Randomised controlled trialindependent cross-checkabstract checked I-UPF-101 standard review
Ultra-processed diet trial in Japanese men
Ultra-processed foods cause weight gain and increased energy intake associated with reduced chewing frequency: A randomized, open-label, crossover study.
Overview
Hamano S et al.. Diabetes Obes Metab 2024 · PMID 39267249 · DOI 10.1111/dom.15922
In 9 men, one week of ultra-processed food led to eating about 800 kcal more per day and gaining 1.1 kg more weight.
Does the study support the specific claim? Yes · Methodological quality: low
Plain-language summary
Study explained simply
- What did the researchers want to find out?
To test UPF effects on weight and intake.
- How was the study done?
Randomised crossover trial.
- How many people, animals or samples were studied?
9 overweight men.
- What was actually found?
More intake and weight gain on UPF; less chewing.
- How large was the observed effect?
+813.5 kcal/day; +1.1 kg.
- What do the results mean in everyday life?
Ultra-processed meals may make it easy to overeat.
- What are the study's limitations?
Tiny, short, open-label.
- What does it say about Elawady's specific claim?
Supports C-UPF-02.
- Do the results apply to Germany and Europe?
Moderate.
- What can explicitly not be concluded from this study?
Cannot show long-term effects.
Scientific in-depth review
1. Full reference
- Authors
- Hamano S et al.
- Journal
- Diabetes Obes Metab
- Year
- 2024
- Identifier
- PMID 39267249 DOI 10.1111/dom.15922
- Verification
- verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
No COI statement in PubMed record; funding listed: Ministry of Education, Culture, Sports, Science and Technology
2. Research question
Do UPF diets increase body weight and ad libitum energy intake compared with non-UPF diets?
3. Study design and population
- Study design
- Randomised controlled trial – Randomised, open-label crossover feeding study (1 week per diet, 2-week washout)
- Population
Overweight/obese Japanese men without regular medical conditions
- Country
Japan
- Period
Not stated in abstract
- Sample size
9 randomised, 9 completed
- Inclusion and exclusion criteria
Excluded diabetes, hypertension or other regular medical conditions
4. Methods and endpoints
- Exposure / intervention
UPF diet
- Comparator
Non-UPF diet matched for total energy and macronutrients
- Endpoints
Body weight change (primary); energy intake; chewing frequency
- Statistical methods
Crossover comparison
5. Actual results
- Results
UPF period: +1.1 kg more weight (0.2-2.0; P=0.021) and +813.5 kcal/day more intake (342.4-1284.7; P=0.0041) vs non-UPF; fewer chews per calorie on UPF (P=0.016).
- Absolute risks
not reported
- Authors' conclusion
Consumption of UPFs causes significant weight gain.
6. Strengths
- Randomised crossover
- Replication of Hall 2019 in another population
7. Weaknesses
- Only 9 participants
- 1-week periods, open-label
- Causal language exceeds the design's generalisability
8. Risk of bias
- Orienting tool
- RoB 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Open-label; very small.
9. Assessment of the statistical interpretation
Wide CI (SE about 240 kcal/day); consistent direction with Hall 2019 (stats/C-UPF-02_trials.py).
10. Relevance to the specific claim
Replicates higher intake and weight gain on UPF in a small Japanese sample.
11. Independent contrary findings
Barros 2026 and Forde 2026 suggest energy density and eating rate explain part of the effect.
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Supportive but very small and short.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | low |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Longer trials.