Thriving vs Surviving

Have you ever wondered how people stay alive when their diet is so very poor?  The answer is the “tropic value” of different foods, described in 1973 by Roger Williams, PhD, a biochemist at the University of Texas who researched areas of nutrition. 

            The tropic value of a food is a descriptor of the quality of a food beyond calorie (energy) content. Substances “beyond calories” include vitamins, minerals, essential fatty acids, essential amino acids, or other as yet unrecognized substances.  Tropic value is determined by feeding a minimal protein intake to sustain life and making the rest of the diet one single food. After a given time period on this combination (12 weeks in rats), results are measured by 1) occurrence of death (rare, considering the protein), 2) amount of weight gain (tissue added, or growth), and 3) whether the stages of sexual maturity were achieved. For normal growth and development foods taken must be totally complete for the specific animal. Obviously, this type of study can’t be ethically conducted on humans, which made the original science not 100% transferable to human nutrition.

            A food or a combination of foods which supply total needs (a high tropic score) will allow an individual to thrive.  A food intake that is not totally complete (a lower tropic score) will allow an individual to survive, but not grow to achieve their genetic potential. A food intake that is even less complete (a very low tropic score) will not allow an individual to mature sexually.

            It has been found that a diet of only rice or potatoes had higher tropic values than predicted – as illustrated by populations who have survived famine on these foods. Individuals survived, but didn’t thrive and children did not reach their growth potential. An early puzzle was that whole milk had a tropic value five times higher than the tropic value of fortified skim milk.  Work on essential fatty acids came later, but even today parents are advised to feed children under two years old whole milk.[i] Other scientists later found that young boys who did not mature sexually were found to be consuming a diet quite low in zinc



[i] Williams, Roger J. , James D. Heffley,  Man-Li Yew, Charles W. Bode. The “Tropic” Value of Foods. Proc Nat Acad Sci USA   1972; 70(3):710-713.

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