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The USDA trypsin inhibitor study. I. Background, objectives, and procedural details


Short-term feeding studies have shown that raw soy flour and purified trypsin inhibitors (TI) cause pancreatic hypertrophy and hyperplasia in certain monogastric animals. Prolonged exposure to high levels of TI in raw soy ultimately leads to pancreatic nodular hyperplasia and acinar cell adenoma in rats exposed to low levels of pancreatic carcinogens. Such change has been observed even in the absence of any exposure to known carcinogens. These results emphasized the need for chronic (2 yr) feeding trials which would clearly reveal dose response relationships of alterations in pancreatic pathology to dietary TI and possible interactions with dietary protein and fat.

Here we report on the objectives and designs of the first phase of the USDA TI Study, including composition of diets, preparation, and analyses of test substances. To provide the requisite TI and protein levels, raw and heated defatted soy flours, soy protein isolates, and lactic casein were used. The interrelationship of dietary level of TI (93–1270 mg/100 g diet) and that of protein (10%, 20%, and 30%) to pancreatic function and pathology will be reported in the following three papers. Both serial and chronic sacrifice regimes, respectively, were employed with 26 diets and 40 weaning male Wistar rats per dietary group.

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Rackis, J.J., Gumbmann, M.R. & Liener, I.E. The USDA trypsin inhibitor study. I. Background, objectives, and procedural details. Plant Food Hum Nutr 35, 213–242 (1985).

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Key words

  • soy flour
  • soy protein isolate
  • trypsin inhibitors biological-physiological-toxicological effects
  • pancreatic function and histology
  • long-term tests
  • Wistar rat