Overconsumption of sugar causes obesity in two primary ways: excess calories and excess insulin (the hormone that shuttles sugar from the blood into cells). The Centers for Disease Control and Prevention report that obesity has overtaken cigarette smoking for the number-one spot on the list of healthcare costs.
Excess calories
Sugar contains no nutrients to speak of, only calories. Because it lacks fiber and nutrients, sugar bypasses your body’s natural leptin response (leptin is the hormone that signals your brain that you have enough body fat), so even after eating hundreds of calories in sugar, you don’t feel satisfied.
It only takes eating 100 extra calories per day to gain 10 pounds over a year! Sugary junk foods are low in nutrients and high in calories. High-sugar diets cause more sugar cravings and a strong desire for more carbohydrates.
Be sure to get your carbohydrates from vegetables, which are high in nutrients and low in calories. The fiber and “crunchy” factor help you feel full. Whole grains are also high in fiber and nutrients.
Fructose appears to affect leptin sensitivity more than other sugars. If you consistently overeat fructose, your brain can become insensitive to leptin — a condition known as leptin resistance. Unable to sense leptin, your brain lowers your metabolism to try to conserve fat stores.
To replace the missing body fat, your body packages up any dietary fat present in the high-fructose food and stores it as body fat. Common foods with high concentrations of fructose are fruit juice, high-fructose corn syrup, and agave nectar.
Excess insulin
Eating too much sugar at one time leads to a large release of insulin to control the amount of sugar in the bloodstream. High insulin levels erroneously tell the brain that, because the system has excess insulin, your cells must be starving for glucose. In response, your brain creates cravings for carbohydrates and signals your body to store fat.
Excess body fat causes insulin resistance, so obesity both causes and is caused by type 2 diabetes.
In women, excess insulin also stimulates the ovaries to produce excess testosterone, which can cause infertility by preventing the ovaries from releasing an egg each month. High levels of insulin also increase the conversion of androgens (male hormones) to estrogens (female hormones), upsetting the delicate balance between the two and having a direct effect on the formation of cystic follicles or cysts in the ovary.
For this reason, women with polycystic ovary syndrome (PCOS) must control their insulin levels through diet.