New research finds that reducing processed animal foods leads to greater weight loss than focusing on food processing levels. A plant-based diet can help, but does ultra-processing matter as much as we thought?
Study: Vegan diet, processed foods, and body weight: a secondary analysis of a randomized clinical trial. Image Credit: Geshas / Shutterstock.com
A recent study in the journal Nutrition and Metabolism determines how consuming vegan processed food may affect weight loss in overweight adults.
Processed foods and weight gain
A plant-based and low-fat diet is associated with numerous health benefits, including weight loss, reduced risk of heart disease, blood sugar control, and anti-inflammatory properties. However, some plant-derived foods are heavily processed, which may negate their potential weight loss effects.
Several studies have reported that consuming certain ultra-processed foods (UPFs) increases the risk of weight gain. Despite these observations, few studies have determined whether this association is dependent on animal- or plant-based UPFs.
About the study
The current study is a secondary analysis of a randomized clinical trial conducted between January 2017 and February 2019. It explores whether the degree of food processing influences the effects of a plant-based diet on body weight. The main hypothesis was that plant—and animal-based foods within the NOVA food classification system affect body weight differently.
The study cohort comprised overweight adults between 25 and 75 years of age with a body mass index (BMI) between 28 and 40 kg/m2. Exclusion criteria were smoking, alcohol or drug abuse, diabetes, pregnancy or lactation, and current intake of a vegan diet.
Study participants were randomly assigned to a vegan or control group in a 1:1 ratio. The control group did not make any changes to their dietary habits, whereas the vegan group avoided animal products and minimized their consumption of oils.
Body weight was measured at baseline and week 16. Using the NOVA system, foods were categorized by their degree of processing and origin.
The average daily intake from a three-day diet record was estimated for each participant and used for the analysis. NOVA category one includes unprocessed or minimally processed foods, whereas category two includes processed ingredients. Category three foods include processed products with added preservatives, salt, and sugar, while category four includes UPFs.
Study findings
Of 3,115 people initially screened by telephone, 244 met the inclusion criteria and were randomly assigned to vegan and control groups. The vegan group increased their consumption of plant-based food and reduced their intake of animal products across all NOVA categories.
In category one, the vegan group reduced its consumption of animal foods and increased its intake of plant-based foods. In all other categories, animal food consumption decreased in the vegan group compared to controls.
The vegan group also reduced its consumption of plant-based foods, with no significant differences observed within the group. However, compared to controls, body weight decreased in the vegan group.
Changes in animal food consumption across all categories were positively associated with alterations in body weight. According to multivariable regression models, the main predictors of weight loss were lower consumption of processed animal foods, reduced unprocessed or minimally processed animal foods, and fewer UPFs derived from animal sources.
Throughout the 16-week study period, reducing the consumption of processed animal foods by 50 g/day was independently associated with a one-kg weight loss without adjusting for changes in energy intake. One-kg weight loss was also independently associated with reduced consumption of unprocessed or minimally processed animal foods by 93 g/day.
Moreover, one kg weight loss throughout the study period was independently associated with reduced intake of ultra-processed animal foods by 120 g/day. No associations were observed between changes in BMI and ratios of category four to category one foods of plant or animal origin.
Minimizing the consumption of animal foods and substituting low-fat plant-derived foods in their place, regardless of their level of processing, was associated with clinically significant weight loss.”
Strengths and limitations
A key strength of the current study is the inclusion of a control group exposed to the same seasonal variations as the vegan group.
Some limitations include the use of self-reported diet records to assess daily dietary habits, which could lead to reporting bias. Additionally, the study cohort may not be representative of the general population, thereby limiting the generalizability of the findings.
Journal reference:
- Kahleova, H., Znayenko-Miller, T., Jayaraman, A., et al. (2025) Vegan diet, processed foods, and body weight: a secondary analysis of a randomized clinical trial. Nuture Metabolism 22(21). doi:10.1186/s12986-025-00912-5