7 Healthy Foods That Can Be Harmful When Eaten Too Frequently

Raw Brazil Nuts

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Some of the healthiest foods contain dastardly ingredients that should only be consumed in moderation, if at all.

The aspirational mantra of “all things in moderation” is so neat and tidy ... as if it were just that simple to say, “no more, thanks” to the things one loves. Beyond the emotional tangle that is desire, we have age-old instinct hard-wired into our human selves telling us things like, “eat fat! eat sugar!” since we don’t know when that next mastodon kill might happen. So we chant “moderation, moderation, moderation” as we have a staring contest with a giant brownie or while a Blooming Onion lures us with its best Siren song.

But what about when we’re consuming something that is supposed to be good for us? As it turns out, when it comes to healthy food, too much of a good thing can sometimes be a bad thing too. All things in moderation is true even for our most noble efforts. While clearly the nutritional deficiencies that plague much of the world are a far more serious problem, our first world abundance leaves us in the strange position of harming ourselves by overeating nutrient-rich food. Consider the following.

1. Brazil nuts

Nuts are a great source of protein, fiber, and essential fatty acids – studies praise them for their health benefits. But Brazil nuts in particular are bursting with the trace element selenium. While selenium plays essential roles in the body, a single Brazil nut delivers close to twice the daily recommended requirement. Selenium can be toxic in high amounts; too much can lead to hair loss, muscle tenderness, neurological abnormalities, kidney failure, and worst case scenario, death.

2. Spinach

Leafy greens, the miracle things! Among the leafy-green family spinach may be the most accessible, both market-wise and taste-wise, but don’t overdo it if you're concerned about kidney stones. Spinach is a workhorse, but it’s also high in oxalates, a naturally occurring compound also found abundantly in beets and Swiss chard. Oxalates aren’t bad in and of themselves, but some kidneys have a hard time filtering them out, which allows them to build up and can lead to kidney stones.

3. Canned tuna

Mercury levels in tuna are no secret, but we would be remiss if we didn’t include canned tuna here. The FDA and EPA urge consumers to eat fish that is low in mercury, but research shows much of it contains the toxin in varying degrees; getting too much of it can do harm to the brain and nervous system. The researchers found children whose mothers had high-mercury exposure during pregnancy can suffer harmful effects, such as problems with attention, memory, and language as well as some difficulties with motor coordination. Canned tuna can be particularly high in mercury, causing the FDA and EPA to recommend pregnant women eat "no more than six ounces of fish per week (of eight to 12 ounces weekly) should be white (albacore) tuna."

4. Red meat

There are a lot of reasons to limit your consumption of red meat, but for this story the reason may be surprising – it can lead to an iron overload. It's true that most people don’t get enough iron ... but if you happen to be taking iron supplements, you can get too much iron when adding in more from dietary sources. And what many people don’t realize is that too much iron can result in a parade of problems. Signs of consuming excess iron include dizziness, fatigue, headache, weight loss, vomiting, nausea, gray skin and shortness of breath. Over time, an excess of iron can damage your liver and other organs and cause arthritis and heart problems.

5. Brown rice

Just when everyone was starting to get used to the swap from white to brown rice because of its much better nutritional profile, we discover that brown rice is chock full of arsenic. Arsenic is a known human carcinogen that rice absorbs from pesticides and poultry fertilizer. In this case, the benefits of brown rice are also its downfall – the reason brown rice is more nutritious is because it is more intact as a grain; the layers removed in processing white rice are where much of the arsenic is.

Experts recommend brown basmati from California, India, or Pakistan as they have lower levels of arsenic than brown rice from other regions. The FDA says rice can be part of a well-balanced diet, but recommends consuming a variety of grains (not just rice).

6. Seaweed

In the 1920s American salt producers began adding iodine to table salt; the body relies on the chemical for normal thyroid function and for the production of thyroid hormones. Globally, iodine deficiency affects about two billion people and is the leading preventable cause of intellectual and developmental disabilities. But too much iodine and the pendulum swings the other way, especially for people who already have thyroid problems, such as nodules, hyperthyroidism and autoimmune thyroid disease. Too much iodine can cause or worsen hyperthyroidism and hypothyroidism, according to the American Thyroid Association. And the leading sources of dietary iodine are seaweed and kelp, some varieties have wildly high levels. A study published in the Thyroid Research Journal concluded that, “High iodine intake from seaweed consumption can cause unexpected health problems in a subset of individuals with pre-existing thyroid disorders. Although it is reported that excessive iodine does not cause thyroid antibody positivity, high intake can cause or worsen symptoms for people with previous thyroid autoimmunity or other underlying thyroid issues."

7. Water

Believe it or not, even too much water can be problematic. While the risks of not getting enough water are well known, the dangers of getting too much water are not. Last year, an international group of 16 experts published hydration guidelines meant to protect athletes from the potentially fatal health risks that come with drinking too much while exercising. As we reported earlier:

Mitchell Rosner, MD, a kidney specialist at the University of Virginia School of Medicine who chaired the guideline development group, says that overhydrating with water or sports drinks can lead to a condition called exercise-associated hyponatremia (EAH). When the body has too much water relative to its salt level, the salt level in the blood drops too low which can lead to significant problems.

This condition was once only relevant in the domain of endurance events, but physicians are seeing EAH in a wider array of sports now. If you are working up a sweat, Rosner says to let your body tell you when you need a drink.

"We recommend using your thirst as a guide," he says. "If you drink when thirsty, you will not become hyponatremic and you will not suffer from significant dehydration." (That said, it can't hurt to get the advice of your health care provider for how to handle your hydration needs.)

View Article Sources
  1. De Souza Ravina Graziany Machado, et al. Nuts and Human Health Outcomes: A Systematic Review. Nutrients. 2017, vol. 9, doi:10.3390/nu9121311

  2. Nuts, brazilnuts, dried, unblanched.” U.S. Department of Agriculture FoodData Central.

  3. Nuts, brazilnuts, dried, unblanched.” U.S. Food & Drug Administration.

  4. Selenium.” National Institutes of Health.

  5. Kidney stones - self-care.” U.S. National Library of Medicine.

  6. Freidig, Amy K., and Irwin L. Goldman. “Variation in Oxalic Acid Content among Commercial Table Beet Cultivars and Related Crops.” Journal of the American Society for Horticultural Science, vol. 136, pp. 54-60., doi:10.21273/JASHS.136.1.54

  7. Mitchell, Tanecia, et al. Dietary oxalate and kidney stone formation. Am J Physiol Renal Physiol, 2019, vol. 316, pp. F409-F413., doi:10.1152/ajprenal.00373.2018

  8. EPA-FDA Advice about Eating Fish and Shellfish.” U.S. Environmental Protection Agency.

  9. Silbernagel, Susan M., et al. Recognizing and preventing overexposure to methylmercury from fish and seafood consumption: information for physicians. J Toxicol, 2011, doi:10.1155/2011/983072

  10. Geissler, Catherine, and Mamta Singh. ”Iron, meat and health.” Nutrients, vol. 2011, no. 3, pp. 283-316.,  doi:10.3390/nu3030283

  11. Stargrove, Mitchell B., et al. Herb Nutrient and Drug Interactions. Elsevier. 2008.

  12. Hemochromatosis: Introduction.” The Johns Hopkins School of Medicine.

  13. Arsenic in Rice and Rice Products Risk Assessment Report. U.S. Food & Drug Administration.

  14. Punshon, Tracy, et al. “Understanding arsenic dynamics in agronomic systems to predict and prevent uptake by crop plants.” Sci Total Environ, 2017, vol. 581-582, pp. 209-220.,  doi:10.1016/j.scitotenv.2016.12.111

  15. Schmidt, Charles W. In search of "just right": the challenge of regulating arsenic in rice. Environ Health Perspect, 2015, vol. 123, pp. A16-9.,  doi:10.1289/ehp.123-A16

  16. How Much Arsenic Is in Your Rice?.” Consumer Reports.

  17. Leung, Angela M., et al. “History of U.S. iodine fortification and supplementation.” Nutrients, 2012, vol. 4, pp. 1740-6., doi:10.3390/nu4111740

  18. Biban BG, Lichiardopol C. “Iodine Deficiency, Still a Global Problem?.” Curr Health Sci J, 2017, vol. 43, pp. 103-111., doi:10.12865/CHSJ.43.02.01

  19. Pearce, E.N. “Monitoring and effects of iodine deficiency in pregnancy: still an unsolved problem?.” Eur J Clin Nutr, 2013, vol. 67, pp. 481-4.,  doi:10.1038/ejcn.2012.215

  20. Sun X, Shan Z, Teng W. “Effects of increased iodine intake on thyroid disorders.” Endocrinol Metab (Seoul), 2014, vol. 29, pp. 240-7., doi:10.3803/EnM.2014.29.3.240

  21. Iodine.” National Institutes of Health.

  22. Yeh, Tai Sheng, et al. “Analysis of iodine content in seaweed by GC-ECD and estimation of iodine intake.” Journal of Food and Drug Analysis, 2014, vol. 22, pp. 189-196., doi:10.1016/j.jfda.2014.01.014

  23. Zava, Theodore T., and David T. Zava. Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis. Thyroid Res, 2011, vol. 4,   doi:10.1186/1756-6614-4-14

  24. Experts: Overhydration potentially deadly for athletes.” University of Virginia Health System.