That fructose can cause insulin resistance has been demonstrated in the nutritional literature. Because sucrose (table sugar) contains a moiety of fructose, sugar is known to cause insulin resistance in mammals. Many experiments have been performed in rats showing that sugar causes glucose intolerance or insulin resistance, and these data have been confirmed by human studies. It is known that increases in insulin sensitivity occur in skeletal muscle following physical activity, and some dietary factors such as fibre are thought to limit insulin release and thus improve sensitivity. Therefore researchers have tested the ability of both fibre and exercise to counter the detrimental effects of sugar consumption on insulin sensitivity in rats. Rats were fed a diet consisting of either low fat complex carbohydrate, high fat complex carbohydrates, low fat sucrose, high fat sucrose, high fat sucrose plus fibre or high fat sucrose plus exercise.
The results showed that diets high in fat and sucrose caused glucose intolerance, with the addition of fibre having no protective effects. All diets containing sucrose caused insulin resistance in the rats, with exercise and fibre have no protective effects. Therefore sucrose is able to cause insulin resistance in mammals even if known protective factors are included in the diet. Only the rats consuming complex carbohydrates were protected from glucose intolerance and insulin resistance. Increases in sucrose consumption in recent decades and concomitant reductions in complex whole grain carbohydrate comsumption has been proposed as a mechanisms for the increase in the prevalence of obesity and lifestyle diseases such as diabetes and cardiovascular disease. These results support that contention and show that even short periods of sucrose consumption (10 weeks) is enough to cause physiological changes that may lead to the development of metabolic syndrome.
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