Insulin resistance is a condition where the sensitivity of the insulin receptor is reduced and the cellular responses caused by an increase in blood sugar become abnormally blunted. Insulin resistance is associated with diabetes, cardiovascular disease, hypertension and metabolic syndrome (also called syndrome X). The causes of insulin resistance are unknown, but evidence suggests that diet quality has a profound effect on the sensitivity of the insulin receptor. High quality diets contain all the essential elements and accessory nutrient in the correct ratios for optimal health, and tend to be high in unrefined whole grains and nutrient dense foods This is in contrast to low quality diets which are high in refined, calorie dense, nutrient poor foods. In particular refined carbohydrates, such as sucrose and fructose, are implicated in the development of insulin resistance
Animal models are useful in understanding metabolic disorders because although animal physiology differs from that of humans, dietary changes can be precisely controlled to allow researchers to understand how individual changes in foods can affect metabolism. Animal studies suggest that increasing the content of sucrose in the diet above around 60% results in the development of insulin resistance. Interestingly, increasing the fructose content of the diet above 34% also results in the development of insulin resistance, which suggests that it is the fructose portion of the sucrose molecule responsible for this effect. In addition, fructose induced insulin resistance in animal models is associated with hypertiglyceridaemia. This would suggest that the high triglyceride levels seen in individuals with insulin resistance are not caused by dietary sources, but are produced endogenously from fructose.
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