Fructose, galactose and glucose - In health and disease

Monosaccharides are important components of the diet, where the sweetness of these common sugars draw animals to eat the tissue within which they are located - especially fruits. Higher (larger) saccharides, within which they are constituents, are ubiquitous throughout nature too - and include disaccharides, oligosaccharides and polysaccharides. These may be converted (hydrolysed) to monosaccharides by the plant tissue enzymes during ripening and stimulate consumption by a predator (whereupon seeds within the fruit are dispersed). Predators may have relevant enzymes in their digestive tract to effect conversion of the larger carbohydrates to its monosaccharides - which are then absorbed from the gut and like free monosaccharides in fruit/vegetables, provide an energy source. Starch is an important source of glucose. This review (on monosaccharides) is part one of a series of three which aim to link the role of carbohydrates in food through processing to health and disease related issues. The emphasis here is to understand the role of the three key monosaccharides from the diet - fructose, galactose and glucose - with perspectives in health and disease.

The review was based on a review of relevant databases for material (e.g. Pubmed, Science Direct, Web of Science, Wiley online library etc.).

Data pertaining to the nutritional role of key dietary monosaccharides were evaluated together with their utilisation and role in health and disease. Disease states and their management in the context of monosaccharide consumption were considered.

The body is designed to utilise carbohydrates - where a physiological balance of ingestion, storage and utilisation is critical. In disease states, the balance is lost and a number of carbohydrate based metabolic disorders are established within the medical community. Overall, this review considers digestive and metabolic issues associated with free monosaccharides commonly consumed in the human diet. Further reviews will focus on common di-, oligo and polysaccharides relevant to digestive energy and overall health.