In large quantities, health foods can do more harm than good

Go ahead, dive into your dinner of tuna and brown rice. Just don't repeat that same meal every night. Even though these foods are very nutritious, you can get too much of a good thing.

Foods high in nutrients can also be high in unwelcome amounts of chemicals, and sometimes too much of such foods can wreak havoc on your health. It's also important to introduce variety into your meals and snacks to make sure you get the balance of nutrients your body needs.

Here are some nutritious foods you should definitely be eating, as long as you don't overdo it.

• Brown rice

We've been told for years to cut back on white rice and replace it with whole grain brown rice instead. And while that's good advice that will net you more fiber, vitamins and minerals, it also comes at a cost: Arsenic. We're not talking toxic levels in one serving or anything scary like that, but eating rice a few times a day (every day) is not a good idea. Excess arsenic is linked to an increased risk of heart disease and some types of cancer.

Rice absorbs more arsenic from the soil than many other grains, and brown rice has 80 percent more inorganic arsenic than white rice. That's because arsenic accumulates in the grain's outer layers, which are removed to create white rice. And it doesn't matter if the rice is organically grown or not - all rice can still contain arsenic.

Instead: Enjoy brown rice as one of many whole grains in your meal plans a few times a week, but not daily. Swap it out for low-arsenic grains, such as quinoa, barley, buckwheat and millet.

• Brazil nuts

These large seeds are crazy high in the antioxidant mineral selenium. Just one nut contains your daily dose. The problem? Too much selenium is toxic, and may cause symptoms such as loss of hair and nails, diarrhea, skin rashes, mottled teeth, and nervous system abnormalities. That's why you often see separate bulk containers of almonds, pecans or walnuts, but not usually for Brazil nuts.

Instead: Stick with mixed nuts. Grab a handful and eat a variety of nuts, but don't pick out and only eat a dozen Brazil nuts.

• Albacore tuna

A scoop of tuna is an easy sandwich option, and raw tuna is common among sushi lovers. In fact, canned tuna is the second-most frequently eaten seafood after shrimp in the United States - that's great since it's a lean source of protein, and is high in heart-healthy omega-3 fats.

The issue is that albacore tuna (the second-most commonly eaten type, after skipjack) is a very large fish, and spends a lot of time in mercury-laden waters. Methylmercury builds up in tuna, and if you eat too many servings per week, it can build up in your body, too, and interfere with the brain and nervous system. Mercury toxicity can cause memory loss, vision loss or trouble regulating blood pressure levels. High mercury intake is especially problematic in children, women of childbearing age, and women who are pregnant or breast-feeding, because mercury affects the development of a child's brain and nervous system. These groups should limit albacore tuna intake to no more than once a week.

Instead: Smaller species of tuna, including skipjack and yellowfin, have less mercury than albacore or bigeye tuna. When choosing canned tuna, look for "light" instead of "white" fish, and choose yellowfin instead of bigeye for your sushi and sashimi. "Ahi" may refer to yellowfin or bigeye, so sushi lovers should ask which species they are getting.

• Cinnamon

If you have a small sprinkle of cinnamon on your oatmeal or chai tea latte, you have nothing to worry about. It adds a delightful flavor. Some research has shown that cinnamon may help lower blood sugar - at doses of a teaspoon or more per day. The trouble is that grocery store cinnamon, a spice known as cassia cinnamon, contains a compound called coumarin, which has been linked to an increased risk of liver disease when consumed in excess (more than a teaspoon per day).

Instead: If, with the approval of your doctor, you are trying the cinnamon treatment, turn to true Ceylon cinnamon, which you can buy at a health food store. The Ceylon variety is lighter in color and flavor compared with cassia, and has about 60 times less coumarin - but is still effective at lowering blood sugar levels when used in high doses.

• Coffee

Coffee is filled with beneficial antioxidants and can certainly help with alertness, so go ahead and start your day with a java jolt. But keep in mind that the average eight-ounce cup of coffee contains about 100 to 150 mg of caffeine, and it's best to stay within 400 mg of caffeine per day (so, about three or four eight-ounce cups of coffee). After that level, you may get symptoms such as jitteriness, rapid heartbeat and insomnia, and at high intakes, coffee acts as a diuretic. And remember, if you order an extra-large coffee (24 ounces), it counts as three cups of coffee.

Instead: If you still need a caffeine bump after you've had two or three cups of coffee, opt for a cup of black or green tea, which has just 30 to 50 mg of caffeine per cup.

Previously:
• How to handle ever-changing nutrition science
• Six foods to eat for a mood boost
• Keep your holidays happy by letting go of food guilt
• A dietitian's four favorite foods that are high in good fats
• Advice that has reached its expiration date
• Going 'lectin-free' is the latest pseudoscience diet fad
• When pills and injections can become downright dangerous
• 10 nutrition mistakes even really healthy people make
• Butter or olive oil? Eggs or no? New nutritional review cuts through the myths
• 8 tweaks to make good-for-you foods even better
• 'Healthy' sweeteners, protein-powerhouse quinoa and other nutrition myths, debunked
• Can't do vegetarian? Try flexitarian, which also has health benefits
• Five red flags that your 'clean' diet is going too far