Even good foods can cause havoc in your life. Here are a few to keep your eye on.

Food: Grapefruit

Problem: Prescription drug interaction and potential kidney failure

What happens: While grapefruit is an excellent source of vitamin C and contains fiber, potassium and lycopene for cancer prevention, it could be off-limits for those on some prescription medications. "It can alter the effects of the drug, causing serious side effects. The biggest concerns are with cholesterol-lowering medications. The grapefruit may prevent the liver from breaking down the drug, causing toxic levels to build up that could cause kidney failure," says Lona Sandon, a professor of nutrition at the University of Texas Southwestern Medical Center at Dallas.

How much do you have to eat? "One glass of grapefruit juice or one grapefruit is enough to interfere with medications. I am not sure at what level kidney failure might occur, but it's probably not a good idea to push it. It likely depends on a person's body weight. No level of grapefruit intake is considered acceptable with these medications," Sandon says.

Food: Broccoli

Problem: Prescription drug interaction and hyperoxaluria

What happens: "Broccoli may interfere with your blood-thinning medications, putting you at greater risk for stroke," Sandon says. This is why it is very important to read the fine print about side effects on any medications you're taking and pay attention to warnings. Additionally, too much broccoli can cause hyperoxaluria, says Maurice A. Ramirez, an emergency-room physician and author of the soon-to-be-released book "You Can Survive Anything, Anywhere, Every Time." "This is increased urinary excretion of oxalate caused by excessive intake of oxalate-containing foods (broccoli, cauliflower, cabbage, Brussels sprouts, etc.) resulting in kidney stones," Ramirez says.

How much do you have to eat? Hyperoxaluria will occur in anyone eating more than 1 to 2 cups of broccoli who has a predisposition to calcium oxalate kidney stones. For these individuals, even small elevations of urine oxalate will result in the formation of crystals in the urine. Enough crystals and you get stones. This is not unlike gout patients getting gout attacks (or kidney stones) from foods high in uric acid (fermented foods including beer, wine, alcohol, yeast bread, cheese, organ meats, shellfish, etc.).

Food: High-grit foods and/or grains (such as the whole cracked-grain pieces common in organic bread or coarsely ground stone-ground whole grains — especially if they contain stone powder or sand) and acidic foods (such as carbonated drinks, uncooked vinegar, uncooked tomato, citrus — especially lemon — and ceviche).

Problem: Odontolysis

What happens: Odontolysis is the degeneration or wearing down of teeth by excessive chewing of high-grit foods and/or grains or excessive use of acidic liquids.

How much do you have to eat? "For acidic foods, concentration and time of contact are what matters. For instance, drinking lemon juice is a relatively short exposure, but sucking a lemon for the same total intake is a much longer and damaging exposure. For acidic odontolysis, the process is to dissolve the enamel and dentin of the teeth. For grits and grains, the process is simple wear, like filing down your teeth ... only slower. Unfortunately, odontolysis is not reversible, and it predisposes one to cavities and broken teeth," says Ramirez.

Food: Vegetables with seeds, such as cucumbers and tomatoes

Problem: Can exacerbate symptoms of diverticulitis

What happens: Diverticular disease occurs when small pouches form in the colon, where nuts and seeds can get stuck. The disease is often caused by a diet with too little fiber and too little water. Although the best way to avoid the disease is to make certain you have ample dietary fiber (both soluble and insoluble), if you do develop diverticulosis (which can lead to diverticulitis), you may be well-advised to initially follow a low-fiber diet, avoiding seeded fruits, vegetables and most nuts and seeds, and gradually ramp up to a high-fiber diet that promotes soft, bulky stools, which pass more swiftly, says Jackie Keller, founder of NutriFit and author of "Body After Baby: A Simple, Healthy Plan to Lose Your Baby Weight Fast."

How much do you have to eat? "As little as a cup or two of the wrong thing can cause gas, bloating and great intestinal discomfort," says Keller.

Food: Tomatoes, potatoes, peppers and eggplant

Problem: Increased arthritis pain

What happens: According to Carol Forman Helerstein, a clinical nutritionist for Chefs Diet (www.chefsdiet.com), "While these vegetables contain many healthy and protective antioxidants, they are not a good food choice for arthritics." The reason? "They are all members of the nightshade family of vegetables, which contain a chemical called solanine," Helerstein says. Solanine is a glycoalkaloid poison that's part of the plant's natural defense system. "All pain and all diseases, including heart disease, are related to an inflammation in the body. Arthritis is simply inflammation of the joints, and the chemicals in certain foods (especially tomatoes, potatoes, peppers and eggplant) cause a chemical response in the body, which is inflammation — i.e., arthritis pain," says Helerstein.

How much do you have to eat? According to Helerstein, "Everyone's body is different and there is not an exact science. Some individuals may be more sensitive than others to certain foods."

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.