Spurred by the observation that the widespread introduction of high-fructose corn syrup into food and beverages in the 1970s coincided with a dramatic rise in the prevalence of diabetes and obesity, many recent studies have set out to characterize the metabolic effects of fructose and compare them to those of other sugars.
Yet despite this deluge of research, it still remains unclear whether – calorie for calorie – fructose is more damaging than traditional sugar, aka sucrose, or if they are equally bad and the former merely gets a bad rap because it is used in processed products.
As more than 400 million people worldwide currently have diabetes, and many millions more suffer from prediabetic impaired blood sugar control, it is more urgent than ever to figure out how different sugary foods contribute to metabolic disease. Only then can we draft better guidelines about what foods are safe to enjoy in moderation and which should we ditch entirely.
But while we’re waiting for these clarifying insights, a consortium of Canadian researchers has released a helpful suggestion: Lay off the sugary drinks.
Their advice is the result of a new meta-analysis that reviewed 155 studies assessing the effect of different food sources of fructose-containing sugars on blood sugar control in diabetic and non-diabetic subjects.
“[Our work] suggests that most food sources of fructose-containing sugars do not have a harmful effect on glycemic control in energy matched substitutions for other macronutrients,” the wrote in the British Medical Journal. “However, several food sources do have harmful effects when adding excess energy to the diet, especially sugar-sweetened beverages (SSBs).”
“Until more information is available, public health professionals should be aware that harmful effects of fructose-containing sugars on glycemic control seem to be mediated by energy and food source.”
Including a total of 5,086 subjects, the selected studies assigned people to one of four types of interventional diet – substitution (energy came from sugar rather than other carbohydrates), subtraction (less total energy taken from sugars), addition (energy from sugar was added), or ad libitum (amount of sugar was not restricted). Each study followed subjects for up to 12 weeks and had its own form of a control group.
After performing pooled analyses of the glycated haemoglobin (HbA1c), fasting blood glucose, and fasting blood insulin level data collected in each investigation, lead author Dr John Sievenpiper and his colleagues concluded that the total amount of fructose-containing sugar participants ate was not linked to worse glycemic control in substitution or subtraction studies, but there was a slight association found in addition and ad libitum studies.
When assessing the influence of sugar source, they noted that sugar-sweetened beverages and fruit juice showed the most significant correlation with poor glycemic control.
"These findings might help guide recommendations on important food sources of fructose in the prevention and management of diabetes," Dr Sievenpiper said in a statement. "But the level of evidence is low and more high-quality studies are needed."
According to Sievenpiper and the other authors, past experiments have demonstrated that consuming fructose induces less extreme blood sugar spikes than consuming the same number of calories in starch, suggesting the sweetener could be beneficial for diabetics.
And despite a handful of well-publicized studies painting fructose as dangerous to cardiovascular and metabolic health, “higher levels of evidence from systematic reviews and meta-analyses of controlled human intervention studies have failed to show adverse glycaemic effects unique to fructose, and have even shown a beneficial effect on glycated blood proteins of fructose in isocaloric substitution for other carbohydrates in the diet in people with diabetes.”