In a study from Indiana University Bloomington School of Public Health, funded by the California Walnut Commission, researchers show that adolescents and young adults who consumed walnuts with other nuts (WON) had the lowest prevalence of obesity.

Researchers analyzed data from the National Health and Nutrition Examination Survey (NHANES), including 8874 adolescents aged 12 to 19 years old and 10,323 young adults aged 20 to 39. The research focused on understanding the associations between consumption of walnuts and other nuts with measures of obesity including relative fat mass (RFM), a tool that estimates body fat percent and regional fat composition.

The study showed that, especially in adolescent girls and young women, the consumption of WON has the strongest inverse association with measures of obesity when compared to non-nut consumers. This association was not found among young men, adolescent boys, or adolescent girls who consumed walnuts only. 

A systematic review of cohort studies indicated that long-term moderate intake of nuts (i.e., 1–2 servings of nuts per week) was associated with less weight gain and reduced risk of overweight/obesity and that consumption of a high-quality diet is inversely associated with body mass index, and even though walnuts and other nuts are energy dense, they may not promote obesity.

Scientists also make the distinction that these observations might be due to revere causality since "that people with obesity have altered their diets in terms of nut consumption to prevent more weight gain."