Selenium is needed by your body in small amounts, which is why it’s referred to as a trace mineral. Some trace nutrients are flushed from your body when you consume them in excess, but selenium can build up over time to toxic levels and become poisonous to tissues. Brazil nuts are a concentrated natural source of selenium. A small handful every once in a while is likely safe, but eating them often or in large amounts is potentially risky. Ask your doctor about the common side effects of selenium toxicity.
Selenium has a variety of functions, but helping the body produce antioxidant enzymes that protect tissues from free radical damage is arguably its most important role, according to the “Encyclopedia of Human Nutrition.” Antioxidants also help combat infections and retard the growth and proliferation of cancer. Thus, selenium is an important part of your immune system. Health problems associated with selenium deficiency include heart disease, hypothyroidism and immune dysfunction. The recommended daily allowance for selenium for adults is 55 micrograms, although it’s considered safe to consume up to 400 micrograms per day. Selenium deficiency, as well as magnesium and boron deficiency, is much more common in regions with poor, depleted soil. Brazil nuts can easily prevent selenium deficiency, although you need to take caution not to eat them to excess.
Brazil Nuts and Selenium
Many nutritionists consider Brazil nuts to be the richest source of dietary selenium. A single ounce, which is about six or seven nuts, can contain up to 600 micrograms of selenium, depending on the soil quality they are grown in. On the other hand, some Brazil nuts contain only 10 micrograms of selenium. Thus, just one Brazil nut may be more than enough to meet your daily selenium needs, but growing conditions are an important factor.
Overdosing on selenium can cause a toxic condition known as selenosis, which leads to hair loss, brittle fingernails, skin rash, nausea, vomiting, abdominal pain, fatigue, irritability and nerve damage. The single overdose level is well over the maximum daily recommended amount of 400 micrograms, so selenosis usually occurs as a result of long-term accumulation. Brazil nuts also contain fairly high levels of phytic acid, which can interfere with absorption of certain nutrients, which might also cause symptoms. Consequently, people should limit their consumption of Brazil nuts to no more than a few per day, or a handful per week, just to be on the safe side.
Other Benefits of Brazil Nuts
Even though the potential of selenium toxicity exists, indigenous peoples have relied on the nutrition of Brazil nuts for countless generations. Brazil nuts are densely packed with other minerals, such as calcium, magnesium, iron, potassium and zinc. They also contain trace amounts of B vitamins, such as thiamine, riboflavin, niacin and folate. Furthermore, they are a good source of a wide variety of fats including saturated, monounsaturated and polyunsaturated fatty acids.
- Encyclopedia of Human Nutrition; Benjamin Caballero et al.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- Nutritional Sciences for Human Health; Stanislas Berger et al.
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.