Butter is not just a big pile of yellow-colored fat.
There are many important nutrients in there, some of which have potent biological effects.
However, this does depend on the type of butter, and the amounts of these nutrients vary greatly depending on what the cows ate.
Butter is basically just milk fat, also known as butterfat.
Butterfat is highly complex. It contains about 400 different fatty acids, and a decent amount of fat-soluble vitamins (1).
Fatty acids are actually more than just energy sources, some of them have potent biological activity.
As it turns out, many of the fatty acids in butter can affect our physiology and biochemistry in some way, leading to major health benefits.
Grass-fed butter contains 5 times more CLA than butter from grain-fed cows (4).
As you can see, butter from grass-fed cows is a healthier and more nutritious choice.
Butter used to be considered unhealthy, because it contains saturated fat.
However, this is actually not a valid argument against butter, because the saturated fat myth has been thoroughly debunked in recent years.
Two massive review studies were published recently, one in 2010 and the other in 2014. Both included hundreds of thousands of people.
The relationship between full-fat dairy consumption and heart disease seems to depend on the country in which the study is performed.
In countries where cows are largely grass-fed, the people who eat the most butter seem to have a drastically reduced risk of heart disease.
An impressive study on this was published in the American Journal of Clinical Nutrition, in the year 2010: Smit LA, et al. Conjugated linoleic acid in adipose tissue and risk of myocardial infarction. American Journal of Clinical Nutrition, 2010. This study looked at the levels of CLA in the fat tissue of 1813 non-fatal heart attack patients, and compared them to 1813 similar subjects who had not gotten heart attacks.
Levels of this fatty acid are a very reliable marker for the intake of fatty dairy products, and this study was done in Costa Rica, where cows are grass-fed.
They split the subjects into 5 groups, from lowest to highest, depending on their levels of CLA. The results were fairly remarkable: As you can see, the more full-fat dairy (like butter) people ate, the lower their risk of heart attack.
In fact, the people who ate the most were 49% less likely to experience a heart attack, compared to those who ate the least.
However, keep in mind that this was a case-control study, a type of observational study. These types of studies can not prove causation.
This study shows that people who eat more grass-fed dairy fat have a lower risk of heart disease, but it can not prove that dairy fat caused the reduction in risk.
But, at the very least, this study is pretty good reassurance that butter is NOT the devil it was made out to be.
This is far from being the only study.
Another study from Australia showed that people who ate the most full-fat dairy had a 69% lower risk of heart disease than people who ate the least (8).
Despite having been demonized in the past, there is no evidence that real grass-fed butter causes harm. If anything, the evidence shows it to be beneficial.
However, just because butter is relatively healthy in reasonable amounts, it does NOT mean that you should go out of your way to eat more of it.
Use it for cooking or in recipes that call for it, but don't add tons of butter to your food (or your coffee) because you expect it will improve your health. Keep it reasonable.
I personally choose to use extra virgin olive oil most of the time. I believe it is the healthiest choice, by far.