Randomised controlled trialindependent cross-checkfull text checked★ key study I-UPF-01 in-depth review
Ultra-processed vs minimally processed healthy diets in England
Ultraprocessed or minimally processed diets following healthy dietary guidelines on weight and cardiometabolic health: a randomized, crossover trial.
Overview
Dicken SJ et al.. Nat Med 2025 · PMID 40760353 · DOI 10.1038/s41591-025-03842-0
Both diets led to weight loss, but about twice as much on minimally processed food.
Does the study support the specific claim? Yes · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Effect of UPF vs MPF within national dietary guidelines on weight.
- How was the study done?
2x2 crossover randomized controlled feeding trial, 8 weeks per diet, ad libitum.
- How many people, animals or samples were studied?
55 randomized; 50 ITT; Adults with BMI 25-<40 and habitual UPF >=50% kcal
- What was actually found?
MPF -2.06% (-2.99 to -1.13); UPF -1.05% (-1.98 to -0.13); difference -1.01% (-1.87 to -0.14), P=0.024; Cohen's d -0.48. Mild GI adverse events common on both.
- How large was the observed effect?
-2.06% vs -1.05% weight
- What do the results mean in everyday life?
Processing level may matter even in healthy diets.
- What are the study's limitations?
About 50 people, mostly women and health workers, 8 weeks per diet; the difference between diets was about 1 kg; dropouts happened only on the minimally processed diet; the order of the diets influenced the result.
- What does it say about Elawady's specific claim?
Supports C-UPF-02 (replicates direction of Hall 2019).
- Do the results apply to Germany and Europe?
High (England).
- What can explicitly not be concluded from this study?
It cannot show long-term effects on weight or disease, nor that UPF are harmful when a diet otherwise follows healthy guidance (both diets led to weight loss).
Scientific in-depth review
1. Full reference
- Authors
- Dicken SJ et al.
- Journal
- Nat Med
- Year
- 2025
- Identifier
- PMID 40760353 DOI 10.1038/s41591-025-03842-0
- Verification
- verified – PubMed efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
Funded by NIHR UCLH Biomedical Research Centre and Rosetrees Trust; funders not involved. COI: lead author receives royalties for a self-published book mentioning UPF and consultancy fees; senior author R.L.B. became an employee and shareholder of Eli Lilly from May 2023 and reports honoraria from Novo Nordisk and others; another author receives royalties for a book on UPF and broadcasting fees; K.D. Hall (author of A-UPF-01) is a co-author.
2. Research question
Effect of UPF vs MPF within national dietary guidelines on weight.
3. Study design and population
- Study design
- Randomised controlled trial – Single-centre, community-based 2x2 crossover randomised controlled feeding trial (UPDATE; NCT05627570): two 8-week ad libitum diets following the UK Eatwell Guide, one minimally processed (MPF) and one ultra-processed (UPF), separated by a 4-week washout; all food delivered free to participants' homes.
- Population
Adults in England with BMI >=25 to <40 kg/m2 and habitual UPF intake >=50% of energy (mean 67.4%); mean age 43.2 years; 90.9% women; mostly NHS staff (e.g. 43.6% nurses); mean BMI 32.7
- Country
England
- Period
Enrolment 3 April 2023 to 7 May 2024
- Sample size
135 screened; 55 randomised (28 MPF-then-UPF, 27 UPF-then-MPF); 50 intention-to-treat; 43 per protocol
- Inclusion and exclusion criteria
BMI >=25 to <40 kg/m2 and habitual UPF >=50% kcal/day; people with dietary restrictions (e.g. vegan, halal, kosher) excluded.
4. Methods and endpoints
- Exposure / intervention
UPF diet following Eatwell Guide (nutritionally improved, reformulated UPF from UK supermarkets; higher energy density)
- Comparator
MPF diet following Eatwell Guide
- Endpoints
Primary: within-participant difference in % weight change from baseline to week 8; secondary: body composition (bioimpedance), BP, heart rate, blood lipids, glucose, HbA1c, CRP, food cravings, appetite, adverse events
- Statistical methods
Mixed-effects models adjusted for randomisation arm and night-shift status with diet-by-arm interaction and participant random effect; ITT primary; sensitivity analyses (PP, repeated measures, inverse probability weighting, multiple imputation, first period only); powered (0.9) for a 2.7% difference with n=44; secondary outcomes not adjusted for multiple comparisons.
5. Actual results
- Results
Weight change at 8 weeks: MPF -2.06% (-2.99 to -1.13); UPF -1.05% (-1.98 to -0.13); difference -1.01% (-1.87 to -0.14), P=0.024; Cohen's d -0.48 (-0.91 to -0.06). Weight -0.96 kg (s.e. 0.40) greater loss on MPF; fat mass -0.98 kg (s.e. 0.32), body-fat % and visceral fat rating also favoured MPF. Triglycerides fell more on MPF (-0.25 mmol/L), whereas LDL-C fell more on UPF (difference 0.25 mmol/L in favour of UPF); BP, HbA1c, glucose, CRP not different between diets. Cravings improved more on MPF. Significant diet-order effect; first-period-only difference -1.86% (s.e. 0.72). Self-reported energy intake 327.3 kcal/day lower on MPF vs UPF. Adherence 84.5% (MPF) and 91.2% (UPF). Adverse events mostly mild gastrointestinal, not different between diets (P=0.088).
- Absolute risks
not applicable (short-term trial; absolute weight differences reported: ~1 kg over 8 weeks)
- Authors' conclusion
Both guideline-based diets led to weight loss, with significantly greater weight and fat loss on the MPF diet; guidance on food processing may be needed in addition to existing dietary recommendations.
6. Strengths
- Randomised crossover with 8-week periods and washout
- Pre-registered; ITT primary analysis; independent statistician verified primary analysis
- Real-world delivery of both guideline-compliant diets; participants blinded to diet labels and primary outcome
- Multiple prespecified sensitivity analyses consistent
7. Weaknesses
- Modest sample (50 ITT, 43 PP), 91% women, mostly health-care staff
- Observed difference (1.01%) much smaller than the 2.7% the trial was powered for; P=0.024 with CI close to zero
- Significant diet-order (carry-over) effect
- All withdrawals (n=10) occurred during the MPF diet; MPF diet rated lower for taste and convenience
- Free-living: adherence from partially returned food diaries; energy intake self-reported
- Researchers not blinded; participants aware of food types even if not of labels
- Secondary outcomes not adjusted for multiplicity; LDL-C favoured UPF
- Authors' COI includes book royalties on UPF
8. Risk of bias
- Orienting tool
- RoB 2 (crossover trial)
- Type of assessment
- structured assessment based on the full text by a single reviewer (no formal double review)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Structured single-reviewer judgement from the full text; a complete formal RoB 2 assessment requires two independent reviewers and the trial protocol.
| Domain | Judgement | Rationale |
|---|---|---|
| D1 Randomisation process | low | Computer-generated block randomisation (Sealed Envelope), stratified; balanced baseline. |
| D2 Deviations from intended interventions (incl. period and carry-over effects) | some concerns | Open diets; significant diet-order effect despite 4-week washout; adherence lower in second periods and on MPF. |
| D3 Missing outcome data | some concerns | 5 of 55 not in ITT and 12 not in PP; withdrawals concentrated in MPF periods; results robust to multiple imputation and IPW. |
| D4 Measurement of the outcome | low | Objective weight; participants blinded to primary outcome; bioimpedance for composition. |
| D5 Selection of the reported result | low | Registered primary outcome and analysis reported as planned. |
Full-text review (25 October 2026): Primary result confirmed. Added: enrolment dates, population (91% women, mostly NHS staff), 4-week washout, ITT 50/PP 43, withdrawals only during MPF, significant order effect, power target 2.7%, body-composition and lipid results (LDL-C favoured UPF), self-reported energy intake, detailed COI (incl. Eli Lilly employment of senior author, book royalties) and public funding. Domain-level RoB 2 (overall some_concerns, unchanged).
9. Assessment of the statistical interpretation
Moderate standardised effect (d -0.48) with a CI close to zero; absolute difference ~1 kg over 8 weeks. The UPF diet, despite being guideline-compliant, also led to weight loss; effects on cardiometabolic markers were small and mixed (triglycerides favour MPF, LDL-C favours UPF).
10. Relevance to the specific claim
Supports C-UPF-02 (replicates direction of Hall 2019).
11. Independent contrary findings
Both diets led to weight loss; LDL-C fell more on the UPF diet.
12. Transferability to Germany and Europe
High (England).
13. Overall methodological judgement
Important real-world replication of the direction of A-UPF-01: within national dietary guidance, a minimally processed diet produced about 1% more weight loss than an ultra-processed diet over 8 weeks; modest, short-term and with attrition and order effects.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Longer duration; mechanisms (energy density, palatability); generalisability to men and low-UPF consumers.