Nuts, encompassing both tree nuts and peanuts, stand out as nutrient-dense powerhouses, boasting intricate profiles rich in unsaturated fats and an array of bioactive compounds. From high-quality plant proteins to fiber, minerals, tocopherols, phytosterols, and phenolic compounds, the diverse composition of nuts suggests promising health benefits. Epidemiological studies link nut consumption to reduced risks of coronary heart disease, gallstones, and diabetes, with emerging evidence indicating positive effects on high blood pressure, cancer, and inflammation. Interventions consistently highlight cholesterol-lowering effects, coupled with promising signs related to oxidative stress, inflammation, and vascular reactivity. Notably, nut consumption appears to positively influence blood pressure, visceral obesity, and metabolic syndrome. Surprisingly, regular nut consumption is not associated with obesity; instead, evidence suggests potential contributions to weight loss. Safety concerns are minimal, primarily limited to rare cases of nut allergy in children. In summary, nuts emerge as nutrient-dense allies, offering broad cardiovascular and metabolic benefits seamlessly integrated into a healthy diet.
Tree nuts, defined as dry fruits with a single seed and a hardening ovary wall at maturity, encompass popular choices like almonds, hazelnuts, walnuts, and pistachios. Edible nuts extend to pine nuts, cashews, pecans, macadamia, and Brazil nuts. Notably, peanuts, though botanically legumes, are widely classified as nuts due to their similar nutritional profiles. Chestnuts, despite being tree nuts, stand apart with their starchiness and distinct nutritional composition.
Nuts, seeds, and legumes, rich in nutrients, have been dietary staples since pre-agricultural times. In Western cultures, nuts feature in various forms: as snacks, desserts, or meal components, whether whole, spread (peanut butter, almond paste), in oils, or subtly embedded in commercial products, mixes, sauces, and sweets. Despite their historical significance, nut consumption experienced a decline in the past century in many industrialized nations.
Nuts are rich in vegetable protein and predominantly contain unsaturated fatty acids, alongside a diverse array of nutrients. This includes dietary fiber, vitamins (folic acid, niacin, tocopherols, and vitamin B6), and minerals (calcium, magnesium, potassium), along with various bioactive compounds.
Despite their high energy density, both epidemiological studies and clinical trials defy expectations by indicating that regular nut consumption does not contribute to obesity or elevate the risk of diabetes.
Undoubtedly nutrient-dense, nuts, excluding chestnuts, boast a high total fat content ranging from 45% in cashews to 75% in macadamia nuts, delivering 20 to 30 kJ/g. Despite their fat richness, the favorable fatty acid composition stands out with low saturated fatty acid (SFA) content (4-16%) and nearly half of the total fat comprising unsaturated fat, primarily monounsaturated fatty acids (MUFA) such as oleic acid. While most nuts balance MUFA and polyunsaturated fatty acids (PUFA), variations include PUFA dominance in pine nuts and a notable presence of both linoleic acid and alpha-linolenic acid (ALA), an Omega-3 fatty acid, in walnuts—the latter being a standout with the highest ALA content among edible plants.
Beyond fats, nuts emerge as rich sources of bioactive macronutrients with potential metabolic and cardiovascular benefits. They pack approximately 25% of energy as protein, often featuring high L-arginine levels, a precursor to nitric oxide (NO) associated with improved vascular reactivity. Additionally, nuts contribute 4 to 11 grams of dietary fiber per 100 grams, fulfilling 5-10% of daily fiber requirements in standard servings.
Nuts not only provide essential micronutrients associated with enhanced health but also contain substantial amounts of folate, a crucial B vitamin. Folate plays a pivotal role in normal cellular function and aids in detoxifying homocysteine—a sulfur-containing amino acid with atherothrombotic properties. Abnormal folate status can lead to homocysteine accumulation in plasma, emphasizing the importance of this B vitamin.
Additionally, nuts serve as rich sources of antioxidant vitamins, such as tocopherols, and phenolic compounds. These antioxidants, initially protecting the seed from oxidative stress, remain bioavailable post-consumption, offering an antioxidant boost. Notably, almonds excel in α-tocopherol content, while walnuts feature significant amounts of γ-tocopherol, a less-explored but increasingly recognized anti-atherogenic molecule. It’s worth mentioning that the majority of antioxidants in nuts are concentrated in the shell or soft outer layer, with over 50% lost when the skin is removed, as observed in almonds and peanuts. Intriguingly, roasting almonds preserves phenolic compounds more effectively than blanching. Walnuts stand out as an exception, commonly consumed raw and unshelled.
Indeed, while nuts themselves are cholesterol-free, their fat component contains notable levels of chemically related non-cholesterol sterols, classified as plant sterols or phytosterols. These compounds, integral to plant membranes, play a crucial structural role, stabilizing phospholipid bilayers much like cholesterol does in animal cell membranes. Phytosterols, being hydrophobic and possessing a bulkier hydrocarbon molecule, have a higher affinity for micelles than cholesterol. This unique property interferes with cholesterol absorption in the intestinal tract, limiting its availability for absorption and contributing to a cholesterol-lowering effect. The mechanism involves displacing cholesterol from micelles, and the phytosterol content in nuts likely plays a significant role in this beneficial impact on cholesterol levels.
Nuts stand out for their favorable nutrient density, particularly in essential minerals such as calcium, magnesium, and potassium, surpassing many common foods. Raw or roasted, unprocessed nuts exhibit very low sodium content, akin to vegetables, ranging from undetectable in hazelnuts to 20 mg/100 g in peanuts. Elevated intake of calcium, magnesium, and potassium, coupled with low sodium, is linked to protection against bone demineralization, arterial hypertension, insulin resistance, and overall cardiovascular risk. Notably, the low sodium advantage is forfeited when nuts are consumed as salty products.
In summary, the comprehensive profile of macronutrients, micronutrients, and nonnutrient components in nuts collectively contributes to lowering the risk of coronary heart disease (CHD) and related metabolic disorders. Whole, unshelled, and unprocessed nuts emerge as a natural health capsule, embodying the principle that the whole is greater than the sum of its parts.
While certain bioactive compounds in nuts, such as tocopherols, phytosterols, folic acid, selenium, and magnesium, exhibit antioxidant, anti-inflammatory, or anti-cancer properties, early epidemiological evidence on the role of nut consumption in cancer incidence was inconclusive. However, more recent reports suggest a preventive role, particularly in women.
For instance, a Greek case-control study indicated a 27% reduced risk of endometrial cancer with a diet high in nuts, seeds, and legumes. In colorectal cancer, a gender difference was noted in a Taiwanese study, revealing a 60% risk reduction in women consuming peanuts, while no protective effect was observed in men. Similarly, a small clinical study in men at risk of prostate cancer, supplementing with 75 g of walnuts daily, showed increased serum gamma-tocopherol and a tendency to boost the ratio of free prostate-specific antigen (PSA): total PSA.
Additionally, recent experimental studies using human cancer cell lines and a mouse model of human breast cancer demonstrated the anti-proliferative effects of walnuts. Despite the complexity of these findings, they collectively suggest a nuanced relationship between nut consumption and cancer prevention, potentially influenced by gender and specific cancer types.
Interventional studies exploring the impact of nut-enriched diets on blood sugar control in diabetic patients and insulin sensitivity in insulin-resistant states have yielded varied results. While nuts showed no significant effects on fasting or postprandial glucose and hemoglobin A1C in diabetic patients, changes in insulin sensitivity have been inconsistent across different populations.
Studies involving healthy subjects, hyperlipidemic patients, and those with insulin-resistant states like obesity or metabolic syndrome did not demonstrate a consistent effect. However, recent small studies reported a decrease in insulin levels in patients with metabolic syndrome and diabetes after consuming nuts. A three-month report from a larger study found that a nut-enriched Mediterranean diet was associated with improved insulin sensitivity and fasting glucose levels in non-diabetic and diabetic participants, respectively. Additionally, research from the same group indicated reduced postprandial glucose and insulin after almond meals compared to meals with high-glycemic index carbohydrates.
In summary, despite their high energy and fat content, nuts do not worsen metabolic control and may even improve insulin sensitivity in insulin-resistant states. However, more evidence is required to establish a clearer understanding of these effects.
Indeed, nuts stand out as a popular and crucial source of unsaturated fat and high-quality plant protein in vegetarian diets, surpassing meat substitutes in common consumption. Their optimal nutrient profile, coupled with compelling evidence from epidemiological and clinical studies showcasing health benefits, underscores their essential role in a well-rounded plant-based diet.
Accumulated knowledge emphasizes the positive health outcomes associated with dietary patterns resembling the Mediterranean diet, where nuts play a key role as a nutrient. Both adherence to the Mediterranean diet and the frequency of nut consumption rank among the dietary factors with robust evidence for a causal relationship in preventing coronary heart disease (CHD). This underscores the significance of incorporating nuts into a balanced diet, especially for those following plant-based lifestyles.