What health effects can we really expect from the increased use of simple sugars in the diet? It’s long been suspected that sugars, consumed in excess, might have deleterious health consequences.

Originally, sugars — referred to by nutritionists as simple sugars — were contrasted with starches — referred to as complex carbohydrates. We assumed that the simple sugars were always more rapidly absorbed than complex carbs, and so caused a sharper, stronger rise in the blood glucose level. Their consumption was linked to obesity and diabetes.

But with time, it became apparent that the glycemic index of white sugar (sucrose) and white bread weren’t so dissimilar, and that some sugars such as fructose were even more slowly absorbed than the glucose from many starches. Furthermore, it turned out that fructose is poorly converted to glucose and so raises the blood glucose far less than once feared.

At one point, fructose was even explored as a potential carbohydrate source for the diabetic diet. A huge potential advantage was that fructose, unlike glucose, could enter cells without the help of insulin. There were, however, problems associated with a raised triglyceride level in sensitive patients who consumed significant amounts. Moreover, because of its slower absorption and ultimately malabsorption, consumption of large amounts of fructose has been linked to abdominal symptoms and osmotic diarrhea, as seen with sugar alcohols such as sorbitol. Recently, the name of fructose has been further tarnished through its association with high fructose corn syrups notoriously used to sweeten soft drinks. Consumption of these has, in turn, been linked to obesity. It may be argued that it’s simply the increase in caloric intake that’s the problem and not the fructose per se. But while this may be true, more bad news about fructose has emerged from a recent publication in the Journal of Clinical Investigation (Stanhope KL, et al J Clin Invest doi:10.1172/JC137385).

Fructose fat deposits

In this paper, overweight dyslipidemic subjects were provided with beverages sweetened with either fructose or glucose to meet 25% of their total daily caloric requirements. The drinks were taken for a 10-week period in a randomized design. At the study’s end, both groups had gained about 1.5 kg. The fasting serum triglyceride concentrates were significantly higher after the glucose drink, but in all other respects the fructose-supplemented subjects fared worse. They showed higher post-prandial triglyceride levels, glucose and insulin levels, not to mention higher fasting LDL-C, oxidized LDL-C and apolipoprotein B concentrations. The fructose group also put on more visceral adipose tissue, which has been linked to insulin resistance. No change was seen in blood pressure in either group.

These data suggest that fructose should be avoided whenever possible. But there are several caveats. This trial examined the effect of fructose in overweight people who gained even more weight. Fructose, being able to enter cells without the aid of insulin, therefore contributed to intracellular triglycerides. This in turn could lead to insulin resistance in insulin-sensitive tissues and begin the observed process where features of the metabolic syndrome are exacerbated. Nevertheless, this study was not carried out in normal weight, physically active individuals who are weight stable. In this situation no ill effects might be seen. If diabetics could refrain from gaining weight, the substitution of fructose might be helpful in keeping their glucose levels under control and preventing glycation of Hb to form HbAIc. In fact, there’s evidence that a small amount of fructose primes the uptake and utilization of glucose in healthy subjects, so actually improving glucose tolerance.

Fruits are not at fault

Fructose is found in fruit, largely in combination with glucose as the disaccharide sucrose. It’s sweeter than glucose. No one has yet suggested that fruit as a source of fructose should be avoided.

The issue therefore is moderation, not just in the amount of fructose eaten, but in the context of the whole diet. Fructose can remain an important part of the diet of healthy people who maintain an appropriate body weight.

It may well be useful in diabetes during weight loss, and possibly even in weight maintenance situations. It appears, though, that large amounts are not good for overweight people who continue to gain weight. So there may be reason for concern when overweight children take substantial portions of their calories as soft drinks sweetened with fructose and glucose. But this concern must surely pale in comparison to the far larger problem of inactivity and weight gain among kids. The prime culprits behind this aren’t fructose or corn syrup, but societal norms that encourage overconsumption and lack of physical activity.