Insulin index

One problem with David Mendosa’s article about the insulin index, which I referenced yesterday, is that the insulin index table he gives doesn’t tell you very much about the foods contained in it. For example, as a correspondent pointed out to me, is the “beef” listed there ground beef with 25 percent fat? or is it a nice, lean sirloin tip steak with only 3 percent fat?

Luckily, I was able to find the original study that Mendosa was writing about: “An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods” by SH Holt, JC Miller and P Petocz, American Journal of Clinical Nutrition, Vol 66, 1264-1276 (1997).

The full article is much more specific than Mendosa’s “popularization” of it on the foods used & exactly how they were prepared. For example, what Mendosa listed simply as beef is revealed in the full study to be:

Food: Beef steak

Variety, manufacturer, or place of purchase: Lean topside beef fillets bought in bulk from supermarket, trimmed and stored frozen

Preparation: Grilled the day before serving, cut into standard bite-sized pieces, and stored at 4° C overnight; reheated in microwave oven for 2 mm immediately before serving [Table 1, page 1265]

The nutritional composition of the beef, according to Table 2 (page 1267), was 7.7 grams of fat & 42.0 grams of protein (0.0 carb), in a 158 gram serving. (All the foods were tested in 1000-kilojoule servings.) The white fish used in the study (ling fish fillets) was even leaner: 1.0 grams of fat & 56.3 grams of protein (0.0 carb). The other protein-rich foods chosen (cheese, eggs, lentils, baked beans) all had more fat & at least some carb (esp. the lentils & beans).

That kind of detail is given for all the foods tested in the study, & the article gives a very full methodology of how the study was conducted, who the test subjects were, etc. Their analysis included comparing the insulin score with the glucose score that they also calculated based on the test subjects’ blood glucose. (Not the same as glycemic index, but also measuring the test subjects’ glycemic response to the test foods).

Things I found most significant:

Overall, glucose and insulin scores were highly correlated…. However, protein-rich foods and bakery products (rich in fat and refined carbohydrate) elicited insulin responses that were disproportionately higher than their glycemic responses. [from the abstract]

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[C]arbohydrate is not the only stimulus for insulin secretion. Protein-rich foods or the addition of protein to a carbohydrate-rich meal can stimulate a modest rise in insulin secretion without increasing blood glucose concentrations, particularly in subjects with diabetes (20-22). Similarly, adding a large amount of fat to a carbohydrate-rich meal increases insulin secretion even though plasma glucose responses are reduced (23, 24). [page 1266]

The numbers in parentheses are references to other scientific studies — i.e., these facts weren’t newly discovered in this study, but were already known. The second fact, about adding fat to a carb-rich meal, is pretty relevant to that well-known phenomenon of the glycemic index where sugar-rich junk food ends up having a low GI because it’s also got a lot of fat in it. The fat makes the GI low, but it doesn’t lower the insulin response.

The high-protein foods except the baked beans (which had a lot of carbohydrate) all had among the lower insulin scores of the foods tested, most of which in other categories had a lot of carbs in them. But just like the abstract says, the insulin response to the high protein foods was a lot higher than you’d think if you think that insulin is only provoked by carbs or fat. This is especially apparent with the lean beef & the white fish.

Yes: protein provokes insulin response even without sugar or starch or significant fat being present, and “fish, beef, cheese, and eggs still had larger insulin responses per gram than did many of the foods consisting predominantly of carbohydrate” (page 1275).

The important Western staples, bread and potato, were among the most insulinogenic [provoking insulin excretion] foods. Similarly, the highly refined bakery products and snack foods induced substantially more insulin secretion per kilojoule or per gram of food than did the other test foods. In contrast, pasta, oatmeal porridge, and All-Bran cereal produced relatively low insulin responses, despite their high carbohydrate contents. [page 1273]

No big surprise about the bread & potato. Very interesting about the pasta, oatmeal, & All-Bran, especially since I eat steel-cut oats almost every day for breakfast.

However, some protein and fat-rich foods (eggs, beef, fish, lentils, cheese, cake, and doughnuts) induced as much insulin secretion as did some carbohydrate-rich foods (eg, beef was equal to brown rice and fish was equal to grain bread). [pages 1273-1274]

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Overall, the fiber content did not predict the magnitude of the insulin response. Similar ISs were observed for white and brown pasta, white and brown rice, and white and whole-meal bread. All of these foods are relatively refined compared with their traditional counterparts. Collectively, the findings imply that typical Western diets are likely to be significantly more insulinogenic than more traditional diets based on less refined foods. [page 1274]

In other words, the more refined the diet, the more insulin you’re probably going to have in your blood after eating. (And the more fat you’re likely to store from any excess carbs you’re eating.)

As observed in previous studies, consumption of protein or fat with carbohydrate in creases insulin secretion compared with the insulinogenic effect of these nutrients alone (22, 30-32). This may partly explain the markedly high insulin response to baked beans. Dried hancot beans, which are soaked and boiled, are likely to have a lower IS than commercial baked beans, which are more readily digestible. [page 1275]

Another call for less refined foods. Again, the numbers in parentheses refer to prior scientific studies.

The results confirm that increased insulin secretion does not account for the low glycemic responses produced by low-GI foods such as pasta, porridge, and All-Bran cereal (33). Furthermore, equal-carbohydrate servings of foods do not necessarily stimulate insulin secretion to the same extent. For example, isoenergetic servings of pasta and potatoes both contained ~50g carbohydrate, yet the IS for potatoes was three times greater than that for pasta. [page 1275]

So if you must have pasta, it’s at least a better choice re: insulin secretion than potatoes.

Similarly, porridge and yogurt, and whole-grain bread and baked beans, produced disparate ISs [insulin scores] despite their similar carbohydrate contents. These findings, like others, challenge the scientific basis of carbohydrate exchange tables, which assume that portions of different foods containing 10-15g carbohydrate will have equal physiologic effects and will require equal amounts of exogenous insulin to be metabolized. [page 1275]

So much for carbohydrate exchange tables. So much for the ADA & American Association of Diabetes Educators truisms (falsisms) that “the quality of carbohydrate isn’t important, the quantity does,” which is what my friend Sylvia was told when she was diagnosed with diabetes.

In the end, I think Berardi is right: if you eat, you can’t avoid insulin secretion — & that’s actually that’s a good thing, since insulin is, it turns out, an anabolic hormone for muscle (as well as for fat). But as an insulin resistant person, I can’t have too much or I continue to get less healthy, not to mention gaining more fat.

So I’ve got to keep working to become more insulin sensitive, so that not so much insulin has to be secreted in order to take care of the metabolic functions I need it for.

I think I’ve already done quite a bit in that direction. I think the programs I’ve decided to take up — Turbulence Training & Precision Nutrition — will help me even further along my health road.