7 healthy foods that can be harmful when eaten too frequently

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

by Melissa Breyer

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 twice the daily recommended requirement. According to Prevention, six to eight nuts fulfill 777 percent of your daily selenium needs. Unfortunately, selenium can be toxic in high amounts; too much can lead to hair loss, brittleness or loss of nails, dermatitis, neurological abnormalities, and worst case scenario, death. Yikes.

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 the dreaded stones ... and nobody wants 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 as Consumer Reports points out, almost all seafood contains the toxin in varying degrees; getting too much of it can do harm to the brain and nervous system. They note that this “is especially true for fetuses, but children and adults who eat too much high-mercury seafood also can suffer harmful effects such as problems with fine motor coordination, speech, sleep, and walking, and prickly sensations.” Canned tuna can be particularly high; the magazine goes beyond the FDA’s guidelines for tuna, noting that they don’t think pregnant women should eat any. You can see how various fish and types of tuna stack up here.

4. Red meat
At TreeHugger we talk about 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. I know, most people don’t get enough iron … but if you happen to be taking iron supplements for whatever reason, 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. SFGate notes that 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 not only stars in Agatha Christie murder mysteries, but it’s 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. Sigh, what tangled webs we weave. Experts recommend brown basmati from California, India, or Pakistan as they have about a third less inorganic arsenic than brown rice from other regions. And no more than two servings of brown rice should be consumed per week. The FDA recommends swapping other grains for rice, think quinoa, barley or millet. For more, see 12 great whole grains to try.

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. Is nothing sacred? 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.)

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