A recent study published in the journal BMC Medicine found that eating a plant-based diet made up of vegetables, legumes, nuts, and whole grains could reduce the risk of bowel cancer in men. This study evaluated 79,952 men and 93,475 women in the United States and found that the male participants who ate the largest quantities of healthy plant-based foods had a 22 percent lower risk of bowel cancer than those who ate the least of these foods.
Here is a closer look at how a plant-based diet could reduce the risk of colorectal cancer.
Format and Methodology
This study was survey-based. The participants were asked how often they ate different types of foods and drinks from a list of over 180 items, along with portion sizes. These multiple-choice responses went from “never or hardly ever” to “two or more times a day” for food items and up to “four or more times a day” for drinks. The foods were classified into three groups:
Healthy plant foods
This group included fruits, vegetables, whole grains, nuts, vegetable oils, legumes (such as chickpeas and lentils), tea, and coffee.
Less healthy plant foods
This group consists mainly of refined grains, added sugars, fruit juices, and potatoes.
Animal foods
This group consists of meat, fish or seafood, animal fat, dairy, and eggs.
The daily consumption per 1,000kcal was divided into five parts, from the largest consumption to the least. Male participants were age 60 on average when the study began, while the women were age 59. The majority of people diagnosed with bowel cancer are more than 60 years old.
Findings
During the course of the study, 4,976 participants (2.9%) developed bowel cancer. The researchers considered other risk factors that were likely to influence the results, such as whether a participant was obese or overweight. Along with a disparity between men and women, the study authors found that the link between diet and bowel cancer risk reduction varied among men by race and ethnicity. For example, white men showed a 24 percent reduced risk, while Japanese American men only showed 20 percent.
Overall, the strongest association between plant-based diets and colorectal cancer risk was found in white, American, and Japanese men. The researchers believe this may be because of differences in other risk factors for colorectal cancer between different ethnicities and races. The authors believe more research is needed to understand the differences between ethnicities. The researchers speculate that the antioxidants in foods like vegetables, fruits, and whole grains could be a contributing factor to lowering colorectal risk because antioxidants can suppress chronic inflammation, which can lead to cancer.
The team believes that the discrepancy in colorectal cancer risk between men and women could partially explain why eating more healthy plant-based foods was correlated with reduced colorectal cancer risk in men but not women. In addition, women eat more plant foods than men on average, which means that eating additional fruits and vegetables might be less likely to decrease cancer risk in a meaningful way.
Study Limitations
This study was strictly observational, which means that researchers are not yet able to draw conclusions about the causal relationship between plant-based diets and colorectal cancer risk. In simpler terms, scientists do not yet know why some foods are associated with better bowel health. However, the results are still encouraging, as they show that a plant-based diet could significantly reduce the risk of colorectal cancer in men.
The study also did not make a distinction between different types of animal-based food. This limited the study since some animal-based foods, such as dairy and fish, could be healthy. In addition, the researchers assessed the diets of the participants using a questionnaire, which is a limited form of information gathering and does not consider lifelong food intake.
Related Research
Previous research has examined whether dietary choices could reduce an individual’s risk of colorectal cancer. There is evidence that diet is an important risk factor for colorectal cancer. For example, researchers have found a link between red and processed meats and an increased risk of colorectal cancer, while foods high in dietary fiber are associated with a lower risk.
Previous research has also found evidence of similar sex discrepancies. For instance, a United Kingdom Biobank study found that men who ate less meat than average were 9 percent less likely to develop colorectal cancer compared to average meat-eaters. These benefits were not observed among women in the study.
While this UK population-level study was comprehensive, it only focused on meat levels in the diet, rather than the consumption of specific plant-based foods. Less meat consumption does not necessarily correlate with an increase in healthier food options, as some plant-based foods are much more nutritional than others, and not all plant-based foods are healthy.