Fructose, Galactose and Glucose happen to be the three important mono saccharides found in nature and play crucial roles in the human metabolic system. The great blame game centered around Fructose, also known widely as fruit sugar since it is present naturally in many fruits, does not seem to be abating amongst the food and health experts, many of whom feel, rightly or wrongly that fructose is the main cause of epidemic obesity being faced by the population in some affluent countries. To the classical food scientists it does not make any sense as to why Fructose should cause obesity while Glucose, its more famous hexose isomer is the main source of biological energy produced through the TCA Cycle at the cellular level. But there appears to be substantial support to the theory that corn based High Fructose Syrup and its omnipotent presence in most of the foods consumed by the Americans could be a major contributing factor for obesity in that country.
Tomato, an inconsequential vegetable in the daily lives of many population, has come to the rescue of Fructose by showing the latter in a better light because of the reported beneficial effect of tomato products in protecting humans from some types of cancers. This phenomenon was first observed when scientists found such an effect with dehydrated product but not with fresh tomatoes. It is true that FDA of USA permits declaring claims for tomato in reducing the risk of cancers like prostate, gastric, ovarian and pancreas. Though lycopene, a major constituent in Tomato, was thought to be the active substance responsible for this effect, in actual experiments pure lycopene did not show the same result as tomato products. This led to the hypothesis that anti-cancer property of tomato is due to the combine action of carotenoids, vitamin C and poly phenols. That fresh tomato did not had the same effect as reconstituted products from dehydrated tomato provided the vital clue that some artifacts formed during the dehydration process could be the real active principle for the anti-cancer property.
Fructose has a ketone functional group and when dissolved in water it forms a ring structure like that of glucose. It undergoes Maillard reaction or non-enzymatic browning as Glucose does by combining with amino acids present in the food at high temperatures. As fructose exists to greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occurs more rapidly than with glucose. An understanding of the role of fructose in the Maillard reaction products helped scientists to isolate several ketosamines, reaction products between fructose and different amino acids and further studies zeroed on one compound, the reaction product with histidine amino acid, as responsible for the beneficial effect of tomato products against cancer. Further proof arrived when this ketosamine, in presence of lycopene was found to stop cancerous growth more than 98% of the time. In rat experiments 45% fewer animals died of prostate cancer. Being an Amadori compound, fructose ketosamine is present in many dry fruits but the significance of dehydrated tomato products being effective is possibly because of presence of lycopene and vitamin also as believed by many.
Fructose thus has a positive role in human diet and if at all it is involved in some way in obesity, it must be due to over consumption by the unsuspecting consumers, affecting their normal glucose-centric metabolism.