By Deena Shanker
Cutting meat and dairy out of your diet is hard. Staying healthy while you do it can be harder.
The wrong kind of exclusively plant-based diet, one that includes a lot of refined grains and sweetened beverages, can actually increase the risk of coronary heart disease, according to a new study from Harvard University. On the other hand, reducing your intake of animal products while boosting your consumption of fruits, vegetables, and whole grains, and continuing to indulge modestly in animal foods, can do you nearly as much good as a healthy vegan diet-and even more good than one that includes a lot of French fries and pasta.
"Less healthy plant foods and animal foods were both associated with increased risk, with a potentially stronger association for less healthy plant foods," according to the study, published in the Journal of the American College of Cardiology.
By now, many people have heard that diets with lots of healthy plant foods can have major benefits, including significantly lowering the risk of coronary heart disease. But going vegan can lead to trouble if you overindulge in the bad stuff. And just try finding something to eat at the airport.
So veganism alone may not help you and could hurt you.
The study, which the authors say is "one of the largest prospective investigations of plant-based diet indices and incident coronary heart disease in the world," reviewed data from two iterations of the Nurses' Health Study and one from the Health Professionals Follow-Up Study.
Each involved tens of thousands of adults who tracked their lifestyles, health behaviours, and medical histories through questionnaires completed every two years. This gave the researchers, at Harvard's T.H. Chan School of Public Health, more than 4.8 million person-years of follow-up data to analyse.
Using these data, the authors created three diet indices. One was an overall plant-based diet index in which plant foods got a positive score and animal foods got a negative score. Another was a healthy plant-based diet index, assigning positive scores to whole grains, fruits, vegetables, nuts, legumes, oils, tea and coffee, and negative scores to juices and sweetened beverages, refined grains, potatoes and fries, and sweets. Then there was an unhealthy plant-based diet, with positive scores for the unhealthy plant foods and negative scores for the healthy plant and animal foods.
The researchers found that the people with a higher adherence to the general plant-based diet index had an inverse association with coronary heart disease, and that this relationship got even stronger for the healthy plant-based diet index. The unhealthy plant-based diet index had a positive association with coronary heart disease. The results track those of an earlier study in which the same researchers studied the relationship between plant-based diets and type 2 diabetes.
"When we examined a diet that emphasised both healthy plant and healthy animal foods, the association with coronary heart disease was only slightly attenuated relative to that with the healthy plant-based diet index," the authors wrote. "Thus ... moderate reductions in animal foods ... can be largely achieved by lowering intake of less healthy animal foods such as red and processed meats."
In an editorial appearing alongside the study, Dr. Kim Allan Williams Sr. of Rush University Medical Center in Chicago translated the findings for cardiologists in the real world. Instead of pushing an "'all-or-none'" diet, he wrote, start with "smaller dietary tweaks."
In other words, he wrote, quoting Michael Pollan, " 'Eat food. Not too much. Mostly plants.' "