Glucose, or blood sugar, is the main component of carbohydrate foods, such as sweets, bread, pasta and rice. Fructose is a different kind of sugar that can be found in table sugar and high fructose corn syrup. Both glucose and fructose can be a risk factor for a range of metabolic conditions. Whether fructose is worse than glucose is a subject of great controversy. Studies suggest that increased consumption of fructose can cause obesity, fatty liver, elevated cholesterol levels and high blood pressure. The question remains, however, whether it is the total sugar consumption that is to blame for these conditions or fructose itself.
Refined Carbohydrates and Insulin Resistance
A diet high in refined carbohydrates, such as sweets, white bread, white rice and white pasta, can negatively affect the body’s metabolism. Refined carbohydrates quickly convert to glucose in the digestive system. When glucose enters the bloodstream, the pancreas produces insulin, a hormone that signals the cells when glucose is available. The cells absorb the excess glucose and store it as fat or glycogen, a stored form of glucose. Once the cells have absorbed the glucose from the bloodstream, glucose levels quickly drop. Over time, these constant fluctuations in blood glucose can make the insulin receptors shut down. This condition is also known as insulin resistance.
Metabolic Syndrome
When cells are insulin resistant, insulin cannot signal to them when glucose is available in the bloodstream. Because most cells cannot absorb glucose without the insulin signal, insulin resistance leads to high blood glucose levels. There is a direct correlation between high glucose and high blood pressure, high cholesterol and weight gain. Together with insulin resistance, these conditions are known as metabolic syndrome. They are a risk factor for type 2 diabetes and heart disease.
Fructose and Fatty Liver
Glucose and fructose are metabolized via different pathways. Whereas most cells in the body can convert glucose into energy, only liver cells can convert fructose into energy. If the body does not need energy, liver cells convert fructose into fatty acids. According to the August 2008 issue of “The Journal of Nutrition,” the conversion of fructose into fatty acids is the main contributor to fatty liver syndrome, a disease associated with obesity. A fatty liver is the stage before liver failure.
Fructose and Metabolic Syndrome
While the evidence for the association between fructose and fatty liver is compelling, it is unclear whether fructose plays a direct role in metabolic syndrome. Fructose does not convert to glucose. So it does not contribute directly to elevated blood glucose levels. There is, however, evidence that it plays an indirect role. A high fructose intake is one of the main contributors to obesity. According to a review in the October 2007 issue of “The American Journal of Clinical Nutrition,” one reason for this may be that fructose does not give rise to as great a feeling of satiation as glucose. If you do not feel satiated after consuming a fructose-sweetened food, you will consume more food, which could contribute to weight gain.
References
- “The American Journal of Clinical Nutrition”; Potential Role of Sugar (Fructose) in the Epidemic of Hypertension, Obesity and the Metabolic Syndrome, Diabetes, Kidney Disease, and Cardiovascular Disease; R.J. Johnson, et al.; October 2007
- "Critical Reviews in Food Science and Nutrition"; A Critical Examination of the Evidence Relating High Fructose Corn Syrup and Weight Gain; R.A. Forshee, et al.; 2007
- "Circulation"; Diagnosis and Management of the Metabolic Syndrome; Scott M. Grundy, et al.; September 2005
- “The Journal of Nutrition”; Nonalcoholic Fatty Liver Disease in Humans Is Associated with Increased Plasma Endotoxin and Plasminogen Activator Inhibitor Concentrations and with Fructose Intake; S. Thuy, et al.; August 2008
