Ed Blonz: Toxic vegetables?

Contra Costa Times correspondent

Posted:?08/09/2011 12:00:00 AM PDT

DEAR DR. BLONZ: As a new vegetarian I’ve become concerned when I began reading about all the toxins that can be found in vegetables. How much of an issue does this become for vegetarians? — B.S., San Jose

DEAR B.S.: Interesting story here. Nature equips many fruits and vegetables with an ability to produce a variety of chemical toxins to help ward off insects, bacteria, fungi and animal predators. Although they’re meant to help these plants survive in their natural environment, if taken by humans in sufficient quantities, these natural toxins can cause illness, cancer or even death. Have no fear, though. Eating fruits and vegetables is healthful, not hazardous. A look at a few of these natural toxins will illustrate the point that it’s the dose that makes the poison. Here are some examples.

Potatoes can produce solanine, a bitter-tasting toxin that affects the nervous system. This toxin is produced when the potato is exposed to sunlight or allowed to sprout. Solanine is most concentrated in the sprout, but it’s also present in potatoes with a greenish tint to the skin. To avoid solanine, potatoes should be kept in a cool, dark place. Carefully cut away all sprouts and green portions before cooking. Discard any potatoes that taste bitter.

Cyanide, a deadly poison, is naturally present inside the seeds of apples and the pits of apricots, peaches, bitter almonds, cherries and other

fruits. There’s no danger if you don’t chew on the pits, because the cyanide isn’t released unless the pit is crushed. Lima beans and other legumes once contained cyanide compounds, but through selective breeding, commercial varieties have been developed that no longer have this trait.

Cabbage, mustard greens, cauliflower and Brussels sprouts contain goitrogens, compounds that prevent the nutrient iodine from being used by the thyroid gland. Without iodine the thyroid cannot function normally and an enlarged thyroid, or goiter, results. Goitrogens are not a concern unless you have an iodine-deficient diet and the above foods are a major part of your daily menu. With the advent of iodized salt and the wide distribution of ocean fish (another good source of dietary iodine), iodine deficiencies are no longer common.

Spinach and rhubarb contain oxalates, another toxic compound. One serving of rhubarb leaves contains one-fifth of the toxic dose of oxalates for humans. However, rhubarb stalks — the much more commonly eaten part — contain lesser amounts, as do spinach leaves.

To put all these natural toxins in perspective, it is essential to appreciate that the body is equipped to handle small quantities of many toxins, rather than large amounts of a few. For example, one potato poses little risk, but the combined solanine from 100+ pounds of green potatoes could be enough to kill a horse. Your best defense against natural toxins is to eat a variety of foods. With variety you not only limit your exposure, you provide the nutrients the body requires to maintain its defenses. And as the name suggests, natural toxins are part of nature; they are not to be feared so much as respected.

Ed Blonz, Ph.D., is a nutrition scientist and an Assistant Clinical Professor at the University of California, San Francisco. He is the author of “Power Nutrition” (Signet, 1998).

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