You can lose twice as much weight on a minimally processed diet

It seems you can lose twice as much weight if you eat a diet based around minimally processed, homemade food, compared with ultra-processed meals and snacks.

Food is generally considered to be ultra-processed if it includes ingredients that are never or rarely used in kitchens, such as high-fructose corn syrup, or additives that make the product more palatable or appealing, such as flavourings and thickeners.

Many studies have linked eating ultra-processed food to adverse health outcomes, such as cardiovascular problems, type 2 diabetes and weight gain, but these studies have been observational. Ultra-processed food also tends to be high in sugar, salt or fat – like cookies and microwave meals – sparking a debate over whether it is simply the ingredients that make ultra-processed food unhealthy or if there is something intrinsically detrimental about the processing itself.

To better understand this in the context of weight loss, Samuel Dicken at University College London and his colleagues have carried out a trial in which 55 people who were overweight or had obesity were randomised to eat a diet of either ultra-processed or minimally processed foods.

“Obviously everyone imagines pizza, chips and that kind of stuff when they think of ultra-processed foods,” says Dicken. However, the researchers made sure that both diets aligned with the UK Eatwell Guide, which encourages a healthy, balanced diet that includes at least five portions of fruit and vegetables a day and several sources of protein, such as beans, fish, eggs and meat. The two diets were also matched so they contained roughly the same levels of fat, sugar, salt and carbohydrate.

Food was delivered to the participants, making it the first trial to compare such diets in real-world conditions, rather than in a hospital or lab. With the ultra-processed group, this involved things like breakfast cereals, protein bars, chicken sandwiches and ready-meal lasagnes, but versions that were low in fat and salt. “The kind of foods that if you go into a supermarket, they’re slapped with nutritional health claims,” says Dicken.

The minimally processed diet featured homemade foods like overnight oats, chicken salad, bread made from scratch and spaghetti bolognese. Both groups were given enough food for about 4000 calories a day and were told to eat as much as they wanted. The researchers set it up so that half of the participants were on one diet for eight weeks, half on the other, and then they switched after a four-week break.

The participants were told the study was investigating the…