History of Research on the Nutritional Value, Biochemistry, and Medicinal Uses of Soybeans and Soyfoods - Page 3
by William Shurtleff and Akiko Aoyagi
A Chapter from the Unpublished Manuscript, History of Soybeans and
Soyfoods, 1100 B.C. to the
1980s
©Copyright
2004 Soyfoods Center, Lafayette, California
The 1960s, Overview . Starting in the 1960s major changes began to take place in the American food system and consciousness. Jerome (1981) called this period the Second American Agriculture, Food, and Nutrition Revolution. Affluence, coupled with the rise of the supermarket and ethnic cuisines, led to "dietary individualism." As consumption of animal fats and proteins rose steadily, so did coronary heart disease and warnings about cholesterol. In 1981 Jerome noted:
A new ideology concerning meat developed in the 1960s to place plant foods in a pre-eminent position. Food in general and meat in particular became a symbol of protest for many Americans . . . Ideology, the major factor associated with the new diet patterns, in conjunction with traditional food technologies, functioned to supply the food and food products deemed appropriate by adherents to a plant-based dietary pattern. An alternative food system developed in response to the alternative diet patterns.
There was an increased interest in natural foods, the role of food in improving health and raising consciousness, and the larger problem of world hunger.
Worldwide there was a growing consensus that developing countries faced a "protein crisis." At the 1961 Peoria conference on soy protein foods it was stated repeatedly by international nutritionists and agricultural planners that protein malnutrition was the most widespread deficiency disease in the world and that it was closely linked with calorie malnutrition, since if calories were deficient any protein in the diet would be used to supply energy. The leading architect and proponent of this view was Dr. Aaron Altschul of Georgetown University School of Medicine. Altschul was also a leading spokesman for the use of soy. In 1968 a United Nations publication entitled "International Action to Avert the Impending Protein Crisis" recommended soybeans as the single most promising protein source to close the "protein gap." During this decade many soy-fortified supplemental foods such as CSM and WSB were first developed and a great deal of nutritional research was done on them. (Elaborate??)
Diet and Coronary Heart Disease, Overview . In 1908 Russian scientists first reported that rabbits fed meat fat, milk fat, and egg yolk developed arteriosclerosis, but these findings went largely unnoticed for 50 years as nutritionists and physicians focused their research on nutritional deficiency diseases and infectious diseases. By the late 1950s coronary heart disease (CHD) had become the number one cause of death in America. Epidemiological (population) studies indicated that diet might well be the cause of the disease and more careful analysis showed that populations with low rates of fat consumption (especially saturated fats) tended to have low rates of heart disease.
By 1958 the evidence was convincing enough that the first scientific organization in the Western world, the National Health Education Committee in New York, sounded the alarm. Their 106 members of the American Society for the Study of Atherosclerosis (how diff from arteriosclerosis??) and eight prominent physicians published a statement which read, "The reduction or control of fat consumption . . . with reasonable substitution of polyunsaturated for saturated fats is recommended as a possible means for preventing heart attacks and strokes." This statement, which introduced the term "polyunsaturated" into the popular consciousness, struck at the roots of the cherished American diet, rich in animal protein foods. The next year the USDA, strongly allied for decades with the meat, dairy, and egg industries, countered with an official policy prohibiting claims of any type about a possible connection between dietary fats and heart disease. A coverup that would last almost 20 years had begun. But the evidence implicating saturated fats as a risk factor in heart disease grew, and in 1961 the American Heart Association became the second group to issue a warning about high-fat diets; they suggested that lowering blood cholesterol might prevent atherosclerosis. A second key word (which??) had entered the popular consciousness. In 1968, based on extensive large-scale investigations of the causes of heart disease, Scandinavian government medical boards in Finland, Sweden, and Norway strongly endorsed a diet lower in saturated fats (i.e. fats of animal products). After 1968 a ground swell of agreement among scientific committees worldwide emerged on the subject, as will be discussed later. An interesting history of these developments is given by Hausman in Jack Sprat's Legacy (1981). The net result of all this was an increased concern with nutrition and diet and a positive reevaluation of the place of plant protein, such as soy, in a healthful diet.
Soybean Trypsin Inhibitor, Update . It was still not clearly understood why moist heat improved the nutritional value of the soybean and soyfoods. In 1960 Booth and co-workers (Ref??) postulated that pancreatic hyperactivity was the cause of growth inhibition, since pancreatic enzymes, rich in sulfur amino acids, were lost from the body. In 1962 A.K. Smith summarized the theories as to why moist heat improved the nutritional value of soybean meal. (What were some of them??) But many questions remained unanswered. Also in 1962 Rackis and co-workers showed that most of the SBTI activity is due to the Kunitz trypsin inhibitor. In 1965 Rackis put the entire issue into good perspective as it concerns soyfoods (which are never eaten raw) by showing that steaming soybeans for 10 minutes at 100*C (the minimum heat treatment received by any soyfood) inactivated about 80% of the SBTI activity and resulted in the maximum protein quality of the food. Rackis went on, with Liener, to become a leading authority on biologically active and antinutritional factors in the soybean. Between 1966 and 1968 new SBTIs were discovered and by 1970 at least four had been identified.
1961 Paul Gyorgy , in the first comprehensive nutritional studies on tempeh, found that the PER was equal to that of skim milk and significantly better than that of cooked, nonfermented soybeans. Most other researchers, however (Steinkraus et al. 1961, Hackler et al. 1964, Stillings and Hackler 1965, and others) found that the PER of tempeh was not significantly better than that of cooked, nonfermented soybeans.
1961 Shurpalekar and co-workers in India gave an excellent review of the chemical composition and nutritive value of soybeans and soyfoods.
1963 Codex Alimentarius Commission was established by FAO and WHO to set international food standards to facilitate international import and export. This commission in turn, in 19??, set up a Committee on Vegetable Proteins to unify standards and terminology worldwide.
1963 Bils and Howell (Ref??) showed that, in developing soybean cotyledons, protein accumulates in conspicuous and discrete "protein bodies."
1963 Standal gave a comprehensive analysis of the "Nutritional Value of Proteins of Oriental Soybean Foods." She found the following values for NPU (Net Protein Utilization) and PER: Fresh green soybeans (71.5, 2.41); tofu (65.0, 1.93), soy sprouts (56.0, 1.36), natto (45.0, 1.52). By comparison, casein was 68.0 and 1.44, lower than fresh green soybeans in NPU and about equal to tofu. In 1964 Matsuno and Tamura (Ref??) gave a similar analysis, but of the general nutritional value of Japanese soyfoods.
1966 L.H. Bean published the often-cited calculation that 1 acre of soybeans will provide enough protein to sustain a man for 2,224 days compared with 877 days for wheat and only 77 days if the land is used to raise beef cattle.
1966 Soyfoods Flatulence . Steggerda, Richards, and Rackis (1966), in the first study of flatulence factors in soyfoods, showed that the gas-producing factors reside mainly in the oligosaccharides stachyose and raffinose, low molecular weight, water-soluble carbohydrates. Compared with a soy-free basal diet which produced an average of 13 cc of gas, they found that soy protein isolate produced 2 cc, okara 13 cc, whole soy flour 30 cc, soy protein concentrate 36 cc, defatted soy flour 71 cc, and tofu whey solids 300 cc. Based on flatulence research on other foods done in the mid-1960s, it was clear that humans do not have the enzyme alpha galactosidase in the small intestine needed to break down oligosaccharides into digestible sugars. Thus the oligosaccharides move into the ileum and colon where they are anaerobically fermented by the bacterium Clostridium perfringens to produce hydrogen and carbon dioxide gases, the main flatulent gases. In 1967 Shallenberger showed that these oligosaccharides were markedly reduced in tempeh during fermentation. In 1971 Calloway and co-workers reported that tempeh and tofu were essentially nonflatulent. Soybeans produced less flatulence than other beans such as navy and California white. In 1972 Ku, at the University of Illinois, did a PhD dissertation on Extraction of Oligosaccharides in Processing Whole Soybeans . He found that boiling whole soybeans for 60 minutes in a 10:1 ratio of water removed 59% of the oligosaccharides. Various studies between 1973 and 1976 reported that in soy sprouts, oligosaccharides decreased by 70-100% after 3-4 days of germination (Rackis 1981). By 1974 Hymowitz and Collins (Ref??) had suggested that oligosaccharides could be eliminated by breeding. In a comprehensive review of the subject, Rackis (1981) noted that they could also be removed by fermentation with lactic acid bacteria (as in lactic soymilk) or by the more complex technique of circulating soymilk through hollow fibers containing immobilized enzymes, a method developed after 1976.
1966 Bressani and Elias at INCAP in Guatemala gave an excellent review of the role of vegetable proteins in human nutrition based in part on their research with corn and soy flour in Incaparina 14 and 15. A similar excellent review was given by Swaminathan (1967) from India.
1969 Mattick and Hand at Cornell Agricultural Experiment Station first showed that the beany flavor in soybeans is not intrinsic to the beans but is caused by the enzyme lipoxygenase, which acts on fats immediately after the cracked soybean is exposed to moisture. This stimulated extensive research on lipoxygenase.
1970-1980s Overview . The 1970s were a decade of unprecedented interest in nutrition in America on the part of both consumers and professionals. As world hunger, energy shortages, and food inflation made headlines starting in about 1973, people looked for ways to make better use of the world's food supplies and agricultural inputs, while trying to keep food prices down. The rise in awareness of the extensive changes that had taken place in the American diet during the past century, and that these changes might well be related to the growth of diseases such as heart disease and cancer, spurred interest in more healthful ways of eating, which were reinforced by a growing number of scientific and government recommendations for improving diet to improve health. Many popular books on nutrition became best-sellers as millions of people became amateur nutritionists.
Interest in Soyfoods . Many factors during the 1970s and early 1980s led to an interest in soyfoods as an alternative protein source, which, in turn, stimulated further research on their nutritional value. These factors were of basically two types: events initiated by people and institutions closely involved with soyfoods which directly stimulated interest in or research on soyfoods nutrition, and larger trends or developments which prompted a demand for soyfoods by consumers and thereby indirectly led to nutritional research.
By far the most significant factor stimulating nutritional research was the introduction of a growing line of new soy protein products by major American food companies, starting in the late 1960s. In February 1971 textured soy protein products were authorized for use as meat extenders in the National School Lunch Program, opening up a vast new market. In 1971 the Soy Protein Council was established as a trade association to help promote these products. In March 1973, as US meat prices soared to all-time highs, beef-soy blends, containing 25% hydrated textured soy flour, were introduced into supermarket chains, opening up a second vast new market. In November 1973, with Western interest in soyfoods at an all-time high, the first World Soy Protein Conference was held in Munich; over 1,100 people from 45 countries participated. Many papers on soyfoods nutrition were presented and published with the proceedings in the Journal of the American Oil Chemists Society (Jan. 1974). In 1978 a special conference on soy protein and human nutrition was held in Keystone, Colorado to discuss new findings on the new soy protein foods. Papers were presented by 34 of the world's top researchers (Wilcke et al. 1979). Additional world conferences on soy protein foods were held in Singapore in 1978 (ASA 1978), in Amsterdam the same year (JAOCS, March 1979), and in Acapulco Mexico in 1980 (Baldwin 1981); many papers on soyfoods nutrition were presented at each of these. Parallel to these developments, starting in the latter half of the 1970s, there was a rapid growth of interest in traditional, lightly processed, low-technology soyfoods such as tofu, soymilk, and tempeh. The Soyfoods Association of North America, founded in July 1978, helped to stimulate research in these increasingly popular foods.
Reappraisal of the Value of Animal and Plant Proteins . During the late 1960s and early 1970s, animal proteins probably reached their historical peak of popularity in the US. A diet rich in animal protein was considered a "better" diet. However during the 1970s a number of major crises and nutritional discoveries led to an important reappraisal of the larger value of plant (and soy) proteins.
Lower Cost . During a decade of rampant inflation and budget cutbacks both consumers and foodservice institutions came to realize that plant proteins are generally less expensive than animal proteins, and that soy proteins are the least expensive of all. One RDA (Recommended Daily Allowance) of usable protein in the form of whole milk or hamburger costs four times as much, and one RDA in the form of steak costs 17 times as much, as one RDA in the form of soybeans (Shurtleff and Aoyagi, 1979; Lappe^ 1971, 1982).
Better Land Utilization . During the 1970s the problem of world hunger made headlines. Many people came to realize that a given area of land can produce 4-20 times as much plant protein (such as soy protein) as it can animal protein in the form of meat, dairy products, or eggs. Yet in the US over 50% of all agricultural land is used to grow crops that are fed to animals, and over 95% of America's non-exported soybeans are used as fodder. Each year's US soybean crop represents a huge renewal protein resource, capable of providing 4.5 times the RDA for all Americans and 2.5 times the amount of protein by the usual food supply. Or it could provide 25% of the protein requirements for every person in the world (Pimentel et al. 1975; Wolf 1980; Shurtleff and Aoyagi 1979; Lappe^ 1975).
Better Energy and Resource Utilization . Before the "energy crisis" and water shortages of the 1970s, the costs of producing protein in terms of energy and water had been given little attention. Calculations by Pimentel (1975 and personal communication) show that to produce 1 pound of protein in the form of a feedlot steer (steak) takes 92 times more total energy, 36 times more fossil fuel energy, and 47 times more water than to produce a pound of protein in the form of soybeans. Thus the inevitable transition to an agricultural system and diet that conserves energy and resources must rely more on plant and less on animal proteins.
More Healthful . A decade in which medical and popular attention focused on coronary heart disease and cancer made Americans aware that animal proteins, in addition to being excellent for promoting growth, are also typically accompanied by large amounts of saturated fats, cholesterol, sodium (in meats) and in many cases hormones and agrichemicals. A growing number of scientific and governmental committees, based on extensive medical research, urged people to reduce their consumption of these substances which were considered to be risk factors in heart disease, cancer, stroke, and hypertension. They also recommended that people increase their consumption of dietary fiber, none of which is contained in foods of animal origin. Plant proteins are accompanied by no cholesterol and very little saturated fats, sodium, and agrichemicals. Many scientific studies show that a vegetarian diet (especially a lacto-ovo vegetarian diet) promotes better health and longer life than the standard American diet (Scharffenberg 1979; see also Chapter 41.13).
More Kind to Animals . The growth of mechanized "animal factories" and interest in minority rights during the 1970s led a small but vocal sector of the population to suggest that animals, as living beings, also have rights. Plants can provide high quality protein without the violence of animal slaughter.
Less Polluting . As pollution problems became more prominent during the 1970s and as feedlots grew in size and number, people came to realize that they cause serious problems of water and air pollution. The production of plant proteins need not cause such problems.
High Quality Protein . The trend during the 1970s to view problems more holistically led to the realization that the concept of "protein quality" was one that was very narrowly defined, largely to suit the interests of the meat and dairy industries. People consume diets not isolated proteins, and the concept of "quality," broadly defined, should include all of the factors listed above plus the traditional measures of growth or nitrogen balance promotion. In the concern with protein during the 1970s a number of important facts concerning protein quality and needs were brought to light: (1) The average per capita protein consumption in the US is 65-100% more than the body can use, and about 70% of this is animal protein. A nationwide survey in 1980 of 13 key nutrients showed that protein was the one nutrient least likely to be deficient (Pao and Mickle 1981 Ref??; Scrimshaw 1980 Ref??). Excess protein is burned as energy or turned to fat. Most cultures with high longevity have low-protein diets. In fact, high protein diets are likely to cause more problems than low protein diets in affluent countries; (2) If a person is maintaining his/her correct body weight (i.e. getting enough calories), it is almost impossible to be protein deficient. Analysis of the diets of lacto-ovo vegetarians and of total vegetarians in the US show that they consume more protein than they need; (3) protein quality and quantity can easily be increased by up to 40% by serving complementary proteins (such as soyfoods and grains) at the same meal, as described at the beginning of this chapter; (4) Tests done during the 1970s feeding soy proteins to humans (rather than the traditional rats) showed that the quality of this protein for humans was equal to that of milk or meat. This point will be discussed in more detail below; (5) By using the terms "complete" and "incomplete," the dairy and meat industries had created the impression in US consumers that there were two distinct types of proteins, animal and plant, and that the animal proteins were clearly superior. [Redo?? During the 1970s, however, it became clear to many consumers that animal proteins were not fundamentally different from plant proteins and that a number of plant proteins (such as soy protein) were equal in quality to beef, chicken, or milk proteins, while containing no cholesterol and less saturated fats.] Furthermore, soy protein contained all of the essential amino acids and was a "complete protein;" the latter term, however, was no longer used by nutritionists after about the 1950s, since it was too vague and unquantifiable; soy protein foods were preferred to animal proteins in a number of special diets such as for heart disease, diabetes, hypoglycemia, and lactose intolerance.
Much of the work of communicating this new nutritional information to the public was done by books and the media. One book that discussed many of the above issues and had a profound effect on changing American dietary patterns was Diet for a Small Plant by Frances Moore Lappe^. First published in 1971, it had sold over 1 million copies by 1981 and inspired numerous other popular books on nutrition and cookery based on its principles. Also by 1984 some 40 books on tofu plus more on soyfoods in general had been published in the US and were selling well. In addition, major soy protein manufacturers did extensive advertising using television and other media.
For all of the above reasons, Americans began to cut back on consumption of animal proteins. Per capita beef consumption declined every year after 1976 from 129.4 pounds in that year to 106.6 pounds in 1980. By the late 1970s polls showed that 7-10 million Americans (3-5% of the population) considered themselves vegetarians, nearly three times the number estimated a generation ago. The reason most frequently cited for the switch was to get a more healthful diet. For the first time in peacetime history, soyfoods started to become an important part of the US diet, with consumption reaching about 9?? pounds per capita a year by 1981 (Shurtleff and Aoyagi 1983, 1984). All these developments stimulated research on soyfoods nutrition.
The "Protein versus Calories" Debate . In 1973 the Joint FAO/WHO Expert Committee (Ref??) issued its report on "Energy and Protein Requirements," which reduced protein requirements for adults by 20%. The National Academy of Sciences in the US followed suit by lowering its RDA for protein by 25%. Protein no longer appeared to be as serious a problem as it was thought to be in the 1960s and early 1970s. Insufficient intake of food energy came to be considered the main nutritional problem in poor countries. It was argued that in most areas, and especially those where cereal grains were the least expensive source of energy (calories), if people could just get enough food (energy), the protein would take are of itself. As Payne (1975) noted in his classic tract on the "calories are limiting" view: "the adequate safe level of protein-energy ratio in the diets of 2- to 3-year-old children is close to 5% and . . . most cereal grains appear to provide utilizable protein levels close to this amount." The other side of the decade-long heated debate was well represented by Scrimshaw at MIT and INCAP of Guatemala. In a classic rebuttal of the "calories are limiting" view, Scrimshaw (1977), in "Through a Glass Darkly," pointed out that while that view may hold for populations as a whole, it does not hold for undernourished or sick individuals, and often not for infants in the immediate post-weaning period, or for poor nursing mothers. Increasing research showed that the 1973 protein recommendations relative to energy were quite a bit too low. Equally important, the Green Revolution, which expanded acreage in cereal grains, often at the expense of legumes, was reducing world protein supplies as much or more than requirements had been reduced. Scrimshaw concluded prophetically, "To the extent that the pendulum swung too far in emphasizing protein in the 1960s, and too far in emphasizing calories in the 1970s, it must come to a more appropriate intermediate position for the 1980s and beyond."
This new downplaying of the importance of protein in a balanced diet affected soyfoods in several ways. While it was no longer possible or fashionable to speak of protein or soy protein as the key nutrient needed to conquer malnutrition, it was increasingly realized that the soybean was the lowest cost source of high quality protein, capable of being grown worldwide. In affluent Western countries the lowering of protein RDAs undercut the mystique of the high protein diet, making it much easier for people who wanted to reduce meat consumption or become vegetarians, using soyfoods as an alternative protein source, without fear of protein deficiencies in the diet.
Critiques of Protein Quality Measurement . During the 1970s the complexity of the problem of measuring protein quality came to be more fully appreciated. Scrimshaw noted in 1977 that the two big protein questions concerned (1) human requirements for protein at different ages and physiological states and (2) the evaluation of the protein quality of foods as related to human requirements. Granted that the quality of any protein depends largely on its composition of essential amino acids (EAAs), and especially of its first-limiting amino acid, still a quick, inexpensive way of measuring protein quality for humans was needed. Researchers realized that rat assays underestimate the value of soy proteins for humans since rats need 50-100% more of the sulfur amino acids (methionine-cystine) than humans; these are used largely in forming the rat's large mass of hair. Thus there was a shift to human tests. Another debate concerned the use of growth tests versus nitrogen balance tests. Some researchers felt that growth studies should be used to measure the protein needs of infants (the group to which protein quality was most important) and nitrogen balance study to measure the needs of adults. Standard official measures of protein quality such as PER and NPU came under sharp attack as relating only to growth and not to maintenance, grossly underestimating the quality of poor proteins, poorly reflecting the biological value of proteins for humans, and being slow and inexpensive. New nitrogen balance tests such as Slope Ratio (Net Protein Ratio), Modified Slope Ratio, and Relative Protein Value were proposed. Various researchers noted that the history of protein nutrition would have been different if nutritionists had concerned themselves with amino acid requirements rather than protein quality. Data for lysine, total sulfur amino acids, tryptophan, and threonine are all that would be needed for most food proteins, and when expressed as a percentage of requirements have tremendous advantage of being additive for mixed or complementary protein diets. Clarify last sentence??
Human Soy Protein Assays . During the 1970s investigations on the nutritional value of soy proteins in human diets became as popular as they were during the 1930s. Now, however, most of the research was done using modern and often highly refined soy protein products. An ongoing theme in this research concerned the need for methionine fortification. Most soy-based infant formulas in the US are not fortified with methionine, which imparts a bitter taste. In 1970 Graham and co-workers, on tests with infants, showed that absorption and retention of nitrogen and growth rates using soy protein isolates fortified with methionine were equal to those obtained with cow's milk. In 1971 Kies and Fox, in experiments with textured soy flour on adults, reported that methionine supplementation improved nitrogen utilization only when low intakes of soy protein were studied; this was confirmed by Zezulka and Calloway in 1976. At the Keystone Conference in 1979 Fomon and Ziegler reported that for infants, "Formulas with protein from methionine-fortified soy protein isolate appear to promote retention and growth to the same extent as do milk-based formulas." Torun (1979) showed with preschool children that nitrogen retention of unfortified soy protein isolates is equal to that of cow's milk and that methionine supplementation is unnecessary. Scrimshaw and Young (1979) reported, with adults, that soy protein isolate is 80% as effective as egg protein in maintaining nitrogen balance, and that methionine supplementation is unnecessary. Each reviewed earlier studies in their respective areas.
Good reviews of research on soy protein and human nutrition were published by Smith and Circle (1972), Bressani (1974), and Young and Scrimshaw (1979). The culmination of this research was reported at the Keystone Conference on Soy Protein and Human Nutrition, which led to a major reevaluation of the quality of soy protein in human nutrition, demonstrating that the quality of soy protein was considerably higher than had formerly been realized.
Diet, Heart Disease, and Cancer??. Update . As we saw earlier, by the late 1960s a consensus had begun to emerge among scientific committees worldwide that diet was a cause of the increasing rates of heart disease and cancer. By 1977 twenty national and international expert committees around the world had issued statements advocating a change in eating habits to lower blood cholesterol and reduce coronary heart disease. The emphasis was on consuming less fat (especially saturated fat) and less cholesterol, although some recommended increases in polyunsaturated fats, which had been shown to lower blood cholesterol. In 1972, for example, the conservative American Medical Association recommended that the 50% of all Americans with cholesterol levels above 220 (what/what??) should reduce their consumption of saturated fats and cholesterol. By 1976 the US Department of Health, Education, and Welfare determined that major cardiovascular diseases accounted for over 50% of all deaths in the US. The problem had reached virtual epidemic proportions, and America had the world's second highest rate of coronary heart disease.
The USDA, strongly allied for decades with the meat and dairy industries, balked at accepting and endorsing the new findings, or at publicizing them to the American people in the form of a new food and health policy. In 1973 Dr. Jean Mayer, one of America's most prominent and respected nutritionists, in an article titled "USDA: Built-In Conflicts," charged that the USDA's record of putting farm interests before public health was so glaring that its consumer protection activities should be transferred to another agency. In 1977, however, things began to change as Bob Bergland was appointed Secretary of Agriculture under President Jimmy Carter. A new and balanced policy was formulated which, in Bergland's words, was no more "responsive to the production and marketing of foods than to the safety, quality, and nutritional content of the foods consumers eat" (Hausman 1981)
The first concrete example of America's new policy on nutrition appeared in January 1977 when the Senate Select Committee on Nutrition and Human Needs, chaired by Senator George McGovern, published Dietary Goals for the United States . The report suggested that, on average, Americans should reduce their intake of total fat by 25%, of saturated fat by 40%, of food cholesterol by 40%, of sugar by 40%, and of salt by 50%. They should increase intake of complex carbohydrates (such as whole grains and vegetables) and try to achieve normal weight. Interestingly, the report was not particularly original; more than a dozen scientific bodies had issued the same advice before the Goals were published. Many of the country's stop nutritionists, including Harvard nutrition professor Mark Hegsted, Jean Meyer, and Johanna Dwyer, strongly endorsed the report, as did eminent scientists who had served as consultants during its drafting. The public, too, apparently welcomed the report, for within two weeks the US Government Printing Office was swamped with 10,000 orders.
The report, however, sent shock waves through the livestock farms of America. There, in plain English, was a recommendation to eat less meat. The meat, dairy, and egg lobbies considered the report blasphemy, a cruel betrayal by their long-time ally, the USDA. A number of prominent nutritionists criticized the report as well. (What did they argue??) A great power struggle ensued to try to get the report changed, to get its supporters voted out of office, and to defend meat, eggs, and dairy products as ideal foods, no matter how strong the evidence showing their dangers at present levels of consumption. The second edition of the report (1977) was only slightly changed ("eat less saturated fat" was substituted for "eat less meat") but key supporters, including McGovern, were voted out of office in part by angry livestock farmers organized by the animal protein lobbies. Pro-industry scientists, including many with extensive research funding from the industry, spoke against the report, creating the illusion that great controversy surrounded the "theory" linking diets high in fats and low in fiber to coronary heart disease and to breast and bowel cancer. The lobbies vigorously fought efforts to inform the public of the recommendations of the Dietary Goals .
For almost two years after the Dietary Goals saga, the USDA and HEW kept cautious silence, but change was in the air. In 1979 the prestigious National Heart, Lung and Blood Institute of the National Institutes of Health advised Americans to eat less saturated fat, cholesterol, calories, and salt. In July of the same year the head of HEW and the Surgeon General issued Healthy People: The Surgeon General's Report on Health Promotion and Disease Prevention , which recommended the consumption of less saturated fat and cholesterol. It was the twentieth scientific report since 1958 giving such advice. A 1979 poll of 200 scientists who had attended heart disease conferences showed that a full 92% favored advising the public to adopt new eating patterns. The most common recommendation was to eat fewer calories, followed by less saturated fat, less cholesterol, and less total fat. Nine out of ten said they had changed their own eating habits. After the survey was completed, respected American nutritionists Drs. Jean Mayer and Johanna Dwyer commented: "It seems clear that this group of eminent international experts agrees with the dietary goals proposed for Americans. And the contention that there are big differences of opinion among the experts is a false one" (Hausman 1981). In 1980 the USDA joined with the Department of Health and Human Services in issuing dietary guidelines that followed the recommendations of Dietary Goals . That same year the USDA hired Dr. Mark Hegsted, a major architect of Dietary Goals , to head its new Human Nutrition Center, established in 1978 to protect consumer food, nutrition, and health interests. (The Center, unfortunately, was disbanded by the Reagan administration in 1981).
As a partial result of the increased awareness among Americans of the link between diet (and lifestyle) and health, between 1968 and 1978, US, heart disease deaths fell 20%. But most important from the point of view of soyfoods, all of the above developments, stimulated a new, broad-based interest in plant proteins which were free of cholesterol, low in saturated fats, low in calories, and in some cases good sources of dietary fiber.
Despite the decades of research on factors causing coronary heart disease, there was no single theory which adequately explained the etiology. Rather a number of "risk factors" were associated with the disease. Several interesting theories, other than the fat-cholesterol theory, appeared during the 1970s, which place soyfoods in a favorable light. The first, proposed by Dr. Kilmer McCully (Ref??) of Harvard Medical School, proposes that homocysteine, a by-product of methionine metabolism, and not cholesterol, is the real culprit. A diet low in methionine and rich in vitamin B-6 prevents formation of homocysteine. Foods having the lowest ratios of vitamin B-6 to methionine, those which should be avoided, are typically animal proteins such as cheese (0.1), eggs (hard cooked, 0.3) and beef brain (0.3). The most favorable of all foods, that with the highest ratio, is the soybean (1.63), followed by soy tempeh (1.37) and peanut butter (1.2).
A second theory, developed by Sirtori and co-workers (1979) in Italy and Carroll (1981) in the US stated that the main problem is high intake of animal protein, which correlates more highly with coronary heart disease than any other dietary variable, including saturated fat and cholesterol. Dr. Sirtori fed soy protein to 60 ?? people with very high cholesterol levels who were unable to lower them by eating low-fat diets. The soyfoods lowered the cholesterol to the normal range. [Explain?? The addition of cholesterol alters the soy protein's cholesterol lowering effect.] Carroll 1981 reported that rabbits fed a low-fat, cholesterol-free diet for 10 months containing either casein or soy protein, had twice as high plasma cholesterol on casein than on soy protein. With rabbits fed mixtures of casein and soy protein, the level of blood cholesterol decreased as the proportion of soy protein increased. The mechanism for this cholesterol lowering effect is not yet understood.
Antinutritional Factors in Soybeans . Although the image of soyfoods was greatly enhanced by discoveries linking coronary heart disease with animal fats and proteins, soyfoods were not without their own problem in the form of various antinutritional factors. Extensive research on these was done during the 1970s. Attention focused on soybean trypsin inhibitors (SBTI) and phytates.
In 1972 Green and Lyman elucidated the negative feedback mechanism for control of pancreatic secretion and showed how dietary trypsin inhibitors interfered with the mechanism, providing a plausible explanation for their mode of action but still leaving questions unanswered about the growth inhibiting effects of raw soybeans. In 1973 Kakade, Hoffa, and Liener, after removing inhibitors from soy meal, found that they accounted for only 40% of the growth inhibitory effect and pancreatic hypertrophic effect of raw soy protein. The remaining 60% of the cause of poor growth was attributed to the fact that raw soybean proteins are difficult for the body's trypsin to digest. Heating, of course, unfolds and denatures the proteins, making them much more digestible; at the same time it inactivates SBTI. Thus, even if SBTI could somehow be removed that would solve less than half the problem in raw soybeans. In 1975 Rackis and co-workers reported that enlargement of the pancreas of rats was eliminated after very short steaming times; only about 4 minutes of steaming to reduce 50% of the SBTI activity was necessary to eliminate this effect. The enlargement was shown to be reversible by returning the rats to a control diet. Finally Liener (1975 Ref??) argued convincingly that SBTI are probably not a nutritional problem at all in humans, only in rats. Species such as humans with small pancreas relative to total body size show no pancreatic hypertrophy. Good reviews of the literature concerning biologically active and antinutritional factors in soybeans were given by Rackis (1972), Liener (1979), and Anderson, Rackis and Tallent (1979), all top researchers in the field. It was concluded that for all practical purposes, none of these factors (trypsin inhibitors, lectins or hemagglutinins, goitrogens, estrogens, allergens, flatulence factors, anti-vitamin factors, or saponins) most of which were inactivated by heat, were cause for concern when using soyfoods in human diets. By 1979 Orf and Hymowitz had isolated and were breeding lines of soyfoods containing no SBTI (or lipoxygenase), although the practical importance of this, even for livestock, was not clear. And Troll (1980 Ref?? Rodale??) had published a controversial report suggesting that the 5-20% SBTI left in soyfoods after typical processing might help prevent cancer??.
Mineral Bioavailability . Starting in the early 1980s, the question of mineral bioavailability (the proportion which is absorbed and utilized) became one of the most important subjects for soyfoods nutrition research, more important than protein quality or antinutritional factors. Research (O'Dell and Savage 1957, 1960; O'Dell 1979) had indicated that mineral bioavailability from foods of plant origin was somewhat less than from foods of animal origin. The three minerals in soyfoods given the most attention were zinc, iron, and calcium. The main factor in soyfoods reducing mineral bioavailability was thought to be phytates. Approximately 70% of the phosphorus in soybeans and soyfoods occurs in the form of phytate, inositol hexaphosphate. Most seeds contain phosphate. Soybeans have about half as much as sesame seeds and rapeseeds, but a little more than most cereal grains. The phytate ion can complex with metallic ions such as zinc, iron, and calcium, and form highly insoluble and poorly absorbed chelate (expl??) complexes. Other factors that can limit mineral bioavailability in soyfoods are dietary fiber and certain processing techniques. Research on mineral bioavailability accelerated in the early 1970s as new soy protein products became popular and began to be substituted for animal proteins, key traditional sources of minerals. Liener (1972 Ref??) gave a good review of mineral content and bioavailability of soyfoods, concluding that availability was quite low. However, the utilization of calcium in soymilk by adults was reported to be about 90% that of cow's milk. By 1974 efforts were being made to reduce phytate content by breeding, or by the use of phytase or fermentation; the process of leavening bread removes 75% of the phytate from soy flour. The fermentation hydrolyzes the bonds between phytates and minerals, releasing minerals for absorption. In 1978 tofu was found to contain only 10% of the original phytate found in soybeans. In 1979 O'Dell gave a good review of mineral bioavailability in soyfoods; Erdman (1979, 1981) noted that zinc was the mineral evoking most concern due to its lack of availability. In 1979 in one of the first studies of soy mineral bioavailability for humans, Van Stratum and Rudrum, showed that for 20-89 adults fed soy protein concentrate for 4 weeks, serum levels of zinc, iron, and calcium were virtually identical to those of people fed on diets of traditional animal proteins. They concluded, as O'Dell had in 1979, that "Iron absorption from soy protein generally appears to approach that of animal proteins. Forbes et al. (1979), in studies on rats, reported that zinc availability from soyfoods, especially concentrates, was poor. However calcium added to all soyfoods was highly available; zinc added to soy protein concentrate was only partially available.
In 1981 the question of iron availability in soyfoods became the hottest topic in soyfoods nutrition. Cook et al. of the University of Kansas Medical Center had reported that soyfoods inhibited the absorption of nonheme iron. (Heme iron, which comes from hemoglobin and myoglobin (def??), constitutes an average of 40% of the iron in all animal protein foods.) When soy protein isolates, whole soy flour, and textured soy flour were substituted for egg albumen in the semisynthetic diet of 10 human subjects for typically one meal, the percentage of nonheme iron absorption was reduced by 92%, 82%, and 65% respectively. Thus the isolate was the most inhibiting. The inhibitory effect could be greatly reduced by adding ascorbic acid or by baking, which increased absorption by factors of 5.7 and 2.0 respectively, highly significant. Other researchers were not sure what to make out of Cook's results, which were very different from those of other studies during the 1970s, which showed good bioavailability (50-60% typically) as long as sodium phytate was not added separately to the diet (Erdman 1981 Ref??). Yet Cook's work was deemed carefully done although very short term. As of late 1981 the FDA and USDA was busy doing further research on soy protein-iron absorption, and suggesting that soy fortified foods (such as those used by PL 480) should perhaps be fortified with iron and zinc. The head of the FDA noted that US soy-based infant formulas contain 7-10 times the minimum iron level recommendations and that studies on total vegetarians using soyfoods indicated no major problems relative to iron status.
Breeding to Upgrade Nutritional Quality . (Repeat??) Since the 1920s soybeans have been systematically bred to increase their oil and/or protein content. During the 1930s Morse and co-workers bred vegetable-type soybeans to get better flavor, larger seed size, and shorter cooking time. But the first work in breeding out antinutritional factors was done by Hymowitz and co-workers at the University of Illinois. In 1968 he started to screen the soybean germplasm collection for lines containing no trypsin inhibitors. It took 12 years before he was able to breed the Kunitz trypsin inhibitor (the major but not only one) out of two lines, to give soybean with 30-50% less antitrypsin activity than normal. Apparently SBTI have no biological function for the seeds. In addition Hymowitz has found lines with no lipoxygenase (19??), no lectins (19??) and no oligosaccharides (1974 Ref??). The breeding approach promises to be important in future improvement of soybean nutritional quality.
Future Prospects . In 1981 Wolf gave a good historical review of progress and future needs in soy protein nutrition and utilization. He suggested further nutritional research in the following areas: long-term studies with humans to determine soy protein quality as well as possible needs for fortification with vitamins and minerals; establishment of need or lack of need for supplementation with methionine; mechanism of action of trypsin inhibitors when ingested from soyfoods; and development of rapid methods of measuring protein quality.
The great majority of the research on human nutrition during the 1970s was on the new, high technology soyfoods. Hopefully this will stimulate similar research on increasingly popular and less highly refined traditional soyfoods such as tofu, tempeh, and soymilk. By the late 1970s such research was already underway at the University of Massachusetts and the University of Illinois.?? (human??)