For normal-weight women, eating meals sweetened with fructose instead of glucose might make their bodies send weaker 'fullness' signals to the brain, because a key hormone called leptin drops by a third in the first 12 hours after eating.

What we've found so far suggests that replacing glucose with fructose in meals may reduce the daily variation of leptin in normal-weight women. The evidence we've reviewed leans toward this idea, based on two supporting assertions and no studies refuting it. Our analysis of the available research shows that when normal-weight women consume fructose instead of glucose, leptin—the hormone involved in signaling fullness—appears to change in its daily pattern. One observation we’ve noted is that leptin levels drop by about a third within the first 12 hours after eating fructose-sweetened meals [1]. This could mean the body sends weaker satiety signals compared to when glucose is consumed. Additionally, what we’ve seen in the data is that the overall daily fluctuation in leptin levels is reduced by roughly a quarter when fructose is used instead of glucose [2]. This blunting of the hormone’s natural rhythm might affect how hunger and fullness are regulated over the course of the day. We want to be clear: our current analysis is based on a limited number of assertions—just two—and while both support the idea that fructose alters leptin variation, we don’t yet have enough evidence to say how strong or consistent this effect is across different people or eating patterns. Also, we don’t know what long-term impact, if any, this change in leptin rhythm might have on appetite or body weight. The takeaway: swapping fructose for glucose may dampen the daily ups and downs of leptin in normal-weight women, which could influence how hunger is managed throughout the day. But based on what we’ve reviewed so far, we can’t say for sure how meaningful this change is in real-life eating habits.