Experimental protein-calorie deficiency.

Many investigations into the effects of malnutrition have as their background the severe calorie and protein deficiencies associated with underdeveloped countries (McCance EL Widdowson, 1968). Mr Miller has already demonstrated that the protein value of a diet is best expressed as net dietary-protein calories yo (NDpCal%), a value that can be obtained by biological assay (Platt & Miller, 1959). The value of a diet is reduced when it is diluted with fat or carbohydrate, or, as is less widely appreciated, from the consumer’s point of view when it is eaten in inadequate amounts (Platt, Miller & Payne, 1961). Both dietary conditions produce protein-calorie deficiency, as defined by the Joint FAO/WHO Expert Committee on Nutrition (WHO, 1962), but the severity of the various symptoms may differ widely. For example, a deficiency produced by feeding an animal on grossly inadequate amounts of a well-balanced diet may lead to a greater inhibition of weight gain than occurs in another animal given unlimited quantities of a diet of low protein value; but the second animal will have the greater amount of body water and fat and a lower concentration of albumin in its serum. The low serum albumin will reduce the transport of albumin-bound vitamin A and calcium (Friend, Heard, Platt, Stewart & Turner, 1961 ; Gutman, 1953). From his experiences in China, Platt (1958) became convinced that there was an underlying ‘protein malnutrition’ in beriberi and probably in other vitamin deficiency states. Certainly, when animals are given diets containing insufficient amounts of vitamins or minerals, for instance thiamine (Cowgill, Deuell & Smith, 1925), retinol (Mellanby, 1950) and calcium (El-Maraghi, Platt & Stewart, 1965), there is often a severe loss of appetite, so that the original deficiency is complicated by some degree of protein-calorie deficiency. Platt believed also that there was an element of protein-calorie deficiency in most, if not all, diseased subjects. Overseas students working in his unit demonstrated that, in rats infected with Plasmodium berghei (Dema, 1959) and Nippostrongylus muris (Orraca-Tetteh, 1964) and in dogs carrying heavy loads of Toxocara canis (Al-Rabii, 1963), the value of the diet to the infected animal was about half that to the uninfected control. Part of this reduction could be related to a reduced intake of food, but the value to infected animals was also lower than to uninfected pair-fed controls. The precise nature of this phenomenon