It is important to begin by acknowledging the enormity of the $50 billion US dairy industry. Due to its massive funding, the dairy industry undoubtedly has influence and sway when it comes to the guidelines that are accessible to the public regarding dairy. One of the industry’s main goals is to increase dairy consumption guidelines, driving more money into the pockets of dairy lobbyists. It is estimated that Americans eat or drink an average of 1.5 servings of dairy each day. However, research indicates that dairy can negatively affect the human body. While each consumer has the right to make their own choices, it is important to be educated on the potential downsides of dairy and to be aware of where the research that one is consuming is coming from as well as who funds it.
One of the biggest claims to fame of the dairy industry is the incredible source of nutrients that dairy provides. While dairy undoubtedly provides an individual with calories, protein, calcium, and fat (depending on fat content), dairy is not a unique source of nutrients. All the nutrients found in dairy products can also be found in other foods. While it is often argued that dairy is a good source of nutrients for growth and bone development in children, it can also be argued that due to the upregulation of growth hormones that occurs with consumption of dairy, dairy is also dangerous for adults. Research shows that milk consumption upregulates mammalian target of rapamycin complex 1 (mTORC1), which is a protein complex that controls protein synthesis within the human body. This upregulation has been shown to be the driving force of the development of disease (1). This makes sense if we look at why milk is produced in the first place: to feed baby cows. Milk is meant for baby mammals who are in need of upregulation in the body for growth. Adults, who are not in need of growth, do not need the process of upregulation, and upregulation can actually lead to disease.
While breastmilk is considered the gold standard for infants and can be the exclusive source of nutrients for the first six months of life, this is very different from cow’s milk. Research indicates that even for children, too much dairy and, as a result, too much upregulation of mTORC1, can also have negative side effects. Some of these side effects include: affecting the growth in height-for-age in children, creating a larger body size in young girls, and leading to earlier sexual maturation in young girls (2). Because of this, milk should be considered an unusual food with bioactive properties and no unique nutrients. Meaning, due to dairy’s ability to affect the human body’s growth processes, dairy intake should be minimized, and nutrients found in dairy should be consumed from other sources.
Several studies examine the different components within dairy and their effect on health. One study looked at the differences between skim milk, whey and casein in overweight adolescents. Ultimately it was found that intake of skim milk, whey and casein increased BMI-for-age Z score and insulin secretion measured by C-peptide. This is important, as overweight adolescents, and individuals in general who may already have higher circulating levels of insulin and be at a higher risk for prediabetes, may benefit from reducing their dairy intake. An increase in insulin, which binds to IGF-1, promotes cellular replication in connective and musculoskeletal tissue, ultimately leads to further weight gain (3).
Similar results were found in a study that examined the effect of dairy on fractures in the elderly. While it is commonly thought that dairy may strengthen bones, too much dairy consumption around age 20 was actually shown to increase one’s risk for hip fracture through the catabolic effect that dietary protein has on bone. This study found that too much dietary protein through dairy intake caused urinary excretion of calcium and increased one’s overall risk for hip fractures into later adulthood (4). This increased risk of fractures coupled with being overweight was shown to increase one’s risk for developing cardiovascular disease, ultimately leading to poorer overall health, potentially increasing one’s risk for falls and fractures in later adulthood (4).
There is also research that exists suggesting that due to dairy’s ability to upregulate growth pathways in the body, too much dairy intake could contribute to the development of cancer. This makes sense if one examines the basic definition of cancer cells: uncontrolled metastasis and growth. One study found that increased high fat dairy consumption in Arabian and Jordanian studies contributed to the development of colorectal cancer (5). These findings were consistent across other studies as well that showed that dairy intake was positively associated with circulating insulin-like growth factor 1 (IGF-1), which is a protein encoded by the IGF-1 gene that plays a role in childhood growth, but that continues to have an anabolic effect in adults. Upregulation of IGF-1 and other growth hormones was shown to occur with higher intake of dairy, which was associated with prostate and colorectal cancers (6).
The upregulation that occurs with the consumption of dairy is important for adults to understand, as it is associated with the overall process of aging and disease development. Ultimately it is beneficial to try and inhibit the upregulation of mTOR to improve overall health and cognition. Because research indicates that upregulation of mTOR could lead to cellular and tissue aging, diabetes, and cancer, it is recommended that mTOR is downregulated as much as possible through diet and lifestyle (7).
In addition to the upregulation processes that dairy promotes, dairy also contains lactose, which many humans may have a sensitivity towards. Part of the reason that one may develop lactose intolerance is actually due to the inflammatory pathways that dairy stimulates. Cow’s milk has a compound known as beta-casein, which research indicates may affect symptoms of lactose intolerance. A1 beta casein has been shown to worsen signs and symptoms of gastric upset and lactose intolerance compared to A2 beta casein, as A1 beta casein has more inflammatory markers (8). Because cow’s milk protein and casein have both been shown to provoke an inflammatory response, it would be recommended that individuals aim to reduce dairy intake overall to promote an anti-inflammatory physiological environment.
Consideration of dairy is important for those with cognitive decline and/or Alzheimer’s Disease (AD) because there have been many studies that link the development of AD to high fat dairy products. It is generally recommended that in order to prevent against AD, one should minimize intake of animal based saturated fats and trans fats, and that fruits, vegetables and whole grains should replace both meat and dairy in one’s diet (9). Because dairy is not a unique nutrient source, and because research indicates that dairy can have adverse effects on cognition, those looking to maximize and/or improve overall cognition should try to minimize dairy intake.