Total Body Potassium and Body Fat Estimation in Relationship to Height, Sex, Age, Malnutrition and Obesity

Abstract

1. Total body potassium was estimated by 40-K measurement with a high-sensitivity whole body counter in normal individuals over a wide age range and in patients who were obese or were grossly wasted as a result of various conditions which restricted food intake. 2. Potassal males and females, but when individuals of different age groups were matched for height, a significant fall in total body potassium with increasing age was observed only in males. Total body potassium of females was about 75% that of males of similar height when young, the sex difference decreasing with ageing. In the normal population, total body potassium was significantly correlated with height and with weight; regression equations for various relationships are given. 3. Fat-free mass was estimated from total body potassium, values of 65 and 56 mmol of potassium/kg fat-free mass being used for males and females respectively. Body fat estimated by this method correlated well with skinfold measurements over a wide range of body weight but in malnourished individuals having inadequate food intake there was considerable fat-free mass from total body potassium appear unsatisfactory in malnutrition. Considerable differences between expected and observed values of total body potassium were found in muscular individuals and in normal individuals who were thin but whose body weight was relatively constant. 4. The patients with malnutrition were low both in body fat as estimated by skinfold thcikness and in total body potassium estimated on the basis of height. Plasma potassium was, however, normal and potassium supplements did not increase the total body potassium. 5. Total body potassium of obese individuals was not significantly different from that of normal weight individuals on the basis of height. Total body potassium fell on weight reduction with a very low energy diet of 1260 kJ (300 kcal.) daily but changed little with a 3300 kJ (800 KCAY POTASSIUM WAS BEST PREDICTED FROM THE INDIVIDUAL'S HEIGHT. For those whose body weight was less than expected, the use of weight gave the best prediction but the error was considerable when the weight deviation was large.

Lack of sensitivity of weight targets compared with body cell mass for determining recovery from malnutrition in adolescents with anorexia nervosa

“…BCM can be reliably determined from the tightly regulated whole body potassium, 98% of which is contained in the BCM (Cohn, Vartsky, Yusumura, Vaswani, & Ellis, 1983), measured by detecting a 1.46 MeV gamma ray emitted by the naturally occurring isotope 40 K which represents a fixed proportion of natural potassium (0.0118%). In both health and disease, potassium concentrations in both BCM and intracellular water compartments are relatively constant, independent of age and gender, kept within strict limits by a range of homeostatic mechanisms (Edmonds, Jasani, & Smith, 1975). We compared TBK values with age-related standards from measurements of healthy female subjects (n = 102) in our laboratory, expressed as percentage of expected TBK for height.…”

Total Body Potassium in Relation to Thyroid Hormones and Hyperthyroidism

“…Ifwe assume, and evidence has been noted above in SUPPOll of the assumption, that the loss of body potassium and body weight occurring when the patient was hyperthyroid was similar to that gained during recovery, then our present measurements can be compared with those obtained from obese, euthyroid patients losing weight because of dietary restriction. We have previously reported (Edmonds, Jasani & Smith, 1975) changes in total body potassium observed during dietary treatment of patients who were obese but otherwise healthy. These patients were treated only by dietary restriction, 12 of them for an initial period of 6 weeks in hospital on a diet of energy value 1·26 MJ daily.…”

“…Euthyroid-obese on diet: '1·26 MJ!day for 6 weeks and 3·5-5 MJ!day for 40 weeks: data fromEdmonds, Jasani & Smith (1975).…”

Potassium and magnesium depletion in patients with cirrhosis on maintenance diuretic regimens.

“…The expected value has a variation (2 SD from regression) of ± 15% and therefore potassium depletion was taken to be indicated by a K obs/K exp ratio less than 0-85. The body weights of two of our patients were less than 80 % of those expected for their heights and ages (Society of Actuaries, 1959) and, therefore, their K exp values were estimated using a regression equation based on weight only (Edmonds et al, 1975). This has been shown to be more appropriate for underweight individuals than an equation based on both height and weight.…”