This article represents part 3 of a series on
how insulin has been unfairly demonized by many in the nutrition
field. If you have yet to read the first few parts, you can
read Part 1 here, and you can
read Part 2 here.
In this article, I will discuss how dairy products are among the most
insulinemic foods out there, yet do not promote fat or weight gain,
which pokes holes in the hypothesis that carbohydrates drive fat
accumulation through insulin secretion.
One of the premises of individuals like Gary Taubes is that
carbohydrates stimulate fat accumulation by stimulating insulin
secretion. I’ve already shown how this premise is flawed in the last
two parts of my series. Namely,
I
showed how protein also stimulates insulin secretion (sometimes as much
as carbohydrate) yet does not promote weight or fat gain. I also showed how
the drug exenatide restores rapid-phase insulin secretion in diabetics yet promotes weight loss.
If the carbohydrate/insulin hypothesis were true, then we would
predict that foods that are extremely insulinemic would be uniquely fat
promoting. What many people do not realize is that dairy foods are
among the most insulinemic foods out there. In fact, they create much
greater insulinemic responses than you would expect based on their
carbohydrate content. Not only that, but lactose, the primary
carbohydrate in dairy foods, is actually low glycemic and produces slow
rises in blood sugar (
lactose has a glycemic index of 46 compared to white bread which is 100). In fact,
the
glycemic index of many dairy products is quite low, with full-fat milk
at 39, skim milk at 37, ice cream at 51, and fruit yogurt at 41.
Despite the low blood sugar responses, dairy products create very large insulin responses. For example,
in one study,
dairy products created similar or greater insulin responses than white
bread, despite the fact that the blood sugar response for some of the
dairy products was 60% lower than the white bread. In this study, the
researchers compared the glycemic and insulinemic responses between
white bread, a low gluten/lactose mixture, a high gluten/lactose
mixture, cod with added lactose, milk, whey protein with added lactose,
and cheese with added lactose. All of the conditions contained 25 grams
of carbohydrate and 18.2 grams of protein, except for the white bread
and low gluten/lactose mixtures, which contained 25 grams of
carbohydrate and 2.8 grams of protein. Thus, lactose was the
carbohydrate in all of the conditions except for white bread.
When you look at the insulin area-under-the-curve (AUC) for the
various conditions, you can see that the dairy products actually created
greater insulin responses than the white bread, despite having similar
amounts of carbohydrate:
Insulin response of dairy foods compared to white bread
It is obvious that it is not the lactose that is responsible for the
greater insulin response, because the gluten/lactose and cod/lactose
mixtures resulted in similar or lower insulin responses to white bread.
The blood sugar response was also not responsible for the greater
insulin response. In fact, the blood sugar response was lower in all of
the conditions compared to the white bread, with the milk creating the
lowest blood sugar response yet 3rd highest insulin response:
Blood glucose response to dairy foods compared to white bread
The insulinogenic index, which relates the amount of insulin
secretion to the blood glucose response, was significantly higher in the
dairy products, indicating that the dairy products stimulated much
greater insulin secretion that you would expect based on the blood
glucose response:
Insulinogenic index of dairy products compared to white bread
This is not the only study to show the insulinemic effects of dairy products. I showed in
my previous article how whey protein, a dairy protein, created the highest insulin response compared to non-dairy proteins.
In a study on type 2 diabetics,
the inclusion of whey protein in a meal increased the insulin response
by 31-57%, while the blood glucose response was reduced by up to 21%.
In another study,
the addition of 400 mL of milk to a bread meal increased the insulin
response by 65%, despite the fact there was no change in the blood
glucose response. In this same study, the addition of 200 or 400 mL of
milk to a spaghetti meal increased the insulin response by 300%; again,
there was no change in the blood glucose response. In fact, drinking
milk with the spaghetti meal created an insulin response that was
similar to white bread.
Here’s the results of
another study showing the glycemic and insulinemic indexes of milk compared to white bread:
Why Does Dairy Stimulate So Much Damn Insulin?
It is clear that dairy products stimulate large amounts of insulin
secretion, as much or more than white bread. One of the reasons dairy
products create large insulin responses is due to their amino acid
content. In fact,
the
postprandial insulin response from dairy products correlates with the
rise in branched chain amino acids leucine, valine, and isoleucine. I already pointed out in
part 1 of this series how leucine will directly stimulate your pancreas to produce insulin.
Another reason that dairy products stimulate so much insulin
secretion is their effects on a hormone called glucose-dependent
insulinotropic polypeptide (GIP). Like GLP-1 which I wrote about in
part 2 of this series, GIP is an
incretin.
This means that it is a hormone produced by your intestines that
stimulates insulin secretion. Dairy products stimulate increased
production of GIP.
In the study I discussed earlier
which compared whey, milk, and cheese to white bread, whey and cheese
resulted in 21-67% greater GIP responses than white bread:
Glucose-dependent insulinotropic polypeptide (GIP) response to dairy foods compared to white bread
The above data illustrates one of the problems with the
carbohydrate/insulin hypothesis…it assumes that carbohydrate is the
primary stimulus of insulin secretion. However, it is clear that amino
acids and incretins play significant roles in insulin secretion as
well. And as I pointed out in
part 1 of this series,
the blood sugar response of a food only explains 23% of the variation
in the insulin response. Thus, a lot more goes into insulin secretion
than the blood sugar response from eating carbohydrate.
Dairy and Weight Gain/Loss
It is clear that dairy products are extremely insulinemic, moreso
than many high carbohydrate foods. Thus, if the carbohydrate/insulin
hypothesis were true, then we would predict that a diet high in dairy
products should promote weight and fat gain. However, studies fail to
show any relationship between dairy product intake and weight gain. For
example,
there is no relationship between intake of dairy products and BMI in Japanese women. In U.S. men,
there is no relationship between an increase in dairy consumption and long-term weight gain. In perimenopausal women,
high
intakes of dairy products are actually inversely associated with weight
gain (i.e, higher dairy product intakes are associated with less weight
gain).
While these are observational studies, the results from controlled
studies on animals and humans are similar. In fact, animal studies show
less weight gain when they are fed dairy products. In mice,
yogurt supplementation results in less weight and fat gain than controls on isocaloric diets. In
another study, transgenic mice lost weight on energy restricted diets. The mice were then allowed to eat
ad libitum (i.e., as much as they felt like). The mice fed dairy products regained less fat and weight during refeeding.
In a third study, the intake of dairy products, but not a calcium supplement, decreased weight gain and body fat in mice fed a high-fat diet.
In a fourth study, dairy protein attenuated fat gain in rodents fed a high-fat, high-sugar diet.
In a fifth study, a dairy diet attenuated weekly weight gain in Sprague-Dawley rats.
Of course, these are animal studies. What about humans?
In one study,
low-fat dairy products did not promote weight gain, while high-fat
dairy products did. Hmmm, could it be that the weight gain in this
study was simply caused by excess calories and not insulin?
In another study, increased intake of dairy products did not affect body composition.
In a third study, increased intake of dairy products did not impair weight loss.
In a one-year study, increased intake of dairy products did not affect changes in fat mass.
In a 6-month follow-up to this study, high dairy product intake predicted lower levels of fat mass.
In a 9-month study,
increased intake of dairy products did not affect weight maintenance,
but the high dairy group exhibited evidence of greater fat oxidation.
Why Am I Not Fat?
My own personal experience with dairy fits right in with the
science. I consume a lot of dairy and have for many years. I go
through 2-3 gallons of milk per week. I also go through a lot of Greek
yogurt, cottage cheese, regular cheese, and whey protein. I have some
type of dairy with just about every meal. Thus, I have large amounts
of insulin flowing through my body pretty much all day. If insulin was
truly the fat-promoting, weight-gaining hormone that some have made it
out to be, then I should be obese by now. Yet, I am not…not even close.
Not only that, but the people who think insulin makes you hungry,
that would imply that I should be starving all of the time with all of
the insulin that is flowing through my body all day. Yet, I’m not.
Got Milk? Got Insulin!
The evidence is overwhelming that dairy products do not promote
weight gain, and they actually inhibit weight gain in animal studies.
This is despite the fact that dairy products produce very large insulin
responses, as much or greater than many high carbohydrate foods. Thus,
it is clear from this article, as well as my previous articles, that the
carbohydrate/insulin hypothesis is incorrect. Insulin is not the
criminal in the obesity epidemic; instead, it is an innocent bystander
that has been wrongly accused through guilt by association.
