April, 1980

Adapted from A Report of the Institute of Food Technologist's Expert Panel on Food Safety & Nutrition and the Committee on Public Information.

The current popular tendency is to assume that the words "natural" and "safe" are synonymous, and that almost anything present in foods that wasn't put there by Mother Nature must be harmful. This assumption overlooks that many "natural" foods contain a variety of substances which are potentially harmful if consumed in large quantities.

The purpose of this article is not to raise alarm over the safety of natural foods, because it is obvious from human experience that most natural foods can be consumed with safety and equanimity in normal dietary amounts.

In spite of occasional assumptions to the contrary, plants and animals that have historically served as foods for man were not designed by nature for that purpose. Man discovered what he could safely eat through trial and error, discarding things that tasted bad or made him sick. Undoubtedly, most of his decisions to discard were based on reactions which occurred so soon after eating that there was little question about what caused them.

However, long-delayed, harmful effects of repeatedly eating certain natural products remained a mystery until relatively modern times. The relationships between diet and such diseases as goiter and ergotism, for example, were slow in coming to light. Increased knowledge has led to new suspicions of long-delayed effects of other normal components of the diet, such as sodium and cadmium on hypertension.

Natural toxicants can occur as contaminants of natural food products or as normal components of such foods. Contaminants can be of microbiological origin, such as toxins produced by bacteria, or they can be taken up by the food product in its normal growth process.

Man-made toxicants can occur in food products in a large variety of ways. Some come from agricultural chemicals, such as pesticides and fertilizers. Others are produced within a food during processing or added to it as additives. They can also occur through accidents or mistakes in food preparation, contamination from food utensils, environmental pollution, or contamination during storage or transport.

Many of the chemical substances that enter foods as a result of man's efforts are the same as those naturally present in food. Toxic metals such as lead, mercury, cadmium, arsenic, and zinc are normally and naturally present in foods; indeed, they are unavoidable, since they occur in soil, water, and plants as a result of the natural geochemistry of the earth and the normal growth cycles of plants and animals.

On a worldwide basis, the greatest known number of food-related injuries to man have occurred from normal components of natural food and from toxins produced in foods by microorganisms. The agents used intentionally to produce, process, and package foods can be subjected to rigid controls, and are relatively free of hazard. On the other hand, regulatory measures have little effect on the natural composition of foods and the natural processes of food contamination.

The greatest amount and the widest variety of chemical substances consumed by man are the normal, natural constituents of foods. In spite of this fact, no single food plant has been well characterized chemically. For example, the potato, usually regarded as one of man's simpler foods, is a complex chemical aggregate. About 150 distinct chemical substances have been identified in this natural product, among which are the solanine alkaloids, oxalic acid, arsenic, tannins, nitrates, and over a hundred other items of no recognized nutritional significance to man. Forty-two chemical entities have been found in orange oil, while the orange as a whole includes a host of other chemical substances. All vegetables, fruits, and other natural food products are similarly complex.

Furthermore, the quantities of some of these substances can be large, compared with those presently used as intentional food additives. For example, along with his average annual consumption of 120 pounds of potatoes, the consumer gets almost 10,000 milligrams of solanine, a relative of the poison found in deadly nightshade - enough to kill a horse if taken in a single dose. It doesn't kill him, of course, or even harm him noticeably, because he eats the potatoes in smaller individual quantities, over a year's time. The body's waste disposal mechanisms are well able to handle the biological load under normal consumption patterns.

Similarly, the average consumer eats 1.85 pounds of lima beans per year, containing about 40 milligrams of hydrogen cyanide, the lethal agent used in a gas chamber. With his annual consumption of seafood, he gets 14 milligrams of arsenic. Even the two teaspoons of nutmeg sprinkled on his food for spice during the year contain 44 milligrams of a strong hallucinogenic drug, myristicin.

Relatively few of the individual chemicals known to be naturally present in our foods have been evaluated for their toxicity. Furthermore, almost any chemical substance can be shown to be toxic, if tested at some sufficiently high level of consumption in experimental animals.

These thousands of toxic substances in natural foods do not, however, automatically create a hazard - (which is defined as the capacity to produce injury under the circumstances of exposure). From the evidence of our daily lives, this hazard is very low. The individual toxicities of each of the thousands of different chemicals present in our diet each day cannot be added up to a total toxicity for that day. For example, if you ate one-hundredth the lethal dose oœ each of 100 different food components, the mixture would be harmless. The human organism readily handles (by many different routes) small amounts of many different chemical substances ingested at the same time, even though any one of them in some larger amount might be harmful.

Many "antagonistic interactions" occur between chemical substances in foods. Such interactions among the trace elements, for example, have been demonstrated in test animals. In these instances, the toxicity of one element is offset by the presence of an adequate amount of another element - the second acts somewhat as an antidote or buffer for the first. For example, the effects of a toxic level of cadmium in the diet are reduced by an accompanying high level of zinc. Similarly, iodine inhibits the action of some goiter-causing agents.

What this means to the consumer and his diet is that there is "safety in numbers". The wider the variety of food intake, the greater is the number of different chemical substances consumed- since all food is chemical- and the less is the chance that any one chemical will reach a hazardous level in the diet. Further, the fact that food is produced and processed in widely scattered geographical locations means that the average consumer in one area dines on foods produced in various other areas, thus avoiding possible hazards from localized geochemical imbalance. Plant breeding programs also have reduced some toxic components.

Numerous substances that occur naturally in plant food sources are known or suspected to cause cancer in animals (Miller, 1973). Among these are safrole, estrogens, antithyroid compounds, lead, and some natural contaminants such as the fungal toxins. More recently, the discovery that nitrosamines and polycyclic aromatic hydrocarbons, both potent carcinogens, are present as natural constituents of some plants has intensified the concern that human cancer may be attributable in part to our natural food supply.

As far as human food intake is concerned, the ultimate goal should include further understanding what constitutes the optimum in nutritional content, and what practices involve the minimum of long-range, life-time toxicological hazard in the diet.