Fructose is a monosaccharide which is abundant in nature. It is the sweetest naturally occurring carbohydrate. The availability of fructose increased substantially when it became possible in the 1960s to economically produce high fructose syrups from corn starch and other starches. Such high fructose syrups are now used to sweeten soft drinks, fruit drinks, baked goods, jams, syrups and candies. The most recent data available suggest that fructose consumption is increasing worldwide. Fructose presently accounts for about 10% of average total energy intake in the United States. Studies in both healthy and diabetic subjects demonstrated that fructose produced a smaller postprandial rise in plasma glucose and serum insulin than other common carbohydrates. Substitution of dietary fructose for other carbohydrates produced a 13% reduction in mean plasma glucose in a study of type-1 and type-2 diabetic subjects. However, there is concern that fructose may aggravate lipemia, particularly in men. In one study, daylong plasma triglycerides (estimated by determining the area under response curves) in healthy men was 32% greater during a high fructose diet than during a high glucose diet. There is also concern that fructose may be a factor contributing to the growing worldwide prevalence of obesity. Increasing fructose consumption is temporally associated with the increase in obesity. Moreover, on theoretical grounds, dietary fructose might increase energy intake. Fructose stimulates insulin secretion less than does glucose and glucose-containing carbohydrates. Since insulin increases leptin release, lower circulating insulin and leptin after fructose ingestion might inhibit appetite less than consumption of other carbohydrates and lead to increased energy intake. However, there is not yet any convincing experimental evidence that dietary fructose does increase energy intake. Although evidence that fructose has adverse effects is limited, adding fructose in large amounts to the diet may be undesirable, particularly for men. Fructose that occurs naturally in fruits and vegetables is a modest component of energy intake and should not be of concern.