Potassium intake, growth and energy metabolism

Abstract

The limitation of a single specific nutrient in an otherwise adequate diet results in a voluntary reduction in energy intake and an impairment of growth. Pairfeeding studies have indicated that the inhibition of growth cannot be attributed entirely to the reduced energy intake. The suggestion has been made that an imbalanced diet may result in changes in energy metabolism such that there is an inefficiency of energy utilisation, with an increase in Total Energy Expenditure (TEE).

This thesis studied the effects of excluding potassium from the diet of young growing rats on their growth and energy metabolism over a period of 14 days. The first study characterised the growth and Resting Energy Expenditure (REE) of male Wistar rats growing normally. The second determined the effects of potassium exclusion and repletion on potassium balance. The remaining three studies explored the effects of potassium exclusion and subsequent repletion on growth, body composition, TEE measured by the carcass balance method, REE measured both longitudinally and cross sectionally by indirect calorimetry, and organ protein metabolism.

The studies consistently supported the hypothesis that the exclusion of potassium from the diet of young rats resulted in an inhibition of growth that was not due entirely to their reduced energy intake, but was the result of an inefficiency of energy utilisation. The inhibition of growth was seen in association with a 17% increase in relative TEE over a 14 day period, and an increase in relative REE of 5-20% after 7 days of potassium exclusion, when compared to pairfed controls. This may be partly attributed to an increase in the proportion of visceral organs to total body weight in potassium excluded rats. In particular, the size of the kidney and its metabolic activity (in terms of the rate of protein synthesis) was increased in rats deprived of dietary potassium as part of the physiological response to regulating potassium homeostasis.

The findings of these studies have important implications when considering the nutritional requirements of individuals who are growing poorly despite receiving adequate amounts of energy. The diet of growing children, and those recovering from illness and malnutrition should provide not only sufficient quantities of macronutrients, but also the micronutrients which are required for the efficient metabolism of the diet as a whole.

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