Dairy proteins stimulate high levels on insulin due partially to the incretin effect. Glucose, though does not seem to increase much. If insulin increases, does this mean that dairy is fattening? Here the answer is far more difficult.
As we saw in our previous posts, protein containing foods may stimulate insulin partially due to the incretin effect. These are hormones secreted in the stomach that help with digestion and stimulate insulin. They are released in response to ingestion of all three macronutrients – fats, proteins and glucose. The implication is that all foods can stimulate insulin release, not just carbohydrates. Dietary fats have the lowest effect on insulin secretion.
By contrast, only carbohydrates have a significant effect on glucose. For starchy foods, there is a very good correlation between the glycemic index and the insulin index. However, in the specific case of milk (dairy) products, there is a large discrepancy. Most dairy foods have very low GI score (15-30) but very high Insulin Index scores (90-98).
At first glance, this may appear to implicate dairy protein as a major contributor to diabesity. Here there is some evidence to suggest that this is true. A recent, very large European observational study published “Dietary Intake of Total, Animal, and Vegetable Protein and Risk of Type 2 Diabetes in the Euorpean Prospective Investigation into Cancer and Nutrition (EPIC)-NL Study“.
There were 38,094 participants in the EPIC study, followed over 10 years prospectively. Increasing total protein and animal protein consumption is associated with a modest but significant increase in the risk of developing type 2 diabetes.
Another dietary recommendation often given is the advice to eat more fish. With its high omega 3 fat content, it certainly seems like good advice. Omega 3 fats are known to alter the expression of peroxisome proliferator–activator receptor genes. Thus they might be expected to have the beneficial effect of reducing type 2 Diabetes.
Researchers from Harvard looked at the data from 3 large prospective cohorts (Nurse’s Health Study 1 and 2, and the Health Professionals Follow Up). This included 195 204 subjects followed over 14-18 years. The paper “Long Chain Omega 3 fatty acids, fish intake, and the risk of type 2 diabetes mellitus” was publshed in 2009 in the AJCN.
To their surpise, there was no benefit from eating more fish. In fact, the opposite seemed to be true. There was a modest but significant increase in diabetes with increased fish intake. The highest intakes of fish had a 24% increase risk of developing type 2 Diabetes.
Looking at these data, it appears that high protein intake, particularly animal proteins may be detrimental perhaps in part due to the increased insulin. Could we all go vegan? The data here is anything but clear. With regards to dairy, other large observational studies seem to indicate that, increased dairy consumption leads to less weight gain.
This relationship was explored in the paper “Association between dairy food consumption and weight change over 9 y in 19 352 perimenopausal women” published in AJCN in 2006. The Swedish Mammography Cohort was a community based observational study that used dietary recall questionnaires to estimate dairy product intake and compared that to weight changes. The effect was relatively modest, but there was no increase in weight gain with increased dairy products. Looking at the different milk products, the consumption of whole milk, sour milk, cheese and butter seemed to be associated with less weight gain. Drinking less low fat milk, on the other hand, resulted in less weight gain.
In the United States, the CARDIA study sampled 3157 young adults in 4 metropolitan areas and measured markers of the metabolic syndrome including obesity over a follow up period of 10 years. The group with the highest intake of dairy seems to have the lowest incidence of obesity.
This study also confirmed these results for the rest of the metabolic syndrome. Higher intakes of dairy were protective, not detrimental. A study in Tehran, published in the AJCN similarly showed that higher consumption of dairy was correlated to a lower risk of the metabolic syndrome.
What about type 2 Diabetes? The Health Professionals Study Follow Up Study prospectively examined the relation between type 2 diabetes and dairy intake. 41 254 people took part in this large study and over 12 years of follow up, dairy intake was associated with a modestly lower incidence of type 2 diabetes after adjustment for age and BMI.
The CARDIA study further investigated the independent effect of fibre on the metabolic syndrome. The reference level of 1.0 is chosen for the group with both high dairy and high fibre. Taking high dairy but low fibre almost tripled the risk of Insulin Resistance Syndrome (IRS), as did low dairy but high fibre. Taking a low dairy, low fibre diet increased the risk by almost 7 times!
This, of course is not very good news for the Standard American Diet (SAD). Milk consumption has been steadily declining since the 1970s. Furthermore, the increased processing of food has resulted in decreasing intake of dietary fibre. That puts the SAD in the highest risk category with almost 7 times the risk of IRS.
So the data are very conflicting. Some studies show that increased protein intake is bad for diabesity while other equally high quality data suggest that it is good. This leads to many heated discussions on internet bulletin boards. There are those who believe that dairy is good because it is high in fat and protein (low carb high fat). There are those who believe all dairy should be excluded from our diet (some paleo folks). There are those who believe that red meat should be excluded from the diet (vegans, vegetarians). There are those who believe that red meat is good because it is high in protein and fat (Atkins).
Are carbs bad? Are dietary fats bad? Are proteins bad?
Oh man, my head is starting to hurt…
Continue here to Hormonal Obesity XXV – Is Protein Fattening?
Start here with Calories Part I – How Do We Gain Weight?
See the lecture – The Aetiology of Obesity 3/6 – Trial by Diet