Dietary sugars are mono-and disaccharides that are naturally present in
fruits, vegetables, and natural syrups or are added to foods as refined
sucrose or high-fructose corn syrup. Dietary sugars are absorbed in the
bloodstream as glucose (indistinguishable from that released from
starch), fructose, and galactose. Galactose is converted into glucose,
and fructose is converted into glucose, lactate, and fatty acids in
splanchnic organs. The main nutritional function of sugars is to
pro-vide usable energy to all cells in the human body. The efficiency of
usable energy transfer is very high for glucose; lower for galactose,
lactose, and sucrose; and lower still for fructose. High dietary sugar
intake may be associated with an increased risk for cardiovascular and
metabolic diseases. This is especially true for fructose and sucrose,
which increase blood lipids and impair hepatic insulin sensitivity when
consumed in high doses. The effects of sugar-containing foods vary
according to food group: fruit and vegetable consumption significantly
protects against cardiovascular and metabolic diseases, while
consumption of sugar-sweetened beverages is associated with an increased
risk. The quality of sugar-containing foods should be assessed not only
based on their sugar content, but also on their overall energy, dietary
fiber, and micronutrient contents.