People often express concerns about toxic substances in their food. Usually, their focus is on things like pesticides, food additives and environmental contaminants — all of which are regulated by agricultural and food industry laws. However, what is rarely appreciated is how many toxic chemicals are present naturally in foods — toxins produced by nature. There is little or no regulation of these toxins.
Generally, this is not a problem for people who consume a wide variety of food and don’t get excessive amounts of any single natural toxin. A healthy person’s body has the means to detoxify thousands of toxic substances, both natural and man-made. In our last column we explained how the liver plays a big role in detoxifying these substances and preparing them for elimination from the body. Where problems can occur is when someone over-consumes one or more foods with a natural toxin. Over time this continuously delivers a specific toxin into the body in amounts that exceed its capacity to handle the toxin.
QUESTION: What are some common natural food sources of toxic substances?
ANSWER: There are many raw plant foods that contain toxic substances that are removed or reduced by heating. For example, raw soybeans contain toxic protein substances that are disabled when the beans are cooked. Feeding raw soybeans to animals was found to impair growth and cause enlargement of the thyroid gland, among other problems.
Taro corms and leaves cannot be eaten raw or undercooked. Anyone who has tried it will describe the dreaded “taro itch” that feels like something is really wrong in the back of your mouth and throat. For a long time people thought this was caused by microscopic spiky-looking calcium oxalate crystals in the plant. However, cooking does not change these much, and based on research by Dr. Robert Paull and colleagues at the University of Hawaii at Manoa, the “itch” is caused by an offending protein that, unlike the oxalate crystals, is altered in cooking.
There are thousands of toxins naturally present in food that are destroyed by cooking. Certainly, having fresh raw food in the diet is a good thing, but so is having cooked food.
Many natural toxins are not affected by cooking. For example, potatoes contain the toxins solanine and chaconine. Commercially available potatoes generally have safe low levels of these toxins. However, when potatoes are exposed to light for too long, they turn green, and these toxins increase to potentially unsafe levels.
Even essential nutrients can be toxic when over-consumed. Although it is difficult to get toxic levels of most essential nutrients from normal foods, the essential mineral manganese appears to be an exception. Foods naturally high in manganese are healthy foods like whole grains, nuts, beans, pineapple, berries and dark greens. It takes excess intake for months or, more likely, several years to eventually cause neurological problems.
The list of foods that contain natural toxins is extensive. Herbal concentrates should be used with caution and moderation for the same reason.
But the natural way humans have avoided problems with these toxins is by eating a wide variety of food and not over-consuming specific foods or food types. The other thing that has helped to protect us is having a healthy liver that excels in detoxifying an amazing array of poisonous substances.
Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. Dobbs also works with University Health Services.
