Dairy and Its Effect on Insulin Secretion (and What It Means for Your Waistline)

The relationship between dairy consumption, insulin, and our health can be confusing. It’s easy to see why: The most common types of dairy undeniably spike our insulin levels, and elevated insulin has been linked to dozens of diseases—most diseases, in fact. When insulin is high, your body holds onto body fat. And insulin resistance, which is when your body doesn’t respond to insulin and must release large amounts of the hormone, makes it harder to lose body fat and is the precipitating factor in a host of degenerative diseases.

So, dairy is bad, right? No. The opposite, in fact.

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 required by life to flourish and prosper.

What is insulin good for?

We need insulin to shuttle all sorts of nutrients into cells, like protein and glycogen into muscles.

We need insulin to activate certain antioxidant systems.

We need insulin to optimize our cognitive function.

In other words, insulin is there for a reason, and “spikes” of insulin are normal as long as they go back down. It’s chronically elevated insulin, especially fasting insulin (high insulin levels in the absence of food), and insulin resistance that are harbingers of disease.

When you’re insulin resistant, insulin is less effective at shuttling nutrients into cells.

When you’re insulin resistant, those antioxidant systems dependent on insulin can’t switch on.

When your brain is insulin resistant, as Alzheimer’s patients’ brains are, your cognition suffers.

Insulin isn’t the problem. Improper, dysregulated insulin signaling is the problem.

Which brings us to dairy and its effect on insulin.

Dairy intake, you see, stimulates insulin secretion. Depending on the type of dairy, it can stimulate insulin a lot or almost not at all. And although we usually think about carbohydrates stimulating insulin, with dairy, it’s the combination of protein (whey and casein) and carbs (lactose) that stimulates insulin secretion.

Both skim and whole milk elicit significant insulin responses that you wouldn’t predict from looking at their carb contents; you must also account for the protein content.
Cream and butter are not particularly insulinogenic because they are mostly fat, with very little lactose or protein.
Cheese has different effects on insulin depending on the cheese, with protein content as the main determinant. Cream cheese has very little effect insulin because it’s mostly fat. Cottage cheese has the most effect on insulin because it’s mostly protein. Brie has very little effect; cheddar has somewhat higher.
Yogurt and kefir elicit moderate insulin spikes.

In one study, milk was even more insulinogenic than white bread, but less so than whey protein with added lactose and cheese with added lactose.¹ Another study found that full-fat fermented milk products and regular full-fat milk were about as insulinogenic as white bread.²

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).³

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: how important is the acute insulin response?

Do Insulin Spikes Make a Food Unhealthy?

A glass of milk and a comparably caloric slice of white bread elicit the same insulin response, but the comparisons stop there.

The milk gives you bioavailable protein, lots of calcium, healthy dairy fats, riboflavin, B12, and small but significant amounts of other vitamins and minerals. That protein will improve muscle protein synthesis. That calcium will improve skeletal health. Those fats will improve metabolic rate. That riboflavin will help you turn the fats and carbs into useable energy. All of which translates to better metabolic health.

The slice of white bread gives you carbs and little else. Maybe some vitamins and minerals from industrial fortification in a form your body has trouble assimilating.

The two foods do not have the same metabolic impact despite having similar effects on insulin.

Or let’s look at kefir, a food high in dairy proteins which stimulate insulin secretion.⁴ When you feed kefir, insulin rises. And yet when you feed kefir to rodents, it directly increases their insulin sensitivity, reduces their blood pressure, and lowers their waist circumference. An insulin spike happened, but insulin signaling improved. Foods are far more than just their effects on insulin levels.⁵

Does Dairy Cause Insulin Resistance?

A 2019 review of available research asked this very question. After reviewing 30 randomized controlled trials, the authors concluded that dairy intake “has a beneficial effect on HOMA-IR, waist circumference, and body weight.”⁶ On average throughout the studies, subjects who were randomly selected to eat dairy improved their insulin sensitivity, lowered their waist circumferences, and lost body weight.

This study found that dairy did increase insulin resistance, but there are some holes.⁷ 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. The milk group also ate 13% more calories than the meat group. Seeing as how excess calorie intakes are a reliable way to trigger insulin resistance, I’m not convinced that milk was the culprit.

Another study found that dairy improved blood pressure but failed to improve insulin and other metabolic risk parameters in overweight and obese subjects, but it used low-fat dairy instead of full-fat dairy.⁸ And again, the insulin numbers didn’t get worse; they just didn’t improve.

If full-fat dairy really did induce insulin resistance, we’d see it in the literature. 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 studies suggesting that if anything dairy reduces the risk of diabetes⁹ and heart disease.

Acute insulin spikes are different from chronically elevated insulin levels, especially when it comes to appetite regulation and metabolic derangement. Insulinogenic foods and insulin spikes can be problematic if you’re insulin resistant, but dairy seems to improve insulin resistance.

Does Dairy Work For You?

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 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.

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 ignore our own experiences. Have your experiences with dairy been positive or negative? Let the answer to that question supersede what PubMed says.

Some suggestions:

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, which will be higher in micronutrients and omega-3s.
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?