A less processed diet may be more beneficial for weight loss, a new study from UCL has found.
When given nutritionally matched diets, participants lost twice as much weight eating minimally processed foods compared to ultra-processed foods, a new clinical trial has found.
It suggests cutting down on processed foods could help sustain a healthy weight long-term.
The study, published in Nature Medicine, is the first interventional study comparing ultra-processed food and minimally processed food diets in ‘real world’ conditions, as well as being the longest experimental study of a UPF diet to date.
The trial split 55 adults into two groups with a total of 50 participants completing at least one diet.
One group started with an eight-week diet of minimally processed foods (MPFs), such as overnight oats or homemade spaghetti bolognese. After a four-week ‘washout’ period during which participants went back to their normal diet, they switched to a diet of UPFs, such as breakfast oat bars or a lasagne ready meal.
The other group completed the diets in the opposite order.
The provided diets were nutritionally matched in accordance with the Eatwell Guide, the UK’s official government advice on how to eat a healthy, balanced diet. Participants were not told to limit their intake but just to eat as much or as little as they normally would.
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“Previous research has linked ultra-processed foods with poor health outcomes,” said Dr Samuel Dicken, first author of the study from the UCL Centre for Obesity Research and UCL Department of Behavioural Science & Health. “But not all ultra-processed foods are inherently unhealthy based on their nutritional profile.”
Processed foods’ effect on weight loss
After eight weeks on each diet, both groups lost weight, likely as a result of the improved nutritional profile of what they were eating compared to their normal diet.
However, this effect was higher (2.06% reduction) on the MPF diet compared to the UPF diet (1.05% reduction), corresponding to an estimated calorie deficit of 290 kcal per day on the MPF diet and 120 kcal per day on the UPF diet.
“The primary outcome of the trial was to assess percentage changes in weight and on both diets we saw a significant reduction, but the effect was nearly double on the minimally processed diet,” said Dicken.
He added that scaling up the results over the course of a year would mean a 13% weight reduction in men and a 9% reduction in women on the minimally processed diet, but only a 4% reduction in men and 5% in women after the UPF diet.
The greater weight loss experienced on the MPF diet came from reductions in fat mass and total body water, with no change in muscle or fat-free mass, indicating a healthier body composition overall.
The findings suggest that, when observing recommended dietary guidelines, choosing minimally processed foods may be more effective for losing weight.
Additionally, the research found that craving control also improved on the MPF diet compared to the UPF one.
“The global food system at the moment drives diet-related poor health and obesity, particularly because of the wide availability of cheap, unhealthy food. This study highlights the importance of ultra-processing in driving health outcomes in addition to the role of nutrients like fat, salt and sugar,” said Professor Chris van Tulleken, an author of the study from UCL Division of Infection & Immunity.
“It underlines the need to shift the policy focus away from individual responsibility and on to the environmental drivers of obesity, such as the influence of multinational food companies in shaping unhealthy food environments.
“Stakeholders across disciplines and organisations must work together and focus on wider policy actions that improve our food environment, such as warning labels, marketing restrictions, progressive taxation and subsidies, to ensure that healthy diets are affordable, available and desirable for all.”
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The trial also measured secondary health markers, such as blood pressure and heart rate, which revealed no significant negative impacts of the UPF diet.
The research was welcomed by the Soil Association, which launched a petition in May calling for the government to make minimally processed foods accessible and affordable for everyone.
“For decades, the UK government’s ‘healthy eating’ guidelines have neglected processing, assuming that whole foods and ultra-processed products might deliver the same health outcomes. We now know that to be false,” said Soil Association head of food policy Rob Percival.
“A minimally processed diet is better for your health. You cannot replicate the benefits of whole foods in an industrial manufacturing facility – nature knows better.”
He has called on the government to update the Eatwell Guide in light of this new research to promote minimally processed foods, and to warn against ultra-processed diets. The Association has also said the government should be using its new food strategy to improve access to minimally processed produce.
“This new government has an opportunity to do things differently and stop allowing policy to be shaped by those who selfishly put corporate profits before public health,” said Percival. “It’s time for a new approach.”
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