The effect of high fat and high carbohydrate diets on rates of weight loss in mice

Abstract

The rate of weight loss in mice produced by restricting calorie intake below normal requirements is influenced by the type of food predominating in the diet; fat producing a rapid loss and carbohydrate a slower one. The amount of weight loss in both instances can be accounted for almost entirely by the extent of the negative carbon balances. The varying rates of weight loss are due to differences in the rate of fat loss and not to changes in total body water. This is confirmed by carcass analysis. In mice on a normal diet and in carbon equilibrium, about half the carbon is excreted as CO2 and half in the form of organic molecules with an energy value of their own. With restricted calorie high carbohydrate diets the proportion excreted as CO2 rises to over 80 per cent of the total while the proportion excreted in the form of complex molecules falls. With restricted calorie high fat diets the proportion excreted as CO2 remains normal. The half excreted as complex organic moleceules is significantly altered as to its distribution between feces and urine. With restricted calorie feeding the proportion of food and/or tissue totally degraded to CO2 influences the amount of energy available to the organism. The demands on its own fat stores are consequently greater when fat is the major constituent of such a diet. It is suggested that this view provides a partial explanation of the different rates of weight loss with alteration in dietary composition. The rate of weight loss in mice produced by restricting calorie intake below normal requirements is influenced by the type of food predominating in the diet; fat producing a rapid loss and carbohydrate a slower one. The amount of weight loss in both instances can be accounted for almost entirely by the extent of the negative carbon balances. The varying rates of weight loss are due to differences in the rate of fat loss and not to changes in total body water. This is confirmed by carcass analysis. In mice on a normal diet and in carbon equilibrium, about half the carbon is excreted as CO2 and half in the form of organic molecules with an energy value of their own. With restricted calorie high carbohydrate diets the proportion excreted as CO2 rises to over 80 per cent of the total while the proportion excreted in the form of complex molecules falls. With restricted calorie high fat diets the proportion excreted as CO2 remains normal. The half excreted as complex organic moleceules is significantly altered as to its distribution between feces and urine. With restricted calorie feeding the proportion of food and/or tissue totally degraded to CO2 influences the amount of energy available to the organism. The demands on its own fat stores are consequently greater when fat is the major constituent of such a diet. It is suggested that this view provides a partial explanation of the different rates of weight loss with alteration in dietary composition.