ll kinds of evidence point to the positive effects a good diet can have on our health. But what about those of us who are just now paying attention to that memo?
A new study shows that such diet changes are better late than never — as long as those new healthy habits stick.
That came from researchers at Harvard’s school of public health who tracked what over 70,000 people have eaten for decades. They found that long-term improvements in diet were associated with a significantly decreased risk of death.
Specifically, making mostly healthier choices for 12 years could decrease someone’s risk of death during the next 12 years by 20 percent.
For example, cutting out most red and processed meat and adding one serving of nuts and legumes — a category that includes beans and lentils — per day could be enough of a change to decrease mortality risk.
Those who improved their diet not only saw reduced overall mortality but also specifically a lower risk of death from cardiovascular disease. (Likewise, people whose diet quality declined over time had a higher risk of mortality.) However, diet changes showed no effect on mortality rates from cancer. The results were published Wednesday in the New England Journal of Medicine.
“This is a big step in nutritional epidemiology research, as we had a large sample size, with a very long follow-up that allowed us to examine changes in diet quality and subsequent risk of mortality,” said Mercedes Sotos-Prieto, a professor of food and nutrition science at Ohio University.
Studying diet in detail
The study used survey data from two massive, national cohorts: the Nurses’ Health Study and the Health Professionals Follow-Up Study. Both studies, based at Harvard, have been ongoing for decades. Participants filled out questionnaires every four years about how often they ate various types of food.
The choices they made were analyzed using three dietary quality scoring systems, including the Alternate Healthy Eating Index. The results were mostly similar across all the systems.
Because there were so many people, researchers were able to adjust their analysis for a bunch of possible lifestyle and health changes, like a person getting diagnosed with a chronic illness or deciding to start or stop smoking.
However, even a large group like this comes with limitations. Not only were the subjects all health professionals, but the group was overwhelmingly white. The findings, while meaningful, are also just an association; there’s no guarantee that eating healthier causes the decreased mortality rates.
“Although generalizability could be one limitation,” Sotos-Prieto said, “the homogeneity of socioeconomic status in our study may help reduce confounding by such variable.”
Other studies with more diversity in their subject pools have found similar results, she noted.
The cost of healthy eating
Renata Micha, a professor at the Tufts Friedman School of Nutrition Science and Policy who was not involved in the research, echoed Sotos-Prieto. “These findings, though derived by a relatively homogeneous U.S. population, are generally in agreement with what are seeing in other settings and populations,” she said — adding that shifting towards better eating habits might have an even larger impact for people with lower income levels.
However, healthier choices can also be more expensive — one meta-analysis published in 2013 estimated that meals made with healthier options could cost someone up to $1.50 more per day.
“Decreasing the cost of healthy food by means of public health interventions, such as economic incentives (subsidies) in existing major systems such as SNAP in the U.S., would be a vital key step towards that direction,” Micha said.