Monosodium glutamate (MSG)

This flavor enhancer has been reported to cause flushing, headache, and other ailments. But research shows that only a few people react to it and only when they are given large amounts. Still, it’s best to limit MSG because it adds to your overall sodium intake.

Mustard seeds and powder

These ingredients add texture and flavor to some processed and prepackaged foods, but are an often-missed source of allergies, which can cause severe reactions.

Red and yellow food dyes

Some people have allergic reactions after consuming certain food colorings: Yellow no. 5 or 6, Red no. 40, Carmine, and Cochineal Extract. (See below for more warnings on 'certified' color additives.)

Sugar alcohols

These sweetening agents, commonly used in ice creams, gums, mints, and candies, can cause gas and diarrhea. If you’re having digestive problems, try avoiding foods with isomalt, or ingredients ending in the suffix “ol,” such as maltitol, sorbitol, and xylitol.

Sulfites

These preservatives can cause mild to potentially life-threatening reactions in about 5 percent of people with asthma. They can be found in some wines, dried fruit, and vinegars.

Artificial sweeteners

Saccharin (necta-Sweet and Sweet’n low) and aspartame (Equal and NutraSweet) have been linked to cancer based on some animal studies, though those results have not been borne out in humans. Research has also linked artificial sweeteners to weight gain, perhaps because some of us view them as a license to overindulge. So don’t overdo it on the diet soda.

BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene)

These synthetic antioxidants are used to keep oils from becoming rancid. Based on studies in rodents and fish, the National Toxicology Program of the National Institutes of Health concluded that BHA is "reasonably anticipated to be a human carcinogen." While saying that there is no evidence of hazard to the public when it’s used at the low levels now found, the Food and Drug Administration has urged further investigation.

'Certified' artificial colors

Synthetic dyes — often identified by a color name and number on the ingredients list ("Red no. 3") — have been linked to hyperactivity in children. Until more is known, try limiting consumption. Grocery chains such as Trader Joe’s and Whole Foods say they do not carry products with artificial dyes.

Olestra (Olean)

This fat substitute, used in Lay’s, Pringles, and Ruffles light chips, passes through your system undigested, so it doesn’t add calories. But it can cause gastrointestinal problems, including stomach cramps and loose stools. An occasional serving is okay as long as it doesn’t upset your stomach.

Potassium Bromate

This dough-strengthening agent has been shown to cause cancer in animals and is banned in other countries. Bakers have significantly reduced the amount of potassium bromate they use, or stopped using it altogether.

Sodium Nitrate

High cooking temperatures and stomach acid can cause these chemicals, used in processed and cured meats, to form compounds associated with cancer in animals. Some research has associated eating large amounts of processed meats with an increased risk of pancreatic and stomach cancers, but the increased risk from eating cold cuts is probably small. Eating plenty of green vegetables and fruits containing Vitamin C appears to negate any added cancer risk. Processed and cured meats tend to be high in sodium and fat, which is reason enough to limit them.

Transfats

While not what you’d consider a classic food additive, these manufactured fats, used in commercial baked goods, crackers, and margarine, can raise your cholesterol levels and increase your risk of heart disease and stroke. So avoid them at all costs by reading labels. Look for "partially hydrogenated" oils on the ingredient list. Note that the words "transfat free" on the front of the package don’t necessarily mean the product has zero transfats — each serving might have a tiny amount. But if you’re eating several servings, the transfats can add up. Also try to limit restaurant-fried foods because they pack a lot of calories, no matter what they’re fried in.