Nutritional determinants of the insulin resistance syndrome

Recent data show that fat balance is the only component of macronutrient balance which is not precisely regulated. The adherence to a lifestyle characterized by high fat food habits and sedentariness thus favor a positive fat balance which may persist for a long period of time. The resulting body fat gain contributes to the restoration of fat and energy balance because of the enhancing effect of fat gain on fat oxidation. Individuals predisposed to obesity seem to be particularly vulnerable to a positive lipid balance because they are characterized by a reduced fat oxidation when their body weight is normal and by a reduced capacity to increase fat oxidation when exposed to a high fat diet. Body fat gain, particularly in the deep abdominal area, is also associated with an increase in insulinemia which is known to acutely inhibit fat mobilization and oxidation. Beyond these peripheral metabolic effects, hyperinsulinemia with euglycemia can influence neuronal regulation of energy balance which ultimately results in an increase in sympathetic nervous system activity. An increased sympathetic tonus exerts an enhancing effect on fat oxidation and energy expenditure and a reducing effect on food intake. As discussed in this report, hyperinsulinemia thus appears to be an adaptation which is part of a regulatory system aimed at restoring fat and energy balance under conditions favoring body fat accumulation.