Meta-analysisindependent cross-checkabstract checked★ key study I-INS-117 in-depth review
Calories, carbohydrates and body fat in controlled feeding studies
Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition.
Overview
Hall KD, Guo J. Gastroenterology 2017 · PMID 28193517 · DOI 10.1053/j.gastro.2017.01.052
When calories were fixed, cutting fat led to slightly more fat loss than cutting carbohydrate, even though carbohydrate cuts lower insulin.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Test whether lowering insulin via low-carbohydrate diets increases fat loss.
- How was the study done?
Meta-analysis of 32 controlled feeding studies.
- How many people, animals or samples were studied?
Adults in metabolic studies.
- What was actually found?
Lower-fat diets: +26 kcal/d expenditure, +16 g/d fat loss.
- How large was the observed effect?
Small effects.
- What do the results mean in everyday life?
Insulin is one factor, but calories matter.
- What are the study's limitations?
Short studies.
- What does it say about Elawady's specific claim?
Contradicts 'insulin is the only cause of obesity'.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Cannot settle long-term diet debates.
Scientific in-depth review
1. Full reference
- Authors
- Hall KD, Guo J
- Journal
- Gastroenterology
- Year
- 2017
- Identifier
- PMID 28193517 DOI 10.1053/j.gastro.2017.01.052
- Verification
- verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
NIH intramural research (record).
2. Research question
Do lower-carbohydrate (lower-insulin) diets increase energy expenditure and fat loss at equal calories?
3. Study design and population
- Study design
- Meta-analysis – Narrative review including a meta-analysis of 32 controlled feeding studies with isocaloric carbohydrate-for-fat substitution
- Population
Adults in controlled feeding studies
- Country
Various
- Period
Studies to 2016
- Sample size
32 controlled feeding studies
- Inclusion and exclusion criteria
Isocaloric substitution of carbohydrate for fat, controlled feeding
4. Methods and endpoints
- Exposure / intervention
Lower-carbohydrate diet
- Comparator
Lower-fat diet at equal calories
- Endpoints
Energy expenditure; body fat change
- Statistical methods
Meta-analysis
5. Actual results
- Results
Energy expenditure (26 kcal/d; P<.0001) and fat loss (16 g/d; P<.0001) were greater with lower-fat diets.
- Absolute risks
not reported
- Authors' conclusion
Data are most commensurate with a set-point model; low-carbohydrate diets do not offer a metabolic advantage for fat loss at equal calories.
6. Strengths
- Controlled feeding (tight intake control)
7. Weaknesses
- Short studies
- Small effects
- Authors are proponents of the energy balance view
8. Risk of bias
- Orienting tool
- AMSTAR 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Meta-analysis within a review; search methods not detailed in abstract.
9. Assessment of the statistical interpretation
Effect sizes are small (tens of kcal/day; grams of fat/day) but direction opposes the insulin-only model.
10. Relevance to the specific claim
If insulin were the only cause of fat storage, lowering insulin by cutting carbohydrate should increase fat loss at equal calories; controlled feeding shows the opposite small effect.
11. Independent contrary findings
Ebbeling 2018 (I-INS-118) found higher energy expenditure on low-carbohydrate diets during weight maintenance.
12. Transferability to Germany and Europe
Directly applicable; same biology and clinical standards in Europe.
13. Overall methodological judgement
Moderate evidence against 'insulin is the only cause'.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | mixed |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Insulin is the single and only cause of obesity (local or generalised) because it is the only hormone that builds fat and blocks fat breakdown (lipolysis). – Studies contradicting or limiting the claim
- Calories are not a relevant concept ('there is no such thing as calories'); his system is based on high calorie intake, and people lose weight while eating sugar, juices, fats, potatoes and rice, because with 'zero insulin' no fat is formed (the passage continues: 'even if you drink oil, even if you swallow bags of sugar'). Elsewhere he says he drinks 6 litres of sugar-cane juice and eats baladi ghee, rice and potatoes every day. – Studies contradicting or limiting the claim