Randomised controlled trialindependent cross-checkabstract only checked I-SYS-05 standard review

Low-fat and low-carb diets led to similar weight loss

Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial.

Overview

Gardner CD et al.. JAMA 2018 · PMID 29466592 · DOI 10.1001/jama.2018.0245

After a year, weight loss was 5.3 kg vs 6.0 kg - no real difference.

Does the study support the specific claim? Yes · Methodological quality: high

Original publication

Plain-language summary

Study explained simply

What did the researchers want to find out?: Compare diets.
How was the study done?: RCT.
How many people, animals or samples were studied?: 609.
What was actually found?: No difference.
How large was the observed effect?: 0.7 kg.
What do the results mean in everyday life?: Total diet quality and quantity matter more than fat share.
What are the study's limitations?: Adherence.
What does it say about Elawady's specific claim?: Supports 'fat is not the origin'.
Do the results apply to Germany and Europe?: High.
What can explicitly not be concluded from this study?: Long-term weight maintenance.

Scientific in-depth review

1. Full reference

Authors: Gardner CD et al.
Journal: JAMA
Year: 2018
Identifier: PMID 29466592 DOI 10.1001/jama.2018.0245
Verification: verified – PubMed esummary + efetch 2026-10-25
Retracted: no
Corrections: ErratumIn: JAMA 2018;319(13):1386; JAMA 2018;319(16):1728
Extent checked: abstract only
Conflicts of interest and funding: not stated in abstract; NIH funding; errata published

2. Research question

Healthy low-fat vs healthy low-carbohydrate diet for weight loss.

3. Study design and population

Study design: Randomised controlled trial – Randomised clinical trial
Population: Adults 18-50, BMI 28-40, no diabetes
Country: USA
Period: 2013-2016
Sample size: 609
Inclusion and exclusion criteria: Overweight/obese adults without diabetes

4. Methods and endpoints

Exposure / intervention: Healthy low-fat diet
Comparator: Healthy low-carbohydrate diet
Endpoints: 12-month weight change
Statistical methods: Between-group difference

5. Actual results

Results: Weight change -5.3 kg (low-fat) vs -6.0 kg (low-carb); difference 0.7 kg (95% CI -0.2 to 1.6). No genotype or insulin-secretion interaction. Fat intake 29% vs 45% of energy.
Absolute risks: not applicable
Authors' conclusion: No significant difference in weight change between the two diets.

6. Strengths

Randomised, 12 months
Large

7. Weaknesses

Free-living adherence variation

8. Risk of bias

Orienting tool: RoB 2
Type of assessment: simplified assessment (abstract only)
Full formal assessment: no
Overall risk of bias: low
Rationale: Well-conducted RCT.

9. Assessment of the statistical interpretation

Fat share of diet (29% vs 45%) did not determine weight loss.

10. Relevance to the specific claim

Supports that dietary fat per se is not the decisive cause of weight gain.

11. Independent contrary findings

12. Transferability to Germany and Europe

High.

13. Overall methodological judgement

Strong evidence.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	high
Risk of bias	low
Precision of results	high
Directness	direct
Reproducibility	replicated
Consistency with the overall evidence	consistent
Regional transferability	high
Adequacy of the interpretation (by the archive)	not applicable