Many studies of soy protein isolates prepared for food use have been carried out with experimental animals and with human subjects. In most studies of experimental animals, fortification of soy protein isolate with methionine increased nutritional quality. Under certain experimental conditions, feeding of soy protein isolates as the sole or major source of protein to animals has impaired the utilization of fat-soluble vitamins or of minerals, especially calcium, phosphorus, magnesium, zinc, and copper. In a number of studies of experimental animals and in a few studies of human infants, growth was reported to be more rapid when proteins of animal origin were fed than when equal amounts of soy protein isolate were fed. However, in other studies of human infants, rates of gain in weight in infants fed formulas with protein from cow milk were similar to those fed formulas with protein from soy protein isolate. In most studies of human subjects, nitrogen balance has been similar with isonitrogenous diets supplying protein of animal origin or methionine fortified soy protein isolate.
A 24 week study of six men in a metabolic ward failed to demonstrate adverse effects from consumption of a diet in which all of the protein was provided from soy protein isolate. It is estimated that 10 percent of infants in the United States receive formulas with protein from soy protein isolates during the early months of life, some consuming more than 4g of soy protein per kg per day, without evidence of adverse effects. Several multigeneration studies of rats fed soy protein isolates have failed to indicate evidence of long term toxicity. Thus, it seems likely that well- processed soy protein isolate adequately supplement with methionine, vitamins and minerals, either by addition to the soy isolate product or as provided by other components of the diet, is without hazard.
Soy protein isolates subjected to relatively severe alkali treatments that modify their viscosity and adhesive properties are used as sizing and coating adhesives in the production of certain paper and paperboard products used in food packaging. These alkali treatments also result in marked loss of certain nutritionally essential amino acids and formation of lysinoalanine as a component of the protein molecule. Renal cytomegalic changes have been demonstrated in rats fed diets containing high levels (20 to 30 percent) of alkali modified soy protein isolate as the sole source of protein. Alkali-treated casein and lactoalbumin at high levels in the diets of rats, and free lysinoalanine above certain levels, also produce cytomegalic changes. Removal of alkali-treated protein from the diet appears to reverse the changes. Cytomegaly was reduced or did not occur in rats in which alkali-treated protein was supplemented with an untreated protein suggesting that the renal syndrome was caused by protein bound lysinoalanine in diets deficient or imbalanced with respect to one or more amino acids. Feeding free lysinoalanine at 1000ppm in the diet to five mammalian species other than the rat, including subhuman primates has failed to produce renal cytomegalic changes.
Data available to the Select Committee suggests that alkali-treated soy protein isolates account for less than 1 percent by weight of paper and paper board products in which they are used. Because of this relatively small concentration of soy protein and because only a small fraction of the coating from a food package would be expected to be transferred into the food by attrition or migration, the intake of alkali- treated soy protein entering the diet from food packaging materials is assumed to be exceedingly small, and, accordingly, the lysinoalanine intake from this sources is of no moment.
Lysinoalanine has been reported at relatively low levels in some samples of food grade soy protein isolate including spun fibers of soy protein isolate used in fabricating meat analogs. Lysinoalanine also has been found in a number of milk, meat, egg and vegetable protein products that had been heated at neutral or alkaline pH in processing. While the available information indicates that the levels of lysinoalanine in food grade soy protein isolates as currently used pose no hazard to the consumer, a limitation with respect to lysinoalanine in the specifications for food grade isolates and products derived from them would avoid possible future problems in this regard.
It is important to ensure that preformed nitrosamines are not present in soy protein isolates and are not formed in processed foods containing soy protein isolates. Many nitrosamines have been shown to be carcinogenic in experimental animals. Specifications should be developed for food grade soy protein isolates which exclude nitrosamines.
The presence of up to 50 ppm nitrite in soy protein isolates raises other possibilities of concern. The potential for nitrisamine formation in vivo from the ingestion of foods containing nitrite, and the latter reacting with other nitrogen- containing compounds in foods, drugs and endogenous amines, must be considered. Many natural and processed foods, including spray dried products, contribute to the total human intake of nitrite even though bacterial reduction of nitrate to nitrite in saliva is the major source of nitrite reaching the gastrointestinal tract. It was reported from recent unpublished work with rats fed nitrites that the frequency of lymphoreticular neoplasms was increased. The possibility that nitrite has an adverse effect of this type raises questions about the total body burden of nitrite and the relative contribution from food, saliva and the estimated larger amount produced by bacteria in the intestinal tract. A study of these sources and their relative importance is required for individuals of different age groups and dietary habits to obtain reliable figures.
It is recognized that soy protein isolates constitute a currently minor source of nitrite as far as human exposure is concerned. Preliminary estimates of per capita exposure indicate that they account for less than 0.5 percent of the amount ingested as food ingredients, less than 0.05 percent of that taken in as food ingredients and present in the saliva; and less than 0.0075 percent of the total taken in as food ingredients, present in the saliva, and generated in the intestinal tract. From the standpoint of relative contributions to the controllable nitrite load and/or total body burden, soy protein isolates do not appear to be cause for concern at this time. Nevertheless, the possible adverse effects of nitrite call for more explicit knowledge and actions for maintaining a low level of the compound in the commercial products and for continued monitoring of its relative contributions, with adjustments as necessary, as the major sources of commercially added nitrites are progressively decreased through regulatory procedures underway.
The Select Committee has weighed the available information and concludes:
1. It is essential that specifications for food grade soy protein isolates be established including provisions for acceptable levels of lysinoalanine, nitrite and nitrosamines.
2.Assuming that acceptable levels of lysinoalanine, nitrite and nitrosamines are established, there is no evidence in the available information on soy protein isolates that demonstrates or suggests reasonable grounds to suspect a hazard when they are used at levels that are now current or that might reasonably be expected in the future.
3. There is no evidence in the available information on soy protein isolates that demonstrates or suggests reasonable grounds to suspect a hazard when used in paper and paperboard products for food packaging at levels that are now current or that may reasonably be expected in the future.