In the mood for some chocolate? How about a piece of lettuce, instead?
Yeah, I didn’t think so.
No one likes being told what to eat. That’s why nutrition studies are so difficult to conduct.
Even if I paid you $1000, chances are you’d have difficulties substituting all chocolate in your diet with lettuce for the next 20 years.
Let’s say you cheated and ate a piece of chocolate around Year Five. Would you tell me you ate that piece of chocolate?
This would be so much easier if I just surveyed you and asked you how much chocolate and how much lettuce you ate each week.
A lot of nutrition studies are done in reverse like this. Instead of telling people what to eat, you ask them what they ate. Then you sort them into groups based on diet and follow their long-term health. You have a lot less control over your experiment this way, but it still works with a large enough sample size.
This is what Harvard researchers did with their Nurses’ Health Study. The researchers recruited 121,700 nurses, aged 30-55 years, to participate in the study. Every four years the nurses completed a questionnaire on their diet. They were given a list of foods, some healthy and some not healthy, and asked how often they ate these foods. Then, 15 years later, the researchers started asking these women questions about their overall mental and physical health. At this time, the researchers sorted them into groups based on diet.
To determine the effects of the Mediterranean diet on long-term health, they analyzed data from 10,670 of the study participants — all healthy women in their fifties and sixties during the mid-1980s. They wanted to know if following the Mediterranean diet in midlife would affect a person's odds of healthy aging, which they defined as making it to 70 with "no major chronic diseases or major impairments in cognitive or physical function or mental health." After 15 years, their results suggested that women who adhered to the Mediterranean diet had 46% greater odds of healthy aging compared to those who did not.
How did plant-based diets fare? This time the Harvard group analyzed data from both the Nurses' Health studies and the Health Professionals Follow-Up Study. Altogether, the sample size was over 200,000 healthcare professionals, all free of chronic disease at the study's onset. They found that the more you substitute animal foods in your diet with healthy plant foods, the more you reduce your risk of developing coronary heart disease and Type 2 diabetes in the future. Simply lowering your intake of red and processed meats can lower your risk of heart disease, the researchers suggested, though probably not to the same extent that going full-on vegetarian would.
In light of these studies and others like them, advising patients on nutrition is rapidly becoming less alternative and more mainstream. So put that coconut oil back on the shelf and talk to your doctor about nutrition.
This article appears in May 17-24, 2018.