For many years I’ve known that consuming one Brazil nut a day supplies the human body with its daily requirement for selenium, an important trace mineral high in antioxidants. But here’s what I recently learned that gave me a bit of a jolt. Recent studies show that while Brazil nuts have many positive attributes, they also have a hidden side that sparked researchers to express cautionary advice.
I turn to nature rather than food manufacturers to provide the most nourishing foods for human consumption. I’m also cognizant that we humans absorb our vitamins and minerals best from pure, natural foods rather than from synthetically manufactured supplements. Human nature is kind of funny, though. We often have a tendency to believe that if a small amount of a nutrient-dense food or supplement is good for us, wouldn’t gobbling down double, triple, or five times the amount be even better?
That theory works well for some foods, like dark leafy greens, but it doesn’t apply across the board. That mind-set is especially problematic when it comes to Brazil nuts.
The good news
On the positive side, Brazil nuts, like all nuts, are highly nutritious and densely packed with minerals like calcium, copper, iron, magnesium, manganese, potassium, and zinc. Brazil nuts also possess trace amounts of thiamine, riboflavin, and niacin in the B vitamin family, along with healthy levels of folate and vitamin E. Clearly, these nuts are remarkably nutritious.
Brazil nuts stand apart from all other nuts with their exceptionally high levels of selenium. The Recommended Daily Allowance (RDA) for selenium for adults 19 years and up is 55 micrograms a day. According to the USDA National Nutrient Database for Standard Reference, one Brazil nut delivers 95.8 micrograms of selenium, well over the daily requirement for the mineral.
In comparison, other nuts do not even come close to measuring up. Pine nuts contain the least selenium, registering only 0.2 micrograms for one ounce, while cashews weigh in with 5.6 micrograms per ounce, the highest quantity after Brazil nuts.
A randomized controlled study conducted at the University of Otago in New Zealand found that consuming two Brazil nuts daily is as effective in boosting selenium levels in the blood as taking selenomethionine, a synthetic selenium supplement. The group that ate two Brazil nuts a day also measured higher in antioxidant levels than those taking the supplement. Selenium, required only in small amounts, helps the body to produce antioxidant enzymes that protect the cells from free radical damage. Study authors also found that those with adequate levels of selenium in the blood have a reduced risk for breast and prostate cancer.
A double-blind, placebo-controlled study, known as the Nutritional Prevention of Cancer trial noted that in populations where selenium consumption was low, there was a rise in the incidence of cancer. The long-term trial involving 1312 individuals found supplementation with selenium reduced the total cancer incidence by 48% to 63%, especially prostate, colorectal, and lung cancer. Generally, the dietary selenium levels in the U.S. population are considered good. The trial was conducted where dietary levels were poor. Considering the results of the study conducted at the University of Otago, two Brazil nuts a day may have been equally as effective in this population as the selenium supplement.
Selenium is found in the soil where plant foods can absorb it through their root systems. Other plant-based foods high in natural selenium include most nuts, whole grains like corn, wheat, oats, and rice, along with foods of the legume family, including soybeans.
An exceptional plus for Brazil nuts is their high level of the antioxidant glutathione peroxidase (GPx), that may bestow benefits on our health in multiple ways:
• Boosting the immune system
• Protecting from cardiovascular disease
• Improving fertility
• Helping ward off the growth of cancerous cells
• Increasing thyroid metabolism
Not only does our immune function work best when selenium levels are adequate, but the mineral is an important component that prevents deficiencies that could impair thyroid function.
The bad news
In spite of their many positive qualities, Brazil nuts might be considered the bad boys of the nut family. Because Brazil nuts have an exceptionally high concentration of phytic acid, measuring 2% to 6% in their hulls, they might interfere with the absorption of some nutrients like iron, zinc, calcium, and magnesium. While their monounsaturated and polyunsaturated fats may be beneficial in lowering cholesterol when ingested in small quantities, Brazil nuts high level of saturated fat (25%) could possibly raise cholesterol levels if the nuts are consumed in large quantities.
Overdosing on selenium can cause a toxic condition known as selenosis, leaving patients with a host of nasty symptoms like hair loss, nausea, vomiting, abdominal pain, sloughing of the fingernails, fatigue, irritability, and nerve damage. Less common are cirrhosis of the liver and kidney failure.
While a 12-week study of 60 volunteers published in the American Journal of Clinical Nutrition, February 2008, found that study participants consuming two Brazil nuts a day had higher levels of selenium compared with those consuming a 100-microgram supplement or taking a placebo, the research concluded with a cautionary message.
Professor Christine Thomson, Department of Human Nutrition University of Otago, says, “People should be careful to limit themselves to no more than a few Brazil nuts per day, otherwise selenium could potentially accumulate to toxic levels in body tissues. Also, as the nuts can contain relatively high amounts of the elements barium and thorium, people should avoid eating too many as it is still unclear what intake of these elements might be harmful.”
Another study, prompted by the UK National Diet and Nutrition Survey, was conducted because of concern that the average selenium consumption in the UK is far below the recommended levels of 75 micrograms per day for men and 60 micrograms for women.
Several studies have shown an association of high levels of selenium in the blood and increased risk of type 2 diabetes, high cholesterol, and risk of heart disease. Researchers at the Warwick Medical School in Coventry, England, conducted an observational study involving 1,042 individuals, aged 19 to 64, to measure how selenium levels in the blood compared to their blood cholesterol status. In this UK National Diet and Nutrition Survey conducted 2000 to 2001, participants’ blood selenium was measured, and they were asked specific lifestyle questions about diet and alcohol consumption.
The findings revealed that participants with 1.20 micromols (about 94 micrograms) of selenium in the blood showed an average 8 percent rise in total cholesterol and a 10 percent rise in LDL cholesterol, the bad cholesterol associated with heart disease. Study authors noted that while these results raise concerns, they were unable to show positively that increased selenium levels in the blood were the cause of the jump in cholesterol levels or whether it was due to other factors. Those individuals who tested in the upper levels of selenium in the blood revealed they were regularly taking selenium supplements.
Lead author Dr. Saverio Stranges says, “The cholesterol increases we have identified may have important implications for public health. In fact, such a difference could translate into a large number of premature deaths from coronary heart disease.” Dr. Stranges expressed further concern, “We believe that the widespread use of selenium supplements, or of any other strategy that artificially increases selenium status above the level required, is unwarranted at the present time. Further research is needed to examine the full range of health effects of increased selenium, whether beneficial or detrimental.”
Study authors also examined the levels of the antioxidant glutathione peroxidase and found that those with the higher levels of selenium in their blood had an 8 to 10 percent increase in total cholesterol.
When published studies revealed that selenium may be able to fight off cancer, the news sparked interest in the mineral and created a demand for the supplements. However, there still remains no definitive evidence that the antioxidants in selenium can prevent such diseases.
While a handful-a-day of most nuts is beneficial in raising antioxidant levels and effective in lowering total and LDL cholesterol levels, the handful-a-day mantra is off the table for Brazil nuts. Stick with the recommended quantity of one or two Brazil nuts per day. A whole handful of the nuts could easily boost one’s blood selenium to unhealthy levels.
As much as I love nuts and consider them a healthy food source for my everyday diet, I have adopted the safe mantra that nut researchers conclude in study after study: A LITTLE BIT GOES A LONG WAY. In the case of Brazil nuts, eat one or two nuts a day, then, STOP.
“Brazil Nuts Health Benefits.” Suite101.com.
“Eating Just Two Brazil Nuts a Day Ensures Adequate Selenium Levels.” Health Freedom Alliance.
Jackson, Malcolm J., Caroline S. Broome, and Francis McArdle. “Marginal Dietary Selenium Intakes in the UK: are There Functional Consequences?” The American Society for Nutritional Sciences. Supplement: 11th International Symposium on Trace Elements in Man and Animals. The Journal of Nutrition, 133:1557S-1559S, May 2003
“Selenium.” Wikipedia, the Free Encyclopedia
Stranges, Saverio, Martin Laclaustra, Chen Ji, Francesco P. Cappuccio, Ana Navas-Acien, Jose M. Ordovas, Margaret Rayman, and Eliseo Guallar. “Higher Selenium Status is Associated with Adverse Blood Lipid Profile in British Adults.” Journal of Nutrition. doi:10.3945/jn.109.111252, November 11, 2009.
Thompson Christine .D., Alexandra Chisholm, Sarah K. McLachlan, and Jennifer M. Campbell. “Brazil nuts: an effective way to improve selenium status.” American Journal of Clinical Nutrition, Vol. 87, No 2, 379-384, February 2008
USDA National Nutrient Database for Standard Reference