5 Healthy Foods You Shouldn’t Overdose On

Last Update: August 18, 2023

The Inuit people of Arctic Quebec have survived off the natural resources of fish and marine mammals from nearby oceans for centuries. Essential for protein and rich in omega-3 fatty acids, what the Inuits eat would be considered healthy—theoretically. Yet studies have shown the IQs of their children are abnormally low.

Why? The whales they hunt for meat are contaminated with mercury. While the neurotoxicity of mercury has long been a concern, many people don’t think twice about ordering a tuna melt at a restaurant (28 percent of Americans’ exposure to mercury is from canned tuna), let alone realize that they could be eating too much of certain vegetables, nuts, and superfoods.

Though it sounds like a no-brainer to fix up a huge salad for lunch, there can be too much of a good thing when it comes to even the healthiest of foods. Here are five nutritious foods that certainly have a place in a well-balanced diet—but in order to safely reap their health benefits, be conscious of the surprising potential side effects of eating them in bulk.


Although it’s a great source of protein, eating lots of tuna can be dangerous without being mindful. As with whales and other marine mammals and fish consumed in large quantities by Arctic natives,  tuna is highly susceptible to the industrial pollution of mercury, since the fish is high on the food chain and has likely ingested many smaller fish full of the stuff. High exposure to mercury can lead to fertility problems, high blood pressure, heart disease, and in children, impaired brain development.  Fortunately, a few brands have started selling sustainably fished tuna with very strict mercury limits. But for average brands of canned albacore, Consumer Reports recommends eating no more than one can per week.


Don’t take this to mean spinach is bad, but even something as high in nutrients as this dark leafy green can harm the body if you go overboard. According to registered dietician Kathryn Bloxsom, “Kidney stones are often made up of calcium oxalate, [and] eating a diet high in oxalates can contribute to kidney stones. Spinach is a high oxalate food, as other greens like kale, collard greens, Swiss chard, and beet greens.” She adds, “For most people it would take more spinach than anyone could, or would want to, eat in a day—a bowl with lunch and dinner is totally fine.” Also, consider varying intake of greens to include low-oxalate types such as watercress and escarole.

Almonds and brazil nuts

Almonds are also high in oxalates, so kidney stones could be a problem here as well. And since they are the highest fiber nut, noshing on too many can cause gastrointestinal discomfort. In extreme cases, excessive vitamin E and manganese (both found in almonds) can be toxic, but that would only potentially happen if you eat an obscene amount of almonds (more than six ounces) along with other sources of this vitamin and mineral, like whole grains, fortified cereals, eggs, and spinach. Try to stick to an average serving size of one ounce to be on the safe side.

Brazil nuts contain plenty of selenium—a trace mineral your body only needs in small amounts. As Bloxom says, “Eating too many [Brazil] nuts can result in selenium toxicity, which can be slight and lead to brittle hair and nails, or more severe and lead to gastrointestinal and neurological issues as well as kidney failure, heart attack, or even death.” One nut contains 95 micrograms of selenium while the average person only needs 55 micrograms of this mineral per day. Only eat these nuts occasionally.

Lean animal protein

Even though lean meat is generally considered a healthy source of protein, it does contain insulin-like growth factor 1 (IGF-1), a hormone associated with accelerated aging and increased cancer risk. “Those who eat less protein from animal sources tend to have lower levels of IGF-1,” says Bloxsom. “However, low levels of IGF-1 are linked to neurological disorders like dementia and Alzheimer’s.” Whether cutting out this healthy protein source or not, make sure to get plenty of exercise to help balance out hormones.

This millenniums-old superfood from the mountaintops of Peru is known to energize, increase stamina, sharpen memory, promote fertility, stimulate libido, and balance hormones. It’s powerful stuff. So can things get out of hand when it’s consumed in excess? Sure.  Avoid going overboard by consuming only the recommended dose of maca on the label. Maca purveyors suggest taking a few days break from this superfood each month to allow the body to stabilize its hormones.

Photo credit: Paul Delmont

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Dana Poblete

Dana's love for all creatures under the sun (bugs, too) drives her in her advocacy for ethical eating, environmental sustainability, and cruelty-free living. A natural born islander, she surfs when she can, and writes, always.

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