Emily Ho of Oregon State University and principal investigator with the Linus Pauling Institute said to absorb the many health benefits associated with eating broccoli or other cruciferous vegetables such as cauliflower or Brussels sprouts, people need to eat the real thing.
"Some vitamins and nutrients, like the folic acid often recommended for pregnant women, are actually better-absorbed as a supplement than through food," Ho said in a statement.
"Adequate levels of nutrients like vitamin D are often difficult to obtain in most diets. But the particular compounds that we believe give broccoli and related vegetables their health value need to come from the complete food."
A necessary enzyme, myrosinase, is missing from most of the supplement forms of glucosinolates, a valuable phytochemical in cruciferous vegetables, Ho said.
Without this enzyme found in the vegetable itself, the body absorbs five times less of one important compound and eight times less of another, Ho added.
In addition, if broccoli is cooked until it's soft and mushy, its health value plummets.
The study, published in the Journal of Agricultural and Food Chemistry, suggested it's best to lightly cook cruciferous vegetables for 2 or 3 minutes, or steam it until it's still a little crunchy to retain adequate levels of the enzyme.