| Abstract | [Summary] The nutritive value of food has in the past been estimated from its composition. However, it is also related to its digestibility, yet information on food digestibility in vivo is totally lacking. In our first attcmpt, we have chosen inorganic 59Fe and 57Co-vitamin B12 as gamma emitters, and in addition, 35S-labeled thiamine was used to see if a beta emitter can also be used. To prepare labeled foods, a model experiment was carried out by injecting 59Fe Cl3 and 57Co-B12 to laying hens and and culturing beans in a medium containing 59Fe or 35S-B1. It was found that eggs, meats and bean sprouts were readily labeled, and that only egg yolk was labeled in the egg. Two methods have been used to determine digestibility of food with respect to a nutrient: (1) A radionutrient is incorporated in a food, fed to test subjects and the absorption compared with that of graded doses of pure radionutrient; digestibility is assessed from percentage ahsorption and chemically determined content of the nutrient after thorough in vitro digestion and / or extraction. (2) A small quantity of radionutrient is added to an unlabeled food, and digestion (amount of nutrient liberated in the digestive tract) is estimated from the decrease of percent absorption using a calibration curve obtained with increasing doses of pure radionutrient. It is desirable that percent absorption of the nutrient declines sharply as the dose increases and the test amount of food falls in the range. Using 57Co-B12 as food labeling tracer and testing by method 1, digestibility of cooked egg yolk was found to be poor, while, digestion of cooked chick liver and rat liver powder was almost complete. In method 2, 57Co-B12 was thoroughly mixed with egg white, yolk, ready-mix powder of Gelle, agar, pudding, ice-crem, or rice grains: they were then cooked and digestion was assessed from the scale. Egg yolk was found to be most poorly digested, while B12 in rice, pudding, and agar was almost completely liberated for absorption. Varying amounts of steak were fed shortly before the tracer dose, and liberation of beef B12was assessed from the decrease of absorption of the test dose. The result suggested that 100-150gm of steak was well digested, but the averages of digestion for 250-300gm were less than 50%. When 35S-thiamine was incorporated in food and tested by method 1, chicken meat and liver were digested fairly well, but 35S in bean sprouts was not. Digestion of eggs estimated with this marker was roughly the same as that measured with 57Co-B12. Detection of selective maldigestion as assessed by a method similar to ours will have a potential diagnostic value in the future in clinical medicine. |
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