A recent study from a group of highly-respected scientists shows that the fats in milk are unlikely to cause heart attacks and that fermented milk products such as cheese and yogurt may actually help to prevent heart attacks (Am J Clin Nutr, Sept 2018;108(3):476–484). The researchers followed 2907 U.S. adults, aged 65 and older and free of heart disease, for 22 years. They measured their blood levels of milk fats at baseline and again six and 13 years later. None of the milk fats in their bloodstream were associated with increased death rate, and surprisingly, high levels of one type of milk fat, heptadecanoic acid, was associated with prevention of heart attacks and strokes.
Most previous studies on milk have depended on self-reporting, which is known to give inaccurate and often biased results. Instead, this study measured dairy fats in the subjects' bloodstreams to prove exactly how much dairy they had consumed. When you eat or drink dairy products, the specific types of fat in dairy products goes into your bloodstream and can be easily measured. Then researchers can correlate blood levels of dairy fat in the bloodstream with people's medical histories and death rates over many years.
History of Studies on Milk
After more than 70 years of studies that have promoted or criticized dairy products, nobody has proven whether they are either harmful or healthful. Yet it has been:
• almost 70 years since studies started to blame saturated fat in milk products for causing heart attacks,
• more than 40 years since the U.S. government first recommended that everyone except young children use low-fat or non-fat milk instead of whole milk to reduce saturated fat intake and calories,
• 30 years since sales of low-fat and skim milk began to exceed those of whole milk, and
• Eight years since the Healthy Hunger-Free Kids Act required schools to replace whole milk with nonfat or low-fat unflavored milk (JAMA, published online December 5, 2018).
The U.S. Department of Agriculture still recommends low-fat dairy products, but now it appears that saturated fat in milk may not be the culprit after all. A review of 76 studies showed that saturated fats in foods were not associated with increased risk for heart attacks (Ann of Int Med, March 18, 2014;160(6)). See my report on The Saturated Fat Debate
Adults Don't Need the Sugar in Milk
Milk is a high-sugar drink. It is full of a double sugar called lactose that gets broken down to galactose and glucose, pro-inflammatory single sugars that can cause oxidative damage and chronic inflammation associated with diabetes, heart attacks, certain cancers and bone loss in adults (Biogerontology, 2004;5:317-25). People who drink milk have increased urine levels of 8-iso-PGF2a (a biomarker of oxidative stress) and serum interleukin 6 (a major inflammatory biomarker). The sugar in milk can be a perfectly good source of energy for babies, active children and teens, but most adults do not need additional sugar, particularly in a rapidly-absorbed liquid form.
Several studies show that eating fermented milk products (yogurt and many cheeses) is associated with decreased risk for heart attacks and death. Bacteria make cheese and yogurt from milk, and in the fermentation process they consume most of the galactose in the milk (J Hum Nutr Diet, 2009;22:400-8), so these cheeses and yogurt are different from other dairy products because they have very low levels of that harmful sugar. While milk has been linked to increased risk for heart attacks, cheese and yogurt are associated with lower heart attack risk and longer lives (European Society of Cardiology Congress, Aug 28, 2018; J Agr and Food Chem, April 2015;63 (10):2830-9). People who ate a lot of cheese had very high levels of butyrate in their stool and urine and much lower blood levels of the bad LDL cholesterol. This means that the fermented dairy products are being converted by bacteria in the intestines to short chain fatty acids, such as butyrate, that prevent food from forming the bad LDL cholesterol that is associated with increased heart attack risk. The authors believe that they have shown that fermented dairy products encourage the growth of healthful intestinal bacteria that may help to prevent heart attacks. See Milk, Cheese or Yogurt?
Accumulating research suggests that the high galactose (sugar) content of milk may be harmful to your health, and that most cheeses and yogurt may be healthful because the fermenting process removes the galactose. We do not know if milk causes diabetes or heart attacks, or whether cheese and yogurt help to prevent them. However, based on these studies, I recommend that you limit or avoid milk but that cheese and yogurt may be included as part of your healthful, high-plant diet.