Of Nuts and Seeds

Source of healthy fats…and so much more

Life is rarely as simple as we would like it to be. Just as soon as we think we’ve gotten things figured out, along comes some new information. Nutritional science is no exception. Research published in the last year has forced me to reassess the value we place on eating nuts and seeds. The long-standing idea that the health benefits of nuts and seeds come solely from the healthy fats they contain is losing ground. We’ve always considered them to be healthy foods, but now realize that nuts and seeds may be of greater value than previously thought.

Both nuts and seeds tend to be good sources of healthy fats, so the knee-jerk explanation of benefits has focused on those healthy fats: “Nuts provide omega-3 fats like fish do, so that’s why they are good for the heart,” or “flax seeds provide alpha linolenic acid (ALA), so they are good for reducing inflammation.” If only life were this simple.

Since a study appeared in 2000 telling us that a daily serving of pecans can lower  cholesterol levels, there has been a flood of research on nuts and heart disease.[1] We now acknowledge that eating pretty much any kind of nut, even peanuts (which are technically legumes), will lower cholesterol. Over the last ten years many other studies have confirmed that most kinds of nuts, including peanuts, are good for the heart. Until recently, the explanation that nuts contain omega-3 fats like those found in cold water fish has sufficed to explain the benefits.

The weakness of this explanation showed up in 2008 in a review of four large epidemiological studies confirming the benefits of nuts on cholesterol and cardiovascular health—people who ate a lot of nuts reduced their risk of heart disease by more than a third. What was surprising was that the nuts lowered cholesterol more than they should have based on predictions. Something more complex was going on. The researchers wrote that “… nuts and peanuts contain other bioactive compounds [besides omega-3s] that explain their multiple cardiovascular benefits.”[2] The researchers came to what we find an unsurprising conclusion, “… nuts and peanuts contain other bioactive compounds that explain their multiple cardiovascular benefits. Other macronutrients include plant protein and fiber; micronutrients including potassium, calcium, magnesium, and tocopherols; and phytochemicals such as phytosterols, phenolic compounds, resveratrol, and arginine.”[3]  In other words, nuts contain lots of other nutrients besides omega-3 fats that are good for us. No surprise there.

The results of a study published in early 2010, however, did come as a surprise. The study, published in the journal Clinical Nutrition, suggests that nuts trigger the repair of damaged DNA.[4]

In this study, researchers measured a host of biochemical markers in fifty patients with metabolic syndrome before and after a three-month period of eating one ounce of nuts per day. The only striking difference, and it was quite statistically significant, was a reduction in DNA damage in the nut-eating group compared to the control group.  The researchers concluded that the decrease in DNA damage could explain the beneficial effects of regular nut consumption on several chronic diseases. [5]

The idea that nuts repair DNA is striking. The list of other substances that trigger DNA repair is short: curcumin from the spice turmeric, resveratrol from grape skins, genestein from soy beans, 1,3 carbinol in cruciferous vegetables, and ellagic acid from raspberries and pomegranates.[6] Caloric restriction—a euphemism for staying hungry most of the time—also appears to trigger repair.[7] But not eating doesn’t exactly qualify for a list of foods that trigger DNA repair, which leaves nuts as the new addition to this short list.

It is important to understand that nuts have far more benefits than can be explained by the fats they contain. That old “nuts are like fish oil” explanation is now outdated, a drastic oversimplification. As we read future studies about the protective effect nuts have against chronic disease, we should think of this DNA repair concept; something in nuts repairs not just tissue, but the DNA that serves as a blueprint to cellular activities.

Similar advances in understanding have been published on the health benefits of seeds.  No longer are scientists focused solely on the healthy oils contained in seeds, but on their lignan content. Lignans are one of the major classes of phytoestrogens and some studies have reported a positive association between high levels of lignans in the body with a reduced risk of prostate, ovarian, and breast cancers, osteoporosis, and cardiovascular disease. A study published last summer reported that even a slight increase in dietary lignans lead to significant improvements in survival for women who have been diagnosed and treated for breast cancer. The study suggests that higher lignan diets may reduce the risk of dying from breast cancer by 71 percent.[8] Adding flax seeds to the diet may make a significant difference for many women.

Bacteria living in the intestines can convert certain lignans into chemicals that bind to hormone receptors inside the human body. These plant-derived chemicals appear to lower the risk of certain hormone-related cancers, in particular breast cancer. Flax seeds, which have long been valued for their oils, may prove to be more valuable because of their extremely high lignan content, the highest of any food source. But much to our surprise, sesame seeds, which contain only a fraction of the amount of lignans compared to flax, may be equally effective. The lignans found in sesame seeds are far better converted by the body, thus sesame seeds raise blood hormones equally as well as flax seeds; but remember, it’s not just the healthy oils, but the whole seed that’s important.

The world is a complex place. It’s tempting for us to latch onto simple explanations, sound bites of a sort, to bring a sense of order to our lives. Why nuts and seeds are so good for us is still poorly understood, but we do know that there’s much more to them than meets the eye. We may never fully understand the synergistic way that the nutrients and phytochemicals in nuts and seeds work, but then that’s the beauty of the natural world.


References

[1] Iwamoto M, Sato M, Kono M, Hirooka Y, Sakai K, Takeshita A, Imaizumi K. Walnuts lower serum cholesterol in Japanese men and women. J Nutr. 2000 Sep;130(9):2407.

[2] Kris-Etherton PM, Hu FB, Ros E, Sabaté J. The role of tree nuts and peanuts in the prevention of coronary heart disease: multiple potential mechanisms. J Nutr. 2008 Sep;138(9):1746S-1751S.

[3] Kris-Etherton PM, Hu FB, Ros E, Sabaté J. The role of tree nuts and peanuts in the prevention of coronary heart disease: multiple potential mechanisms. J Nutr. 2008 Sep;138(9):1746S-1751S.

[4] López-Uriarte P, Nogués R, Saez G, Bulló M, Romeu M, Masana L, Tormos C, Casas-Agustench P, Salas-Salvadó J. Effect of nut consumption on oxidative stress and the endothelial function in metabolic syndrome. Clin Nutr. 2010 Jan 9.

[5] López-Uriarte P, Nogués R, Saez G, Bulló M, Romeu M, Masana L, Tormos C, Casas-Agustench P, Salas-Salvadó J. Effect of nut consumption on oxidative stress and the endothelial function in metabolic syndrome. Clin Nutr. 2010 Jan 9.

[6]Chakraborty S, Roy M, Bhattacharya RK. Prevention and repair of DNA damage by selected phytochemicals as measured by single cell gel electrophoresis. J Environ Pathol Toxicol Oncol. 2004;23(3):215-26.

[7] Koltai E, Szabo Z, Atalay M, Boldogh I, Naito H, Goto S, Nyakas C, Radak Z. Exercise alters SIRT1, SIRT6, NAD and NAMPT levels in skeletal muscle of aged rats. Mech Ageing Dev. 2010 Jan;131(1):21-8.

[8] McCann SE, Thompson LU, Nie J, Dorn J, Trevisan M, Shields PG, et al. Dietary lignan intakes in relation to survival among women with breast cancer: the Western New York Exposures and Breast Cancer (WEB) Study. Breast Cancer Res Treat. 2010 Jul;122(1):229-35.

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