Nuts & Health

Although nuts were considered unhealthy by most people 15 to 20 years ago, new research is continuously surfacing to support the role of nuts as part of a healthy and balanced lifestyle. As research continues to enhance the body of evidence, it is important to recognize the role nuts play in promoting health.

Cardiovascular Disease

Numerous studies conclude that nuts are beneficial in improving blood cholesterol levels. Nut consumption may decrease the LDL:HDL ratio as well as decrease total cholesterol and LDL cholesterol (1). In one particular study where subjects consumed walnuts, total cholesterol was decreased by 12.4%, LDL cholesterol by 16.3%, and LDL:HDL ratio by 12.0% (1). Blood cholesterol levels appear to improve in a dose-related manner, with a higher nut consumption being associated with a greater improvement in blood cholesterol levels. Improvements in blood cholesterol levels are also more distinct in individuals with higher baseline levels of LDL cholesterol or lower BMI (2). One of the proposed mechanisms for the ability of nuts to lower blood cholesterol levels is based on the plant sterols found in nuts. These plant sterols hinder cholesterol absorption, therefore helping to lower total cholesterol levels (2).

Lower blood cholesterol levels decrease the risk of developing coronary heart disease (CHD) and multiple studies find frequent nut intake decreases the risk of CHD (2). These findings resulted in the following health claim issued by the United States Food and Drug Administration:

“Scientific evidence suggests but does not prove that eating 1.5 ounces per day of most nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease (2).”

When compared to sixty-five other food items in a food frequency questionnaire, nuts were found to have the strongest inverse relationship with myocardial infarctions and the development of CHD (1). Four or more servings of nuts per week reduces the risk of coronary heart disease by an average of 37% (1). More specifically, individuals who consume two servings of nuts each week may reduce their risk of CHD death by 16% (1). The presence of monounsaturated and polyunsaturated fatty acids in nuts may provide additional cardiovascular benefits by reducing clotting, vasoconstriction, and inflammation (1).

Insulin Resistance and Inflammation

Although a large amount of research has focused on the cardiovascular benefits, recent research shows nut consumption may also be beneficial in decreasing inflammation and insulin resistance (3). Nuts contain large amounts of magnesium and high magnesium intake is associated with decreased insulin resistance due to decreased inflammation and endothelial damage (3). Nuts are also a good source of fiber with a standard serving providing 5 to 10% of the daily requirement. Fiber lowers post-prandial glucose, helping to prevent inflammation. Monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) are also plentiful in nuts. These healthy fats may protect against the development of insulin resistance and diabetes (3). The fiber and fat found in nuts can help decrease glucose and insulin response as they decrease the glycemic index. Foods with a low glycemic index (GI) result in a slow increase in blood glucose. Low GI foods have also been shown to decrease LDL cholesterol levels in diabetics (3). Antioxidants play a role in decreasing inflammation as well. Studies examining the Mediterranean diet and its protective influence against inflammation found consuming nuts resulted in lower concentrations of inflammatory markers in the body, especially interleukin-6 (3). Evidence suggests inflammation plays a role in the development of insulin resistance, and the effect of nuts on both of these needs to be studied more in the future.

Weight Maintenance

Studies find nut consumption is not associated with weight gain. It is thought their strong satiety effects, incomplete energy accessibility, and possible ability to increase resting energy expenditure allow for weight maintenance in individuals (4). The combination of fiber, protein, unsaturated fats, and phytochemicals play a role in satiety as they require a large amount of oral processing before swallowing. A low glycemic index may also contribute to satiety. Nut cells walls do not completely break down during digestion so the body cannot use all the energy. Consequently, the total caloric content of nuts is not what is actually absorbed. More research is needed to determine if nut consumption increases energy expenditure, but several studies have found up to an 11% increase (4). The mechanism behind the increase is unclear, although the oxidation of unsaturated fats results in a high thermogenic effect (4).The high fat content slows digestion which may results in a temporary energy imbalance, resulting in increased energy expenditure.

        Table adapted from Sabaté et al.(2)

Reference List:

1.       Sabaté, J. & Wien, M. Nuts, blood lipids and cardiovascular disease. Asia Pac J Clin Nutr 19(1): 131-136, 2010.

2.       Sabaté, J., Oda, K., & Ros, E. Nut consumption and blood lipid levels. Arch Intern Med 170(9): 821-827, 2010.

3.       Casas-Agustench, P., Bulló, M., & Salas-Salvadó, J. Nuts, inflammation, and insulin resistance. Asia Pac J Clin Nutr 19(1): 124-130, 2010.

4.       Mattes, R. D. & Dreher, M. L. Nuts and healthy body weight maintenance mechanisms. Asia Pac J Clin Nutr 19(1): 137-141, 2010.