Insulin is an old, old hormone. Evolution has preserved its structure across hundreds of millions of years and hundreds of thousands of species. Fish, insects, reptiles, birds, and mammals all secrete insulin with fairly similar amino acid arrangements (insulin from certain species of fish has even been clinically effective in humans), so, clearly, it is a vital hormone. But insulin gets a bad rap in our circles. Why? With metabolic syndrome laying waste to the citizenry and with insulin playing an undeniable role, it’s difficult not to be soured on this hormone.
And yet we need insulin to shuttle all sorts of nutrients into cells, like protein and glycogen into muscles. It’s there for a reason, so to demonize it is misguided. It’s chronically elevated insulin and insulin resistance – you know, the hallmarks of metabolic syndrome – that are the problem. You might have noticed a softening stance on carbohydrates around the paleo and Primal blogosphere. I think it’s simply an acknowledgment that in healthy people with healthy glucose control and healthy insulin responses who engage in glycolytic activity, starch is fine in measured amounts. And if insulin increases to shuttle that starch and protein into the insulin sensitive muscle cells, so be it. That’s why it’s there.
But not everyone (anyone?) lives a perfect Primal existence. And even if you did an understanding of how insulin works and what foods and behaviors affect it’s production should be high priority. Especially for the millions of people immersed in the modern, industrial lifestyle, with deranged metabolisms from years of poor eating habits (i.e. most of us).
Dairy intake, you see, stimulates insulin secretion. Lots and lots of it – more than can be explained by the lactose (a sugar) content. In fact, the lactose content of dairy doesn’t even have a big insulin effect when compared to other carbs. This is surprising to some, since the general understanding is that insulin is released primarily in response to carbohydrate intake. What gives? Well, in evolutionary terms, think about a growing beast needing to maximize the utility of every drop of the precious liquid. With dairy, it’s the protein plus the carbs that are responsible for the large insulin release. Take milk, the most egregious “offender.” Both skim and whole milk  (PDF) elicit significant insulin responses that you wouldn’t predict from looking at their protein and carb contents, and the fat in whole milk doesn’t blunt it (maybe non-homogenized whole milk would be a different story… I don’t know). Cream and butter  are not particularly insulinogenic, while milk of all kinds, yogurt, cottage cheese, and anything with casein or whey, including powders and cottage cheese, elicits a significant insulin response. In one study  (PDF), milk was even more insulinogenic than white bread, but less so than whey protein with added lactose and cheese with added lactose. Another study  (PDF) found that full-fat fermented milk products and regular full-fat milk were about as insulinogenic as white bread.
What’s going on here? It comes down to the amino acid composition of dairy proteins, specifically the amino acids leucine, valine, lysine, and isoleucine. These are the truly insulinogenic proteins, and they’re highest in whey (which is probably why whey protein elicits the biggest insulin response ).
This isn’t new. I’ve written  about protein’s insulinogenicity before, but dairy goes above and beyond Primal protein sources like meat, eggs , and fish . The question we should be asking is this: if you wish to include dairy in your diet AND have no issues with lactose or casein intolerance are the insulinogenic properties of certain types of dairy still problematic from the standpoint of health and/or weight control?
This study  claims they are. Children were given strict diets of either lean beef or skim milk, and the skim milk diet induced hyperinsulinemia and insulin resistance after just seven days. It sounds troublesome, but they used skim milk – a refined, fundamentally altered food. I’m not prepared to render judgment. Another study  found that dairy failed to improve insulin and the metabolic risk parameters in overweight and obese subjects, but it again used low-fat dairy instead of full-fat dairy. I’m simply not convinced they’re interchangeable.
If full-fat dairy really did have similarly negative effects on the insulin response that eventually led to the metabolic syndrome, you wouldn’t see studies  showing that people who ate the most dairy fat were at the lowest risk for diabetes. You also wouldn’t see the high number of epidemiological studies  (I know, I know) linking full-fat dairy intake with lower risk of heart disease and stroke, both of which are strongly linked with insulin resistance.
I think it’s more accurate to say that acute insulin spikes are different from chronically elevated insulin levels, especially when it comes to appetite regulation and metabolic derangement. Consider this study , whose authors gave either whey protein isolate or whey protein hydrolysate to subjects 30 minutes before a pizza meal. Subjects given whey protein isolate, but not hydrolysate, reduced post meal blood glucose and insulin levels, and ate less pizza. The whey still released insulin, but it didn’t linger for very long and it led to improved post meal numbers. It wasn’t chronically elevated. The subjects weren’t hungrier, contrary to what you might expect from someone who’d just experienced a jump in insulin.
No Easy Answer.
Dairy’s not for everyone. I don’t like milk, so I stick to good cheese , pastured butter , cream and the whey  in Primal Fuel  when I’m in a hurry, while avoiding most straight-up milk, but I think good milk may be fine for many people. As always, experiment. Dairy seems to stall weight loss for some people, so you might try taking it out of the diet if you can’t lean out. Dairy also seems to improve strength and mass gains for lifters , so you might try adding it if you’ve been lifting particularly hard. See what works, and what doesn’t. Insulin doesn’t have to be feared as much as it should be managed, just so long as the rest of your metabolic toolkit – in which insulin takes a prominent position – is in order, you’ve got stress  dialed in (or out), you’re getting good sleep , and you’re putting in the necessary physical work .
It’s also important to consider the big picture when judging the suitability of various foods. It helps to tell stories about the food we eat, to think about narratives. Grains  aren’t just little morsels of protein, carbs, and fiber bred for our enjoyment. They are baby plant eggs. Those macronutrients are there to sustain the seed’s growth and those micronutrients are there to protect it. They are the plant’s lifeline to immortality. They are literally shaped by the hand of evolution to survive and ravage the digestive tract of the poor sap that swallows them and discourage further consumption. Grain is only food because we deemed it so. Dairy? Dairy is objectively, absolutely food. Its fat, protein, and carbs are there to be consumed, albeit by young cows, sheep, and goats. It’s meant to spur growth, to pack on muscle and fat and weight. And yeah, eating dairy protein causes an insulin spike, but that can be useful if you know what you’re doing.
In the end, personal results matter most. Health outcomes concern us; detached insulin response numbers sitting in a table in some paper mean little if your personal experiences corroborate the evidence that consistently shows that untouched, full-fat dairy likely promotes better glucose tolerance, better weight control, and more resistance to chronic diseases like diabetes  and heart disease. On the other hand, those studies mean little to the person whose weight loss stalls after a couple glasses of non-homogenized, raw pastured milk. Try as we might, we can’t – nor should we – ignore our own experiences. Have your experiences with dairy been positive or negative? Let the answer to that question supersede what PubMed says.
- Go fermented. Stick to full-fat yogurt, kefir, and cheese.
- Go heavy. Stick to butter, cream, and half-and-half.
- Go pastured. Find a source of pastured dairy. From what I understand, Trader Joe’s carries a cream-top organic milk that hails from the Strauss Family Creamery  in Northern California (they never provide sources, but the TJs stuff tastes remarkably similar to the glass bottle stuff from Strauss and the cream has the same consistency), which uses mostly grass and grass silage. Their “European Style Yogurt” also comes from Strauss and is very good (and cheaper than Strauss-labeled yogurt in other stores).
- Go raw. Stick to trusted sources.
What are your experiences with dairy’s insulinogenic effects? They are very real, but do they seem to bother you? Are you worried about insulin spikes in response to dairy protein?