Consuming minimally processed foods — such as those home-cooked from raw ingredients — could make it easier to shed weight while on a diet.Credit: Filippo Carlot/Alamy
Eating ultra-processed foods might hinder attempts to lose weight even when the diet accords with national healthy-eating recommendations, a study has found.
The study, published in Nature Medicine on 4 August1, highlights a lack of focus on the impact of UPFs in national dietary recommendations in the United Kingdom — where the study was conducted — and elsewhere, the authors say.
Ultra-processed foods (UPFs) are products that have been developed by combining food extracts with additives and industrial ingredients. The result is food items that are cheap, profitable and widely accessible.
It is well established that the high salt and sugar content of many UPFs makes the products unhealthy, but some research has suggested that how they are processed could also have a role.
Samuel Dicken, an obesity and behaviour researcher at University College London and lead author of the paper, says that the motivation behind this study was to address a gap in national dietary recommendations, and to do so in the participants’ everyday environment. “It will be the longest-ever trial of a UPF diet to date. It’s the first one to do it in the real world to try and apply all those behavioural influences” associated with daily life.
In the United Kingdom, more than half of the energy in the average person’s diet comes from UPFs, with similar figures found elsewhere in Europe and in the United States.
Socio-economic factors
The wider availability of affordable UPFs over less-processed alternatives could have a disproportionate effect on people from low-income areas. “Issues around diet and obesity related to these [UPFs] are very much related to socio-economic inequalities,” says Dicken, adding that people might have unhealthy diets not because they aren’t trying to eat healthily, but “because our food environment is just setting us up to fail”.
The study examined the impacts of UPFs on 55 adults on a diet based on UK national dietary guidelines. Participants followed an 8-week diet based on minimally processed foods (MPFs) and an 8-week diet based on UPFs, with a 4-week period between the two, where participants returned to their usual diet. Both diets followed the UK Eatwell Guide, which focuses on food groups and macronutrients including fat, protein, and carbohydrate content. During both phases, the participants had all meals, snacks, and drinks delivered to their homes, but could choose how much to eat at any one time, and when it was consumed.
The researchers found that participants’ weight and body-mass index decreased during both phases. However, participants lost more than twice as much weight — 1.84 kilograms on average, compared with 0.88 kilograms — while following the MPF diet. Changes in body composition, such as decreases in fat mass, body-fat percentage and visceral-fat rating occurred on the MPF diet but not on the UPF one. Cravings were also decreased on the MPF diet.
