Evidence suggests that high carbohydrate diets are associated with weight gain when the majority of that carbohydrate is refined in nature. Whole grains protect against obesity, but refining cereals and other carbohydrates alters their digestion and absorption rates and this affects subsequent metabolic activity. Fructose is often promoted as an alternative source of carbohydrate for diabetic patients, but research suggests that high intakes of fructose are associated with weight gain, obesity, metabolic syndrome, cardiovascular disease and detrimental changes to lipoprotein concentrations. Galactose is a hexose sugar that is converted to glucose without affecting blood glucose levels or insulin production. Galactose is therefore possibly of interest in weight loss because it may allow fat oxidation to proceed under conditions of carbohydrate intake. Galactose is one of the monosaccharide sugars incorporated into the lactose molecule, making milk a particularly good source.
The effects of galactose on lipid oxidation has been investigated1 in a small sample of 14 women. The subjects were all obese otherwise healthy women, 7 who were breastfeeding and 7 who were non-lactating. In a cross-over single blind study the women were randomly assigned to receive an isocaloric drink that provided 70% of their daily calories needs, 60% of which was either glucose or galactose. Post-prandially, those women receiving the galactose drink had lower plasma glucose and insulin levels than those receiving the glucose drink. Glycerol, palmitate, free fatty acids and triglycerides appearance rates were higher, and glucose appearance rates lower, in those consuming the galactose drink, compared to those consuming the glucose drink. However, fat oxidation rates were higher and protein oxidation rates were lower in the galactose group compared to the glucose group for both lactating and non-lactating women.
These results tend to suggest that the women being fed galactose have higher fat mobilisation rates (as signified by appearance of plasma glycerol, glucose, free fatty acids and palmitate) and higher fat oxidation (as measured by indirect calorimetry). In the lactating women, fat oxidation rates were 30% higher and protein oxidation rates were 45% lower while consuming the galactose drink. As a whole fat oxidation were 28% higher and protein oxidation were 30% lower in all women drinking the galactose drink. No differences in energy expenditure or carbohydrate utilisation were observed in this study. Following an overnight fast post-prandially there was no difference in substrate utilisation suggesting that there was no carry over of altered substrate metabolism. Taken as a whole these result support the idea that oral galactose may increase fat oxidation and fat mobilisation during meal absorption which may suggest it could be effective in fat loss.