Evidence-Based Nutrient Recommendations

Healthful versus Unhealthful Plant-Based Diets

According to a group of Boston-area researchers, eating more plants is good for health but eating the right plants is even better.

This study didn’t look specifically at vegan or vegetarian diets but rather compared outcomes among subjects consuming a range of plant-based diets that included at least small amounts of animal foods. The subjects were women enrolled in the Nurses’ Health Study 1 and Nurses’ Health Study 2, and men enrolled in the Health Professionals Follow-up Study.

The researchers created a plant-based index where plant foods received a positive score and animal foods a reverse score. Participants’ diets were given a score based on how often they ate foods from these different categories.

The researchers also created a healthful plant-based diet index which gave positive scores to whole grains, fruits, vegetables, nuts, legumes, vegetable oils, tea, and coffee, and reverse scores to fruit juices, sweetened beverages, refined grains, potatoes, and sweets, as well as animal foods. An unhealthful dietary index was created to include less healthful plant foods and the animal foods.

After adjusting for weight, people with the highest adherence to diets that emphasized plant foods over animal foods had about a 20% reduced risk for diabetes compared to those with the lowest adherence. Risk dropped even further with a diet that emphasized more healthful plant foods, which lowered the odds of diabetes by about 34%.

Closer adherence to a plant-based diet was only modestly linked to lower risk for heart disease—and the findings weren’t statistically significant. But adherence to a healthy plant-based diet was associated with a 25% lower risk for heart disease. Adherence to an unhealthy plant-based pattern raised the risk by nearly a third.

People who scored highest for an unhealthy plant-based diet consumed nearly double the amount of unhealthy plant foods as those with highest scores on the healthy plant-based diet, suggesting there can be significant differences in the healthfulness of different plant-based diets.

The researchers hypothesized that consuming a diet that emphasizes healthful plant foods leads to higher intakes of fiber, antioxidants, unsaturated fat, and micronutrients, and lower intakes of saturated fat, heme iron, and sugar. These intakes improve cholesterol profiles and insulin regulation, decreases inflammation, reduce blood pressure, and favor a healthier gut microbiome—all factors that may lower the risk for chronic disease.

The take-home message is one that many vegans are familiar with—not all plant foods are created equal. To lower the risk for chronic disease, it’s important to emphasize carbohydrate-rich foods that have plenty of fiber and a low glycemic index, and also to include healthful unsaturated fats. It doesn’t mean that other plant foods are off-limits, just that they should be consumed less frequently.


1. Satija A, Bhupathiraju SN, Spiegelman D, Chiuve SE, Manson JE, Willett W, Rexrode KM, Rimm EB, Hu FB. Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults. J Am Coll Cardiol 2017;70:411-422.

2. Satija A, Bhupathiraju SN, Rimm EB, Spiegelman D, Chiuve SE, Borgi L, Willett WC, Manson JE, Sun Q, Hu FB. Plant-Based Dietary Patterns and Incidence of Type 2 Diabetes in US Men and Women: Results from Three Prospective Cohort Studies. PLoS Med 2016;13:e1002039

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