If you think broccoli pills are a good substitute for the real thing, think again. Available in many formulations, these extracts may be appealing to people who don't like to eat vegetables. But a study published in the Journal of Agricultural and Food Chemistry found that when people took them, they got much less sulforaphane (a key compound that may reduce cancer risk) than they got when they ate broccoli. That’s because the supplements often lack the key enzyme, myrosinase, needed to produce this breakdown compound.
The moral: Food chemistry is complex, and supplements can never duplicate everything that's in the whole vegetable. Some animal research even suggests that very high doses of certain compounds in broccoli extracts may have harmful effects.