The nuts issue

Eating peanuts on a regular basis has already been shown to help prevent cardiovascular disease. But a new study reveals that this may not be entirely due to the high fatty acid content of the nuts.

A small study in the US found that peanuts lower triglycerides and improve total diet quality by increasing a number of nutrients associated with the prevention of heart disease, including magnesium, folate, vitamin E, copper, arginine and fibre.

Lead investigator Dr Richard Mattes, from the Department of Foods and Nutrition at Purdue University, said: "We wanted to determine the impact of peanut consumption on total diet quality. We found that including peanuts in the diet significantly increased magnesium, folate, fibre, copper, vitamin E, and arginine consumption, all of which play a role in the prevention of heart disease."​

The findings, reported in this month's Journal of the American College of Nutrition​, are consistent with several clinical and epidemiological studies, such as the Nurses Health Study, which found that people who consume about one ounce of peanuts, nuts and peanut butter per day improve blood lipid levels and decrease risk of cardiovascular disease.

The Purdue University researchers observed the effects of incorporating peanuts into the daily diet in a study on 15 healthy men and women. The participants either followed a Free-Feeding diet, which involved including 500 calories of peanuts without any dietary guidance. The second Addition treatment entailed adding 500 calories of peanuts to each participant's usual diet. The third Substitution treatment asked participants to substitute peanuts for 500 calories from fat in their usual diet.

The team found that triglycerides, an emerging risk factor for heart disease, were lowered in all treatment groups and were significantly lower in the Addition and Substitution groups at 24 and 18 per cent respectively. This could translate into an 8 and 6 per cent decrease in risk of cardiovascular disease, report the researchers. The findings are consistent with a previous clinical study at Penn State University (American Journal of Clinical Nutrition​ 1999) that found a 13 per cent decrease in triglyceride levels when participants consumed a diet with peanuts and peanut butter, compared to the average American diet.

The peanut diets also affected serum magnesium levels, which when elevated can help to inhibit platelet aggregation and activity, known risk factors for heart disease. It has been shown that the risk of cardiovascular disease increases with magnesium concentrations below 0.81 mmol/L. During the Free-Feeding treatment, each of the six subjects with magnesium concentrations below 0.81 mmol/L improved their status. A significant increase in serum magnesium levels was observed across all treatments (average increase from baseline was 58 per cent).

Dietary intakes of fibre, vitamin E and copper, all nutrients with cardiovascular disease-reducing properties, increased, and the ratio of lysine to arginine decreased significantly from baseline in all treatments. Dietary folate also increased in all treatments, as expected, since peanuts are a good source of folate.

Throughout the study, peanut consumption led to favorable changes in the fat profile of the diet: saturated fat decreased and unsaturated fat increased as a portion of calories. No changes were found in total plasma homocysteine concentration.

The study was funded by a grant from the US Agency for International Development.