TOPLINE:

The association was particularly strong among patients with heart disease and those without depression. Younger adults showed a pronounced increase in the risk for weight gain when exposed to ultraprocessed food.

METHODOLOGY:

• Researchers analyzed data from 24,453 Brazilian adults (79.7% women) in the NutriNet Brasil cohort study, who were followed up for a median of 43.6 months, to assess the association between consumption of ultraprocessed foods and weight gain.
• Dietary intake was evaluated using Nova24h recalls, a self-administered 24-hour recall tool that classifies foods and ingredients into four categories.
• Exposure to ultraprocessed foods was measured as a percentage of contribution to total energy intake, on the basis of two recalls at 6 and 12 months.
• Participants reported their weights every 6 months. Clinically relevant weight gain was defined as a ≥ 5% increase from baseline weight, and the risk for weight gain was assessed according to quintiles of exposure to the ultraprocessed dietary pattern.
• Overall, 10,092 incident cases of ≥ 5% weight gain and 4865 incident cases of ≥ 10% weight gain were documented.

TAKEAWAY:

• Each 10% increase in ultraprocessed food contribution was associated with a 5% increased risk for ≥ 5% weight gain (adjusted hazard ratio [aHR], 1.05; 95% CI, 1.04-1.07) and an 8% increased risk for ≥ 10% weight gain (aHR, 1.08; 95% CI, 1.06-1.10).
• Compared with participants in the lowest quintile of exposure to the ultraprocessed dietary pattern, those in the highest quintile had an increased risk for ≥ 5% weight gain (aHR, 1.23; 95% CI, 1.15-1.31) and for ≥ 10% weight gain (aHR, 1.35; 95% CI, 1.23-1.48).
• Stronger associations between the highest adherence to the ultraprocessed dietary pattern and ≥ 5% weight gain were observed among participants without overweight at baseline (aHR, 1.25; 95% CI, 1.15-1.36) than among those with overweight at baseline (aHR, 1.17; 95% CI, 1.05-1.29).
• The association with an increased risk for ≥ 5% weight gain was also stronger among participants with heart disease (aHR, 1.66; 95% CI, 1.24-2.24) and among those without depression (aHR, 1.26; 95% CI, 1.16-1.37), and the association with an increased risk for 10% or greater weight gain was stronger among participants younger than 40 years (aHR, 1.43; 95% CI, 1.26-1.61).

IN PRACTICE:

“These findings add to growing evidence on the harmful health effects of UPF [ultraprocessed foods] and underscore the urgency of individual-level strategies and public policies aimed at reducing their consumption and the obesity epidemic,” the authors of the study wrote.

SOURCE:

The study was led by Maria Alvim Leite, PhD, Department of Preventive Medicine, University of São Paulo Medical School, São Paulo, Brazil. It was published online on December 27, 2025, in the American Journal of Preventive Medicine.

LIMITATIONS:

Participants were likely more health-conscious and wealthier than the general population, with a higher proportion of women. The validation of the Nova24h tool focused on food processing groups, not total energy or nutrient intakes, potentially leading to imprecision.

DISCLOSURES:

The study was funded by the Harvard University Brazil Research Fund and the National Council for Scientific and Technological Development. The NutriNet Brasil study is funded by the Brazilian Ministry of Health, the São Paulo Research Foundation, and Umane. Some authors reported receiving support from funding sources.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.