THE SEEDS OF ILL HEALTH
Part 2: Nutritional shortcomings
Essential amino acids
No cereal grains can be called complete foods as they all have significant deficiencies in the essential amino acids. Maize is deficient in tryptophan and wheat and most other cereals are low in lysine and threonine. Taurine, considered a conditionally essential amino acid as there is increasing recognition that humans have limited ability to synthesise it, is not detectable in cereals.
Essential fatty acids
Cereal grains are quite low in fats. They average only 3.6 percent fat for their total caloric content, their fatty acid profile is heavily weighted towards omega-6, and their omega-3 content is almost non-existent. Consequently, cereal-based diets, particularly if they are supplemented with vegetable oils, all have an unhealthily high ratio of omega-6 to omega-3.
The omega-3 fatty acid, EPA, is essential for the proper formation of the brain. We do have the ability to synthesise this longer chain fatty acid from its shorter chain precursors, but the process is inefficient. And as omega-6 and omega-3 fatty acids both use the same enzymes, there is competitive inhibition of one another, so that high dietary levels of omega-6 linoleic acid tend to inhibit the formation of omega-3 EPA from alpha-linolenic acid. If preformed EPA is not obtained directly in the diet from fish or meat sources, there is a significant risk of deficiency.
Vitamin A. Cereals contain no vitamin A and, except for yellow maize, neither do they contain its metabolic precursor, beta-carotene. Vitamin A deficiency is a major nutritional health problem in the third world. As many as 40 million children worldwide are estimated to have at least mild vitamin A deficiency. It is a leading cause of blindness among children and also a major determinant of childhood growth and susceptibility to disease. Where infectious diseases are contracted, vitamin A deficiency results in greater frequency, severity and higher death rates. An analysis of twenty trials of vitamin A supplementation in third world children showed a 30-38 percent reduction in deaths in those given vitamin A supplements. It is clear that excessive consumption of cereal grains plays a major role in the high levels of ill health in many parts of the underdeveloped world.
B Vitamins. Many nutritionists consider cereal grains to be good sources of all of the B vitamins except for vitamin B12. And it is true that cereals do contain adequate amounts — at least in terms of the percentage of Recommended Daily Allowances. However, what should concern us is not how much they contain, but how much of what they contain is actually absorbed after milling, processing and cooking. It is somewhat ironic that two of the major B vitamin deficiency diseases which have plagued agricultural man — beriberi and pellagra — are almost exclusively caused by excessive consumption of cereal grains.
Thiamin. Beriberi is caused by a deficiency of thiamin. This is mainly due to polishing rice, which removes the outer thiamin-containing coat of the rice. Beriberi has been largely eliminated with the advent of 'enriched rice' to which thiamin is added, but still occurs in some African countries whose populations consume high quantities of polished rice.
Niacin. Pellagra occurs almost exclusively in peoples whose staple food is maize (corn). The first half of the twentieth century witnessed a pellagra epidemic in the southern states of the USA. Approximately three million people were affected and there were over 100,000 deaths. There have also been similar epidemics in India and Europe, and even today, pellagra is still found in some parts of Africa. Pellagra is thought to be caused by a lack of the B vitamin, niacin, as a niacin supplement cures the condition, perhaps combined with a deficiency of the essential amino acid tryptophan. However, there may be other factors in maize that are responsible for the condition. Maize, like all cereal grains, is rich in lectins, chemicals which are known to decrease intestinal absorption of many key nutrients.
Vitamin B6 is another vitamin that looks to be plentiful in cereals, apart from oats, but whose bioavailability is poor. While almost all of the vitamin B6 in foods of animal origin is absorbed, the amount our bodies actually absorb from cereal grains tends to be very low. Not surprisingly, B6 deficiency is common in populations utilizing cereals and pulses as their staple diet.
Biotin has not been much studied in humans. However, animal studies have shown that, with the exception of maize, most cereal grains have very low levels of available biotin. Like vitamin B6, this contrasts with the high availability or biotin from animal sources.
Vitamin B12. As vitamin B12 is found only in foods of animal origin, diets based primarily or wholly upon plant food sources tend to be either low or deficient in vitamin B12. Vitamin B12 deficiency causes megaloblastic anaemia, which causes irreversible damage to the brain and nervous system. This ultimately results in death. Vitamin B12 deficiencies are common in countries such as India and Mexico where diets are mainly cereal and pulse based, even when small amounts of animal foods are also eaten.
Vitamin C. Cereals contain no vitamin C. Yet vitamin C is essential for us to metabolise the carbohydrates which form the major part of all cereals. Vitamin D. Not only do cereals contain no vitamin D, they can indirectly adversely affect vitamin D metabolism. Animal studies have shown that excessive consumption of cereal grains can induce vitamin D deficiencies in many animal species including primates. Vitamin D deficiency is widespread in human populations consuming high levels of unleavened whole grain breads; and a clinical study of humans consuming sixty grams of wheat bran per day for thirty days clearly demonstrated an increased loss of vitamin D through the intestine.
Cereals appear to provide adequate amounts of most minerals needed for health, but again we have to consider their bioavailability. The phytic acid that all cereals contain chelates (binds with) several key minerals to form insoluble phytates which are not digestible. As the phytic acid is found almost exclusively in the outer husks of the cereal grains — bran — we have the situation where B vitamins and proteins are lost from, say, white bread, and minerals are not available from wholemeal bread.
Calcium. Cereals have a naturally low level of calcium, and calcium is also one of the minerals chelated by the phytic acid. This low calcium intake from cereal grains does not normally represent a problem since full-fat dairy products are good sources of calcium, if they are included in the diet. However, if the dairy is replaced with soya milk and other sources of calcium are replaced by cereals, this can be a recipe for disaster.
Phosphorus. The ideal ratio of calcium to phosphorus is 1:1. However, cereals contain much higher levels of phosphorus, compared to calcium. This relationship has a negative impact on bone growth and metabolism. Consumption of a large excess of dietary phosphorus, when calcium intake is adequate or low, leads to secondary hyperparathyroidism and progressive bone loss.
Magnesium. In addition to the adverse ratio of phosphorus to calcium, cereal grains also have a low ratio of calcium to magnesium. This decreases the intestinal absorption of calcium and also leads to calcium excretion.
The net effect of a low calcium content and low bioavailability of calcium due to the phytic acid, combined with disproportionate amounts of potassium and magnesium, is to induce bone diseases such as rickets, osteomalacia, and osteoporosis in populations where cereal grains provide the major source of calories.
Iron. In addition to their deleterious influence upon calcium metabolism, cereal grains when consumed in quantity can adversely influence the bioavailability of iron. Iron deficiency is probably the most prevalent nutritional deficiency in the world today. It affects 2.15 billion people throughout the world and is severe enough to cause anaemia in 1.2 billion people. The causative factor has been clearly demonstrated to be the poor bioavailability of iron from cereal-based diets, the staple food in many developing countries.
Zinc. Studies of zinc absorption in humans have also demonstrated that zinc absorption is also impaired by consumption of whole grains such as wheat, rye, barley, oats and triticale. Again it is the phytic acid that is mainly to blame. In human populations, zinc deficiency results in a characteristic syndrome called hypogonadal dwarfism in which there is arrested growth, small and undeveloped gonads and delayed onset of puberty. This is despite the fact that the zinc intake of these populations exceeds our recommended daily intakes by a substantial margin.
Other Minerals. The absorption of chromium, manganese and selenium from cereals is not affected, but the bioavailablity of copper in cereal grains is poor.
Up to the middle of the twentieth century, the adverse effects of phytic acid were lessened by processing methods such as malting, soaking, scalding, fermentation, germination and sourdough baking. But these processes take time and, today, time is money. So they have been lost during the emergence of large-scale cereal processing.
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Last updated 31 March 2010