Dairy products are controversial these days.

While dairy is cherished by health organizations as essential for your bones, some people argue that it’s harmful and should be avoided.

Of course, not all dairy products are the same.

They vary greatly in quality and health effects depending on how the milk-giving animals were raised and how the dairy was processed.

This article gives an in-depth look at dairy and determines whether it’s good or bad for your health.

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One common argument against dairy products is that it is unnatural to consume them.

Not only are humans the only species that consumes milk in adulthood, but they are also the only one to drink the milk of other animals.

Biologically, cow's milk is meant to feed a rapidly growing calf. Humans aren't calves — and adults usually don't need to grow.

Before the agricultural revolution, humans only drank mother's milk as infants. They didn't consume dairy as adults — which is one of the reasons why dairy is excluded from a strict paleo diet (1).

From an evolutionary perspective, dairy isn’t necessary for optimal health.

That said, certain cultures have been consuming dairy regularly for thousands of years. Many studies document how their genes have changed to accommodate dairy products in the diet (2).

The fact that some people are genetically adapted to eating dairy is a convincing argument that it’s natural for them to consume.

Summary Humans are the only species that consumes milk in adulthood, as well as milk from other animals. Dairy was not consumed until after the agricultural revolution.

The main carbohydrate in dairy is lactose, a milk sugar composed of the two simple sugars glucose and galactose.

As an infant, your body produced a digestive enzyme called lactase, which broke down lactose from your mother's milk. However, many people lose the ability to break down lactose in adulthood (3).

In fact, about 75% of the world's adult population is unable to break down lactose — a phenomenon called lactose intolerance (4).

While lactose intolerance is rare in North America, Europe and Australia, it is very common in Africa, Asia and South America.

People who are lactose intolerant have digestive symptoms when they consume dairy products. This includes nausea, vomiting, diarrhea and related symptoms.

However, keep in mind that lactose-intolerant people can sometimes consume fermented dairy (like yogurt) or high-fat dairy products like butter (5).

You can also be allergic to other components in milk, such as the proteins. While this is fairly common in children, it’s rare in adults.

Summary Three out of every four people in the world are intolerant to lactose, the main carb in dairy. Most people of European ancestry can digest lactose without problems.

Dairy products are very nutritious.

A single cup (237 ml) of milk contains (6):

  • Calcium: 276 mg — 28% of the RDI
  • Vitamin D: 24% of the RDI
  • Riboflavin (vitamin B2): 26% of the RDI
  • Vitamin B12: 18% of the RDI
  • Potassium: 10% of the RDI
  • Phosphorus: 22% of the RDI

It also boasts decent amounts of vitamin A, vitamins B1 and B6, selenium, zinc and magnesium, alongside 146 calories, 8 grams of fat, 8 grams of protein and 13 grams of carbs.

Calorie for calorie, whole milk is quite healthy. It offers a little bit of almost everything your body needs.

Keep in mind that fatty products like cheese and butter have a vastly different nutrient composition than milk.

Nutrient composition — especially the fatty components — also depends on the animals’ diet and treatment. Dairy fat is very complex, consisting of hundreds of different fatty acids. Many are bioactive and can strongly impact your health (7).

Cows raised on pasture and fed grass have more omega-3 fatty acids and up to 500% more conjugated linoleic acid (CLA) (8, 9).

Grass-fed dairy is also much higher in fat-soluble vitamins, especially vitamin K2, an incredibly important nutrient for regulating calcium metabolism and supporting bone and heart health (10, 11, 12, 13).

Keep in mind that these healthy fats and fat-soluble vitamins are not present in low-fat or skim dairy products, which are often loaded with sugar to make up for the lack of flavor caused by removing the fat.

Summary Milk is quite nutritious, but nutrient composition varies by dairy type. Dairy from grass-fed or pasture-raised cows contains more fat-soluble vitamins and beneficial fatty acids.

Calcium is the main mineral in your bones — and dairy is the best source of calcium in the human diet.

Therefore, dairy has many benefits for bone health.

In fact, most health organizations recommend that you consume 2–3 servings of dairy per day in order to get enough calcium for your bones (14, 15).

Despite certain claims you may hear, there is no conclusive evidence that dairy intake has adverse effects on bone health (16).

Most evidence indicates that dairy improves bone density, reduces osteoporosis and lowers older adults’ risk of fractures (17, 18, 19, 20, 21, 22).

Additionally, dairy provides more than just calcium. Its bone-boosting nutrients include protein, phosphorus and — in the case of grass-fed, full-fat dairy — vitamin K2.

Summary Numerous studies show that dairy has clear benefits for bone health, lowering older adults’ risk of fractures and improving bone density.

Full-fat dairy has some benefits for metabolic health.

Despite being high in calories, full-fat dairy is linked to a reduced risk of obesity.

A review of 16 studies noted that most linked full-fat dairy to reduced obesity — but none identified such an effect for low-fat dairy (23).

There is also some evidence that dairy fat can reduce your risk of diabetes.

In one observational study, those who consumed the most full-fat dairy had less belly fat, less inflammation, lower triglycerides, improved insulin sensitivity and a 62% lower risk of type 2 diabetes (24).

Several other studies associate full-fat dairy with a reduced risk of diabetes, though a number of studies found no association (25, 26, 27).

Summary Several studies link full-fat dairy products to a reduced risk of obesity and type 2 diabetes — but others see no effect.

Conventional wisdom dictates that dairy should raise your risk of heart disease because it is high in saturated fat.

However, scientists have started to question the role of dairy fat in the development of heart disease (28).

Some even claim there is no link between saturated fat consumption and heart disease — at least for the majority of people (29, 30).

The effects of dairy on heart disease risk may also vary between countries, likely depending on how the cows are raised and fed.

In one major study in the US, dairy fat was linked to an increased risk of heart disease (31, 32).

However, many other studies suggest that full-fat dairy has a protective effect on both heart disease and stroke.

In one review of 10 studies — most of which used full-fat dairy — milk was linked to a reduced risk of stroke and cardiac events. Though there was also a reduced risk of heart disease, it wasn't statistically significant (33).

In countries where cows are largely grass-fed, full-fat dairy is associated with major reductions in heart disease and stroke risk (34, 35).

For example, one study in Australia noted that people who consumed the most full-fat dairy had a whopping 69% lower risk of heart disease (36).

This is likely related to the high content of heart-healthy vitamin K2 in grass-fed dairy products, though dairy can improve other risk factors for heart disease as well, such as blood pressure and inflammation (37, 38, 39, 40).

Speculation aside, there is no consistent evidence on whether dairy fat helps or hinders heart health.

While the scientific community is divided in its opinion, public health guidelines advise people to minimize their intake of saturated fat — including high-fat dairy products.

Summary: There is no consistent evidence that dairy fat leads to heart disease. Nevertheless, most health authorities advise people to minimize their intake.

Dairy is known to stimulate the release of insulin and the protein IGF-1.

This may be the reason that dairy consumption is linked to increased acne (41, 42).

High levels of insulin and IGF-1 are also associated with an increased risk of certain cancers (43).

Keep in mind that there are many different types of cancer, and the relationship between dairy and cancer is quite complex (44).

Some studies suggest that dairy may reduce your risk of colorectal cancer but increase your risk of prostate cancer (45, 46).

That said, the association with prostate cancer is weak and inconsistent. While some studies reveal up to a 34% increased risk, others find no effect (47, 48).

The effects of increased insulin and IGF-1 aren't all bad. If you're trying to gain muscle and strength, then these hormones can provide clear benefits (49).

Summary Dairy can stimulate the release of insulin and IGF-1, which may lead to increased acne and a higher risk of prostate cancer. On the other hand, dairy seems to lower your risk of colorectal cancer.

The healthiest dairy products come from cows that are grass-fed and/or raised on pasture.

Their milk has a much better nutrient profile, including more beneficial fatty acids and fat-soluble vitamins — particularly K2.

Fermented dairy products like yogurt and kefir may be even better. They contain probiotic bacteria that can have numerous health benefits (50).

It’s also worth noting that people who can’t tolerate dairy from cows may be able to easily digest dairy from goats.

Summary The best types of dairy come from animals that were pasture-raised and/or fed grass because their milk has a much more robust nutrient profile.

Dairy isn’t easily categorized as healthy or unhealthy because its effects may vary greatly between individuals.

If you tolerate dairy products and enjoy them, you should feel comfortable eating dairy. There is no compelling evidence that people should avoid it — and plenty of evidence of benefits.

If you can afford it, choose high-quality dairy — preferably without any added sugar, and from grass-fed and/or pasture-raised animals.