Several tree nuts are consumed as part of a balanced diet worldwide due to the health benefits. Common tree nuts include cashier's, Brazil nuts, macadamia is, pistachios, hazelnuts, pecans, and walnuts. Peanuts, which are classified as legumes, also have a similar nutrient profile to tree nuts and are identified as part of the nut food group.

Nuts are nutrient-dense foods that have increased in consumption in Western countries following the inclusion of this food group in guidelines for health promotion by several agencies including the Food and Drug Administration.

The evidence to support the claim of nuts as health-promoting foods stems from several randomized controlled trials (RCTs) which have demonstrated a beneficial effect on blood lipid and other markers of coronary heart disease (CHD) and epidemiological observation that correlates frequency of nut consumption to an inverse incident of cancer, cardiovascular disease, CHD, all-cause mortality.

Due to the high energy content of nuts (due to their high lipid content), there is a common understanding that regular consumption would promote weight gain. Contrary to these expectations, evidence from both RCTs and epidemiological studies, suggests that this is unlikely. Moreover, a recent meta-analysis of six cohort studies demonstrated that participants gained a 3 to 5% reduction in the risk of developing overweight or obesity post single serving a day increment in nut intake.

Nutrition content of Mediterranean nuts

Nuts are nutrient-dense foods containing a high total fat content which extends from 46% in pistachios to 68% in pine nuts. Per gram, nuts provide on average, 23 to 27 kJ. They are the second-highest plant food richest in fat, after vegetable oils.

Relative to vegetable oils, however, the fatty acid composition of nuts is beneficial due to the low range of saturated fatty acid (SFA) content, containing between 4 and 6%. Approximately half of the total fat content is comprised of unsaturated fat, namely monounsaturated fatty acids (MUFAs), in the majority of nuts. Among them:

• Polyunsaturated fatty acids (PUFAs) are the dominant unsaturated fatty acid in pine nuts
• PUFAs, namely linoleic and α-linolenic acids (ALA), and the plant form of omega-3 fatty acid in walnuts; among edible plants, walnuts contain the highest content of ALA of all whole foods

Nuts are also rich in other sources of macronutrients that have been shown to beneficially affect health. Nuts are considered to be an excellent source of protein. Approximately 25% of the energy content is derived from protein, and nuts often have a high content of L-arginine.

L-arginine is a substrate for nitric oxide synthesis, which occurs in the endothelium and is responsible for blood pressure and vascular tone.

Nuts also contain dietary fiber, which ranges from 4 to 11g/100g and provides 5%–10% of daily fiber requirements.

Nuts also contain a notable micronutrient profile associated with improved health. Mediterranean nuts contain:

• Vitamins E and B6, folic acid, and niacin: folic acid is essential for DNA synthesis and amino acid metabolism. Niacin is an essential co-enzyme for glycolysis, fat synthesis, and tissue restoration.
• Antioxidant vitamins (e.g., tocopherols) and polyphenols (e.g. catechins and resveratrol): Polyphenols are associated with the prevention of certain diseases, with strong antioxidant effects among an ability to modulate gene expression, decreased platelet aggregation, induce apoptosis, increase vasodilation, modulate cell signaling, and activities associated with carcinogenic activity
• Copper, magnesium, potassium: Magnesium is an essential co-factor in many enzymatic reactions as well as cardiac and pulmonary functions. Potassium is critical for many biochemical cellular reactions such as the maintenance of electrochemical gradients across cell membranes. Copper is also an essential co-factor in many enzymatic reactions
• Plant sterols (phytosterols) These include stigmasterol, campesterol, and sitosterol), and polyphenols (catechins, resveratrol, etc.) and are associated with the cholesterol-lowering due to their role in preventing the absorption of endogenous and dietary cholesterol from the small intestine. Sterols prevent lipid cholesterol incorporation into micelles, which are needed for cholesterol to dissolve

Sunflower Seeds

The effect of nuts on physiology

Nuts have widespread effects on the body. The main focus of epidemiological research with nuts has been its relation to cardiovascular disease (CVD). The conclusion of a recent meta-analysis revealed that nut consumption has a consistent benefit in both fatal and non-fatal CVD, CHD, and atrial fibrillation. The conclusions of this meta-analysis, conducted in 2019, concurred with the outcomes of two earlier meta-analyses in 2016.

These two meta-analyses summarized data from 15 studies, which showed that all-cause mortality was 19% lower in high consumers of total nuts. The second meta-analysis additionally analyzed nine cohort studies and revealed that participants with the highest quantity of nut consumption had an 18% lower risk of cancer incidence.

Outside of CVD and CHD, some epidemiological studies have suggested that nut consumption reduces type 2 diabetes risk; however, the evidence is not conclusive. Nut consumption is also reported to reduce the risk of hypertension, with a recent meta-analysis of studies demonstrating a 15% reduction in the risk of developing hypertension.

In relation to containing plant sterols, MUFAs, and PUFAs, and fiber, nut consumption has been shown to significantly decrease total cholesterol (according to a meta-analysis of 61 RCTs). Results demonstrated a decrease total cholesterol content of 4.7mg/dL, apolipoprotein B (−3.7 mg/dL) and triacylglycerols (TAG) (−2.2 mg/dL). While nuts demonstrated a lower effect on low-density lipoproteins (LDLs), they did not affect high-density lipoprotein (HDL)-cholesterol.

Concerning glucose control, a meta-analysis of 40 RCTs which had a median duration of three months demonstrated that tree nuts or peanuts had a positive effect on homeostatic model assessment (HOMA)-insulin resistance and fasting insulin but did not produce any change in fasting blood glucose or a marker of diabetes, hemoglobin A1c.

Owing to the high content of PUFAs, nuts release carbohydrates slowly and the presence of minerals accounts for these effects on glycemic control. Tying into the finding of a lack of weight gain with increased nut consumption, a meta-analysis of RCTs using nut diets relative to control diets showed significant reductions in the body mass index (BMI) of participants. The mechanistic understanding of this is attributed to the satiation effects of nuts, together with the incomplete digestion, and their ability to impede fat absorption which reduces metabolizable energy.

The following table summarises the main beneficial effects of nuts on health outcomes

*Evidence collected in the PREvención con DIeta MEDiterránea (PREDIMED) trial, among others. PREDIMED tested Mediterranean diets supplemented with extra virgin olive oil or mixed nuts versus a low fat controlled diet in a cohort of approximately 7500 participants at high risk of CVD

**Evidence collected only in the PREDIMED trial

Table adapted from Alsavar et al., 2020

Scientific evidence that suggests that nuts are health-promoting foods several meta-analyses of epidemiological observations and randomized control trials show that notes have a marked inverse association with CHD, associated mortality, total cancer, and all-cause mortality – among other health-promoting abilities.