A large new study from Harvard T.H. Chan School of Public Health suggests that when it comes to reducing the risk of cardiovascular disease, type 2 diabetes, and mortality, the overall nutritional quality of a plant-based diet may be more important than the degree of processing.
The study, presented at NUTRITION 2026 by Dr Xiaowen Wang, investigated whether the health effects of plant-based diets differed according to their level of processing.
Dr Wang and team analysed dietary and health data from three long-running US cohort studies:
- Nurses’ Health Study (1984-2018)
- Nurses’ Health Study II (1991-2021)
- Health Professionals Follow-Up Study (1986-2020)
The analysis included 203,275 adults (160,690 women and 42,585 men) who were free from cancer, cardiovascular disease (CVD), and type 2 diabetes (T2D) at baseline.
Researchers developed six plant-based diet indices that differentiated between healthy and unhealthy plant foods while also accounting for whether foods were ultra-processed (UPF) or non-ultra-processed.
Over the follow-up period, researchers documented:
- 26,209 cases of cardiovascular disease
- 21,006 cases of type 2 diabetes
- 55,493 deaths
Researchers found that overall diet quality was strongly associated with the risk of cardiovascular disease, type 2 diabetes and mortality. Individuals following healthier dietary patterns – regardless of level of processing – experienced better health outcomes, while those consuming poorer-quality diets had higher cardiometabolic disease risks.
Notably, only the unhealthy ultra-processed plant-based diet pattern showed a statistically significant association with increased mortality risk. Importantly, within healthy and unhealthy categories, the health risks were almost identical regardless of processing classification.
This study challenges the assumption that highly processed foods are inherently detrimental within plant-based eating patterns. The findings suggest that the health benefits of a plant-based diet depend more on the nutritional quality of the foods chosen than on how processed they are.
This large prospective study indicates that healthy plant-based foods can support cardiometabolic health regardless of their level of processing, whereas poor-quality plant-based diets are associated with less favourable outcomes.
