Comparing the Insulin and Glycemic Indexes

The food insulin index is a valuable supplement to the glycemic index and glycemic load. But nobody knows yet whether it will replace the glycemic index and glycemic load.

Some foods have little effect on our blood glucose levels but a big effect on the amount of insulin in our blood. This could be good, because the rise in insulin can bring down our blood glucose levels. But maybe not, because it could lead to beta-cell burnout.

Years ago I reviewed the first article about the insulin index on my website. At that time only 16 peer-reviewed articles in MEDLINE even mention the term “insulin index.” By comparison, 244 peer-reviewed articles mention the glycemic index. Now, MEDLINE says that 71 articles mention the “insulin index” and 1,372 the “glycemic index.”

But scientists have published only two peer-reviewed papers on the insulin index. The first one, which my earlier article summarized, came out in 1997. This month the second paper appeared. Both are the work of Dr. Jennie Brand-Miller of the University of Sydney and her team. At the same time, Dr. Brand-Miller is the world’s leading researcher on the glycemic index. (Full disclosure: She was the lead author of The New Glucose Revolution: What Makes My Blood Glucose Go Up…and Down?, which I co-authored.)
Only the abstract of the new insulin index study is free online. But Dr. Brand-Miller sent a PDF of the full-text to a correspondent, who thoughtfully sent it on to me.

“We are still trying to prove (one way or the other) that an insulin index is superior to the glycemic index or glycemic load,” Dr. Brand-Miller wrote my correspondent. “It may not be. We have just published a second paper on the subject. There is nothing else published as far as I’m aware.”

Generally, glycemic and insulin index values are close — when we can measure them. However, the methodology of glycemic index testing doesn’t let us measure the GI of foods that have little or no carbohydrate. Consequently, it can’t give us a guide to the insulin response of a large majority of the foods that we eat, including high-protein foods such as meat, fish, poultry, eggs, and cheese.

Foods high in carbohydrate are the main stimulus for insulin secretion. But protein-rich foods also elicit a significant insulin response. On the other hand, adding fat to a carbohydrate-rich meal limits how high our blood glucose level goes, while not affecting the insulin response.

The new study included only 21 subjects and 13 different meals. The subjects were all lean and young. These are significant limitations, and as usual the study concludes that, “Further research is needed.”

But it may drive the last nail in the coffin of carbohydrate counting, which medical professionals commonly recommend for matching insulin dosage to insulin demand for people who take insulin injections. This is because, as the study says, “Mixed meals with similar carbohydrate content produced widely disparate insulin responses.”

Those meals with the highest protein and carbohydrate content — and therefore the lowest fat content — produced the highest insulin responses. The fat content of the mixed meals used in the study showed a significant inverse relation with the insulin responses and “was a more reliable predictor of insulin demand than the amount of carbohydrate.”

I was an early supporter of the glycemic index. In 1996 I wrote the first American article for people with diabetes about it. Subsequently, I introduced Dr. Brand-Miller to Matthew Lore, who went on to publish more than one million copies of her books on the glycemic index.

Following the glycemic index for years helped me control my blood glucose level, but did very little to help me control my weight. Subsequently, Byetta helped me control my blood glucose level somewhat better and helped me control my weight much better. Eventually, however, I decided to manage my diabetes without any drugs. The only way that I know how to do that is to eat a very low-carb diet, which is necessarily high in fat. Our bodies can use only carbohydrates or fat for the energy we need.

Now I am considering the insulin index more in making my food choices. While our bodies need some protein, we can see from the results of this index that a lot of it will stimulate a lot of insulin production, which may well be something we don’t need.

This article is based on an earlier version of my article published by HealthCentral.