The paper is organized into three sections:
- A comprehensive review of the observational studies that have examined the relationship between high-fat dairy and/or dairy fat consumption and obesity, metabolic health, diabetes, and cardiovascular disease.
- A discussion of the possible mechanisms that could underlie the observational findings.
- Differences between pasture-fed and conventional dairy, and the potential health implications of these differences.
We wrote this paper because after reviewing the evidence, we found it to be surprising and fairly contradictory to conventional ideas on nutrition and health. I wrote the sections on obesity, metabolic health and diabetes, Mario wrote the sections on cardiovascular disease and fatty acids, and Ton wrote the section on husbandry practices and dairy fat composition. Mario was the lead author and did most of the editing/formatting, submitted the manuscript, etc. Our paper went through a rigorous peer review process.
Here are our basic findings:
- High-fat dairy consumption is not associated with obesity, in fact, 11 out of 16 studies found that higher dairy fat intake is associated with lower body fat and/or less fat gain over time. None identified an association between high-fat dairy consumption and fat gain, although some did find an association between low-fat dairy consumption and fat gain.
- High-fat dairy consumption is not associated with poorer metabolic health. Six of 11 studies found that higher high-fat dairy consumption is associated with better metabolic health, while only one found that it was associated with one marker of poorer metabolic health (and this study used an odd design).
- The association between high-fat dairy intake and diabetes risk is inconsistent. Zero of eight studies found that high-fat dairy consumption is associated with diabetes risk, and three found that it was protective. However, three studies also found that low-fat dairy intake was inversely associated with diabetes risk, compared to no association with high-fat dairy, suggesting by inference that the fat content of the dairy could be harmful. These studies all adjusted for body fatness. Since body fatness is a key risk factor for diabetes, and dairy fat intake is inversely associated with body fatness, this is obviously a major confound. We discussed this and other potential confounds in the paper.
- The evidence on cardiovascular disease is inconsistent, with a number of studies suggesting a protective association, a few suggesting a harmful one, and several suggesting no association.
- Dairy fat is a complex substance. There are major differences in the fatty acid composition of dairy from pasture-raised vs. conventionally raised cows, and many of these fatty acids are bioactive and could influence human health.
- We also discuss the limitations of observational studies in some detail, and many other issues that I won't touch on here.
This is the first comprehensive review of studies on the association between high-fat dairy intake and obesity, metabolic, and cardiovascular health. Typical dietary advice includes the recommendation to eat low-fat or skim dairy products. This is based on the hypothesis that avoiding the (mostly saturated) fat in dairy will reduce the risk of obesity, metabolic problems, and cardiovascular disease. This idea is logical, but not every idea that is logical is correct when tested scientifically, particularly when it pertains to a complex natural food. We asked the question "what does the evidence say about this hypothesis?"
The research to date suggests that high-fat dairy overall does not have a negative impact on obesity risk, metabolic problems, diabetes risk, or cardiovascular disease. In fact, these studies offer fairly strong support to the hypothesis that high-fat dairy may protect against obesity. However, there was variability between studies and this may be explained by factors such as a) differences in the quality of dairy products between countries/regions, b) the form in which dairy is consumed (e.g., traditional cheeses vs. ice cream and pizza), and c) other confounding factors discussed in the paper.
Please keep in mind that these studies are observational and therefore can not establish cause and effect. They're best viewed as a springboard for future research.
What This Paper Doesn't Mean
I want to be very clear about this. This paper does not mean that adding butter to all your food will make you lose fat or become healthier. In fact, if you do that you will most likely gain fat and become less healthy. Say what?? The studies we reviewed examined the role of high-fat dairy in the context of normal varied diet patterns. They did not compare people eating normally to people who put extra butter on everything, which is an excellent way to increase your calorie intake. Essentially they compared people eating high-fat dairy to people eating other types of fats as part of a mixed diet. The difference is subtle but critical to understand: addition vs. replacement.
So does this mean that replacing other types of fats with dairy fat (pasture-raised in particular), in the context of a normal varied diet, could lead to less fat gain and perhaps even better health over time? Perhaps. That is what the studies suggest overall. But again, these are observational studies with major limitations, so we'll have to wait for more evidence before we can hang our hats on the idea. In the meantime, it's clear that typical dietary recommendations to favor low-fat dairy over high-fat dairy are on thin ice.