Fructose or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose andgalactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water-soluble of all the sugars.From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables. In plants, fructose may be present as the monosaccharide and/or as a molecular component of sucrose, which is a disaccharide.Because it does not cause blood sugar rise tremendously (has a low glycemic index), it was once thought that fructose was a good substitute for sucrose (table sugar). However, the American Diabetes Association and nutritional experts have changed their minds about this.
A small amount of fructose, such as the amount found in most vegetables and fruits, is not a bad thing. In fact, there is evidence that a little bit may help your body process glucose properly. However, consuming too much fructose at once seems to overwhelm the body's capacity to process it. The diets of our ancestors contained only very small amounts of fructose. These days, estimates are that about 10% of the modern diet comes from fructose.
"Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance. Fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion, and central administration of fructose provokes feeding in rodents, whereas centrally administered glucose promotes satiety," According to new study.
"Thus, fructose possibly increases food-seeking behavior and increases food intake." How brain regions associated with fructose- and glucose-mediated changes in animal feeding behaviors translates to humans is not completely understood.
According to a preliminary study published in the January 2 issue of JAMA possible factors regarding the associations between fructose consumption and weight gain, brain magnetic resonance imaging of study participants indicated that ingestion of glucose but not fructose reduced cerebral blood flow and activity in brain regions that regulate appetite, and ingestion of glucose but not fructose produced increased ratings of satiety and fullness.
Recent Study conducted by Kathleen A. Page, M.D., of Yale University School of Medicine, New Haven, Conn.,to examine neurophysiological factors that might underlie associations between fructose consumption and weight gain. The study included 20 healthy adult volunteers who underwent two magnetic resonance imaging sessions in conjunction with fructose or glucose drink ingestion. The primary outcome measure for the study was the relative changes in hypothalamic (a region of the brain) regional cerebral blood flow (CBF) after glucose or fructose ingestion.
The researchers found that there was a significantly greater reduction in hypothalamic CBF after glucose vs. fructose ingestion. "Glucose but not fructose ingestion reduced the activation of the hypothalamus, insula, and striatum -- brain regions that regulate appetite, motivation, and reward processing; glucose ingestion also increased functional connections between the hypothalamic-striatal network and increased satiety."
"The disparate responses to fructose were associated with reduced systemic levels of the satiety-signaling hormone insulin and were not likely attributable to an inability of fructose to cross the blood-brain barrier into the hypothalamus or to a lack of hypothalamic expression of genes necessary for fructose metabolism."
Reference:
- Kathleen A. Page et al. Effects of Fructose vs Glucose on Regional Cerebral Blood Flow in Brain Regions Involved With Appetite and Reward Pathways. JAMA, 2013 DOI: 10.1001/jama.2012.116975
- http://lowcarbdiets.about.com/od/nutrition/a/fructosedangers.htm
- wikipedia encyclopedia