Avoiding ultra-processed foods might double weight loss, says study

NEW YORK – New research suggests that people can lose more weight by avoiding ultra-processed foods, even those that are typically considered healthy.

The study, published in the journal Nature Medicine on Aug 5, is the largest and longest clinical trial yet to examine the effects of ultra-processed foods on weight.

Participants lost twice as much weight when they followed diets made up of minimally processed foods, such as pasta, chicken, fruit and vegetables, as they did when they followed diets with ultra-processed foods that met nutrition standards, such as ready-to-heat frozen meals, breakfast cereals, protein bars and shakes.

Federal officials have been sounding the alarm about ultra-processed foods, which account for about 70 per cent of the food supply in the US. Health Secretary Robert F. Kennedy Jr said ultra-processed foods were “poisoning” Americans and called them a primary culprit of high rates of obesity and chronic diseases.

Although numerous studies have linked ultra-processed foods to obesity, most have been observational, meaning they cannot prove that the foods directly cause weight gain.

Two previous trials found that adults consumed about 500 to 800 more calories per day when their diets were made up of ultra-processed foods than when they were made up of minimally processed foods. But those studies were small and short; the larger of the two, conducted at the National Institutes of Health, included 20 participants who followed each diet for just two weeks.

Critics argue that the results might have been different if the trials were longer, or if they included healthier ultra-processed foods.

The new study, though still small, was designed to address some of those concerns, said Dr Samuel Dicken, a research fellow at University College London and lead author of the study.

Losing weight and body fat

Dr Dicken and his colleagues recruited 55 participants, most of whom were women, ranging in age from their early 20s to their mid-60s, he said. All had body mass indexes in the overweight or obesity ranges and, before the study, about two-thirds of their calories came from ultra-processed foods – more than the average for adults in Britain.

The researchers designed two diets and provided the meals. Both diets met Britain’s nutrition guidelines, with limited sugars, saturated fats and sodium, but one was composed mostly of minimally processed foods, such as overnight oats, plain yogurt and scratch-made spaghetti Bolognese; the other was mostly made up of ultra-processed foods considered healthy, like whole grain breakfast cereals, plant-based milk, flavoured yogurt and frozen lasagna.

Half the participants followed the minimally processed diet for two months, after which they returned to their normal diets for a month. Then they followed the ultra-processed diet for two months. The other half followed the diets in the opposite order. All could eat as much or as little as they liked.

This kind of “crossover” study design is strong because it can show how each diet affected each participant, rather than averaging the responses across a group, said Dr Brenda Davy, a professor of nutrition at Virginia Tech, who was not involved in the study.

Most of the participants lost weight on both diets. But on average, they lost more weight during the two months on the minimally processed diet – about 2kg compared with just 1kg on the ultra-processed diet.

Dr Dicken and his colleagues estimated that if the weight loss had continued over one year, even as it naturally slows with time, it could have added up to 9 per cent to 13 per cent of body weight on the minimally processed diet, compared with just 4 per cent to 5 per cent on the ultra-processed diet.

The participants also lost over twice as much body fat on the minimally processed diet than they did on the ultra-processed diet.

Fewer calories per bite and fewer food cravings

It was somewhat surprising – and encouraging – that people lost weight on the ultra-processed diet, said Dr Kevin Hall, a nutrition scientist and a co-author of the study.

This was likely because the study’s ultra-processed diet was more nutritious than the typical diets of the participants, he said. But participants still lost more weight on the minimally processed diet – a finding that aligns with those of previous studies.

That may be because minimally processed foods tend to have fewer calories per bite, said Dr Filippa Juul, a nutritional epidemiologist at Suny Downstate Health Sciences University, who was not involved in the study.

Those foods generally have a harder texture that requires more chewing, so people may eat more slowly and consume fewer calories before feeling full, she said.

The participants also reported feeling like they had better control of food cravings on the minimally processed diet. That is surprising, Dr Dicken said, because “when people lose weight, they tend to want to eat more”. Better craving control may help them keep the weight off longer, he added.

Dr Juul speculated that perhaps following a diet of mostly minimally processed foods may “reset cravings” and reduce “food noise”, helping people eat only when they are hungry.

A growing body of evidence

The study was relatively short, said Dr Walter Willett, a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, who was not involved in the study.

“We need about a year, at minimum, for serious weight loss studies because early changes often reverse or don’t continue,” he wrote in an e-mail.

The researchers could not measure exactly what and when people ate, or how much they consumed, and the participants reported eating some foods besides those provided. Prof Davy said most of the participants were women; men or children may have responded differently.

Still, Dr Juul said, the study suggests that even if a person follows a healthy diet, there is an added benefit to choosing minimally processed foods over ultra-processed ones. Evidence consistently suggests that diets high in ultra-processed foods can make it harder for people to stay at a healthy weight, she added.

Avoiding ultra-processed foods can be a challenge, though, since they are so ubiquitous and tend to be cheaper than minimally processed foods, Dr Juul said. She advises choosing foods with recognisable ingredients.

Food manufacturers could help by making more minimally processed products that are convenient, affordable and appealing, she added. “It’s a shift in food culture that’s needed.”

You do not have to cut out ultra-processed foods entirely, Dr Davy said. But try to cook at home as much as you can, focusing on fresh fruit and vegetables, lean proteins and whole grains – “things that we know are good for us”. NYTIMES