Updated: Jan 20
A plant-based diet is a nutritious and sustainable way to eat. However, it is important to note that not all plant-based diets are equally healthy or environmentally friendly.
To assess food quality in a plant-based diet, three indices have been developed:
· overall plant-based diet index (PDI),
· healthful plant-based diet index (hPDI)
· unhealthful plant-based diet index (uPDI)
Several studies have shown that the overall plant-based diet index (PDI) and healthful plant-based diet index can lower the risk of heart disease, diabetes, kidney disease, cancer, and even dementia. However, unhealthful plant-based index diets can increase the risks of these outcomes.
The data on colorectal cancer is less clear between the different indices. In a study published in BMC Medicine, researchers looked at 79,952 men and 93,475 women, ages 45-75, who did not have colorectal cancer before baseline. The participants were from five racial/ethnic groups:
· African American
· Native Hawaiian
· Japanese American
The researchers classified whole grains, vegetables, vegetable oils, and nuts as healthy plant foods versus refined grains, fruit juices, and potatoes as unhealthy plant foods. The participants were followed on average for 19.2 years, and a quantitative food frequency questionnaire was used to assess diet quality.
The researchers found that among men, the risk of colorectal cancer was 23% lower for the overall plant-based diet index and 20% lower for the healthful plant-based diet index. This risk reduction with a healthful plant-based diet index was found consistently across racial and ethnic groups. The same relationship was not seen among women.
In the subgroup analysis, there were some interesting findings:
Reduction of colorectal cancer by:
· 9% when whole grains replaced added sugars
· 8% when fruits replaced added sugars
· 8% when vegetables replaced added sugars
· 12% when legumes replaced added sugars
The potential mechanisms for the benefits of plant-based diets on colorectal cancer could be high fiber, polyphenols, and carotenoids. In addition, plant-based diets have been shown to improve gut microbiome, and this could also play a role.