The Impact of Fructose on Appetite, Metabolism, and Health Risks

Fructose and Appetite: Understanding the Connection

The new understanding of fructose came about after scientists discovered a hormone called leptin in 1994. Like insulin, leptin is a hormone involved in metabolism, and it plays a key role in telling your brain that you have eaten enough. After a meal, leptin is released by your fat cells, producing a feeling of satiety. When you go on a fast or eat a low-calorie diet, your fat reserve falls, and the decreasing leptin levels make you want to eat more. Leptin thus acts to regulate your energy balance through your appetite. While insulin regulates your glucose balance, leptin regulates your fat balance.

We now know that fructose increases your appetite in several ways:

• Leptin Resistance: When you consume too much fructose, leptin levels may be suppressed for up to 24 hours. This is called leptin resistance, meaning that consuming fructose makes you want to eat more.
• Ghrelin Rersistence: Fructose further affects appetite by failing to suppress ghrelin, a hormone released by the stomach to stimulate your appetite when it is empty. Most foods suppress the level of ghrelin, so once you are full, your urge to eat stops. Fructose does not suppress ghrelin levels as much as other foods do. So when you consume fructose-rich fruits or drinks before or during a meal, you are likely to continue eating even though you are full. Therefore, it is a good idea to eat fruits only after meals and avoid drinking fructose-rich beverages during mealtime.
• Sugar Addiction: The sweetness of fructose is addictive. This happens because fructose stimulates the brain's release of dopamine, a hormone that induces a pleasurable response. Studies on laboratory rats show that repeated feeding of sugar (which contains glucose and fructose) produced symptoms similar to those of addiction. Moreover, sugar addiction can lead to generalized addiction.
• Cell Hunger: Your cells can burn glucose instantly and directly into adenosine triphosphate (ATP) for energy. Fructose must first be converted to glucose before it can be burned for energy. So the first step in fructose metabolism consumes ATP, depleting the cell of its energy reserve. To compensate for the energy loss, your appetite is increased while your level of physical activity is decreased. Eating fructose makes you eat more and yet expend less energy.

Metabolic Syndrome: The Consequences of Fructose Consumption

The effects of fructose do not stop there. Leptin resistance, in turn, induces insulin resistance, which eventually leads to metabolic disorders like obesity and diabetes. In our earlier discussion, we learned that when we do not use up all the energy provided by starchy carbohydrates, the excess gets converted into fat. The bad news about fructose is that it converts excess glucose into fat faster than glucose acting alone. In fact, fructose helps convert all forms of excess calories—whether from carbohydrates, fatty acids, or amino acids—into fat reserves. In other words, fructose is Nature's prime fat accumulator. It's Nature's secret agent that helps animals accumulate fat rapidly, in preparation for winter famine or hibernation. It's no wonder that fructose appears in fruits when they ripen during the summer-winter season for this purpose.

Health Risks of Excessive Fructose Consumption

Eating fructose excessively comes with other potential problems:

• Liver Damage: The body has to convert fructose into glucose, and this can only be done by the liver. If the excess glucose is not used, fructose accelerates the conversion of glucose into fat, which is stored in liver cells. Eating too much fructose will cause fatty liver, leading to liver cirrhosis, where the liver hardens and eventually fails to function. The way the liver processes fructose is similar to how it processes alcohol. However, with alcohol, the body produces various signs—from "feeling high" to drunkenness—that tell us to stop drinking. But there are no signs that tell us to stop taking fructose.
• Heart Disease and Gout: One waste product of fructose metabolism is uric acid, which causes gout, a condition of swollen and painful joints, usually in the feet. Raised levels of uric acid also block an enzyme that makes nitric oxide, an essential chemical that dilates arteries to lower blood pressure. Lack of nitric oxide leads to hypertension and heart problems.
• Glycation: Excess glucose causes glycation, where excess glucose combines with cell protein and gets oxidized to form harmful advanced glycation end-products (AGEs) that cause cell damage. Fructose is seven times more active than glucose in inducing glycation.
• Lethargy: Earlier, we saw that large amounts of energy are used in fructose metabolism, depleting the cell's ATP reserves. Because of this, you feel lethargic and reluctant to exercise.