Cyanide Poisoning: A Low-fat Diet Disease

Diets low in fat and high in vegetables have become increasingly popular in the past few years. Major medical journals are now endorsing low fat and vegetarian diets as a health strategy.i However there may be a downside to the low fat health diet. In 1991 we began hearing reports of large numbers of people with blindness and nerve damage in Cuba. Over 50,000 cases have been reported,ii almost one victim for every two hundred people in Cuba, a country of about 10 million. Half the cases involved loss of vision and the others suffered pain and numbness. Imagine if that were to happen in the United States, with a population of 250 million: there would be almost a million Americans, some of them totally blind and others complaining of a dark cloud, blind spots and loss of color vision, and an equally large group with tingling, burning pain and numbness. Would that not be our number one national health problem? You bet.

What caused the Cuban epidemic? Pesticide exposure was at first suspected because of the greater number of cases in the agricultural areas. But why now and not for the many years of pesticide use before? Case control studies have implicated tobacco smoking, vitamin B complex deficiency, being underweight-and a diet low in animal fat and protein. Most of the patients improved when given injections of B vitamins; and in 1993 supplements of B complex and vitamin A were provided as public health measures in Cuba. Within two months there was a dramatic drop in the number of cases and the epidemic was under control.

In retrospect it is easy to see that the end of the Cold War and the break-up of the Soviet Union had imposed hardship conditions in Cuba as Russian subsidies came to an end and meat and dairy products, fats and oils were in short supply. Cubans were forced to adopt a low fat, low animal, high carbohydrate diet.

Sound familiar? The Cuban national diet is actually similar to the recently popular Pritikin-Ornish diet for arteriosclerosis and the macrobiotic diet for cancer-except that in Cuba even rice and beans are rationed and the people have increased their intake of cassava as a cheap, home-grown substitute. We know cassava in the U.S. as tapioca; and we use it to make puddings and desserts and as a substitute for flour in Asian cookery. As a staple it is tasty and fairly nourishing but it is also toxic, for it is well known to contain cyanogenic glycosides, a natural source of cyanide.iii

As a therapy for malaria, sickle-cell disease and perhaps for some cancers, these plant cyanides have medical value. As a steady diet, however, they require detoxification into thiocyanate, a process that depletes our antioxidant systems. The 'thio' of thiocyanate comes from the sulfur amino acids, cysteine and methionine, which are also essential to a number of vital enzymes, including glutathione peroxidase, the major natural enzyme antioxidant of cell membranes.

Thiocyanate carries similar electronic charge and size characteristics as iodide; hence it substitutes for iodide, enters the thyroid gland, and blocks the production of the thyroid hormone, thyroxine. A low thyroid state interferes with vitamin A production, essential to regeneration of the retinal pigments and healing of the retina. Night blindness and retinal damage are only the most obvious of the consequences, for vitamin A is required for healing and repair in every cell of the body.

Thiocyanate levels increase after cigarette smoking because of cyanogens in tobacco leaf. Thus, thiocyanate can amplify retinal damage along with carbon monoxide and nicotine. Nicotine is toxic, of course, but it is not known to cause eye damage. Carbon monoxide, however, blocks the transport of oxygen from hemoglobin to the tissues, and this adds to the damage caused by cyanide, which blocks the cytochrome enzymes within cells, thus preventing oxygen transfer inside the mitochondria of the cells. The combination of carbon monoxide and cyanide is worse than either alone so that even at relatively low doses of dietary cyanides, irreversible damage to the retina of the eye can and does occur in smokers. Smoking and cyanogenic vegetables, such as flaxseed, millet, tapioca and fruit seeds, don't mix!!

Chronic cyanide poisoning symptoms commonly go undiagnosed.iv Dr. M. Vincent researched the effects of low doses of hydrocyanic acid from cyanogenic vegetables and from cigarette smoke. Anemic patients are more vulnerable, especially so if low in B12 and sulfur amino acids. Dr. Vincent concluded that these are the main determinants of intoxication. Dr. Vincent treated 34 patients with optic nerve damage, mostly from tobacco. The hydroxycobalamin form of vitamin B12 combines with cyanide to form cyanocobalamin, thus altering the cyanide into a safe vitamin. Over 60 percent improved after receiving 45 mg. doses of vitamin B12 for two weeks. Note: this is truly a megadose, about 10 million times RDA. Injections of hydroxycobalamin thus can be used to antidote acute cyanide poisoning but the minimum required dose is estimated to be 50 times the toxic dose of cyanide, which is 50 mg. That adds up to the unwieldy amount of 2500 mg and would require 2.5 liters per injection at the usual concentration of 1 mg per ml that is available!

Chronic exposure to cyanide can deplete the body reserves of B12. This may be why vegetarians are extra-vulnerable to the effects of toxins. Depletion of B12 in vegetarians is not just a matter of dietary deficiency due to lack of meat, which is the best dietary source of B12; there is also the depletion of B12 reserves used up in the act of detoxifying vegetable cyanides. Vegan diets can induce B12 deficiency in unexpectedly short time periods. The presence of sulfur amino acids shelters B12 by providing methionine, an essential amino acid that otherwise uses B12 for its re-vitalization cycle. This is why both B vitamins and sulfur amino acids were so helpful to the patients in Cuba.

Gasoline shortage has forced the Cubans to be physically active-because they have to get around more on foot or by bicycle. But exercise uses up more calories and more of the B vitamins, hence increasing their vulnerability to cyanide toxicity! In the United States there is a widespread belief that lots of exercise can only improve health. The Cuban experience teaches us that it isn't that simple. Exercise as a drain on nutrient supplies and a stress to the antioxidant systems must be considered in relation to diet, environment and total person, otherwise it is only a fad, sometimes helpful and sometimes dangerous.

It came as a surprise to the Cuban health officials that the incidence of the eye and nerve disease was lowest in those who are usually most vulnerable to poisonings: children under age 7, the elderly, over age 65, and pregnant women. Why were these groups not the most affected by the epidemic? It turned out that in Cuba these groups receive supplemental dairy products, rich in the sulfur amino acids; and the pregnant women get prescribed vitamin pills as well.

A low fat diet is likely to be low in meat and dairy products, hence low in B12 and sulfur amino acids, e.g. methionine and cysteine. That is what made the victims of cyanide poisoning so vulnerable to eye and nerve damage from their cassava and other vegetables. Animal fat is also protective to nerve membrane because it induces production of Cholesterol, which is essential to stabilize and repair cell membranes. Saturated fats and cholesterol are less vulnerable to oxidation than are the polyunsaturated fatty acids found in vegetable oils. A low fat, low cholesterol diet carries an increased risk for nerve damage, particularly due to environmental oxidants, herbicides, pesticides and dietary toxins, such as cyanides.

Cyanogenic glycosides in cassava root, bitter almonds (not the sweet almonds commercially available in the US) and black lima beans (not the white lima beans eaten here) form hydrogen cyanide, which attach to iron-containing enzymes of the cytochrome redox system. This blocks the production of ATP, oxidation ceases and oxygen uptake from the blood into the cells stops. This is suffocation at the cell level. The nervous system is particularly vulnerable and sub-clinical cases damage the eyes and nerves. Demyelination of the brain, similar to multiple sclerosis, can also occur. And there is interference with intestinal cell function, which can cause malabsorption, specific for active transport mechanisms, affecting B12, folic acid, manganese, zinc, copper, calcium and magnesium.

©2009 Richard A. Kunin, M.D.