Insulin levels had always been assumed to go up or down with the blood glucose levels which led to the glycemic index which had always been assumed to be a surrogate measure of insulin levels. The glycemic index did not turn out to be as successful in weight control because glucose does not drive obesity. Insulin drives obesity. With the insulin index, it was realized that only 23% of the variability of insulin response depends on the glucose. In other words, how much the glucose increases only accounts for 23% of the insulin response. Even taking into account the other macronutrients fat and protein, this only accounted for another 10% of the insulin response. The vast majority of the insulin response is still unknown. Some of the factors that are suspected or shown to affect the insulin secretion include presence of dietary fibre, an elevated amylose/amylopectin ratio of the starch, preserved botanical integrity (whole foods), presence of organic acids (fermentation), addition of vinegar (acetic acid), and addition of chili peppers (capsaicin). We will explore some of these factors in future posts. Nevertheless, the main point here is that there are many factors in the co-ingestion of foods that affect insulin. Things are about to become very complicated.
The simplistic “Carbs make you fat!”, or “Calories make you fat!” or “Red meat makes you fat!” or “Sugar makes you fat!” sort of arguments simply are not able to capture the complexity of the human condition of weight gain. Among breakfast cereals, there is wide variation in the insulin response. All-Bran, with its high fibre and promise of colonic regularity, seems be stimulate insulin much less than cornflakes for instance.
Protein containing foods turn out to be surprisingly potent at stimulating insulin. Beef and fish, for instance, have virtually no effect on the blood glucose levels. Yet they stimulate insulin almost as much as most cereals. Nevertheless, we are able to discern some general patterns here. If we look at carbohydrates, there is a noticeable trend here. As the total grams of carbs goes up, the insulin level also tends to go up. This is what we expect. This is the basis of many low carbohydrate diets from the original Banting diet of the 1850s to the modern day Atkins diet and its many imitators. It has been recognized for well over a century that the amount of carbohydrates consumed plays a role in the development of obesity. However, this study indicates that the correlation is far from perfect.
The correlation between carbohydrate content and insulin is relatively low (23%). Dietary fat, on the other hand tends to have a lowering effect on insulin scores. As the amount of fat increases, the insulin score tends to decrease. Fat also tends to have minimal effect on blood glucose, so this is pretty much as we expected as well. Carbohydrates tend to raise glucose and insulin. Dietary fat tends not to raise glucose and tends not to raise insulin as well. So far, so good.
The surprise here is dietary protein. Looking at the protein, there seems to be a slight trend here as drawn by the line. As protein goes up, the insulin score tends to go down. But you can see that this relationship is mostly driven by 2 main outliers at the extremely high protein intake levels (40 and 60 grams). If we remove these outliers, then it seems that there really is not much relationship between the amount of protein and the rise in insulin. Some proteins raise insulin a lot and some proteins raise it only a little. Dairy protein especially whey, seems to be the biggest culprit here. The implication is that some protein containing foods can lead to obesity while other protein containing foods are not likely to do so. Here the data become extremely murkily and there are numerous inconsistencies in the literature.
In the study “The acute effects of four protein meals on insulin, glucose, appetite and energy intake in lean men” published in the British Journal of Nutrition in 2010, insulin levels were measure in 30 men after a test meal. Four different proteins were tested – eggs, turkey, fish and whey protein. Whey protein is one of the proteins found in dairy. Cow’s milk protein is composed of 80% caseins and only 20% whey. Casein is mostly responsible for milk allergies. Whey is well known as the byproduct left over in cheese making. Milk is separated into curds and whey. Whey protein is often used by bodybuilders as it is high in Branched Chain Amino Acids (BCAA) that are felt to be important in muscle formation. Compared to the other proteins, whey resulted in the highest insulin levels. This is despite the fact that none of the proteins had a very large effect on blood glucose. In this study, after the test meal, participants were given a buffet lunch 4 hours afterwards so that effects of protein on satiety could be measured. The whey protein suppressed appetite to the largest degree. It is certainly possible that whey protein may have two different effects on weight gain. The increase in insulin may promote weight gain, but the decrease in appetite may suppress it. Again, I will stress that I do not have all the answers here. The field of study is new and ever evolving at this point. The propensity for dairy to cause insulin to increase was confirmed in the paper “Glycemia and insulinemia in healthy subjects after lactose equivalent meals of milk and other food proteins” published in 2004 in the AJCN. Here the effects of milk and particularly whey are seen clearly. In fact, the increase in insulin far exceeded even that of whole wheat bread. The effect on glucose is negligible but the incretin effects of the stomach (release of Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1)) are felt to be responsible for the increase in insulin. We discussed the incretin effect in a previous post. The insulin stimulating effect of whey may also be seen when taken with foods. A recent study in Israel gave whey protein to type 2 diabetics after a breakfast of white bread and jelly – a breakfast designed to increase sugars significantly. Whey protein supplementation reduced blood sugar levels by 28%. The incretin hormones total and intact GLP-1 increased 141% and 298% suggesting that the increased insulin is largely the incretin effect. Here’s the problem, though. Blood glucose does not drive weight gain and diabetes. Increased insulin does. What happens to that blood sugar? It is not removed from the body? It is merely shuttled to the liver where it is turned into fat. So, in effect we have removed sugar from the blood where we can see it, and put it in the liver, where we cannot. Is that good? Hardly The high insulin secretion may lead to the development of insulin resistance. This can explain the findings of this paper “High intakes of milk, but not meat, increase s-insulin and insulin resistance in 8-year-old boys” published in the European Journal of Clinical Nutrition in 2005.Here they studied eight year old children. Given a test meal of meat or dairy, the insulin levels were measured. Not surprisingly, the insulin response was higher to the milk. After seven days of milk versus meat, the milk group started to develop insulin resistance. This is, of course, the first step towards the development of type 2 diabetes and a key player in the time dependent effects of obesity. The fact that this develops after only 7 days of milk overfeeding is downright scary. This data would seem to indicate that dairy consumption may lead to weight gain. Is this actually true? The truth, as usual, is far more nuanced.
Continue here for Hormonal Obesity XXIV – Is Dairy Fattening?
Start here with Calories Part I – How Do We Gain Weight?
See the entire lecture – The Aetiology of Obesity 3/6 – Trial by Diet