Cooking from scratch and avoiding ultra-processed foods like pre-packaged sandwiches and protein bars could help people lose twice as much weight, a study has found.
Ultra-processed food (UPF) is typically high in saturated fat, salt and sugar, contains ingredients you would not find in your kitchen cupboard like emulsifiers and preservatives, and is ready-to-eat or heat.
The study published in the journal Nature compared a UPF diet to a minimally processed one, and found avoiding UPFs helped curb food cravings, increased weight loss and improved fat loss.
The trial, led by experts at University College London (UCL) and University College London Hospitals NHS Foundation Trust (UCLH), involved 55 people who were overweight but otherwise healthy.
Half of the participants were given an eight-week diet plan comprising minimally processed foods such as overnight oats, cottage pie and chicken salad cooked from scratch. The other half were given a diet of ready-to-eat protein bars, shop-bought sandwiches and microwave lasagne.
Both diets were matched nutritionally and contained the recommended levels of fat, saturated fat, protein, carbohydrates, salt and fibre.
After completing one diet for eight weeks, the groups switched.
Dr Samuel Dicken, of the UCL centre for obesity research and UCL department of behavioural science and health, said: “Previous research has linked ultra-processed foods with poor health outcomes.
“But not all ultra-processed foods are inherently unhealthy based on their nutritional profile.”
Researchers aimed to find out whether eating more processed foods impacts weight, blood pressure, body composition and food cravings.
Results showed those on the minimally processed diet lost twice as much weight (2.06 per cent) compared to the UPF diet (1.05 per cent loss).
Those on the UPF diet also did not lose as much fat, researchers said.
Dr Dicken explained that although a 2 per cent reduction may not seem like much weight loss, it is a significant amount for eight weeks.
“If we scaled these results up over the course of a year, we’d expect to see a 13 per cent weight reduction in men and a 9 per cent reduction in women on the minimally processed diet, but only a 4 per cent weight reduction in men and 5 per cent in women after the ultra-processed diet,” Dr Dicken said.
However, researchers measured other markers like blood pressure, heart rate, liver function, glucose levels and cholesterol but found no significant negative impacts of the UPF diet.
Gunter Kuhnle, professor of food science and nutrition at Reading University, who was not involved in the study, told The Independent: “I think it confirms it is not processing that is important but rather food composition.”
He suggests consumers should focus more on composition, such as carbohydrates and fats, rather than on processing.
However, those on the UPF diet ate more calories than those on the minimally processed diet.
The NHS recommends the average woman should consume around 2,000 calories a day, while the average man should consume 2,500.
Participants were given more food than they needed, but those on a minimally processed diet spontaneously had 230 calories less than is recommended and those on the UPF diet had 120 calories less.
A questionnaire also revealed those on the minimally processed diet had fewer cravings than people on the diet of ready meals and packaged snacks.
Rob Hobson, registered nutritionist and author of Unprocess Your Family Life, who was also not involved in the study, told The Independent: “The findings support the idea that cutting back on UPFs may help with appetite control and weight regulation and not because UPFs are inherently toxic, but because of how they affect eating behaviour.
“Many are designed to be hyper-palatable, easy to eat quickly, and less satisfying. They don’t give us the same satiety signals as minimally processed foods.”
Professor Rachel Batterham, senior author of the study, said: “The best advice to people would be to stick as closely to nutritional guidelines as they can by moderating overall energy intake, limiting intake of salt, sugar and saturated fat, and prioritising high-fibre foods such as fruits, vegetables, pulses and nuts.
“Choosing less processed options such as whole foods and cooking from scratch, rather than ultra-processed, packaged foods or ready meals, is likely to offer additional benefits in terms of body weight, body composition and overall health.”
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