The Beneficial Health Effects of Nuts in the Diet

Abstract

Nuts are nutritional containing foods that nature has gifted with complex matrix of bioactives and beneficial nutrients including poly- and monounsaturated fatty acids, antioxidant phenolics, phytosterols, tocopherols, minerals, fibers, and high-quality proteins. Because of their unique nutritional composition, they are beneficial to human health. Many epidemiological studies reported the beneficial effect of nuts on coronary heart diseases as well as in diabetes for both males and females. Nut crops also have good effects on inflammation, vascular damage, oxidative stress, cancer, and hypertension. Interventional studies reported that nut consumption has lipid lowering effect. Nuts are thus among the most highly nutritious foods available. When left in their shells, many nuts have a long lifespan and can be easily kept for winter use. Much research has been conducted on nuts and their beneficial effects on health. This chapter discusses the current knowledge of nuts crops and their beneficial effects on health. Currently available literature suggests that consumption of nuts particularly as part of healthy diet is associated with beneficial outcomes such as better cognitive function, decreased risk of cardiovascular and metabolic abnormalities, and cancer. Further, long-term and interventional studies are required to make a definitive conclusion on the health-promoting effects of nuts consumption through the diet.

1. Introduction

Nuts are a rich source of protein, healthy fats, fiber, vitamins, and minerals. In addition, they contain an amount of unsaturated fats that reduce heart disease. Nuts are difficult to characterize in a way to be acceptable by the botanists and compatible for general use. The groundnut or peanut, for example, is a legume, whereas the chufa nut, which is found in southern Europe and Africa, is a tuber. In some languages, such as French, don’t even have a generic term for nuts. In French, “Noix” appears like one, but it simply means walnuts. Nuts consist of dry fruits consisting of one or two edible kernels inside a hard shell. They are included Brazil nuts; cashew nuts; hazelnuts; macadamias; pecans; pine nuts; pistachios; Walnuts; peanuts. They are a rich source of protein, carbohydrates, vitamins (B1, B2, B3 and vitamin E), unsaturated fats, and minerals such as (magnesium, potassium, calcium, plant iron, and zinc), so nuts have a medical importance as it works to maintain weight, diabetes control, heart disease prevention through reducing low-density lipoprotein (LDL). Nuts are extremely healthy and important to people in many parts of Asia and Africa. The majority of nuts are high in fat (e.g., pecan 70%, macadamia nut 66%, Brazil nut 65%, walnut 60%, almonds 55%, and peanut butter 55%). Only very few have a very high content of starch [1], while most have a significant protein level (in the 10–30% range). Many nuts have recently been discovered to be particularly high in antioxidants [2]. Nuts are thus among the most highly nutritious foods available. When left in their shells, many nuts have a long lifespan and can be easily kept for winter usage. Much research has been carried out on nuts and their beneficial health outcomes. The published report from the pioneering Adventist Health Study showed a relationship of nut consumption and lower risk of coronary heart disease (CHD) in 1992 [3]. Ros [4] published a clinical study indicating that a walnut-enriched diet lowers serum cholesterol levels when compared to a balanced diet. A recently published book [3] and the papers of a Symposium on Nuts and Health held at the U.S. Department of Agriculture Studies Laboratory in the University of California at Davis [5] provided extensive information on research published about nuts and their beneficial health outcomes up to 2005. Nuts contain one seed, they are dry fruit, and upon maturity the ovary wall becomes hard. The most consumable nuts are Juglans regia (walnut), Corylus avellana (hazelnut), Pistachia vera (pistachios), Anacardium occidentale (cashew nut), and Prunus amigdalis (almond). Other commonly consumed nuts are (Macadamia integrifolia) macadamias, (Pinus pinea) pine nuts, (Carya illinoiensis) pecans, and (Bertholletia excelsa) Brazil nuts. Pea nut (Arachis hypogea) is a legume or ground nut and also comes under the definition of nut by consumers. Peanut contains similar nutrients as other nuts [6]. Nuts, pulses, and seeds are all high in nutrients and have been part of mankind’s diet from pre-agricultural era [7]. Nuts are ingested whole (roasted or fresh), in spreads (almond paste, peanut butter), as oils, sauces, mixed dishes, pastries, ice creams, and baked goods in Western countries as desserts, snacks, or as part of meal. Except for vegetarians and other health-conscious community, such as Seventh-Day Adventists, nuts consumption is reduced in most industrialized countries throughout the last century, becoming only a minor source of energy in daily diets [8]. Recently, nut consumption increased in Western region. This food has wide media coverage and also included in healthy eating as these have many beneficial health effects. The nuts are considered as part of optimal diet and are found involved in preventing the chronic heart disease [9]. In 2003, the US Food and Drug Administration reported that intake of nut reduces the risk for CHD and lowers the serum cholesterol level. Since then, nuts have become part of healthy diet [10], and the American Heart Association reported that the nut consumption through diet is ideal for cardiovascular health and overall general health 2020 [11].

The scientific data for nuts as cardio-protective foods come from a combination of epidemiological observations suggesting a consistent inverse relationship between nut consumption and the development of CHD [12] and the several clinical trials revealed the potential benefits of nut consumption on the lipid profile [13] and other intermediate markers of CHD [13, 14]. The synergistic effect of various bioactive elements of nuts, which may all favorably influence the human physiology, is most likely the mechanism for these beneficial effects. As a result, nuts are high in vegetable protein and fat, primarily unsaturated fatty acids. They are also high in dietary fiber [14], vitamins (such as niacin, folic acid, vitamin B6, and tocopherols), minerals (calcium, potassium, and magnesium), and many other bioactive elements such as phytosterols and phenolic compounds. Despite the fact that nuts have a high energy density, evidence from epidemiological research and clinical studies suggests that frequent consumption does not lead to obesity or raise risk of diabetes [15]. This chapter discusses the common edible nuts, their nutrient composition and beneficial health effect.

1.1 Almonds

Almonds are scientifically called Prunus dulcis and are also known as sweet almonds. It belongs to Rosacea family. It is a good source of nutrients and is popular in general population as a healthy food. The demands for almonds consumption increases day by day. It consists of many nutritious constituents such as amino acids, lipids, fatty acids, carbohydrates, proteins, vitamins, and secondary metabolites. The environmental and genetic factors affect the nutritional composition of almonds. Almond has therapeutic and protective effect as well. Research confirmed the prebiotic potential of Prunus dulcis. Clinical studies reported the modulatory effect of almond on serum lipid, glucose, and uric acid level and its role on body weight, obesity, cardiovascular diseases through raising the levels of good cholesterol and reducing the levels of bad cholesterol, diabetes, and metabolic syndrome [16].

Almond is native to Central Asia, but now it grows all over the world in temperate region [17].

In present days, USA produce almond largely and followed by Australia and Spain. The different varieties of almond have different chemical composition because of different genetic, ecological, and processing conditions. Regular intake of nut produces beneficial health effects against many ailments including cardio-metabolic disease [18]. Several epidemiological and clinical studies reported the beneficial health effect of almond against number of diseases such as metabolic syndrome, hypertension, obesity, and diabetes mellitus [19]. Regular consumption of nuts reduces body weight and improves the metabolic health [19].

The prunus kernel consists of a seed, which is edible part. The seed is covered by brown skin. Externally hull is present, which protects the seed. The hull is an intermediate shell [16]. When fruit mature, hull opens and seed separates. Almonds contain lipids, proteins, and carbohydrates. They have low moisture content and less bioactive compounds. The macro and micro-nutrients present in almonds are responsible for its beneficial health effects [20]. The diversity is present among the verities. The method of cultivation and climatic factors affect the chemical composition of almond [21].

Chemical composition also changes in raw and roasted form. Roasting processes alter the lipid composition and further involve in oxidation process, which lessens the antioxidant compounds. Almond acts as prebiotics that promote gut microbes. The polyphenols and fiber contents act as a substrate for microorganism for microbial fermentation [22].

1.2 Pistachios

Pistacia vera L., commonly known as pistachio, belongs to Anacardiaceae family. It is an ancient nut tree. It is distributed in central and south-west Asia and in the Mediterranean region. Valle del Platani and Bronte are two main cultivars of Pistachio. The soil composition and climate conditions of Asia and Mediterranean regions are much favorable, and the pistachio nuts grown in these regions are of dark green color, good nutritional contents, and pleasant aromatic taste. Its bioactive phytoconstituents, fatty acid composition, and pharmacological activities have been evaluated. Research showed its biological and pharmacological properties [23]. Pistachio contains dietary fibers, protein, vitamins, magnesium, unsaturated fatty acids, polyunsaturated fatty acids, vitamin K, Vitamin B, and vitamin A. It also contains phytosterols, lutein, γ-tocopherol, and polyphenols. All these phytoconstituents are antioxidant in nature. The pistachio nuts have therapeutic role in type II diabetes mellitus, obesity, and cardiovascular diseases. It has antioxidant and anti-inflammatory activities. Regular intake of pistachio nut improves health and dysmetabolic condition and helps in preventing chronic degenerative diseases [24].

1.3 Walnuts

United States produced 504,000-ton walnut in 2010 positioned after almond, i.e., 820,000 ton. Juglans regia L. is commonly known as Walnut OR English walnut. Its origin is Persia and is distributed to United States. California produces 90% of English walnuts. Black nut is another variety produced largely by United States. Walnut is largely consumed worldwide. In the USA, almonds, pistachios, and pecans are largely consumed nuts [4]. English and black walnuts are used in cooking items for cereals, candies, snacks, and backed goods. Black walnut has small kernels and thick hard shell, the commercial value of which is lower than that of English walnut.

The clinical and epidemiological studies showed the therapeutic and beneficial effects against several diseases, including diabetes mellitus, oxidative stress, cardiovascular diseases, inflammation, cancer, and neurodegenerative disorders [25]. The beneficial effects of health have been due to the presence of bioactive nutrients such as tocopherls, phytosterols, proteins, fibers, minerals, and fatty acids [26].

In spite of the black nut being rich in a variety of chemical constituents, the English walnut is more investigated.

The importance of nuts as antioxidants is due to the fact that they contain polyphenols compounds that reduce oxidative stress by neutralizing free radicals [27]. A scientific study has proven that walnuts have a greater antioxidant capacity than fish, in addition to protecting the fats in sensitive cells from being damaged as a result of exposure to oxidative stress [28].

A study conducted on 13 people who ate a regular meal of walnuts and almonds confirmed that polyphenol levels increased and oxidative stress was significantly reduced [29]. Research has also proven that eating nuts reduces bad cholesterol levels by 26–33% within 2–8 hours of eating them, and it is known that an increase leads to heart complications [30].

1.4 Cashew nut: Anacardium occidentale

Cahew nut botanically known as Anacardium occidentale belongs to Anacardiaceae family. Anacardiaceae family has 400–600 species. Among these species, cashew from Anacardium genus is rich source of nutritive constituents. It is a tropical plant distributed in South America and Brazil.

Cashew plant is 5–14 m in height. It has short trunk and irregular branches scattered on the ground. Leaves are green, and flowers are short. Cashew nut fruit is edible and is used for medicinal and food purposes. Cashew nut gained fame in Second World War due to its by-product nut shell liquid.

It has nutritional properties and pleasant taste. Cashew nut lowers the serum low density lipoprotein and cholesterol level, hence preventing coronary disease. Cashew contains fats and protein. Protein includes cysteine, lysine, valine, arginine, and vitamins such as E, D, and C. Cashew gum is used against many ailments. Cashew nut contains many unsaturated fatty acids and less saturated fatty acids. It has health effects against many diseases such as oxidative stress, diabetes, and cardiovascular disease. It is used in diabetes, obesity, heart disease, digestive disorders, urinary disorders, and in several other ailments such as bone relaxation, common cold and flu, etc. It is also effective in cancer and has antiaging properties [31].

1.5 Peanuts

Arachis hypogaea (peanut) belongs to the family leguminoseae. It is also known as ground nut. It is distributed worldwide. Asia is the largest producer of peanuts and accounts for 60% of world production [32]. There are many cultivars of peanuts but four major cultivars include Virginia, Spanish, Runners, and Valencia [33]. Peanut is the rich source of vitamins, fibers, proteins, oils, and carbohydrates. Peanuts contain vitamins, proteins, fibers, oils, and carbohydrates in abundant amount and consumed worldwide due to easy availability and low cost as compared to other nuts [34]. Peanuts are commonly used in snacks, butter, and confectionary. Peanut oil is extracted and used worldwide. In the United States, peanut crop is used in making peanut butter and snacks.

The oil extracted from peanut is rich source of protein, vitamins, minerals, antioxidant, and dietary fiber. The oil is consumed by human beings and used in animal feed. The clinical studies reported that peanut intake reduced certain chronic ailments such as diabetes, cholelithiasis, and coronary diseases in both males and females. The peanut reduces the body weight and also cures hypertension. It has anti-inflammatory and anticancer activity. Peanuts have many health benefits, which are because of their valuable nutrient components. The vitamin B, E, and fibers play protective role in health. Peanuts have economically low cost, easily available and affordable to general population. It can also be used against malnutrition in developing countries due to its nutrient contents. The Indian raw peanut kernel contains 47.27% fat, 17.43% carbohydrate, 5.25% moisture, 25.48% protein, and 1.84% ash. Peanuts contain essential amino acids and are easily digestible. Vegetarians who are not taking animal meal depend upon plant sources for protein such as soybeans and peanuts.

Peanut protein is an alternate source of animal protein. All 20 amino acids are present in peanuts in different ratios. The arginine is present in highest amount. It also contains cysteine and methionine in limited amount [35].

1.6 Betel nut

Areca catechu is the source of betel nut. It belongs to family Palmae. Betel nut is masticatory, stimulant, astringent, sialagogue, sweeten breath, emmenagouge, anthelmintic, resolving, and repercussive. It stimulates the peristaltic movement of intestine. Due to its astringent properties, it constricts bronchial muscles. It is anthelmintic and works against tape worm, round worm and also used in veterinary practice. Beetle nut is also effective in dysentery and diarrhea. This nut is effective in dyspepsia and has emmenagouge properties. Betel nut is astringent used in gingivitis to stop bleeding from gums and gives strength to teeth. It is used in female vaginal discharges and in heart burning condition of pregnancy. Chief use of betel nut in the Orient is as breath-sweatening masticatory enjoyed by people from centuries and used in Pan. In conjunctivitis and epiphora, the nut is made into ash, made more fine, and applied as collyrium giving relief [36].

1.7 Nutrient composition of nuts

Nuts are nutrient-rich foods. Nuts are the richest source of fat after vegetable oils. They are nutrient-containing plants, Table 1.

Nuts	Energy (kJ)	Fat (g)	Saturated fatty acid (g)	Mono saturated fatty acids (g)	Polysaturated fatty acids (g)	Linoleic acid (g)	α-linolenic acid (g)
Almonds	2418	50.6	3.9	32.2	12.2	12.2	0.00
Brazil nuts (dried)	2743	66.4	15.1	24.5	20.6	20.5	0.05
Cashews	2314	46.4	9.2	27.3	7.8	7.7	0.15
Hazelnuts	2629	60.8	4.5	45.7	7.9	7.8	0.09
Pistachios	2332	44.4	5.4	23.3	13.5	13.2	0.25
Peanuts	2220	49.2	6.8	24.4	15.6	15.6	0.00
Walnuts	2738	65.2	6.1	8.9	47.2	38.1	9.08

Table 1.

Average nutrient composition of nuts (per 100 g).

Fatty acids present in nuts are beneficial because saturated fatty acids present in lower amount. They are also the rich source of bioactive constituents such as proteins, minerals, fibers, tocopherols, and phytosterols, Table 2.

Nutrients	Almonds	Walnuts	Cashews	Pistachio	Hazelnuts	Brazil- nuts	Chest- nuts
Water (g)	4.14	4.07	5.20	4.37	5.31	3.42	48.65
Energy (kcal)	579	654	553	560	628	659	213
Protein (g)	21.15	15.23	18.22	20.16	14.95	14.32	2.42
Carbohydrates (g)	21.55	13.71	30.19	27.17	16.70	11.74	45.54
Dietary fiber (g)	12.5	6.7	3.3	10.6	9.7	7.5	8.1
Total sugars (g)	4.35	2.61	5.91	7.66	4.34	2.33	-
Total lipids (fat) (g)	49.93	65.21	43.85	45.32	60.75	67.10	2.26
Phosphorus (mg)	481	346	593	490	290	725	93
Potassium (mg)	733	441	660	1025	680	659	518
Calcium (mg)	269	98	37	105	114	160	27
Magnesium (mg)	270	158	292	121	163	376	32
Iron (mg)	3.71	2.91	6.68	3.92	4.70	2.43	1.01
Zinc (mg)	3.12	3.09	5.78	2.20	2.45	4.06	0.52
Manganese (mg)	2.179	3.414	1.655	1.200	6.175	1.223	0.952
Copper (mg)	1.031	1.586	2.195	1.300	1.725	1.743	0.447

Table 2.

Nutritive values of nuts per 100 gram.

1.8 Nuts and health

This chapter was planned with the aim to explore and highlight the beneficial health outcomes identified through nut consumption, which are categorized as oxidative stress, inflammation, prevention of cardiovascular diseases, management of body weight, and the modulation of glucose level in the body, Figure 1.

Figure 1.

Medical benefits of nuts.

2. Oxidative stress and inflammation

Nuts are sources of phenolic compounds and tocopherols with anti-inflammatory and antioxidant activities. The beneficial effects of cashew nuts on oxidative stress and acute and chronic inflammatory processes have recently been investigated in various in vivo experimental models on mice, such as ischemic injury, lung injury, pancreatic injury induced by cerulean, paw edema induced through carrageenan, osteoarthritis induced through monosodium iodoacetate (MIA), and colitis induced by dinitrobenzene sulfonic acid (DNBS) [37]. Antioxidative, anti-inflammatory, and analgesic activities of cashew nuts have been highlighted and hypothesized that these beneficial effects have correlation with the high phenolic contents in cashews mediating the 5-LOX COX pathway activation [37]. The effectiveness of Brazil nut and pistachio against inflammation and oxidative stress has also been demonstrated through in vivo studies [38].

Published study findings suggest that intake of nuts may contribute in the protection against inflammatory processes and oxidative stress, which is mainly because of the abundantly present bioactive metabolites such as carotenoids, flavonoids, and phenolic compounds found in the kernel and skin as reported in published studies.

Clinical and epidemiological studies suggested that antioxidant vitamins, ω-3 PUFA, magnesium, L-arginine, and dietary fiber may play an essential role in the modulation of inflammation. The relationship observed between inflammatory markers and frequent nut consumption has reported mixed results when investigated in controlled feeding intervention [39].

3. Prevention of cardiovascular diseases

Association between nut consumption and decreased risk of ischemic heart disease (IHD), cardiovascular disease (CVD), and the incidence and mortality of CVD has been consistently proven by the epidemiological studies [40]. Consumption of nuts also increases longevity in addition to protection against CVD [41]. Nuts being the dense source of energy due to the high content of bioactives play significant role in decreasing the risk of CVD through multiple mechanisms: by having positive influence on lipid and/or glucose homeostasis [42], hypercholesterolemia [43], obesity [44], oxidative and inflammatory biomarkers, and antioxidant defenses.

Nuts consumption has positive effects on various CVD risk factors including improvements in lipoprotein cholesterol, total cholesterol (TC), and triglycerides [45]. The authors of the published studied attributed that cardioprotective potential of almonds is due to their dense bioactive contents such as phytosterols, dietary fiber, and high poly-unsaturated fatty acids contribute to their conserving HDL-C and LDL-C lowering effects [46]. Later on, it was reported that almonds incorporated [47]. Additionally, walnut supplementation increases the HDL-C after treatment for 6 months possibly due to the higher intake of PUFA.

The reduced risk of CVD through almond snacking by increasing variation in heart rate in healthy adults during mental stress and the consumption of whole almond was linked with better quality diet and reduced CVD risks in the adult population of UK have been demonstrated in a randomized controlled trial study [48]. The authors also reported the association of almond snacks consumption with significant endothelial function improvement, in addition to the lowering LDL-C among adults with above average risk of CVD.

Numerous studies have indicated that eating nuts reduces the risk of heart disease and stroke, due to the fact that they contain polyphenol compounds that reduce the level of bad cholesterol and work to reduce the rate of inflammation in the body by reducing inflammatory markers C-reactive protein (CRP) and interleukin 6 (IL-6) [49].

Also, in one study of five people who took cashews, lower blood pressure was observed in addition to lower triglyceride levels [50].

4. Modulation of glucose

The beneficial role of nuts in the metabolism of glucose and insulin has been associated with secondary active metabolite, minerals, fats, and fiber contents. It has been shown that PUFA, carotenoids such as β-carotene and lutein, γ-tocopherols, and procyanidins content of pistachio [40], PUFA content of walnuts and the fat and fiber content of almonds are responsible for these beneficial effects [44]. A published study reported that walnuts induced significantly positive effect at the initial phases of nutritional change in a PUFA-delivered healthy diet. The effect of pistachios on insulin and postprandial glucose, endothelial function, and gut hormone has been assessed by Kendall et al. The results demonstrated that the consumption of pistachios reduced the postprandial glycemia, insulin-sparing properties and increased glucagon-like-peptide levels [45].

In one 12-week study of people with metabolic syndrome who ate 1 ounce (25 g) of pistachios twice 2 days, there was a 9% decrease in fasting glucose [51].

5. Conclusion

Nuts are the richest source of healthy nutrients. They are loaded with vitamins, minerals, fibers, and other bioactive compounds. Nuts are nutrients-containing plants. They are used all over the world for nutritional purposes. These have many beneficial effects on health. Bioactive phytochemicals present in nuts are vital for the cognitive function, with positive impact on neurodegeneration and aging. A novel phytochemical present in pistachios, which is called Lutein, provides significant health impacts affecting the cognitive function. Nut consumption reduces the risk of coronary heart diseases, cancer, inflammation, diabetes, and osteoporosis. They are also involved in weight loss.