Hunger, Blood Glucose, and the Glycemic Index

We don't exactly know how the feeling of hunger is caused in the body. One theory, first formulated in the 1950's, is that low levels of glucose in the brain are a cause of the feeling of hunger and the increase in appetite that goes along with it. More recent theories expand on that theory by speculating that it's the changes in blood glucose levels that lead to the feeling of hunger. Even more recently, studies have indicated that the sharp fall in blood glucose levels, caused by drinking a high-glycemic beverage, made the test subjects involved choose to eat again sooner than if they had drunk a low-glycemic beverage, which makes blood glucose levels fall more gradually.

A study published recently in the journal Appetite (2008;50:215-222) looked at their subjects' feelings of satiety as well as their feelings of hunger after high-GI and low-GI meals. The fourteen subjects for this study were overweight and obese women between the ages of 25 and 60 who did not smoke and were otherwise healthy.

Because each person's blood glucose levels will react a little differently to various foods, the scientists sought to standardize each subjects' post-meal blood glucose levels in one of two ways: to imitate a high-GI meal, each woman was given a large glucose beverage to drink all at once after a standardized breakfast and lunch. To imitate a low-GI meal, each woman was given the same amount of glucose beverage after the standardized breakfast and lunch, but they drank equal, small portions of it every 20 minutes. Note that each woman received the same amount of the glucose beverage - the only difference was how long it took to drink it.

Each woman had their blood drawn every hour after each meal in order to test their blood glucose levels, and every 20 minutes they were asked to describe how hungry they felt and how much they felt they could eat if they were to eat. The researchers found that drinking the single, large glucose beverage - the high-GI meal - led to greater feelings of hunger than the smaller, more frequent glucose beverages (the low-GI meal).

What this means for you

While I am not all that convinced that the Glycemic Index is the perfect way to look at foods, as some suggest, it is a good tool to consider whether an ingredient might be better from the standpoint of being higher in fiber and better for you. What I do find interesting is that the subjects ate the same number of calories over the course of their standardized meals plus their glucose beverages - the only difference is that those calories were consumed all at once or spaced out over time. This would support the idea that healthy snacks between meals might be a good way to help you manage your appetite so that you don't arrive starving at every meal and eat more than you really need.