Sucrose is the chemical name for table sugar. Structurally, sucrose is a disaccharide composed of a molecule of fructose and a molecule of glucose. Sucrose ingestion results in hydrolysis of the glycosidic bond between the two sugars to produce glucose and fructose, which are absorbed to the circulation. While glucose is able to be oxidised as a fuel for brain activity, and can be oxidised and stored by skeletal muscle, the fate of the fructose moiety is more limited. Only the liver can metabolise fructose, and this creates problems if large quantities of sugar are consumed. High intake of fructose over short periods of time result in an overload of fructose to the liver and this shifts metabolic regulation towards the synthesis of fatty acids through the de novo lipogenesis pathway. The fatty acids produced then accumulate in tissue including the skeletal muscle and liver, where they cause insulin resistance by interfering with the insulin signal cascade. Even modest intakes of sugar can have this effect, when in its refined crystalline state.
For example, one group of researchers fed varying concentrations of sugar to 24 carbohydrate sensitive individuals for 6 weeks1. Subjects consumed 5, 18 or 33 % of their energy in the form of sucrose in a crossover designed study. The carbohydrate, fat and protein content of the diet was 44, 42 and 14 % of energy intake, respectively. The subjects consume 25 % of their energy at breakfast and 75 % at dinner with the energy intake of each individual averaging 2780 kcal per 70 kg of body weight. No change in the body weights of the individuals were noted over the 6 week study. However, fasting serum insulin levels increased with increasing sucrose content from baseline, and increased more for men than women. Consumption of 18 and 33 % of energy as sucrose also significantly increased the fasting glucose levels of the subjects. A sucrose load of 2 g per kg body weight caused significantly higher insulin levels following all three diets and significantly higher glucose responses after the 18 and 33 % sucrose diets.
The levels of sucrose in this study were chosen because they fell within the amounts found in typical Western diets. That the consumption of such quantities of sucrose cause detrimental changes to blood sugar homeostasis in just 6 weeks highlights why the typical Western diet is so unhealthy. The development of insulin resistance is problematic because it leads to weight gain, and the secondary disorders associated with weight gain include an increased risk of other Western diseases such as cardiovascular disease, cancer and type 2 diabetes. This study also highlights the absurdity of consuming commercially processed low fat foods in order to lose weight. Such foods remove the fat and replace it with sugar to maintain the taste to the consumer. These products increase the sugar burden of the individual and this increases insulin resistance which raises insulin levels and prevents weight loss. Effective weight loss requires insulin resistance to be reversed which necessitates abstaining from all refined crystalline sugar.
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