21.5: Preservatives

Although many people recognize flavoring additives on ingredient lists, few recognize the preservatives, and those who do often view them with alarm. What are these chemicals?

Among the most common are calcium and sodium propionate, whose names are often found on labels with the words, “added to retard spoilage.” These are intended to keep molds and bacteria from making foods such as bread inedible. They aren’t poisons. They are salts of propionic acid, which is produced naturally in Swiss cheese. They are completely metabolized by the body, e.g., calcium propionate is broken down in the body to calcium, carbon dioxide, and water.

Additives used for preserving are often substances present in nature to protect foods. For example, vitamin E occurs naturally with unsaturated oils. It functions in the body as an antioxidant, slowing down the oxidation of the unsaturated fat in our cell membranes. Vitamin E does the same thing on the grocer’s shelf; it’s added to slow down the oxidation of the oil in foods, and thus helps prevent rancidity. (Even though vitamin E is a natural food constituent, it’s still only used sparingly as a food additive.)

Citric acid (found in citrus fruits), and ascorbic acid (vitamin C) are also antioxidants, and both are used to prevent oxidation and discoloration. We use citric acid and vitamin C as antioxidants ourselves, when we combine citrus fruit or its juice with sliced avocados, apples, etc. Sliced oranges in a fruit salad retards the oxidation-caused browning of the sliced apples.

BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are more commonly added to foods as antioxidants. (BHA and BHT aren’t normal food constituents.)

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Because of some studies showing that BHA and BHT inhibit cancer in mice and rats, capsules of BHA and BHT (“man-made chemical food additives”) are sold as dietary supplements.

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Are Food Additives Safe to Eat?

The public has a single question about these substances: Are they absolutely safe? In realistic scientific terms, the answer to that question can be extremely succinct. No. Then how can we dare to put additives in food? The scientist’s answer, and a confusing one for the layman, is: “Because we don’t think that they will hurt anyone.”

The apparent conflict between these two answers is best understood by looking more closely at the meaning of safety. Webster defines safety as “freedom from danger, injury or damage.” In these terms, stop to think of just one thing which you do or eat which is absolutely safe. Remember that, as a measurement, “freedom from” must be considered as zero. Zero what? Zero risk.

Is it safe to cross the street at a quiet intersection with a traffic light and a crossing guard? One can’t really say that it is; there’s a very low possibility that you’ll be hurt, but it’s not zero. Is it safe to drink water or eat a banana? In absolute terms, it isn’t. Anything we eat or drink can be toxic, if we take enough of it, or take it under certain conditions.

It’s hard for many people to understand that the only real measurement of “safety” is risk. In crossing the street, we may say that we feel safe, and mean that we think the risk is very low. At rush hour, the risk is somewhat higher, but not really threatening.

To thicken: Agar Calcium alginate Carob bean gum Cellulose Gelatin Guar gum Gum ghatti Locust bean gum Modified food starch Pectin Potassium alginate Sodium alginate Tragacanth gum	To color: Annatto Caramel Carotene Carrot oil Citrus red no. 2 Dehydrated beets FD & C blue no. 1 FD & C red no. 40 FD & C yellow no. 5
To control acidity: Acetic acid Citric acid Lactic acid Sodium acetate Sodium citrate Tartaric acid	To prevent oxidation: Ascorbic acid (vitamin C) BHA (butylated hydroxyanisole) BHT (butylated hydroxytoluene) Citric acid EDTA (ethylenediamine tetraacetic acid) Propyl gallate Sulfites Tocopherols (vitamin E)
To whiten: Benzoyl peroxide Calcium bromate Hydrogen peroxide Potassium bromate	To enhance flavor: Disodium guanylate Hydrolyzed vegetable protein Maltol Monosodium glutamate (MSG)
To retain moisture: Glycerol Propylene glycol Sorbitol	To make baked goods rise: Calcium phosphate Monocalcium phosphate Potassium bitartrate ("cream of tartar") Sodium aluminum phosphate Sodium bicarbonate ("baking soda")
To emulsify: Carrageenan Diglycerides Gum arabic Lecithin Monoglycerides Polysorbate	To retard microbial growth: Benzoic acid Calcium lactate Calcium propionate Calcium sorbate Lactic acid Methylparaben Potassium sorbate Propionic acid Propylparaben
To prevent caking: Ammonium citrate Calcium silicate Magnesium carbonate Silicon dioxide	To improve tartness: Phosphates Phosphoric acid

Table 21-1: Some Food Additives

And we have something to gain from crossing the street—getting to work, perhaps. So we’re willing to undertake the very small risk. It’s in the same context of assessing risk, and balancing that risk with the benefit that a decision about whether to use an additive is made. 

There must, of course, be a clear benefit to be gained, and the aim is to use the smallest amount of additive necessary to achieve that benefit. The hard questions are: What’s the hazard (risk), in terms of specific amounts of the additive and the conditions of its use? And what level of risk should we say is acceptable? In crossing our quiet street, one condition we impose is to look both ways for traffic. With this condition we accept the risk without any fear of danger.

Legislating Additive Safety

The safety programs of the FDA began with Dr. Harvey Wiley, a chemist with the USDA from 1883-1930. Dr. Wiley used a volunteer “poison squad” of twelve men, who consumed quantities of food additives to see if they were harmful. Those were the days in which manufacturers could put what they chose in food, and it was up to government agencies to learn if it was harmful, prove that it was, and take action to have the substance removed (this is generally the situation for many dietary supplements today). For the first 52 years of the FDA’s existence (from 1906 to 1958), it was the government’s duty to prove danger, not the manufacturer’s to prove “safety.”

In 1958, this process was reversed with the Food Additives Amendment. This requires that manufacturers first run extensive tests to prove the safety of an additive, then apply to the FDA for an order permitting use within a specific tolerance of amounts of the substance considered safe.

The amendment outlawed the addition to food of substances of unknown or uncertain toxicity. It established that a newly proposed additive must undergo strict testing designed to establish the safety of the intended use.

This law and its procedures provide protection for the consumer—and a major expense for the manufacturer. Since this amendment, very few additives have been added to the approved list.

Assessing the Risk

A primary step in testing an additive is to determine the no-effect dose. Groups of animals are given various doses over their lifetimes. Suppose there’s no apparent harmful effect at lifetime doses of up to 100 mg/day, but animals given 1,000 mg/day or more show an impairment of kidney function (doses are commonly tested in 10-fold increments). We’ve found a “no-effect” dose and an “effect” dose. The measurements are important, for usually FDA requires that there be a 100-fold safety factor. In other words, usually the highest expected use of an additive should be no higher than one-hundredth of the no-effect dose.

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Vitamin A at RDA levels doesn’t cause birth defects. But it can in big doses.

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A no-effect lifetime dose of 100 mg/day would mean that the highest expected use should be no higher than 1 mg/day. In many cases, the highest expected use is much lower. If, in this example, the highest expected use was 0.1 mg/day (1/10 of the highest allowed dose), the safety factor would be 1,000-fold.

Some scientists argue that the high doses given to test animals often produce effects unique to the high dosage—effects from the massive amounts exceeding what the body can safely handle.

But to find effects at low doses usually means having to use many more animals over a long time. Using thousands of animals to test each substance over a period of years is extremely expensive and time consuming. So we’re left with the alternative of testing substances at high doses on relatively small groups of animals.

Animal tests are extensive. For each proposed additive, studies must be done on both male and female of at least two species of animals, and over at least two generations. Obviously, we aren’t biochemically or physiologically identical to the test animals, but the effects on them suggest how we might be affected.

Even with extensive studies, it’s clear that estimates of risk have to be made on incomplete knowledge. What’s hazardous to an animal may not be hazardous to us; what’s safe for an animal may not be safe for us. A substance may be toxic at a given dose for some people and not others; and under some conditions and not others. There may be effects that aren’t measurable by current technology.

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Very high doses are often given to animals in testing.

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Because these uncertainties can never be completely addressed, a lot of the assessment of human risk will remain subjective, and there will continue to be arguments about risk assessment among scientists themselves. As a result, industry, consumer and environmental groups, people writing to congress, etc., sometimes have more influence than scientists do in determining whether a particular food additive is approved or not.

The GRAS List

Most of the additives we use are in a group known as GRAS, or Generally Recognized as Safe. The GRAS list came into being with the 1958 Additives Amendment which, as we’ve seen, emphasizes safety testing for newly proposed additives. The list includes hundreds of substances (including salt, sugar, and some common spices) which had been added to foods for an extended period of time prior to 1958 without apparent harm, on the theory that these substances had been tested by use.

As an extra precaution, these substances were widely accepted as safe by scientists surveyed at that time. And since 1958, the safety of each has been reevaluated. The safety of GRAS additives (and new additives) continues to be reevaluated whenever there’s new scientific information—or sometimes when there’s a public outcry to do so.

The Delaney Clause

The 1958 Food Additives Amendment also contains what’s now popularly referred to as the Delaney Clause, named for Congressman James Delaney of New York. The Clause reads: “No additive shall be deemed to be safe if it’s found to induce cancer when ingested by man or animal, or if it’s found, after tests which are appropriate for the evaluation of the safety of food additives, to induce cancer in man or animals.” In short, it specifies that any substance shown to cause cancer in any amount in any animal can’t be allowed as a food additive.

This clause has been the subject of much debate and litigation. The controversy has arisen because no limit or condition was set upon the amounts of a substance or the terms of an experiment which might cause cancer. Several much-publicized bannings of additives have stemmed from this legislation. 

In 1969, the artificial sweetener cyclamate was banned because of evidence that it caused bladder cancer in rats. When saccharin also was found to cause bladder cancer in rats, it also was to be banned in 1977. This caused a huge public outcry because, at that time, saccharin was the only artificial sweetener left on the market for use in diet products (e.g., diet soft drinks). (When cyclamate had been banned, we still had saccharin.)

As a result of public pressure, Congress put a moratorium on banning saccharin as a food additive; it’s been since concluded that neither cyclamate nor saccharin causes cancer in humans.

The Delaney Clause has generated a lot of heated rhetoric. Some argue that the Clause should be modified to allow for an assessment of risk versus benefit, or that an additive shouldn’t be banned if its risk of causing cancer is “negligible.”

The Delaney Clause stems from a widespread belief that food additives are a major cause of cancer. This belief isn’t supported by scientific evidence.

Putting Additives in Perspective

There are reasons to be concerned about additives, but there are also reasons to be unconcerned. As we’ve seen repeatedly, the same substance can be both “toxic” and “safe,” depending on how much is used and how it’s used. A very toxic substance given in a small enough dose can be harmless; and a very safe substance given in a large enough dose can be harmful. Because this isn’t well-understood by the public, public support for the banning of an additive can often be engendered by merely citing the harm caused by occupational or accidental exposures to large doses of the additive.

We’ve also seen that there’s an overlap between “natural” and “man-made” or “chemical” substances (i.e., a food additive can be exactly the same as that found naturally in food); and that so far as we can determine one isn’t inherently better or worse than the other. So it’s important to look at food additives in the wider context of all substances found in our food.

There are a large variety and a large amount of natural toxicants in foods. Dr. Bruce Ames, a renowned expert on cancer biochemistry and food toxicants, says that the amounts and effects of food additives and pesticide residues are trivial compared to those of the natural toxicants in our food.^1-3 But this doesn’t keep him from eating plant foods—even those he knows to contain large amounts of natural toxins. Dr. Ames emphasizes that plant foods are also an abundant source of substances (e.g., carotenoids, vitamin C) that protect us from toxicants.