Friday, January 11, 2008

Two hunger-fighting tools: Glycemic Index and Satiety Index

We know there's no miracle munchie, but if you had to choose just one food for snacking, based on how long it would keep you from getting hungry again, what would you choose to eat?

Maybe a better question is how would you choose? Diners and dieters familiar with the index could run through the numbers they know from that nifty scale and come up with a pretty good response for the question, but others may be more stymied.

There's actually another measurement tool might help us identify the best hunger-fighter foods of all. It's called the "Satiety Index," meaning that it's a gauge of how well a food keeps you feeling satisfied and keeps hunger sensations at bay. It's similar to the glycemic index, and it's a pretty nifty tool in its own right.

All the scores can seem a little daunting at first, but after a while, you just learn which foods you want to eat in order to achieve your particular result. And you don't have to memorize any of this anyway. You can get handy little resource materials like wallet card references for either index, so you might as well arm yourself with the best information from both ideas to help you pick the best foods for your own defensive diet.

Reviewing the Glycemic Index

The GI Index is a ranking of foods based on their immediate effect on blood sugar levels. It measures how much your blood sugar increases over a period of two or three hours after a meal.

Glucose, a simple, very quickly digested sugar, is used as the "index," or the standard against which other foods are measured. It's assigned a value of 100. Highly processed carbohydrate foods that break down quickly during digestion end up with the highest rankings. High-protein foods and high-fiber complex carbohydrates tend to rank low. And generally speaking, when it comes to identifying healthy, hunger-abating foods, low GI is good.

The index has been around for years, and it supports arguments in favor of low-fat, high carbohydrate diets for weight loss, as well as prevention of cardiovascular disease and diabetes. In fact, diabetics are often urged to memorize the index with the same diligence they used in going after the multiplication tables in fourth grade. That's because foods that take longer to digest (low GI scores) produce less dramatic spikes and drops in blood sugar and insulin production.

While those fluctuations can actually be dangerous for diabetics, for nearly any dieter, they are at least a misery, causing urgent, even painful hunger sensations to race off to the brain. So the glycemic index has also been used as a good measure of the "stick-to-your-ribs-ness" of foods. People who want to lose weight choose foods with the lowest glycemic index.

Meet the Satiety Index

Of course, for dieting in general, the limitation of the glycemic index is that it mostly includes carbohydrate foods, those most likely to have a significant effect on blood sugar. And that's not all most of us eat.

So a few years ago, Susanna Holt, PhD, of the University of Sydney wanted a system specifically to measure different foods' ability to produce satiety and fend off hunger; in other words, an even better indicator of their "stick-to-your-ribs-ness," and one that would include other sorts of foods.

In Holt's Satiety Index, a slice of white bread is the index, and it's also assigned a value of 100. The satiety value of other foods is rated relative to the bread, with foods offering longer-lasting hunger abatement scoring higher. That means on this scale, people trying to lose weight would choose foods with the highest numbers.

In developing the satiety index, Holt's test subjects were college students, not famous for their wise diet choices. The students were invited for 'breakfast' which consisted of 240 calories worth of various specific foods, anything from jelly beans to bacon.

After eating, the students were asked to rank their feelings of hunger every 15 minutes for the next two hours, during which they could continue to eat more of that particular food, but nothing else. Holt's various tests yielded the scores used in the Satiety Index.

Here are a few samples from each scale, for comparison. There's no Satiety Index score for the plain sugar, because, well, who wants to eat plain sugar? Yuck.


glucose (sugar) 100

white bread 70 100

croissant 67 47

whole wheat bread 68 154

potatoes(boiled or baked) 59 323

french fries 72 116

chocolate bar 49 70

lentils 30 133

Now, looking at the differences between the two scales, you might start to suspect that there is more to satiety than the effect a food has on your blood sugar. Indeed, protein and fat both have minimal effects on blood sugar.

And here is where Dr. Holt's studies produced some real surprises. She and her hungry student volunteers demonstrated that foods high in fat made people want to eat more, even though we usually think of rich, high-fat foods as filling. This explains the apparent contradiction between potatoes, the runaway winner on the Satiety Index, and french fries, which scored poorly on both scales. It's not the spud that's to blame, it's all that fat!

Dr. Holt speculated that because the body responds to fat as something to be stored for a 'rainy day,' a period of scarcity, rather than something to be used immediately, the gut doesn't stop sending hunger signals as soon, so we go on wanting to eat more.

But let's don't forget the function of sheer mass. A 240-calorie serving of boiled potatoes is just a lot more food than a 240-calorie serving of greasy French fries. As a rule, it's going to take longer to digest and therefore, it will hold off the next round of hunger signals for a longer time.

But why would whole wheat bread be 54 percent more satisfying than the same number of calories in white bread? It's not any bigger a slice, is it? It may or may not be, but what's at play here is the fact of processing. As foods become more refined, the seed coats and other fiber components that are removed are the very ones that slow the passage of food through the digestive tract, resulting in prolonged "I'm not hungry" messages to the brain.

The Satiety Index really only measures short-term satiety, because the experiments ran for just two hours. Fruit was very satisfying initially, because 240 calories worth of fruit is a rather large portion, that matter of mass again. But because fruit is really mostly water and sugar and a little fiber, it leaves the gut rapidly, so hunger returned at the end of the second hour for the fruit eaters.

On the other hand, participants who had eaten whole grain bread or lean protein kept their nibbling impulses at bay for much longer as their bodies continued to work on what they were still processing.

Taken together, the best scoring items on these two indexing tools offer a variety of really good choices for healthy, low-calorie foods to incorporate into your daily diet. And if you can only pick one for snack time, go for something with some staying power.

This article provided by Bistro M.D.

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