What We Know About Dairy So Far
Article by Namrata Ashok
The oldest evidence of dairy consumption dates to at least 6000 years ago in modern Kenya and Sudan. Without the genes to digest dairy, locals fermented dairy products to break down the lactose and make dairy more digestible before consumption. Although all human infants can digest milk, adults require the production of the lactase enzyme, a substance that breaks down the lactose sugar in milk. Unfortunately, 65% of the human population are lactose intolerance after infancy (Bayless et al, 2017).
In 2020, milk production in the UK accounted for 16.4% of its total agricultural output, making it the 13th largest milk producer in the world. Unfortunately, industry-sponsored researchers are likely to have an “economic interest to produce the right results,” creating biased results (Collier, 2016). Therefore, the debate on whether dairy is bad for you continues. So, what impact does dairy actually have on our bodies and what is the research behind this?
What is dairy?
Dairy products are food products made from milk from cows, buffalos, goats, and ewe, and most commonly include milk, cheese, yoghurt, and butter. They are a rich source of calcium, vitamin B2, vitamin B12, phosphorus, zinc, potassium, magnesium, vitamin A, and protein in highly bioavailable forms. These nutrients help with growth, reduce the risk of musculoskeletal disorders, and improve peak bone mass and density (Górska-Warsewicz et al., 2019).
Does dairy increase cholesterol levels?
Traditionally, we have understood that the consumption of saturated fats is linked to increased low-density lipoprotein cholesterol levels, and therefore coronary heart disease. However, these findings relating cholesterol levels, cardiovascular disease, and ultra-processed sources of saturated fats have been generalised to all foods with saturated fats, not just dairy alone (Dowden, 2019). Yet, recent evidence utilising dairy products questions these claims by demonstrating no increase in total and LDL cholesterol levels when consuming whole-fat milk. In fact, most meta-analyses - a type of study which combines results from lots of similar studies to help come to more meaningful conclusions - found no or weak associations between dairy intake and cardiovascular disease as saturated fats have been linked to reduced fatty deposits, diabetes, and inflammation. Furthermore, the consumption of yoghurt and cheese is not linked to increased all-cause mortality and has also been linked to a reduced overall risk of cardiovascular disease, even with long-term consumption (Górska-Warsewicz et al., 2019). These findings were first supported by a hallmark study on the African Maasai ethnic group, which reported an inverse relationship between blood cholesterol levels and large dairy consumption (Gibney and Burstyn, 1980).
The gut microbes typically produce bioactive peptides from dairy products. These bioactive peptides are produced in abundance when fermented dairy products, such as yoghurt and cheese, are consumed. A study performed on 18,770 individuals concluded a positive relationship between circulating HDL cholesterol and cheese consumption. Therefore, cheese has been praised for its weakest effects on increasing LDL cholesterol among other dairy products (Visioli and Strata, 2014).
Finally, there is research to suggest that the levels of LDL and HDL in relation to one another are better measures of cardiovascular disease risk than measures of LDL or HDL on their own (Millán et al., 2009).
Does dairy worsen period cramps?
Based on a review of studies between 2002 and 2011, severe period cramps, also known as dysmenorrhea, affects between 16% - 91% of women in their menstruating years (Ju, Jones and Mishra, 2013).
Cramps arise when type 2 prostaglandins are over-produced from the breakdown of the uterine lining. Type 2 prostaglandins are made from omega-6 fatty acid compounds (e.g. arachidonic acid) which can be found in dairy products. So, is the arachidonic acid in dairy products to blame for period cramps?
Several studies demonstrated no or weak relationships between increased dysmenorrhea and dairy consumption. In one study, fewer female students who consumed 3-4 servings of dairy products per day reported dysmenorrhea (Abdul-Razzak et al., 2010). The researchers spotlighted the role of calcium and its ability to regulate muscle activity, modulating uterine contractions during cramps (Bajalan, Alimoradi and Moafi, 2019).
On the other hand, dairy has been criticized for its high Omega 6 content. However, the dairy food matrix may have inhibitory effects on the pro-inflammatory effects of omega 6. Approximately 44 known nutrients are packaged into dairy, forming a dairy matrix (Weaver, 2021). Dairy matrices have a unique combination of nutrients that interact with one another and alter physiological effects of certain compounds and pathways in the body (Feeney and McKinley, 2020). Therefore, the interactions between omega 6 and the other nutrients within the dairy matrix may disrupt the omega 6 and type-2 prostaglandin pathway.
Does dairy increase inflammation?
On one hand, the hormonal components present in milk have been shown to promote insulin resistance, increase sebum production, which is commonly seen with acne, and activate inflammatory markers. However, these findings are relatively limited (Juhl et al., 2018). Zemel et al found reduced oxidative stress markers after the consumption of milk and/or yoghurt. Furthermore, a meta-analysis concluded no adverse effects of dairy products on inflammation (Visioli and Strata, 2014).
Bloating from dairy?
The national institute of health claims that approximately 65% of adults have some degree of lactose intolerance. Lactose intolerance is characterised by gas, bloat, abdominal cramps, watery diarrhoea, vomiting, nausea, short-term memory disruption, headaches, fatigue, and pain after consuming lactose-containing foods. Because many adults lack the lactase enzyme, lactose is fermented into gas and short-chain fatty acids by the gut bacteria. These metabolic products and their rate of production are responsible for the characteristics of lactose intolerance, such as bloating. (Cancarevic et al., 2020).
Research suggests that the symptoms of lactose intolerance can be mediated by consuming full-fat milk, avoiding hot peppers and coffee when consuming lactose-containing foods, and consuming fermented dairy products. Consuming lactose-containing products with fat (e.g full-fat milk) tends to slow gastric (stomach) emptying, reducing the volume of lactose exposed to the small intestine at a time. Furthermore, casein, a predominant milk-containing protein, hinders enzyme access and delays gastric emptying compared to its whey protein counterpart (Turgeon and Brisson, 2020). Coffee and hot peppers increase the rate at which lactose is delivered to the intestines, increasing symptoms. Fermentation reduces the lactose content in foods through bacterial metabolism.
Does dairy increase the risk of cancer?
There is substantial evidence to suggest that dairy consumption does not have a significant effect on overall cancer mortality risk. On one hand, there is research to suggest some protective effects of dairy products on colorectal cancer. The casein and lactose in dairy increase calcium bioavailability and the production of the short-chain fatty acid, butyrate, by the gut bacteria have anti-cancer properties.
Calcium has inhibitory effects on cell growth and division, binding to fatty acids and bile acids that threaten the gut lining. A large study performed on approximately 294,000 men and 199,000 women concluded a 16% and 23% reduction in colorectal cancer respectively. On the other hand, limited evidence suggests that calcium interactions with vitamin D and insulin-like growth factor 1 increase cell proliferation, and therefore the risk of prostate cancer (Górska-Warsewicz et al., 2019).
Moreover, the oestrogen that is found in milk has been associated with hormone-dependent cancers, such as breast cancer and prostate cancer. While studies on pre-menopausal and post-menopausal women have found protective effects of low-fat dairy consumption on breast cancer, other reviews have found “no convincing evidence that milk consumption is associated with lower breast cancer incidence” (Visioli and Strata, 2014). Additionally, Doug et al performed a review on 18 studies that included 1,063,471 participants and suggested that increased dairy consumption, although not milk, was linked to reduced breast cancer risk. Although, the evidence is unclear on the effects of dairy consumption on the risk of breast cancer, some populations (e.g Japan) are reporting strong correlations with breast cancer rates and milk consumption since World War II (Schwarcz, 2020).
Does dairy protect your bones?
Dairy products contain many of the nutrients needed to develop peak bone density and architecture (Szilagyi and Ishayek, 2018). Bian et al demonstrated protective effects over hip fractures with the consumption of yoghurt and cheese, but not cream. Furthermore, probiotic-containing dairy products can accelerate the healing process post-fracture and increase bone mineral density. (Weaver, 2021). These benefits are attributed to the highly bioavailable forms of nutrients available from the dairy matrix and the production of short-chain fatty acids from the gut bacteria, which affects bone metabolism directly (Ratajczak et al., 2021). However, several animal and human studies delineate similar degrees of bone loss protection with fortifies soy milk and cow’s milk. On one hand, a women’s health study on 24,403 Asian post-menopausal women correlated decreased fracture incidences with increased soy protein intake, such as tofu (Matthews et al., 2011). On the other hand, USA and European populations found no significant benefit of soy consumption and bone health compared to dairy consumption. Although fortified soy products attempt to match the nutritional profile of milk, the bioavailability and interactions of these fortified nutrients within the plant matrix is unknown and may not elicit the same protective effects as the dairy matrix, especially when considering the genetics of different ethnic groups (Geiker et al., 2019).
Eat dairy to prevent type 2 diabetes?
The findings related to type-2 diabetes and dairy consumption are inconsistent. A longitudinal study on approximately 37,000 nurses reported a 38% reduction in risk of diabetes with 2 servings of dairy a day. Furthermore, another study found a 12% reduction in risk of diabetes with cheese consumption in 8 nations. A similar relationship was also found in a study looking at post-menopausal and women’s health. These positive correlations between reduction in risk of diabetes and dairy consumption are attributed to the presence of casein rather than lactose. Casein protein has blood sugar regulatory and delayed gastric emptying properties. However, a review of 7 cohort studies concluded no benefit in risk reduction of type 2 diabetes with dairy consumption (Górska-Warsewicz et al., 2019; Visioli and Strata, 2014).
Summary and tips:
Consider eating dairy products in moderation as with most foods.
Fermented dairy products (e.g yoghurt and cheese) tend to be highly beneficial to health within the dairy category.
Contrary to traditional views, the dairy matrix reduces the physiological effects typically associated with processed forms of saturated fats.
For specific nutrition needs and inquiries, please seek dietary recommendations from a registered Dietitian, GP, and nutritionist. Other resources available to you include the NHS, British Nutrition Foundation and British Dietetics Association websites.
Consult your GP to best navigate your specific intolerances and any supplementation advice.
References:
(1) https://www.vegansociety.com/news/media/statistics/worldwide
(2) https://pubmed.ncbi.nlm.nih.gov/29778512/