cell tumor) OR (mixed glioma) OR (malignant glioma) OR (glioblas-
toma) OR (astrocytoma, grade IV) OR (glioblastoma multiforme) OR (giant cell
glioblastoma) OR (high-grade glioma) OR (neoplastic stem cell) OR (cancer stem
cells) OR (Warburg effect, oncologic) OR (astrocytoma) OR (brain tumor) OR (brain
neoplasms) OR (glial cell) OR (glial precursors) OR (astrocytic tumor) OR (oligoastro-
cytic tumor) OR (neuro-glial tumor)] AND [(ketogenic diet) OR (low carbohydrate
diet) OR (glucose) OR (glycolysis) OR (ketone bodies) OR (low carbohydrate) OR (diet
therapy) OR (ketosis) OR (caloric restriction) OR (therapeutic ketosis) OR (low carb
diet) OR (metabolic therapy) OR (adjuvant therapy) OR (energetic restriction) OR
(energy restriction) OR (high-fat diet) OR (low carbohydrate high-fat diet) OR (keto-
induction) OR (ketotherapy) OR (glucose restriction) OR (carbohydrate-restriction)
OR (low carb) OR (hyper lipidic diet) OR (high-fat diet) OR (dietary intervention)].
The research included original articles published between January 2005 and May 2021
that included KD as a therapeutic intervention for the treatment of gliomas. After remov-
ing duplicate papers, the article selection was carried out according to titles, abstracts,
and full texts. Case-control studies, retrospective and prospective cohort studies, and
randomized clinical trials were included. The web-based application Rayyan, a software
for systematic reviews and meta-analyses to facilitate initial screening through titles and
abstracts, was used to analyze the identified studies [
25
]. This analysis for the identification
of relevant publications was practiced by two reviewers who examined the articles inde-
pendently for their inclusion, not knowing each other’s decisions. All divergences were
resolved by consensus, and the divergences that did not reach consensus were resolved by
a third reviewer.
For the analysis of the risk of bias, software designed for the development of systematic
reviews and meta-analyses, Cochrane RevMan 5, was used. All the studies obtained were
evaluated in depth by two reviewers regarding the risk of various biases to evaluate the
quality of evidence. The risk of bias was classified as high risk, low risk, uncertain, or
unapplicable risk [26].
Information was collected on the type of study (controlled or uncontrolled), the
study design (prospective or retrospective), number of patients, age of patients, type of
investigated glioma, stage of the disease, type of interventions performed, follow-up time,
and type and duration of KD.
An initial survey was carried out on 24 April 2021 and repeated on 7 June 2021 to
verify that all recent studies were covered, including the latest ones.
Microsoft
®
Excel
®
for Mac, version 16.41 (Microsoft Company), was used for the
analysis and processing of statistical data.
2.1. Inclusion and Exclusion Criteria
For this systematic review, inclusion criteria were considered:
•Original studies, published between 1 January 2005 and 30 May 2021;
•Clinical studies;
•Studies evaluating patients with malignant gliomas;
•Studies using the KD as an intervention/treatment for malignant gliomas;
•Studies published in English or Portuguese;
•Studies including patients of all ages, genders, and ethnicities in any country.
For the exclusion criteria, we considered:
•
Articles such as comments, letters to the editor, reviews, conference editorials, opinion
articles, or case reports;

Nutrients 2022,14, 1007 4 of 17
•
Articles associating KD with non-conventional therapies (e.g., intermittent fasting or
perillyl alcohol);
•Studies that did not include results;
•Animal studies.
3. Results
The procedure for the study selection in this systematic review is presented in Figure 1.
Nutrients 2022, 13, x FOR PEER REVIEW 4 of 17
• Original studies, published between 1 January 2005 and 30 May 2021;
• Clinical studies;
• Studies evaluating patients with malignant gliomas;
• Studies using the KD as an intervention/treatment for malignant gliomas;
• Studies published in English or Portuguese;
• Studies including patients of all ages, genders, and ethnicities in any country.
For the exclusion criteria, we considered:
• Articles such as comments, letters to the editor, reviews, conference editorials,
opinion articles, or case reports;
• Articles associating KD with non-conventional therapies (e.g., intermittent fast-
ing or perillyl alcohol);
• Studies that did not include results;
• Animal studies.
3. Results
The procedure for the study selection in this systematic review is presented in Figure
1.
Figure 1. PRISMA flow chart—study selection procedure.
Figure 1. PRISMA flow chart—study selection procedure.
The bibliographic research in PubMed/Medline, Scopus, and Web of Science databases
resulted in 6071 results. This research was supplemented by research in previously pub-
lished systematic reviews, which identified two additional studies. After excluding non-
relevant studies, a total of nine original articles were included.
The analysis of the included studies regarding the type of study, study design, number
of patients, age of patients, type of investigated glioma, stage of the disease, type of
interventions performed, follow-up time, and type and duration of the KD is presented in
Table 1.
Table 2presents the detailed data regarding patient survival, symptoms, and quality
of life.

Nutrients 2022,14, 1007 5 of 17
3.1. General Characteristics of Studies
The studies included in this review were published between 2014 and 2021, and more
recent data were included in this systematic review in comparison with previous reviews.
Of the nine included studies, six (66.7%) were prospective studies and two (22.2%)
had a control group. In most studies, it was found that the number of included patients
was low, with an average of 8.3 (3 to 17) patients per study.
The age of patients included in the studies ranged from 5.3 years old to 72 years
old. Two studies were conducted in children between 2.5 and 15 years old, and 5.3 and
15.5 year
s old. The remaining studies were performed on adults aged between 45 and
72 year
s old. The overall mean age of patients with gliomas included in the analyzed
studies was 42.1 years old, with a standard deviation of 19.9 years old.
The time of dietary intervention ranged from three weeks to 26 months. The follow-up
period ranged from 12 weeks to 26 months.
3.2. Characteristics of Gliomas
Concerning the type of investigated glioma, the studies observed elevated stage
gliomas such as glioblastomas in 66.7% of the studies, astrocytomas in 22.2% of the studies,
intrinsic pontine gliomas in 22.2% of the studies, and glioblastomas multiforme in 11.1%
of the studies. Grade II (22.2%) and grade III (33.3%) gliomas were included, and patients
with grade IV glioma were present in all studies.
Regarding the treatment of gliomas, in these studies, all patients underwent joint
radiotherapy with temozolomide. However, these were not the only interventions applied.
Drugs such as temozolomide, gemcitabine, prednisolone, bevacizumab, and lomustine
were applied individually in four different studies (33.3%): temozolomide in the studies
by van der Louw et al., 2019b [
15
] and Perez et al. [
27
]; bevacizumab and lomustine in
the study by Rieger et al. [
8
]; lomustine in the study by Martin-McGill et al., 2018 [
17
];
and gemcitabine and prednisolone in the study by van der Louw 2019a [
10
]. In one study,
patients received chemotherapy and concomitant radiotherapy as therapeutic interventions
since the initial treatment with radiotherapy had no effect [28].
3.3. Features of the Implemented Diet
In the analyzed studies, we verified the implementation of different types of KD.
In the study by Rieger et al., KD restricted carbohydrate intake to 60 g per day,
including intake of 500 mL of highly fermented yogurt drinks and two vegetable oils. No
energy restriction was applied [8].
Martin-McGill et al., 2018 applied a Modified Ketogenic Diet (MKD) comprising 70%
dietary lipids, while carbohydrates were limited to 20 g per day, corresponding to 3–5% of
TEV. The protein content had no restriction [17].
In the study by van der Louw et al., 2019b, KD included two phases. During the initial
eight weeks, associated with radiotherapy and temozolomide, KD was exclusively liquid
with a ratio of 4:1. Over the next six weeks, KD transitioned to solid foods at a ratio of
1.5–2.0:1, with MCT [15].
Champ et al. restricted carbohydrate intake to <50 g per day, corresponding to 8% of
TEV. Lipids accounted for 77% of the energy value and proteins 15% [16].
In the study by van der Louw et al. 2019a, patients started KD with a commercial
liquid enteral formula at a ratio of 4:1 for a maximum of two weeks. When ketone levels
reached 3 mmol/L, the KD was changed to a ratio of 1.5:1–2.0:11. During the study, MCTs
were administered with KD [10].
In the study by Klein et al., the authors applied a KD in a ratio of 4:1 in two different
groups. In group 1 included patients with recent glioblastoma; in group 2, patients with
recurrent glioblastoma were included. The diet included 1600 kcal per day, with a total of
10 g of carbohydrates [29].

Nutrients 2022,14, 1007 6 of 17
Perez et al. grouped patients undergoing various types of KD, including KD with
MCT, CKD, and MAD. However, this study did not specify the proportions or amounts of
macronutrients applied [27].
Martin-McGill et al. 2020 divided patients into two groups with the aim of imple-
menting two different KDs: group 1 corresponded to a KD with MCT, and group 2 to an
MKD. However, as in the study by Perez et al., no proportion or amount of administered
macronutrients were reported [30].
In the study by Panhans et al., a 3:1 ratio KD was applied. The intake of carbohydrates
was limited to ≤20 g per day [28].
Although the analyzed studies implement different types of KD, we can verify that
the studies by Martin-McGill et al., 2018, Klein et al., and Panhans et al. applied more
restrictive diets, having a maximum carbohydrate intake of 20 g per day. On the other
hand, the studies by Rieger et al. and Champ et al. implemented more liberal KDs with
daily carbohydrate intakes of ≤60 g and 50 g, respectively.
3.4. Overall Patient Survival
Patient survival varied from study to study. The study by Martin-McGill 2018 et al.
made no reference to patient survival.
The mean of maximum overall survival was 25.4 months in the study by Klein et al.,
while the lower overall survival corresponded to the study by Rieger et al., with a median
of 32 weeks (≈8 months) of survival [8,29].
Rieger et al. implemented KD for 16 weeks, where ketosis was reached and kept
stable in most patients. There was stabilization of the disease at six weeks of diet, with
this stabilization being balanced in an average duration of 12 weeks. The median overall
survival after starting the diet was 32 weeks (
≈
8 months), ranging between 6 weeks
(≈1.5 months) and 86 weeks (≈21.5 months) [8].
Overall survival in the study by Champ et al. had an average of 14 months, and the
recurrence of the disease was, on average, 10.3 months. KD was implemented throughout
the follow-up period (14 months) [16].
In the study by van der Louw et al. 2019a, the KD implementation lasted three months.
In this study, diffuse intrinsic pontine gliomas that have a median overall survival of 9 to
11 months were evaluated [
10
]. The overall survival times observed in this study were 6.4,
16.5, and 18.7 months for each of the participants. The 6.4-month survival was explained
by a severe decrease in consciousness after a generalized tonic–clonic crisis in one of the
patients, who had only completed three weeks of the dietary intervention. Survival after
starting nutritional therapy was 6.5 months for the remaining cases [10].
In the study by van der Louw et al. 2019b, overall survival averaged 12.8 months,
with two patients achieving survival times of 17.7 and 19 months. Ketogenic therapy was
performed for 14 weeks, and patients reached ketosis after an average of 4.5 days [15].
The study by Klein et al. was divided into two groups. Both groups received KD as
therapy, with group 1 including patients with recent glioblastoma and group 2 including
patients with recurrent glioblastoma. KD was implemented for six months. The mean
survival from the onset of KD was 20 months for group 1 and 12.8 months for group 2.
However, in terms of overall survival, group 1 had an average of 21.8 months and group 2
had an average of 25.4 months [29].

Nutrients 2022,14, 1007 7 of 17
Table 1. Overview of studies regarding their design, subjects, type of investigated glioma, and therapeutic interventions.
Study Type of Study Study Design NAge of Patients Type of Glioma Disease Stage Interventions KD Duration Follow-up Time Type of KD
Rieger 2014 [8] Controlled Prospective 17 Med 57 years
(30–72) Glioblastoma Grade IV
RT +
Temozolomide;
Bevacizumab and
Lomustine
3 to 16 weeks 16 weeks
Max. 60 g carbs/day;
highly fermented yogurt
drinks (500 ml per day)
and two different
vegetable oils (base oil
and addition oil)
Champ 2014 [16] Not controlled Retrospective 6 Med 54 years
(34–62) Glioblastoma Grade III–IV RT +
Temozolomide 14 months 14 months KD ≤50 g carbs/day
Martin-McGill 2018 [17] Controlled Prospective 6 Med 46 years
(34–49)
Glioblastoma
Anaplastic
astrocytoma Grade II–IV RT +
Temozolomide;
Lomustine 12 weeks 12 weeks Max. 20 g carbs/day,
70% lipids
van der Louw 2019a [10] Not controlled Prospective 3 Med 11.6 years
(5.3–15.5)
Diffuse intrinsic
pontine glioma Grade IV
RT +
Temozolomide;
Gemcitabine;
Prednisolone;
Temozolomide
3 months 3 months Liquid KD: 4:1 (+MCT)
van der Louw 2019b [15] Not controlled Prospective 9 Med 53.8 years
(33.5–65.5) Glioblastoma Grade IV RT +
Temozolomide 14 weeks 14 weeks
Liquid KD 4:1 (8 weeks):
11 g carbs
solid KD + MCT 1.5-2:1
(6 weeks): 57 g carbs
Klein 2020 [29] Not controlled Prospective 5 Med 49.8 years
(40–64) Glioblastoma Grade IV RT +
Temozolomide 6 to 26 months 26 months KD 4:1; 10 g carbs/day
Martin-McGill 2020 [30] Controlled Prospective 12 Med 57 years
(44–66) Glioblastoma Grade IV RT +
Temozolomide
38 days to
12 months 12 months KD with
MCT/Modified KD
Panhans 2020 [28] Not controlled Retrospective 12 Med 45 years
(32–62)
Glioblastoma
multiforme,
astrocytoma, oligo-
dendroglioma
Grade II–IV Chemotherapy +
RT; RT; RT +
Temozolomide 120 days 120 days KD 3:1; ≤20 g carbs/day
Perez 2021 [27] Not controlled Retrospective 5 Med 4.4 years
(2.5–15)
Diffuse intrinsic
pontine glioma Grade IV
RT +
Temozolomide;
Chemotherapy
HIT-SKK;
Temozolomide
6.5 months (0.25 to
2 years) 2 years Classic KD/KD with
MCT/Modified
Atkins Diet
RT, radiotherapy; Med, median; MCT, medium-chain triglycerides; carbs, carbohydrates; N, number of patients; KD, ketogenic diet; Max., maximum; HIT-SKK, Therapieprotokoll für
Säuglinge und Kleinkinder mit Hirntumoren (Therapy protocol for infants and young children with brain tumors).

Nutrients 2022,14, 1007 8 of 17
Table 2. Overview of study results on survival, symptoms, and quality of life.
Study Patient Survival Symptomatology Associated with Dietary
Intervention Quality of Life
Rieger 2014 [8] Med 32 weeks (between 6 and 86 weeks). Weight loss, diarrhea, constipation, hunger Decreased quality of life
Champ 2014 [16] Med 14 months Constipation, asthenia, weight loss,
nephrolithiasis, hypoglycemia Not available
Martin-McGill 2018 [17] Not available Constipation Improved quality of life
van der Louw 2019a [10] Between 16.5 and 18.7 months Hypoglycemia, hyperketosis, vomiting,
refusal to eat, asthenia, constipation Decreased quality of life
van der Louw 2019b [15] Between 9.8 and 19.0 months (Med 12.8 months)
Constipation, nausea/vomiting,
hypercholesterolemia, hypoglycemia,
diarrhea, low carnitine concentration
Decreased quality of life
Klein 2020 [29]Group 1: ¯
x=21.9 months (between 11 and 29.2 months)
Group 2: ¯
x=25.4 months (between 13.9 and 38.7 months)
Weight loss, hunger, nausea, dizziness,
asthenia, constipation Improved quality of life
Martin-McGill 2020 [30] Med 67.3 weeks Hypokalemia, hypocalcemia, hypernatremia,
hyperkalemia, constipation Improved quality of life
Panhans 2020 [28] Between 9.8 and 19.0 months Asthenia, weight loss, nausea, vomiting,
headache, decreased appetite Improved quality of life
Perez 2021 [27] Med 18.7 months Hypoglycemia, constipation, hyperketosis,
vomiting, asthenia, hyperuricemia Not available
Med, median; ¯
x, mean.

Nutrients 2022,14, 1007 9 of 17
Martin-McGill et al., 2020 divided the patients into two groups, distinguishing the
implemented KDs. Group 1 corresponded to a KD with MCT and group 2 to an MKD. In
both groups, ketosis was reached within the first six weeks. Overall survival had a median
of 67.3 weeks (≈16.8 months) [30].
Panhans et al. applied KD for at least 120 days. Ketosis was achieved in most patients
within the first week of therapy. Overall survival ranged from 9.8 to 19 months [28].
The study by Perez et al. included patients who had implemented ketogenic therapy
for a period longer than three months. The estimated overall survival was 18.7 months.
There were also two patients who achieved survival times of 22 and 30 months [27].
The study by Martin-McGill et al., 2018 did not report patient survival [
17
,
31
]. How-
ever, the KD was implemented for 12 weeks, and three patients continued this therapy for
more than 360 days [17], which is a possible assumption regarding survival in this study.
3.5. Associated Symptomatology
The symptoms associated with KD intervention detailed in the studies included
75 patients and are shown in Figure 1.
In Figure 2, we can see that constipation was the most reported symptom in the
analyzed studies (88.9%). This was followed by asthenia, which was reported in 55.6% of
the studies.
Nutrients 2021, 13, x FOR PEER REVIEW 5 of 17
Nutrients 2022, 13, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/nutrients
Martin-McGill et al. 2020 divided the patients into two groups, distinguishing the
implemented KDs. Group 1 corresponded to a KD with MCT and group 2 to an MKD. In
both groups, ketosis was reached within the first six weeks. Overall survival had a median
of 67.3 weeks ( 16.8 months) [30].
Panhans et al. applied KD for at least 120 days. Ketosis was achieved in most patients
within the first week of therapy. Overall survival ranged from 9.8 to 19 months [28].
The study by Perez et al. included patients who had implemented ketogenic therapy
for a period longer than three months. The estimated overall survival was 18.7 months.
There were also two patients who achieved survival times of 22 and 30 months [27].
The study by Martin-McGill et al. 2018 did not report patient survival [17,31]. How-
ever, the KD was implemented for 12 weeks, and three patients continued this therapy for
more than 360 days [17], which is a possible assumption regarding survival in this study.
3.5. Associated Symptomatology
The symptoms associated with KD intervention detailed in the studies included 75
patients and are shown in Figure 1.
Figure 2. Symptomatology associated with KD therapy in glioma patients.
In Figure 2, we can see that constipation was the most reported symptom in the ana-
lyzed studies (88.9%). This was followed by asthenia, which was reported in 55.6% of the
studies.
In 44.4% of the studies, weight loss, vomiting, or hypoglycemia were reported as as-
sociated symptoms, whereas in 33.3% of the studies, nausea was reported.
Patients reported diarrhea, hunger, or hyperketosis as associated symptoms in 22.2%
of the analyzed studies, and only 11.1% of the studies reported dizziness, anorexia, food
refusal, hypernatremia, hypokalemia, hypocalcemia, low carnitine concentration, head-
ache, hyperuricemia, or hypercholesterolemia.
Important symptoms associated with KD include hypoglycemia, weight loss, vomit-
ing, diarrhea, and nausea. In this review, hypoglycemia was reported in the studies by
Champ et al., van der Louw et al. 2019a and 2019b, and Perez et al. Hypoglycemia, re-
ported in the study by Champ et al., was asymptomatic [16]. Weight loss was reported in
studies by Rieger et al. [8], Champ et al. [16], Klein et al. [29], and Panhans et al. [28].
Vomiting was reported in the two studies by van der Louw et al. [10,15], in the study by
Panhans et al. [28], and in that of Perez et al. [27]. Nausea was reported in the studies by
88.9%
55.6%
44.4%
44.4%
44.4%
33.3%
22.2%
22.2%
22.2%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
11.1%
Constipation
Asthenia
Weight loss
Vomiting
Hypoglycemia
Nausea
Diarrhea
Hunger
Hyperketosi
Hypercholesterolemia
Hyperuricemia
Headache
Low carnitine concentration
Hypokalemia
Hypernatremia
Hypocalcemia
Anorexia
Dizziness
Nephrolithiasis
Refusal to feed
Symptomatology
Figure 2. Symptomatology associated with KD therapy in glioma patients.
In 44.4% of the studies, weight loss, vomiting, or hypoglycemia were reported as
associated symptoms, whereas in 33.3% of the studies, nausea was reported.
Patients reported diarrhea, hunger, or hyperketosis as associated symptoms in 22.2%
of the analyzed studies, and only 11.1% of the studies reported dizziness, anorexia, food
refusal, hypernatremia, hypokalemia, hypocalcemia, low carnitine concentration, headache,
hyperuricemia, or hypercholesterolemia.
Important symptoms associated with KD include hypoglycemia, weight loss, vomiting,
diarrhea, and nausea. In this review, hypoglycemia was reported in the studies by Champ
et al., van der Louw et al., 2019a and 2019b, and Perez et al. Hypoglycemia, reported in
the study by Champ et al., was asymptomatic [
16
]. Weight loss was reported in studies
by Rieger et al. [
8
], Champ et al. [
16
], Klein et al. [
29
], and Panhans et al. [
28
]. Vomiting
was reported in the two studies by van der Louw et al. [
10
,
15
], in the study by Panhans
et al. [
28
], and in that of Perez et al. [
27
]. Nausea was reported in the studies by van der
Louw et al., 2019b [
15
], Klein et al. [
29
], and Panhans et al. [
28
]. Diarrhea was referenced in

Nutrients 2022,14, 1007 10 of 17
the studies by Rieger et al. [
8
] and van der Louw et al., 2019b [
15
]. The authors referred to
weight loss as a minimal side effect [8,16,17].
It should be noted that in the study by van der Louw et al., 2019b, patients with
dexamethasone were excluded [
15
], while in the studies by Champ et al., Rieger et al.,
Martin-McGill et al., 2018, Panhans et al., Klein et al., and Martin-McGill et al., this exclusion
was not made, which could influence the symptomatology and the interpretation of blood
glucose values [8,16,17,28–30].
Only one study reported the occurrence of hypercholesterolemia [
10
]. The remaining
studies did not report changes in the lipid profile.
3.6. Quality of Life
Quality of life is a parameter that must be evaluated with appropriate objective or
subjective measures, with the implementation of a validated questionnaire, for example.
Only three studies applied quality of life perception questionnaires [
8
,
15
,
30
]. The remaining
studies presented subjective results.
The perception of quality of life felt by patients with the implementation of ketogenic
therapy is shown in Figure 3.
Nutrients 2022, 13, x FOR PEER REVIEW 6 of 17
van der Louw et al. 2019b [15], Klein et al. [29], and Panhans et al. [28]. Diarrhea was
referenced in the studies by Rieger et al. [8] and van der Louw et al. 2019b [15]. The authors
referred to weight loss as a minimal side effect [8,16,17].
It should be noted that in the study by van der Louw et al. 2019b, patients with dex-
amethasone were excluded [15], while in the studies by Champ et al., Rieger et al., Martin-
McGill et al. 2018, Panhans et al., Klein et al., and Martin-McGill et al., this exclusion was
not made, which could influence the symptomatology and the interpretation of blood glu-
cose values [8,16,17,28–30].
Only one study reported the occurrence of hypercholesterolemia [10]. The remaining
studies did not report changes in the lipid profile.
3.6. Quality of Life
Quality of life is a parameter that must be evaluated with appropriate objective or
subjective measures, with the implementation of a validated questionnaire, for example.
Only three studies applied quality of life perception questionnaires [8,15,30]. The remain-
ing studies presented subjective results.
The perception of quality of life felt by patients with the implementation of ketogenic
therapy is shown in Figure 3.
Figure 3. Perception of quality of life in glioma patients undergoing KD.
As previously stated, not all studies analyzed the quality of life of patients undergo-
ing treatment—22.2% did not report any results on quality of life, since they were not
indicators studied by the authors themselves.
In 44.4% of the studies, there was an improvement in the quality of life with the im-
plementation of KD, regardless of the symptoms felt.
In 33.3% of the studies, there was a decrease in the quality of life. In two of these
studies (Rieger et al. and van der Louw et al. 2019b), the authors estimated that this de-
crease was related to the symptoms experienced throughout the studies and to tumor pro-
gression [8,15].
Martin-McGill et al. 2020 reported that patients who withdrew from KD therapy jus-
tified it with a decrease in quality of life in comparison to the beginning of treatment.
However, patients who remained on therapy reported an improvement in quality of life,
as they had a sense of control during tumor treatment [30].
Studies that did not objectively assess the quality of life assumed a good quality of
life or an improvement in quality of life. Martin-McGill et al. 2018 reported a good quality
of life for patients, with an improvement in symptoms [17].
Figure 3. Perception of quality of life in glioma patients undergoing KD.
As previously stated, not all studies analyzed the quality of life of patients undergoing
treatment—22.2% did not report any results on quality of life, since they were not indicators
studied by the authors themselves.
In 44.4% of the studies, there was an improvement in the quality of life with the
implementation of KD, regardless of the symptoms felt.
In 33.3% of the studies, there was a decrease in the quality of life. In two of these
studies (Rieger et al. and van der Louw et al., 2019b), the authors estimated that this
decrease was related to the symptoms experienced throughout the studies and to tumor
progression [8,15].
Martin-McGill et al., 2020 reported that patients who withdrew from KD therapy
justified it with a decrease in quality of life in comparison to the beginning of treatment.
However, patients who remained on therapy reported an improvement in quality of life, as
they had a sense of control during tumor treatment [30].
Studies that did not objectively assess the quality of life assumed a good quality of life
or an improvement in quality of life. Martin-McGill et al., 2018 reported a good quality of
life for patients, with an improvement in symptoms [17].
The study by Panhans et al. mentioned that a qualitative assessment of the quality of
life was carried out, in which there was an improvement in energy, mood, neurocognitive
function, general well-being, and symptoms [28].

Nutrients 2022,14, 1007 11 of 17
Klein et al. did not assess the quality of life. Nonetheless, they referred to a patient
who improved his quality of life. It should be noted, however, that in this study, the meals
were prepared by a company and provided free of charge to patients [29].
In the study by van der Louw et al., 2019a, it was mentioned that KD was not com-
patible with a better quality of life for patients [
10
], which led to the understanding that
with the implementation of KD, there was a decrease in the quality of life. In this study,
the children were in palliative care, and hospitalization of two children was necessary for
the management of epileptic seizures and implementation of enteral nutritional support
through a nasogastric tube due to swallowing difficulties. These data were not related
to the implementation of KD, however, with direct influence in the perceived quality of
life [10].
The studies by Champ et al. and Perez et al. did not make any reference to the patients’
perception of quality of life during or after treatment with implementation of KD [
16
,
27
,
32
].
Even so, in the study by Perez et al., it was mentioned that patients had an improvement in
symptoms [27].
3.7. Bias Risk Analysis
The results of the quality assessment of the clinical trials are shown in Figure 4. To
assess the risk of bias, Cochrane RevMan 5 software (Review Manager 5.4.1) [
26
] was used.
Nutrients 2022, 13, x FOR PEER REVIEW 8 of 17
Figure 4. Risk of bias summary—risk of bias analysis for each included study [8,10,15–17,27–30].
4. Discussion
Evidence for the use of KD in clinical practice is still very limited. There has been an
attempt to further investigate this topic, which implies new studies to be implemented in
the search for more reliable, promising, and relevant results.
The main objective of the present systematic review was to analyze and systematize
the clinical studies that tested KD in the context of glioma treatments, focusing the analy-
sis of the evidence on the potential therapeutic value of KD as a treatment option in patient
survival, and to further evaluate the potential effects of KD on associated symptoms and
quality of life of these patients. A total of nine original studies that reported at least one
of the study objectives were identified and analyzed.
It should be noted that, of the nine studies included, two were applied to children
between 2.5 and 15 years old and 5.3 and 15.5 years old. The remaining studies were ap-
plied to adults aged between 45 and 72 years old.
4.1. Overall Patient Survival
KD, being a therapy that reduces blood glucose levels and increases ketone body lev-
els, can be an effective therapy to increase the survival of patients with gliomas [32].
In the studies included in this review, we found that different results were described,
with survival values between 32 weeks (approximately eight months) and 25.4 months.
Survival is a factor that may vary mainly with age, disease stage, adherence to therapy,
Figure 4. Risk of bias summary—risk of bias analysis for each included study [8,10,15–17,27–30].

Nutrients 2022,14, 1007 12 of 17
The performance bias includes the knowledge of the interventions by the participants
and the team that is part of the study. Due to uncontrolled studies, there was no blinding,
which led to a high risk of performance bias.
The detection bias refers to the concealment of the investigators about the therapeutic
interventions in order not to influence the results. There was a high risk of detection bias
because the authors were not blinded to the diet therapy.
Attrition bias encompasses the tendency to attrition due to the quantity, nature, or
manipulation of incomplete result data. Data on patient survival (essential variable),
symptomatology, and quality of life (secondary variables) were evaluated.
A high risk of attrition bias due to incomplete assessment of the quality of life outcomes
was notable in most studies. Only the study by van der Louw et al. 2019b presented a
low risk of bias [
15
], being the only study that applied a quality of life questionnaire and
presented those results.
We verified a low risk of attrition bias regarding the nature of the data and the
evaluation of the results for survival in four studies [
8
,
10
,
15
,
30
]. In the remaining four
studies, there was a high risk of bias [
16
,
27
–
29
] since it was observed that survival was
reported by observation of patients or through qualitative data, so there was no application
of statistical tests.
Regarding symptoms, we found a low risk of attrition bias for most studies [
8
,
10
,
15
,
16
,
29
].
However, three studies showed a high risk of bias [
17
,
27
,
28
]: the study by Martin-McGill et al.
2018 and by Panhans et al., due to the reporting of symptoms (no questionnaire or structured
interview method was applied), and in the study by Perez et al., as results were presented for
only three patients, with incomplete data. The study by Martin-McGill et al., 2020 presented
an uncertain risk of bias [
30
] and reported that they evaluated ketosis, food acceptability, and
gastrointestinal adverse events and, later, also presented mineral deficits.
Reporting bias considers bias due to the description of selective results. The studies by
Champ et al., Klein et al., Martin-McGill et al., 2018, Martin-McGill et al., 2020, and Rieger
et al. were at high risk of bias [
8
,
16
,
17
,
29
,
30
]. The studies by van der Louw et al., 2019a and
2019b had a low risk of bias [10,15].
4. Discussion
Evidence for the use of KD in clinical practice is still very limited. There has been an
attempt to further investigate this topic, which implies new studies to be implemented in
the search for more reliable, promising, and relevant results.
The main objective of the present systematic review was to analyze and systematize
the clinical studies that tested KD in the context of glioma treatments, focusing the analysis
of the evidence on the potential therapeutic value of KD as a treatment option in patient
survival, and to further evaluate the potential effects of KD on associated symptoms and
quality of life of these patients. A total of nine original studies that reported at least one of
the study objectives were identified and analyzed.
It should be noted that, of the nine studies included, two were applied to children
between 2.5 and 15 years old and 5.3 and 15.5 years old. The remaining studies were
applied to adults aged between 45 and 72 years old.
4.1. Overall Patient Survival
KD, being a therapy that reduces blood glucose levels and increases ketone body
levels, can be an effective therapy to increase the survival of patients with gliomas [32].
In the studies included in this review, we found that different results were described,
with survival values between 32 weeks (approximately eight months) and 25.4 months.
Survival is a factor that may vary mainly with age, disease stage, adherence to therapy,
treatment efficacy, and tumor location. In this review, the mean overall survival was found
to be around 15.9 months.
The survival interval of patients with gliomas on common therapy is between 12 and
15 months [
13
]. With the implementation of KD, it was possible to verify that survival in the

Nutrients 2022,14, 1007 13 of 17
studies by Champ et al. and van der Louw et al. 2019b corresponded to this interval [
16
],
with no improvement in comparison to the survival time considered in the literature.
Patients included in the studies by van der Louw et al., 2019a, Klein et al., Martin-McGill
et al., 2020, and Perez et al. exceeded the average survival of those undergoing common
therapy [
10
,
27
,
30
]. The study by Rieger et al. was the only one in which the survival time
was lower than the average time of patients with gliomas undergoing common therapy [
8
].
According to the authors, the reasons for the low clinical activity may be due to the failure
to significantly reduce glucose through KD or to the hypothesis that tumor cells bypassed
the glucose reduction using ketone bodies [8].
The study that showed a longer survival was reported by Klein et al., where a KD
with a ratio of 4:1 was implemented, with 1600 kcal per day and a total of 10 g of carbohy-
drates [
29
]. On the other hand, patients from Rieger et al., who implemented a KD without
energy restriction but with restriction of carbohydrate intake to 60 g per day, had the lowest
survival [8].
In this analysis, the type of KD that presented the highest overall survival was CKD,
with a ratio of 4:1, verified in the studies by Klein et al. and van der Louw et al. 2019b.
Although the studies by Martin-McGill et al. and Perez et al. showed an increase in overall
survival, they applied different types of KD, with no description of the proportions of
macronutrients provided.
In most of the studies analyzed with the implementation of KD therapy, the overall
survival exceeded the prognosis of patients with the usual chemotherapy and/or radio-
therapy associated with temozolomide. A previously published review also mentions that
KD improved the survival of most patients [33].
In this systematic review, all studies included grade IV gliomas, two studies included
grade II gliomas, and one study included a grade III glioma. The overall survival data
shown in the included studies are not presented according to glioma type. As such, it is
not possible to assess if this variable is affected by the glioma type.
As gliomas have different levels of malignancy, it is expected that the type of tumor
can impact overall survival. Further analysis of this matter is recommended to fully
understand how overall survival varies according to malignancy. Therefore, future large-
scale perspective studies including a greater variety of glioma types are needed.
4.2. Associated Symptomatology
The symptoms associated with KD may involve gastrointestinal problems such as
vomiting, diarrhea, constipation, gastroesophageal reflux, and others such as hypoglycemia,
dizziness, asthenia, hyperketonemia, or metabolic acidosis. Other complications may also
arise, such as dyslipidemia, with hyperlipidemia, hypercholesterolemia, and hypertriglyc-
eridemia; cardiovascular diseases, such as cardiomyopathy; nephrolithiasis, and vitamin
and mineral deficits [34–37].
The symptomatology associated with the therapy, or the adverse effects felt by the
patients, were consistent in most of the studies, and the symptom most reported by the pa-
tients was constipation [
8
,
15
–
17
,
27
,
29
,
30
]. Asthenia was the second most mentioned symp-
tom, being described in studies by Champ et al. [
16
], Klein et al. [
29
],
Panhans et a
l. [
28
],
van der Louw et al., 2019a [10], and Perez et al. [27].
The most expected adverse effect in KD is hypoglycemia, due to the low concentrations
of carbohydrates and the amount of energy provided in the diet [
10
,
15
,
16
,
27
]. In this review,
hypoglycemia was found in four studies, but it promptly resolved with a change in dietary
and medical therapy. Other important symptoms associated with all types of KD were
weight loss, vomiting, diarrhea, and nausea.
Although these symptoms were described during dietary therapy, they were consid-
ered to have a mild and transitory incidence. Some authors considered that there was no
severe symptomatology associated with KD and related the occurrence of serious side
effects to the disease itself and/or medical treatment [15,27,31].

Nutrients 2022,14, 1007 14 of 17
According to the literature, the KD type that has the most side effects is CKD. How-
ever, in this review, it was possible to verify that the symptoms felt by the patients were
transversal, regardless of the diet implemented. Thus, side effects should not be a reason to
select a less restrictive diet.
4.3. Quality of Life
Quality of life is a parameter that must be evaluated with the appropriate objective
and subjective measures to obtain reliable results [
38
]. With the implementation of quality
of life questionnaires, it would be possible to assess this parameter with some certainty.
In this review, we were able to verify that only three studies applied quality of life
questionnaires, namely, Rieger et al., Martin-McGill et al., 2020, and van der Louw et al.,
2019b [
8
,
15
,
30
], and the only validated questionnaires were those used by Martin-McGill
et al., 2020. Although the authors applied these questionnaires, only the study by van der
Louw et al., 2019b presented the results obtained, while Rieger et al. reported qualitative
results and Martin-McGill et al., 2020 mentioned global health status.
The association between the symptoms felt by the patients and their quality of life was
notable. This is supported by Rieger et al., van der Louw et al., 2019b, and Martin-McGill
et al., 2018, who associated a decrease or improvement in quality of life with an increase or
improvement in symptoms, respectively.
In this systematic review, quality of life was a variable related to a high risk of attrition
bias. Therefore, we recommend that other variables should be considered in future inter-
ventions, as these represent a directly dependent factor on the stage of the disease, general
well-being, symptoms, and the patient’s response to therapy. With the results obtained, it
became difficult to establish a relationship between quality of life and the implementation
of KD, so we could only see its inconsistency.
4.4. Study Limitations
This systematic review applied a consistent methodology, with well-defined inclusion
and exclusion criteria, and covering different databases. All studies published to date
were included.
The analysis of articles for the selection of relevant and quality publications was
carried out by two reviewers, reducing the risk of errors in the selection of studies. In cases
of doubt or contradictory opinion, a third element was involved in the selection of studies
to be included.
The present systematic review followed the PRISMA recommendations and was
published in PROSPERO, with the identification CRD42021264173. Cochrane RevMan 5
software, indicated for the development of systematic reviews, was used to analyze the
risk of bias of the included studies. This made it possible to analyze and evaluate these
studies in depth.
Although there is a recent publication that included most of the studies here analyzed,
in the present study, a recent 2021 study (Perez et al.) [
27
] was also analyzed, including
these data in a systematic review for the first time. Additionally, our review is the only one
to date that includes the analysis of side effects, survival, and quality of life.
5. Conclusions
Some limitations were found in the quality of the analyzed data, including the sample
size in the studies (between three and seventeen patients), the different types of gliomas,
and the absence of a control group in most studies. This lack of control makes it difficult to
establish a solid conclusion on the efficacy of KD in the treatment of gliomas.
Since patients must be informed and accept the dietary modifications that KD requires,
performance bias or even the placebo effect could be present. Although the results are
made more robust when interventions are hidden, in the implementation of this kind of
therapy, this is a challenge.

Nutrients 2022,14, 1007 15 of 17
However, in most studies analyzed with the implementation of KD therapy, overall
survival exceeded the prognosis of these patients with the usual chemotherapy therapy
and/or radiotherapy associated with temozolomide. Both the use of different types of KD,
and the presentation of data as a report and not in a more structured way, made it difficult
to compare the side effects felt by patients during the implementation of the different types
of diets.
Furthermore, in the assessment of the quality of life, the use of reported data without
the application of objective and validated measures constituted a limitation to the interpre-
tation of the results. This represented a high risk of friction, and therefore, in most studies,
the data collected were considered as having a high risk of bias. It was not possible to
establish a relationship between quality of life and the implementation of KD. However,
concerning overall survival, in most studies, the prognosis of patients with gliomas who
implemented KD as therapy was higher compared to common therapy.
Although the results obtained point to a positive effect of KD as adjuvant therapy of
malignant gliomas, it is still important to develop new research of high quality that aims to
minimize the risks of bias.
Author Contributions:
Conceptualization, B.S. and A.C.M.; methodology, B.S., A.C.M. and M.L.A.;
software, B.S., M.L.A. and P.A.O.; validation, B.S. and A.C.M.; formal analysis, B.S., A.C.M. and
P.A.O.; investigation, B.S. and A.C.M.; resources, A.C.M. and M.L.A.; data curation, B.S. and P.A.O.;
writing—original draft preparation, B.S.; writing—review and editing, B.S., A.C.M. and P.A.O.;
supervision, A.C.M. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The protocol for this systematic review was registered in the Inter-
national Prospective Register of Systematic Reviews (PROSPERO) under the registration number
CRD42021264173.
Acknowledgments:
This study was part of the MSc thesis in clinical nutrition of one of the authors
(B.S.), which was supervised by another author (supervisor A.C.M.) from the Faculty of Medicine of
Lisbon and Lisbon School of Health Technology, Lisbon, Portugal. The H&TRC author gratefully
acknowledges the FCT/MCTES national support through UIDB/05608/2020 and UIDP/05608/2020.
Conflicts of Interest: The authors declare no conflict of interest.
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