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A re-analysis of an ultra-processed food clinical trial looks at food choice, energy and nutrient intake on an unprocessed diet.
Prof Nita Forouhi, MRC Epidemiology Unit, University of Cambridge, said:
“The missing piece between research and policy action on ultra-processed foods has been the lack of understanding of mechanisms. Resolving this gap is critical. This research adds importantly to the scientific understanding of why and how ultra-processed food consumption promotes higher calorie intake than unprocessed food.
Two clear hypotheses emerged that have implications: First, that ultra-processed foods don’t just add calories — they steer people toward higher calorie intake through affecting food choice. The finding that people eat more food yet consume fewer calories on a whole food unprocessed diet directly challenges narratives that suggest lack of individual restraint as an underlying cause of excess caloric intake, and instead points to the design of modern (ultra-processed) foods as a key driver. Second, the research suggests that fortifying UPFs with vitamins/minerals may inadvertently encourage overconsumption by bundling high energy and micronutrients together, weakening the natural appetite cues that whole foods preserve.
The study has many strengths and it applies a clever study design to maximise use of existing data from a well conducted previous trial. Among limitations, it did not study processed foods, a substantial part of modern diets, as distinct from ultra-processed and unprocessed foods – a gap that should be studied in other research. The current research was limited by the small sample size of 20 men and women of the original, highly controlled intervention study and the findings should be replicated in other trial and observational studies that reflect more real-world settings. The authors present fascinating data on the carbohydrate-fat blend and its impact on caloric intake but a discussion on the role of protein would have been additionally informative. This research is appropriately focused on understanding mechanisms of food selection, food volume and caloric intake in a controlled trial setting but it is important to recognise the role of access and affordability of unprocessed foods versus UPFs that will also be important factors influencing food choice.”
Prof Martin Warren, Chief Scientific Officer and Group Leader in Synthetic biology and biosynthetic pathways, Quadram Institute, said:
“This reanalysis of a previous feeding trial suggests that ultra-processed foods drive overeating not simply because they are calorie-dense, but because they align with deep-rooted human tendencies to combine fat and carbohydrate while delivering micronutrients in the same foods. In contrast, unprocessed diets appear to limit energy intake by forcing a nutritional trade-off: meeting micronutrient needs requires consuming large volumes of low-energy foods such as vegetables, a process the authors term “micronutrient deleveraging.” While the findings offer a compelling new framework for understanding how modern foods may bypass natural dietary constraints, they are based on post-hoc analyses of a small, short-term study and rely on assumptions about optimal macronutrient balance that remain untested. The work therefore opens important new questions about food design and public health, but calls for confirmation in larger, purpose-built trials before firm policy conclusions can be drawn.
“If confirmed, these results suggest that effective dietary strategies should focus less on calorie restriction and more on restoring natural nutritional trade-offs. If it were confirmed, in practice this could mean designing meals and food environments where micronutrients are delivered primarily through low-energy-dense foods (such as vegetables), rather than being bundled with calories via fortification and processing. For public health and food policy, limiting the routine co-formulation of fat and carbohydrate in highly processed foods, and prioritizing minimally processed, component-based meals in schools, hospitals, and workplaces, could help reduce passive overconsumption without relying on individual restraint.”
Prof Jules Griffin, Director of the Rowett Institute, University of Aberdeen, said:
“The paper by Brunstrom and colleagues raises an interesting theory as to why unprocessed meals may be better for us by encouraging us to eat more fruit and vegetables. They make the interesting observation that when presented with unprocessed foods, people opt for lower energy dense, higher micronutrient options, while on ultra-processed diets, people opted for energy dense, fortified products for their nutrition.
“While an interesting academic study that is sure to prompt more research into this area about what motivates us to seek out certain foods, one question is how the research helps the consumer to make healthier choices. The study suggests that unprocessed meals benefit from promoting fruit and vegetable consumption. While individuals on this diet ate more total food by weight, they ate fewer calories, in part because unprocessed foods, and in particular fruit and veg, are less energy dense.
“The big question is what is driving this motivation to eat more fruit and vegetables when on an unprocessed diet? The authors suggest that this might be due to where we get our nutrients from and the energy that comes along with these nutrients – e.g. cereals that have been fortified but could contain lots of sugar in the ultra-processed diet or blueberries in the unprocessed diet for one comparison. However, there are alternative explanations as to why the unprocessed meals were healthier. They would have provided more fibre in its natural form, and we know this has a beneficial effect on the gut as well as making us feel fuller for longer, in part by releasing GLP1. Given the recent questions about weight regain following GLP1-agonists, so called ‘fat-jabs’, this research highlights that governments should be thinking about improving peoples access to fruit, vegetables and unprocessed foods as well as drugs for treating people living with obesity.”
Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:
“This publication reports secondary analysis of a well known but small short term randomised controlled trial comparing a diet high in ultraprocessed food with predominantly unprocessed foods. The authors claim that that “wholefoods” are richer in micronutrients and bulkier. It is suggested that you can eat more on a wholefood diet.
Limitations
“This is not what the original trial was designed to test. It is only exploratory statistical analysis of foods eaten in one controlled study. The findings may not be more broadly applicable as many processed foods have a higher micronutrient content than wholefoods because of nutrient fortification. This is particularly notable for processed breakfast cereals fortified with thiamin, riboflavin, niacin, folic acid, vitamin B12, vitamin D, iron and zinc.
Interpretation
“The analysis suggests that “wholefoods” can provide fewer calories but can still provide sufficient micronutrients. However, some caution is needed particularly with regard to plant based diets. It well known that bulky diets consisting of unrefined cereals and lots of fruit and vegetables can cause malnutrition in children under the age of five years. However, in the case of older children and adults, individuals are able adapt to a bulkier diet and they get used to eating larger volumes of food. We have observed this in our own research on adult vegans who have similar energy intakes compared to meat-eaters despite their diet being very high in wholefoods. We also found that the vegans were are more likely to suffer from micronutrient (especially vitamin B12) deficiencies. Micronutrient fortification has played a major role in eliminating malnutrition.”
‘Consuming an unprocessed diet reduces energy intake: A post-hoc analysis of an RCT reveals a role for human ‘nutritional intelligence’’ by Jeffrey M. Brunstrom et al. was published in The American Journal of Clinical Nutrition at 00:01 UK time on Tuesday 20 January 2026.
DOI: 10.1016/j.ajcnut.2025.101183
Declared interests
Prof Nita Forouhi: “I have no conflicts of interest to declare.”
Prof Martin Warren: “The Quadram Institute is a UK science national capability strategically supported by the Biotechnology and Biological Sciences Research Council. I declare that I have no associated interests with this paper and am not sponsored by any food company.”
Prof Jules Griffin: “I am a consultant for Sitryx, a company specialising in designing drugs to target immunometabolism. (The company is looking at drugs for irritable bowel disease and psoriasis.)
I have received funding from the European Union to investigate endocrine disrupting chemicals and hold a grant from UK Research and Innovation examining the health benefits of a fish diet.
I hold shares in GlaxoSmithKline and Haleon plc.”
Prof Tom Sanders: “I was Chair of the British Nutrition Foundation Report on Nutrition and Development: Short and Long term consequences for Health.
I have received grant funding for research on vegans in the past. I have been retired for 10 years but during my career at King’s College London, I formerly acted as consultant for companies that made artificial sweeteners and sugar substitutes.
I am a member of the Programme Advisory Committee of the Malaysia Palm Oil Board which involves the review of research projects proposed by the Malaysia government.
I also used to be a member of the Scientific Advisory Committee of the Global Dairy Platform up until 2015.
I did do some consultancy work on GRAS affirmation of high oleic palm oil for Archer Daniel Midland more than ten years ago.
My research group received oils and fats free of charge from Unilever and Archer Daniel Midland for our Food Standards Agency Research.
I was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.
Member of the Science Committee British Nutrition Foundation. Honorary Nutritional Director HEART UK.
Before my retirement from King’s College London in 2014, I acted as a consultant to many companies and organisations involved in the manufacture of what are now designated ultraprocessed foods.
I used to be a consultant to the Breakfast Cereals Advisory Board of the Food and Drink Federation.
I used to be a consultant for aspartame more than a decade ago.
When I was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.”