A recent review article analyzed the nutritional value of tree nuts and their role in preventing, slowing down, or reversing the aging process. The article also explored how different processing techniques of tree nuts affect their nutritional value.
The last two decades have witnessed extensive research on health outcomes associated with the consumption of tree nuts. There has been compelling evidence of the benefits of tree nuts that has led to the inclusion of tree nuts in most recommended dietary guidelines.
By definition, tree nuts are dry fruits, almost always with a single seed, in which the ovary wall becomes hard at maturity. The most common edible tree nuts include almonds, walnuts, pistachios, cashews, hazelnuts, brazil nuts, pine nuts, and macadamias. Peanuts, that are commonly included in the nuts family and have a comparable nutrient profile, are botanically legumes. As per an FDA (food and drug administration) authorized health claim, the consumption of 43 grams of most tree nuts in combination with a low saturated fat and cholesterol diet can significantly reduce the risk of cardiovascular disease.
Tree nuts are a nutrient dense food, rich in several essential vitamins, minerals, mono- and polyunsaturated fatty acids, and fiber. In addition, most tree nuts provide phytochemicals that contribute to their health benefits. Several studies have proven the role of tree nuts on inflammatory pathways and oxidative stress, thus highlighting the potential of tree nut consumption in preventing and delaying diseases associated with aging, such as cardiovascular disease, stroke, type 2 diabetes mellitus, neurodegenerative diseases, and cancer.
Many review articles published in the past describe the health benefits of tree nuts. More recently, an article published in the Journal of Royal Society of Chemistry, Food & Function, by a group of researchers in Romania, described in detail the nutritional benefits of macronutrients and micronutrients as well as phytochemicals present in tree nuts. The review also emphasized the anti-aging effects of bioactive compounds in tree nuts and their mechanism of action. Lastly, the researchers evaluated how the processing techniques used to prepare tree nuts affected their antioxidant activity.
Nutrients in tree nuts
After vegetable oils, nuts are the richest dietary source of fat. The saturated fatty acid content, however, is low in tree nuts while heart-protective monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) make up most of the total fat content. For instance, walnuts have the largest quantity of alpha-linolenic acid (ALA). This is the plant omega-3 fatty acid contributing to the health benefits associated with walnuts. Studies suggest that the presence of different types of fatty acids; saturated, MUFAs, and PUFAs, exert a synergistic effect resulting in favorable lipid profile and better health.
Tree nuts are a very good source of proteins, without the disease-causing and pro-aging effects of animal proteins. The proteins in tree nuts are of high biological value containing the amino acids that are necessary for protein creation. In addition, nuts have a high concentration of the amino acid L-arginine, which helps in the formation of nitric oxide (NO), a potent vasodilator.
Tree nuts are a source of fiber and a standard serving provides 5-10% of the daily fiber requirement. Tree nuts also contain a significant amount of vitamin E, making them powerful antioxidant, anti-inflammatory, and antibacterial foods. Vitamin E (tocopherols α, β, γ, and δ) is also known to protect against cardiac, hepatic, and renal damage as well as cancer. Almonds have the highest level of a-tocopherol while walnuts, pecans, and pistachios have a high amount of g-tocopherol.
Nuts also contain folate in good amounts. Folate is a B-vitamin that plays an important role in maintaining normal cellular function. Furthermore, nuts are rich in healthy minerals such as calcium, magnesium, and potassium but low in sodium.
Other biologically active compounds in tree nuts
Phytochemicals are biologically active compounds found in plants. Although scientists are still working to fully characterize phytochemicals, there are broad categories of these compounds that have been studied. The important phytochemicals present in tree nuts include polyphenols, carotenoids, phytosterols, phytates, and lignans. These compounds contribute to the health benefits associated with nut consumption. Studies have shown that these phytochemicals have antioxidant, anti-inflammatory, anti-mutagenic, and anti-cancer properties. This broad range of bioactivity of phytochemicals helps in preventing or slowing down aging and age-related diseases.
Health benefits of the unique composition of tree nuts
Chronic inflammation and oxidative stress are the main causes of age-related diseases and cancer. Inflammatory processes induce oxidative stress in the body that leads to a reduced antioxidant capacity of the cell. A resulting increase in free radicals can lead to DNA damage and mutations. Studies have linked chronic inflammation and oxidative stress to neurologic disorders, metabolic syndrome, diabetes, cancer, and cardiovascular diseases. The bioactive compounds present in tree nuts act through complex mechanisms to slow down or even reverse the damage done by inflammation and oxidative stress.
Studies show that polyphenols work as powerful antioxidants that neutralize free radicals thus protecting DNA, proteins, and lipids from damage. In addition, polyphenols act as indirect antioxidants by suppressing the formation of free radicals. Polyphenols also modulate cell signaling pathways that are responsible for cellular defence mechanisms against oxidative stress. Interestingly, these signaling pathways of cellular defence get weaker with age causing susceptibility of an individual to age-related diseases. However, polyphenols from tree nuts may help delay the aging process by modulating these pathways.
Furthermore, polyphenols are associated with improving gut microbiota. Studies show that polyphenols increase the strains of bacteria related to cancer prevention, reduction of C-reactive protein levels, and increase in plasma HDL levels. Other polyphenols such as resveratrol prevent aging and carcinogenesis by UV radiation.
In addition to polyphenols, the presence of phytosterols, tocopherols, folic acid, L-arginine, low sodium, high calcium, magnesium, and potassium, and a good ratio of omega-3/omega-6 fatty acids among many other nutrients in tree nuts contribute to enhanced health and an increased lifespan.
Bioavailability of nutrients based on the processing method of tree nuts
Undoubtedly, polyphenols and other bioactive compounds in tree nuts benefit human health. But the positive effects of these compounds depend on their stability and bioaccessibility. The cooking and processing techniques of tree nuts were reviewed in this article and some valuable information was shared.
Almond skin has the highest content of phenolic acid and flavonoids. Almonds roasted at 2000C for 20 minutes have the highest antioxidant levels while blanching leads to a loss of polyphenols from the almond skin. For cashews, high-temperature treatment for shorter periods of time increases the total phenolic content and antioxidant capacity compared with the raw cashews. Roasted cashews prove to be the most beneficial.
Hazelnuts are usually consumed roasted. However, hazelnut skin, which is removed during processing, has the highest concentration of polyphenols. Studies found a microwave assisted hot air roasting process had a positive effect on total phenolic content and antioxidant activity.
Pecans have a very high PUFA concentration and researchers recommend storing pecans at low temperatures and consuming them raw. The total phenolic content and antioxidant activity of stir-fried pine nuts were found to be higher than raw pine nuts. However, high-temperature processing for long periods of time results in a decrease in the health benefits of pine nuts. Pistachios have the maximum health benefits if eaten roasted in the microwave at 640 W for four minutes. Lastly, fresh kernels of walnuts have the highest nutritional value and it is recommended that walnuts should be stored at low temperatures and eaten raw.
Evidence suggests a correlation between antioxidants and an increased lifespan
Growing evidence suggests a direct correlation between antioxidants and an increased lifespan. The present review highlights the array of biological compounds present in tree nuts and the role they play in preventing, delaying, and treating age-related diseases. Tree nuts are also a vital source of healthy fats, vitamins, and minerals. Studies have proven the antioxidant and anti-inflammatory effects of tree nut consumption in maintaining good health and improving lifespan. Therefore, it is vital to include tree nuts as an essential part of a healthy diet.
Written by Preeti Paul, MS Biochemistry
Reference: Marius Emil Rusu et al. Anti-aging potential of tree nuts with a focus on the phytochemical composition, molecular mechanisms and thermal stability of major bioactive compounds. Royal Society of Chemistry, Food & Function. February 2018. DOI: 10.1039/c7fo01967j