March 2019 Issue
Nuts & Seeds
By Densie Webb, PhD, RD
Vol. 21, No. 3, P. 20
Nuts and seeds have been part of the human diet for centuries, but they’re being increasingly recognized for a growing list of potential health benefits. Among nuts, walnuts and almonds have been studied the most and, as a result, have gotten the most press, but several others also are healthful additions. Of the seeds on the scene, chia and flaxseeds have long been thought of as healthful additions to the diet. But hemp may be stepping into the spotlight with the recent passing of the 2018 Farm Bill, which removes hemp from the list of controlled substances, eliminating the legal barrier to growing hemp.
The health benefits of specific nuts, especially in relation to CVD risk, have been widely studied and are well established, though the mechanisms aren’t fully understood. A recent systematic review and meta-analysis found that nut consumption significantly improved endothelial function (endothelial dysfunction precedes development of atherosclerosis and a loss of elasticity of the arterial walls).
Popular seeds, such as chia and flaxseeds, either intact or ground, are less researched, but data suggest they offer similar health benefits. Seeds are high in healthful fats and are rich sources of phytochemicals such as carotenoids, phenolic acids, phytosterols, and flavonoids, all of which have been studied individually for their health effects.
“People know that nuts are good for you,” says Sonya Angelone, MS, RDN, CLT, a consulting dietitian in the San Francisco Bay area and a spokesperson for the Academy of Nutrition and Dietetics, but they may not be aware of just how good they are. “There have been some really good epidemiologic and clinical studies that show eating 1.5 oz of nuts and seeds a day can reduce cardiovascular disease by 30% to 50%,” she says.
Angelone says that while nuts are calorically dense, it’s been estimated that 10% to 15% of the energy isn’t absorbed, resulting in a net decrease in calories compared with what is shown in calorie analyses.1,2
Higher nut intake is associated with reduced risk of not only CVD but also total cancer, all-cause mortality, and mortality from respiratory disease, diabetes, and infections.3
The antioxidant and anti-inflammatory compounds found in nuts and seeds also are thought to have possible effects on the remodeling of the gut microbiota. The fiber and polyphenol content of nuts may have a positive effect on the gut microbiota by promoting intestinal homeostasis, increasing synthesis of short-chain fatty acids, and maintaining the integrity of the gut, all of which may aid the management of obesity and other inflammatory diseases.4
A 2017 study suggested that consumption of nuts and seeds might delay the aging of cells. It was found that adults who consumed 5% of their total energy intake from nuts and seeds experienced 1.5 years of reduced cell aging, compared with what would be expected. Cell aging was measured by telomere length. Telomeres are structures at the end of chromosomes that shorten with age.5
While fish may be the first food that comes to mind as a rich source of heart-healthy omega-3 fatty acids, alpha-linolenic acid (ALA)—an essential omega-3 fat—is a health-promoting ingredient that most nuts and seeds have in common. However, it’s important to recognize that the omega-3 fats present in nuts and seeds, while beneficial, aren’t the same as the omega-3s found in fish.
The ALA found in some nuts, especially walnuts, and seeds must first be converted by the body into the omega-3s EPA and DHA, which are found naturally in fatty fish and seafood. DHA and EPA are then incorporated into cell membranes, involved in anti-inflammatory processes and in maintaining the integrity of cell membranes. In addition, EPA and DHA are essential for fetal development and are key components in the brain and retina. These omega-3s also are associated with lower blood lipid levels and may be beneficial in the prevention or treatment of several chronic diseases, including arthritis and Alzheimer’s disease.6
When the Institute of Medicine last reviewed omega-3s, there weren’t enough data to determine an Estimated Average Requirement, so it established Adequate Intakes for ALA for all ages based on current omega-3 intakes in healthy populations. Adequate Intakes of ALA for adults has been set at 1.6 g per day for men and 1.1 g per day for women.7 However, a review of the research concluded that consuming 2 to 3 g per day of ALA reduces the risk of coronary heart disease, both in primary and secondary prevention studies.8
Estimates of the conversion rate of ALA to DHA and EPA vary greatly, but studies have shown they range from less than 1% to as much as 9.2%.9,10 Some people who have a genetic variation that makes conversion impossible must get DHA and EPA from their diet or supplements. Only genetic testing can reveal this anomaly.10
While nutrient content of a wide variety of nuts has been studied, tree nuts are probably the most widely researched for their potential health benefits. In botanical terms, nuts are dry fruits that have a single seed, a hard shell, and a protective husk. Hazelnuts, pecans, and walnuts fit the true definition of a nut, but peanuts and almonds don’t. Peanuts are legumes, and almonds are encased in a fuzzy coat rather than a hard outer layer.
Much of the research on nuts has looked at overall nut consumption, rather than assessing the health effects of individual types of nuts. However, almonds, walnuts, and peanuts have been studied the most individually.
A recent review of the literature, which included results from the INTERHEART study, the Physicians’ Health Study, and the PRIMO study, reinforced the findings that adding almonds to the diet (about 1.5 oz per day) reduces LDL cholesterol levels and maintains HDL cholesterol levels.11
Rich in vitamins and minerals, almonds are a good source of vitamin E (tocopherols), riboflavin, calcium, magnesium, phosphorus, potassium, zinc, copper, and manganese.12 Almonds also contain a wide variety of phenolic compounds, mainly proanthocyanidins, flavonoids, and phenolic acids found mainly in the skin. These compounds are responsible for almonds’ antioxidant properties. Phytosterols also are found in significant amounts and may be responsible for reducing blood concentrations of LDL cholesterol.12 However, unlike most other nuts, most notably English walnuts, almonds contain no ALA, an indication that other compounds in almonds are responsible for their health benefits.13
In comparison with other tree nuts, hazelnuts rank among the highest in vitamin E, folate, monounsaturated fat, and proanthocyanidins. In fact, hazelnuts have the highest proanthocyanidin content of any tree nut, as well as the highest folate content, providing 8% DV per serving. A 1-oz serving of raw hazelnuts contains 20% DV of the antioxidant vitamin E.14
Consumption of hazelnuts in the United States is low at 3.5 oz per person per year. However, consumption in Italy is high. In a systematic review, researchers in Italy found that consuming 1 to 2.5 oz of hazelnuts per day for 28 to 84 days resulted in reductions in total and LDL cholesterol but had no effect on HDL cholesterol or BMI.15,16
While peanuts are botanically legumes, they’re considered nuts for culinary, research, and nutritional purposes.17 Peanuts, which make up about 67% of all nuts consumed in the United States, provide protein, niacin, folate, thiamin, vitamin B6 and E, copper, manganese, iron, and phosphorus, as well as several bioactive compounds, most notably resveratrol (a polyphenol antioxidant believed to have several health benefits, including protecting against cancer and Alzheimer’s disease).
Peanuts have more protein than any other nut, similar to the amount in a serving of beans.18 Several studies have found that consuming 1 to 1.5 oz of peanuts per day improves glucose metabolism and lipoprotein profiles while not affecting body weight.2 Consumption of about 3 oz of peanuts per day, as part of a high-fat meal, improved immediate triglyceride levels and maintained vascular function in healthy overweight or obese men.2
Peanuts are rich in phytosterols, which are known to block the absorption of cholesterol, but, like almonds, they contain no ALA.18
Like all nuts, pecans are a good to excellent source of several vitamins, minerals, and phenolic antioxidant compounds. They’re an excellent source of vitamin E and provide several B vitamins, fiber, and protein as well as the carotenoids beta-carotene, lutein, and zeaxanthin. Pecans also are a source of epigallocatechin-3-gallate, better known as EGCG, a polyphenol with a variety of beneficial health properties and most often associated with green tea.19 They contain a small amount of ALA (about 0.5 g/oz).
A recent research review concluded that consumption of pecans, as well as other nuts, is linked to reduced markers of CVD and metabolic disorders and can affect adiposity and insulin resistance. A recent randomized controlled trial found that when 15% of total calories were replaced with pecans, insulin sensitivity improved and there was a positive effect on other markers of cardiometabolic disease, including improvements in serum insulin and the ability of beta cells in the pancreas to function properly in overweight and obese adults.20
Pistachios make up only 2% of total nut consumption in the United States, but limited research suggests significant health benefits. The nuts are a good source of protein and are higher in fiber than other nuts (about 8 g/oz). They’re also a source of potassium, phosphorus, magnesium, calcium, and vitamins (especially vitamin E), as well as a rich source of the antioxidants lutein, zeaxanthin, anthocyanins, flavonoids, and proanthocyanidins.21,22
A systematic review of epidemiologic studies concluded that including pistachios in the diet may have a favorable effect on blood lipids, lowering total and LDL cholesterol while increasing HDL cholesterol. Regular pistachio consumption also has been found to have a positive effect on factors related to glucose metabolism and insulin resistance, both in the gut and blood.23,24 A laboratory study using colon cancer cells found that pistachios, whether raw or roasted, had a chemopreventive effect on the cells.25
English walnuts have been studied extensively and found to contain five times as much ALA as pecans and be beneficial for cardiovascular health.
In addition to containing several vitamins and minerals, walnuts are a source of ellagic acid, an antioxidant found in several fruits and vegetables. A study published last year found that consuming walnuts not only improved cardiovascular health but also improved the gut microbiota and increased production of microbial-derived secondary bile acids in adults.26
Several animal studies show that including walnuts in the diet slows or prevents the growth of breast and prostate cancers. Intervention trials, including consuming walnuts as part of a Mediterranean diet, show other potential benefits, such as helping people lose abdominal fat, reduce blood pressure, and lower triglycerides.27
Though studied much less than nuts, research suggests that seeds, especially the following three varieties, offer health benefits similar to those of nuts.
Chia seeds are the tiny seeds that come from Salvia hispanica, a member of the mint family. They’re an excellent source of ALA, calcium, phosphorus, and fiber (10 g per 2 tablespoons).
Research suggests that chia seeds, as part of a healthful diet, may lower cholesterol, triglycerides, and blood pressure. In addition, a recent study found that consuming 5 g of chia seeds over three weeks improved cognitive function in young adult subjects.28,29 However, there are few studies on humans (most research has been done on animals), and the majority of them are small. A recent study on rats found that regular consumption of chia seeds increased bone mineral content and improved liver and intestinal health.29
Chia seeds absorb liquid and can be soaked in fruit juice or water and used in cooked cereals and smoothies.30
Flaxseed (Linum usitatissimum) is an ancient crop tracing back to the beginning of civilization. Used for fiber and animal feed, it’s best known today for its health benefits, including a reduction in CVD, diabetes, cancer, arthritis, osteoporosis, and autoimmune and neurological disorders.31
Not only are flaxseeds the richest source of ALA of all the nuts and seeds (1 tablespoon provides 2.4 g ALA, more than the AI set for men or women), they contain the compound secoisolariciresinol diglucoside, which is believed to have antioxidant, antihypertensive, antidiabetic, hypolipidemic, anti-inflammatory, and antiatherogenic properties.32 A recent systematic review and meta-analysis of 45 randomized, placebo-controlled trials also found that including at least 1 oz of flaxseeds per day improved BMI among the overweight and obese subjects studied.33
The hemp plant is related to marijuana (both are varieties of Cannabis sativa L) but generally has less than 0.2% THC, the intoxicating ingredient in marijuana. Varieties of marijuana commonly used as intoxicants typically contain 2% to 5% of THC per dry weight. However, you may be seeing more hemp food products, now that the finalized 2018 Farm Bill has removed the seed from the list of controlled substances, making it much easier to grow and promote. Until recently, its legal status has been somewhat murky, depending on the state you live in, and it’s been legal to grow hemp only under a state pilot program for academic research. The legality question has been based on its THC content. However, if cleaned and processed properly, hemp products contain almost no THC.34
Hemp seeds are high in protein (about 30% by weight), antioxidants, and ALA (about 20% of the total fatty acids). These relatively soft seeds can be eaten raw or roasted and can be sprinkled on salads, added to smoothies, or used as an ingredient in muffins and cookies. One tablespoon of hemp seeds (10 g) provides 60 kcal and 5 g total fat.
The conclusion from the vast majority of research on nuts and seeds is that they’re healthful additions to any diet and may help reduce the risk of several chronic diseases. They’re also the ultimate fast food. “People choose processed and packaged foods because they’re easy, but nuts and seeds are easy,” Angelone says.
And while research suggests that nuts aren’t as calorically dense as stated on nutrition labels, because of poor absorption, they’re still relatively high-calorie foods. Angelone adds, “As long as it’s not ‘mindless snacking,’ nuts are a healthful addition to your diet.”
— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.
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