When it comes to promoting weight gain, not all sugars are equal, Yale researchers report. A recent brain imaging study on healthy adults who consumed either a fructose- or glucose-laced beverage found that while one triggered feelings of fullness and satiety, the other encouraged study participants to eat more.
Fructose – aka ‘fruit sugar’ – failed to reduce blood flow and activity in areas of the brain that regulate appetite in the same way as glucose, according to data published in the January 2 issue of JAMA. And that’s a bad thing. After drinking a sweetened beverage, those whose drink contained glucose reported feelings of ‘satiety and fullness,’ but those whose beverage was made with fructose did not.
According to Ask Men, ”the fructose vs. glucose debate first made headlines in 2009,” when University of California Davis researchers found study participants given 25% of their daily calories as either a fructose or glucose drink both gained weight.
But it was the fructose group that gained a significant amount of unhealthy, visceral abdominal fat (the kind that sets the stage for heart disease). The fructose group also had increased fasting blood sugar, cholesterol levels and insulin resistance, while the glucose group did not.”
The authors speculated that this difference is because of the way that the sugars are metabolized. Put simply, when the liver metabolizes glucose, there are feedback mechanisms in place that stop the liver from absorbing too much. On the other hand, those same mechanisms do not exist for fructose, so when the liver takes up and metabolizes too much fructose, it leads to the increased fat production, blood sugar and insulin resistance seen in the study.
In other animal studies, “fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion,” and rats given fructose want to eat more (“fructose possibly increases food-seeking behavior,” researchers note). But it’s been unclear whether the same would be true in humans.
So does this Yale study count as another strike against high-fructose corn syrup? Not especially. Most added sweeteners — from high-fructose corn syrup to table sugar (sucrose), honey and stevia — contain a ratio of glucose to fructose between 50/50 and 45:55.
High fructose corn syrup = 55% fructose, 45% glucose
Table sugar = 50% fructose, 50% glucose
Agave nectar = up to 92% fructose
Agave nectar, on the other hand, is mostly fructose — some brands have 92% fructose. That’s not to say that agave nectar is less healthy than high-fructose corn syrup overall (HFCS has been linked to other nasty health effects), but it is more likely to stimulate your appetite.
According to Web MD, “one of the most celebrated properties of agave” is its low glycemic index profile. But there’s “inconsistent evidence” that glycemic value matters. The American Diabetes Association lists agave nectar along with table sugar, honey, brown sugar, molasses, fructose, maple sugar and confectioner’s sugar in substances that should be limited in diabetic diets.
For more on agave nectar, corn syrup and fructose, see this piece from the Weston A. Price Foundation.