Everybody has heard that an apple a day keeps the doctor away, but a handful of nuts a day may do the trick, too — and new research suggests a possible reason why.
The study from Brigham and Women’s Hospital suggests that inflammation may be the key to previous findings of a link between eating nuts and lower rates of chronic disease.
The study, led by Dr. Ying Bao, an assistant professor at the Brigham and Harvard Medical School, looked at over 5,000 people and found that participants who ate tree nuts or peanuts at least five times a week had lower levels of biomarkers — proteins in the blood — for inflammation. Inflammation has been linked with chronic conditions including heart disease and type 2 diabetes.
“This is an association study, and association is not causation,” Bao pointed out in an interview. “We found that in this study, people who ate nuts five or more times a week had lower levels of inflammatory markers than those who didn’t eat nuts." (Bao's research was partially funded by a grant from the International Tree Nut Council Nutrition Research & Education Foundation.)
Some studies have shown that nuts reduce the risk of coronary heart disease by up to 47%. While nuts' link with lowering rates of mortality and chronic disease, as well as their reduction of inflammation biomarkers, have been shown in other studies, more work must be done before scientists know exactly why, and how, nuts are beneficial.
Bao hopes to be able to conduct a more telling experiment, a randomized clinical trial, in an attempt to show that eating nuts causes a reduction in inflammation. But it would be very expensive and the cost poses a major obstacle, she said.
Bao's study looked at over 5,000 people involved in two long term studies: the Nurses’ Health Study, which looks at all-female nurses, and the Health Professionals Follow-Up Study, which looks at male health care professionals. Participants filled out a questionnaire that looked at 131 different dietary factors as well as lifestyle decisions, like whether they smoked and how much exercise they got.
Biomarkers in their blood were then measured. The study found that people who ate nuts five or more times a week had about 20% lower levels of the measured biomarkers.
Bao and her team found that people who ate nuts also tended to exercise and not smoke. “Nut eaters have all these healthy habits that could confound the results. In this study, we, in a statistical model, adjusted for those factors to a great degree,” Bao said. "We are able to adjust for all kinds of related factors to really tease out the association between nuts and inflammation.”
Bao was surprised to find that nut eaters also tended to drink a lot.
The researchers also found that replacing protein from red meats and refined grains could lower levels of inflammatory biomarkers.