UPFs are typically industrial products that are made from refined ingredients like white flour, oils, and sugars and additives like flavorings, preservatives, and emulsifiers. Think of foods far removed from their original form: packaged snacks, sodas, processed meats, cookies, and ice cream.

UPF intake is consistently linked with a higher risk of cardiometabolic disease and mortality in observational studies, though the certainty of evidence is often low to moderate. A 2024 umbrella review that covered 14 meta-analyses and involved almost 10 million participants reported associations across 32 outcomes, which highlighted the need for randomized trials to probe mechanisms and causality.^[1]

Adverse health outcomes associated with ultraprocessed food intake

Adapted from Lane et al., 2024, BMJ.

Two highly controlled metabolic ward studies that used crossover designs compared ultraprocessed and minimally processed diets and demonstrated greater weight gain on UPF-based diets. The first study from 2019, covered here, found that just 2 weeks on an ultraprocessed diet increased calorie intake and body weight (+1 kg/+2.2 lb), whereas a minimally processed diet decreased calorie intake and body weight (–1 kg/–2.2 lb).^[2] The more recent study covered in this Editor’s Pick from 2024 showed that just 1 week on a UPF diet increased weight gain (+1.1 kg/+2.4 lb) and energy intake (+800 calories/day).^[3]

Both studies proposed that food texture is an additional explanation for weight gain^[4] and reported an increased eating rate (17 kcal/minute) and reduced chewing frequency on the UPF diet.^[2] Processing can change the food structure, texture, and eating rate; softer textures shorten the oral processing time, increase eating speed, and reduce satiation, which ultimately nudges the energy intake up.^[3]

The summarized study asks a more pragmatic question: If people hold to a national “healthy eating” template like the UK Eatwell Guide, does food processing level still matter? The results suggest the answer is yes because the participants lost an extra 1% of body weight over 8 weeks while following a minimally processed diet. That’s a modest amount for individuals but meaningful at the population scale, especially because both diets involved free eating and were consistent with nutritional guidelines. Moreover, the increase in craving control on the minimally processed diet compared to the ultraprocessed diet supports the concept of heightened reward pathway activation from UPF foods that further nudge energy intake.^[5] At the same time, it’s not clear whether the weight loss would continue with longer diet durations or at what point weight may stabilize.

This study distinguishes itself from the previous two primarily because it followed national dietary guidelines and the participants weren’t kept in a laboratory setting. Although only a small fraction of people in the UK follow all of the guidelines, this study showed that: 1) if people did follow dietary guidelines they may lose weight and 2) UPFs should be included in the guidelines to further extend the public health impact of the guidelines. This suggests that limiting UPFs provides additional benefits beyond nutritional quality. The community-based intervention increases its real-world relevance, despite the reduced control compared to the metabolic ward studies.

This study has some other notable limitations. The predominantly female participants and high baseline UPF intake reduce the generalizability of the results, although most energy intake comes from UPFs in Europe and the U.S.^[6]^[7] The secondary outcomes were also not adjusted for multiple comparisons and carry some methodological concerns. Although body composition was assessed using bioelectrical impedance analysis (BIA) after an overnight fast and with participant instructions (no alcohol or strenuous activity 24 hours before) to minimize the method's limitations, BIA does make assumptions based on hydration status, can lack standardization, and prediction equations can vary, which leads to different results.^[8]^[9] Also, daily energy imbalance was estimated using the energy densities of fat mass and fat-free mass from BIA, and energy intake estimates were based on two 24-hour dietary recalls.

Finally, there’s the issue of classifying foods as ultraprocessed and properly capturing the nuance of their effects on health. For example, some foods that may be classified as UPFs aren’t necessarily associated with weight gain and may actually support weight loss, such as artificially sweetened beverages^[10] and breakfast cereals.^[11] This Editor’s Pick from 2025 covers limitations of the often used NOVA classification for UPFs and the potential for metabolomics to enhance dietary assessment and risk prediction associated with UPFs.

Should dietary guidelines limit ultraprocessed foods? Original paper