What’s your favorite superfood? Kale? Quinoa? Avocado? These and other superfoods deserve their superstar status. They’re loaded with protein, fiber, healthy fats and ­other important nutrients. But it is possible to go overboard on even the healthiest of foods—and too much of a good thing can be a bad thing.

See if you face any of these superfood risks…


For the average person, the risk from this superstar green is remote. But some people—particularly those who engage in lengthy, juice-based diets and ­detoxes—consume extreme amounts of kale. I had a client who drank more than 64 ounces of “liquid kale” a day on a juice cleanse, and it was replacing other vital nutrients in her diet.

Risk: Kale contains thiocyanate, a chemical compound that, in large amounts, interferes with iodine ­metabolism. Insufficient iodine can cause a drop in thyroid hormones and lead to hypothyroidism. Kale is goitrogenic, meaning that it can affect thyroid hormones if consumed in excess. The body can develop an enlarged thyroid gland (a goiter) in an attempt to compensate for low thyroid levels.

Bottom line: Normal amounts of kale shouldn’t cause thyroid problems. Extended juicing, on the other hand, could pose a problem, particularly for those who avoid foods high in iodine. It would be hard to overdo it on cooked kale, but limit juiced kale to less than 10 cups of raw kale per week.


Few things are more refreshing or more all-American than having a glass of juice with breakfast. Millions of people start their day with a glass of orange, grapefruit or other juice.

Risk: A Harvard study found that people who consumed one or more servings of fruit juice daily were up to 21% more likely to develop type 2 ­diabetes.

Studies also show that people who ingest liquid calories typically don’t compensate by eating fewer calories, so they may be more likely to gain weight.

You can blame the lack of fiber. Fruit juices retain the sugary sweet fructose found naturally in whole fruits, but they don’t have the fiber found in whole fruits. Fiber is a key component of satiety, or fullness, as well as a factor in weight control and ­digestive health.

An average-sized ­orange contains just over 60 calories. The calorie count nearly doubles when you swig an eight-ounce glass of ­orange juice. And with little fiber, juice is less filling, so you may consume more calories overall.

The same Harvard study found that people who ate at least two servings per week of whole fruit—notably blueberries, grapes and apples—had a 23% reduced risk for type 2 diabetes, compared with those who ate no fruit at all.

Bottom line: You should always try to stick to whole fruits when possible. But if you really love juice, look for one with no added sugar and limit yourself to only an occasional glass of six ounces or less.


Quinoa is one of the rare plant foods considered a complete protein, containing all of the essential amino acids. One cup of quinoa has eight grams of protein, twice the amount found in rice or a baked potato. It’s also a great source of fiber, with five grams in a one-cup ­serving, and it is high in folate, manganese, magnesium and B vitamins.

But the outer layer of the quinoa seed contains saponin, a coating that acts as a natural insect repellent. One advantage of saponin is less need for chemical pesticides. The disadvantage of saponin is the potential for stomach upset and even damage to the lining of the small intestine.

Many quinoa brands are prewashed to remove the saponin, but it’s a good idea to thoroughly rinse the seeds again prior to cooking.

In addition, try not to overdo it on quinoa. Rapid increases in fiber intake can cause ­digestive issues and discomfort, such as flatulence, bloating and diarrhea.

Bottom line: If you’re not already consuming 21 grams to 38 grams of fiber a day (the recommended amount), increase your quinoa intake slowly. Give your body time to adjust by increasing fiber intake by three to five grams every few days.

Also important: Drink an extra glass or two of water while you’re eating more fiber. Fiber absorbs water in the gastrointestinal tract, so you’ll need more fluid to keep things moving ­efficiently.


Avocados are loaded with healthy mono- and polyunsaturated fats, which are linked to heart health and cholesterol management. And they’re not just for guacamole anymore—avocados add delicious flavor to salads, sandwiches, omelets and tacos. Their creamy texture also provides a healthier alternative to mayo, cheese, sour cream and other high-fat spreads.

Risk: Avocados are shockingly high in calories. One medium-sized avocado delivers 320 calories and 30 grams of fat.

The healthy fats make it worth the calories. One study published in Journal of the American Heart Association found that people who ate one avocado a day, in addition to other healthy foods, ­decreased their LDL (bad) cholesterol by 14 mg/dL.

Bottom line: Enjoy avocados, but limit yourself to one per day and include them in your calorie count.


Dietitians often encourage their clients to eat more fish because it’s a nutritional powerhouse. Fish boasts the rare combination of high protein and heart-healthy omega-3 fatty acids.

Risk: Virtually all fish contain some mercury, a neurotoxin that is particularly dangerous for developing brains. This explains why pregnant women and young children are advised to limit their seafood consumption. Adults who consume too much mercury can ­develop numbness, tremors, headaches and problems with balance or coordination.

Bottom line: Salmon, along with sardines, crab, shrimp and tilapia, is one of the lower-mercury seafoods. (The highest mercury sources include ahi tuna, king mackerel, swordfish and shark.) But mercury poisoning still is possible with excessive salmon intake. Adding salmon to your menu two or three times a week carries little risk and has big health benefits for the whole family. Even pregnant women and children now are encouraged to eat more seafood, with a weekly recommendation of eight to 12 ounces of lower-mercury seafood. However, even adults who are not pregnant should be cautioned against eating salmon much more than that.