Too Much Good can be Bad

Flax seeds:

Negative effect: Increase the risk of prostate cancer

What happens: Its high content of alpha-linolenic acids (ALA) has made the ancient flax seed our modern miracle food, says Gloria Tsang, R.D., of HealthCastle.com. "It offers a vegetarian alternative to provide omega-3 fatty acid and has been shown in many studies to offer heart-healthy benefits by lowering total cholesterol and low-density lipoprotein (LDL or "bad") cholesterol levels. Flax seed may also help lower triglycerides and blood pressure and keep platelets from becoming sticky, thereby reducing the risk of a heart attack," adds Tsang.

However, a few studies have also linked high concentrations of ALA to a higher risk of prostate cancer. Until more is known, men who are not vegetarians are recommended to choose fish sources for heart-healthy omega-3s instead, says Tsang.

How much do you have to eat? As ALA is concentrated in oil form, it's OK for men to eat the actual seeds, but until more studies are done they should completely stay away from the oil form (flax seed oil and flax seed oil pills), says Tsang.