Insulin resistance is the pivotal factor in many Western lifestyle diseases. The metabolic changes that accompany insulin resistance leads to cellular dysfunction and this in turn leads to the diseases of the West, particularly obesity, cardiovascular disease and diabetes. One of the possible causes of insulin resistance is the acceleration of endogenous lipid formation through the consumption of refined carbohydrates, particularly refined crystalline fructose containing sugars. Diets high in refined carbohydrates, particularly if hypercaloric, increase flux through the de novo lipogenesis pathway, and the resulting fatty acids and their triglycerides accumulate in tissues, particularly the skeletal muscle and liver, where they induce insulin resistance, possibly through interference with the insulin signal cascade. These fatty acids may also overload the cells of the body with energy, initiating a free radical induced desensitisation of the insulin receptor, a protective mechanism to inhibit oxidative stress to the cell.
Lowering the carbohydrate intake is therefore an effective strategy to prevent endogenous fatty acid and triglyceride synthesis. One way this can be achieved is through replacing a certain amount of carbohydrate in the diet with protein. For example, in one study1, researchers observed the effects of hypercaloric diets, which are known to increase endogenous triglyceride synthesis, on the accumulation of lipids in tissues. In a crossover design study, subjects consumed a high protein low carbohydrate diet (26 % protein and 37 % carbohydrate) or a low protein high carbohydrate diet (15 % protein and 45 % carbohydrate) for 2 weeks each. The results showed that there was a trend for a reduction in intrahepatic lipids with the high protein low carbohydrate diet when compared to the low protein high carbohydrate diet. Significant reductions in plasma triglycerides, fat mass and significant increases in lean mass were also observed in subjects following the high protein low carbohydrate diet.
These results suggest that high carbohydrate intakes may increase the risk of lipid accumulation in tissues when an excess amount of energy is consumed. However, if that excess energy contains a higher component of protein foods, that lipid accumulation is reduced. This scientifically falsifies the energy balance theory of weight gain, and so the theory should be abandoned. It is known that carbohydrates can lead to lipid accumulation when isocaloric diets are followed, and this relates to the way in which certain carbohydrate foods are digests rapidly and this flood the cells with nutrients which in turn increases lipid formation. Protein can prevent this process because the protein slows the passage of starch through the gut and has beneficial postprandial glycaemic effects. Studies such as this highlight the importance of macronutrient ratios and high quality food sources as primary determinants of body weight change. Addition of protein to isocaloric diets induces weight loss for the same reasons.
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