Dairy is a controversial subject. Many health authorities tout its benefits for bone health and muscle building, while others raise concerns that dairy may cause obesity, bone loss, "leaky gut," and even some types of cancer! But, before you swear off milk forever, get the facts and find out whether dairy is a good choice for you.

Lactose Intolerance

Lactose intolerance is caused by a deficiency of the enzyme lactase, which is responsible for breaking down lactose, the form of sugar in milk. If you have lactose intolerance, consuming too much dairy can cause bloating, abdominal pain, gas, diarrhea, and vomiting.

While lactose intolerance (or lactase deficiency) is more common in adults, its prevalence varies widely across ethnic backgrounds. For example, only 15 percent of adults from Northern European descent are lactose intolerant, compared to 80 percent of adults of African or Latino descent, and almost 100 percent of adults of Asian or Native American descent.[1] Across the globe, lactose intolerance is present in an estimated 75 percent of adults, most of whom live in Asia, Africa, South America, and the Middle East.

Lactose intolerance doesn't necessarily mean you have to give up dairy entirely. People who are mildly lactose intolerant can typically digest some types of dairy more easily, such as cultured yogurt and hard cheeses. Gradually introducing small amounts of milk products, or taking a digestive enzyme with meals, may help some people have fewer symptoms of lactose intolerance over time.

Lactose intolerance is not the same as a milk allergy, which is a much rarer condition. A milk allergy is characterized by a systemic allergic response, leading to anaphylactic shock or even death.

Bone Health

Reports that countries with low dairy consumption (like China) have lower rates of osteoporosis than countries with high dairy consumption (like the United States), have led some people to jump to the conclusion that dairy is detrimental to bone health. In cases like these, it's important to remember that correlation does not equal cause, and no study has shown that dairy consumption weakens or damages bones. Countless other variables, such as lifestyle or food choices, could account for this discrepancy. In fact, in the elderly, dairy intake has been shown to improve bone density, reduce osteoporosis, and lower the risk of fractures.[2]

The United States Department of Agriculture and the American Heart Association recommend two or three servings of dairy per day for bone health, since dairy is a great source of calcium and the complementary, fat-soluble vitamins D and K. However, if you have a milk allergy or severe case of lactose intolerance, you can get these nutrients from non-dairy foods, too.

Calcium is present in many foods, including fortified juices, non-dairy milks, canned salmon, and leafy greens. Vitamin D is naturally present in salmon, tuna, and egg yolks, and is also often added to non-dairy milks and breakfast cereals. Vitamin K is found in leafy greens and can also be manufactured by your own gut bacteria!

The consensus: Research shows no definitive correlation between poor bone health and low milk consumption, and milk can actually improve bone health in many cases.

Weight Loss

A 2013 scientific review of 29 controlled studies showed that dairy does have modest weight-loss benefits, at least in short-term, calorie-restricted instances.[3] Another review showed that subjects on a high-dairy weight-loss diet lost more fat and gained more lean muscle than subjects not on a high-dairy weight-loss diet.

Part of this could be due to calcium's ability to hinder fat storage and increase fat breakdown in fat cells with the aid of phosphorus and magnesium, minerals found in dairy. Dairy also contains whey protein, which may benefit body composition by helping you burn fat while retaining muscle.[5]

You don't necessarily have to stick to skim milk to lose weight. Full-fat dairy from grass-fed cattle has five times more conjugated linoleic acid (CLA) and significantly higher omega-3 content than low-fat conventionally raised dairy.[6-8] CLA has been shown to reduce body fat and promote fat metabolism.[9, 10] Omega-3 fatty acids found in full-fat dairy have been shown to improve obesity-related risk factors, such as high blood pressure and unfavorable blood-lipid levels.[11,12] Still, it's worth noting that it is possible to get these beneficial fat-loss nutrients (calcium, magnesium, phosphorus, CLA, and omega-3) on a dairy-free diet as well.

The consensus: Dairy isn't necessarily detrimental to weight loss, and full-fat milk from grass-fed cows can still help you keep off the pounds.

Heart Disease

It was once thought that saturated fat from dairy could increase your risk of heart disease, but this theory has not stood the test of time. Results are on the fence for this one, but they favor dairy. A 2014 review of current research found that dairy intake does not contribute to cardiovascular disease.

In fact, it reported a "potential protective effect of full-fat milk, cheese, and yogurt on risk of cardiovascular disease."[13] Other reviews are more neutral, stating that high intakes of full-fat dairy seem to neither increase nor decrease the risk of heart disease.[14]

The consensus: Research indicates that dairy does not contribute to cardiovascular disease, and the full-fat variety may even have a protective effect.

Gut Health

One of the biggest arguments against dairy is its ability to aggravate digestion issues, particularly for people who are lactose intolerant. If you're not lactose intolerant, or only experience mild symptoms, fermented dairy products (such as cottage cheese, yogurt, and kefir) can be quite beneficial to gut health.

Fermented dairy products contain probiotics, which help to boost health-promoting microflora in the gut. These microflora support immune function, and help regulate gut integrity, by preventing unwanted substances from leaking into the body and provoking an immune response.

The consensus: Unless you're extremely lactose intolerant or allergic, fermented dairy products can help promote gut health.

Cancer

The link between dairy products and cancer is not straightforward. Several researchers have proposed that dairy may promote cancer growth via stimulation of insulin and IGF-1, hormones that inhibit cell death and stimulate cell proliferation.[15] One study linked high dairy intake to an increased risk of prostate cancer, but a more recent scientific review clarified that elevated prostate cancer risk was related to high calcium intakes—not dairy specifically.[16]

Conversely, other research has indicated that dairy proteins, like casein and whey, may protect against certain cancers, including colon, breast, and prostate.[17] In addition, many nutrients present in full-fat grass-fed dairy (such as the fat-soluble vitamins A, D, E, and K) have known antioxidant properties.

The consensus: While research results are mixed and inconclusive, there is currently no definitive link between dairy proteins and cancer risk.

The Takeaway

While dairy is certainly not necessary for optimal health, and may not be well-tolerated by some people, it does provide numerous health benefits, especially full-fat dairy from grass-fed cows. Evidence indicates that there's no reason to eliminate dairy unless you notice gastrointestinal upset or allergy symptoms.

If you love dairy, but think you might be lactose intolerant, try cutting back on milk products, or limiting yourself to fermented dairy products (yogurt, cottage cheese, and hard cheeses). This alone may provide enough relief.

References

1. Swagerty, D. L., Jr., Walling, A. D., & Klein, R. M. (2002). Lactose intolerance. American Family Physician, 65(9), 1845-1850.
2. Varenna, M., Manara, M., Galli, L., Binelli, L., Zucchi, F., & Sinigaglia, L. (2013). The Association Between Osteoporosis and Hypertension: The Role of A Low Dairy Intake. Calcified Tissue International, 93(1), 86-92.
3. Chen, M., Pan, A., Malik, V. S., & Hu, F. B. (2012). Effects of dairy intake on body weight and fat: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition, 96(4), 735-747.
4. Abargouei, A. S., Janghorbani, M., Salehi-Marzijarani, M., & Esmaillzadeh, A. (2012). Effect of dairy consumption on weight and body composition in adults: a systematic review and meta-analysis of randomized controlled clinical trials. International Journal of Obesity, 36(12), 1485-1493. doi:10.1038/ijo.2011.269
5. Pal, S., Ellis, V., & Dhaliwal, S. (2010). Effects of whey protein isolate on body composition, lipids, insulin and glucose in overweight and obese individuals. British Journal of Nutrition, 104(05), 716-723.
6. Kratz, M., Baars, T., & Guyenet, S. (2012). The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease. European Journal of Nutrition, 52(1), 1-24.
7. Staszak, E. (2005). Conjugated Linoleic Acid (CLA) Content of Milk from Cows Fed Different Diets. Folia Biologica, 53(4), 103-106.
8. Hebeisen, D. F., Hoeflin, F., Reusch, H. P., Junker, E., & Lauterburg, B. H. (1993). Increased concentrations of omega-3 fatty acids in milk and platelet rich plasma of grass-fed cows. International Journal for Vitamin and Nutrition Research, 69(3), 229-233.
9. Thom, E., Wadstein, J., & Gudmundsen, O. (2001). Conjugated Linoleic Acid Reduces Body Fat in Healthy Exercising Humans. Journal of International Medical Research, 29(5), 392-396.
10. Blanks, H., Stakkestad, J. A., Fagertun, H., Thom, E., Wadstein, J., & Gudmundsen, O. (2000). Conjugated Linoleic Acid Reduces Body Fat Mass in Overweight and Obese Humans. Journal of Nutrition, 130(12), 2943-2948.
11. Lorente-Cebrián, S., Costa, A. G., & Navas-Carretero, S. (2013). Role of omega-3 fatty acids in obesity, metabolic syndrome, and cardiovascular diseases: a review of the evidence. Journal of Physiology and Biochemistry, 69(3), 633-651.
12. Cox, A. J., West, N. P., & Cripps, A. W. (2015). Obesity, inflammation, and the gut microbiota. Lancet Diabetes Endocrinology, 3(3), 207-215.
13. Rice, B. H. (2014). Dairy and Cardiovascular Disease: A Review of Recent Observational Research. Current Nutrition Reports, 3(2), 130-138.
14. Liang, J., Zhou, Q., Kwame, A. W., Su, Y., & Zhang, Z. (2016). Biomarkers of dairy fat intake and risk of cardiovascular disease: a systematic review and meta analysis of prospective studies. Critical Reviews in Food Science and Nutrition, 00-00.
15. Kaaks, R. (n.d.). Nutrition, Insulin, IGF-1 Metabolism and Cancer Risk: A Summary of Epidemiological Evidence. Biology of IGF-1: Its Interaction with Insulin in Health and Malignant States. Novartis Foundation Symposia, 247-264.
16. Lampe, J. W. (2011). Dairy products and cancer. Journal of the American College of Nutrition, 30(5), 464S-470S.
17. Davoodi, H., Esmaeili, S., & Mortazavian, A. (2013). Effects of Milk and Milk Products Consumption on Cancer: A Review. Comprehensive Reviews in Food Science and Food Safety, 12(3), 249-264.