New studies link whole-milk foods to reduced heart and diabetes risks
Milk and apple pie have long been viewed as the iconic “all-American” foods.
But not everyone likes or can comfortably consume animal milk, whether from cows, sheep, or goats.
Some people can’t easily digest lactose — the major sugar in milk — unless they choose a brand that fortified with lactase: the enzyme that digests lactose.
The ability to easily digest lactose is a genetic trait known found most commonly in people of East African or European ancestry.
In much of the world, the gene that triggers production of lactase switches off after early childhood — perhaps because people in those regions didn’t have or rely on animal milk as they grew into adulthood.
However, a chance mutation that occurred in Europe about 5,000 years ago among cattle-herding people — and probably even earlier in East African cattle-herders — preserved the ability to produce lactase throughout life.
Members of such populations who carried the mutation tended to survive at higher rates, so the mutation became regionally dominant.
Many Americans consume milk and/or milk products like yogurt and cheese, but the alleged benefits or harms of milk have been hotly debated over the past several decades.
That debate began in the early 1970s, when some natural health advocates asserted claims that milk generates mucus and promotes various health problems. However, the mucus-generating claim has been disproved, we lack hard evidence that milk promotes health problems is lacking.
Later, fans of traditional diets actively advocated for milk — especially raw, whole, unpasteurized milk, milk from grass-fed cows, and fermented milk products like yogurt, cottage cheese, and kefir.
For more on these topics, see Grass-Fed Milk Beat Conventional — and Organic — Counterparts, Raw Milk Fight Heats Up, and Got Milk? Whole Beats Skim, Hands Down.
But there’s ample evidence that people’s reactions to foods and nutrients vary, and no one diet or food is good for everyone.
Having said all that, let’s look at three recent studies that put milk in a positive light regarding the risks for diabetes and cardiovascular disease — and a fourth that muddies the picture a bit.
Importantly, their findings match the results of previous meta-analyses of observational (population) studies and randomized clinical trials.
Study #1: Whole-fat dairy does not raise cardiovascular risk
A recently published study concluded that whole-fat dairy is not a cardiovascular risk.
The study was led by Dariush Mozaffarian, M.D., of Boston’s Tufts University and Dr. Marcia Otto, Ph.D., from the University of Texas Health Science Center (de Oliveira Otto MC et al. 2018).
Its findings undermine advice from the U.S. Departments of Agriculture (USDA), whose
2015–2020 Dietary Guidelines for Americans recommend choosing fat-free and low-fat (1 percent) dairy overfull fat milk and milk products.
That advice is based on the ability of some of milk’s saturated fats to raise levels of low-density lipoprotein (LDL) cholesterol, which is typically, but misleadingly, termed “bad” cholesterol.
In fact, the link between LDL and risk for cardiovascular disease is inconsistent, while other forms of cholesterol — such as VLDL — are much more dangerous, especially if oxidized by free radicals.
To study the effect of dairy on the risks for death and cardiovascular disease, Drs. Mozaffarian and Otto and their colleagues analyzed data collected from 2,907 Americans aged 65 or older.
Every participant was also surveyed to assess their lifestyle, medical history, and current medical status, and was re-contacted every six months through the year 2000 and every two years thereafter until the end of the 22-year study.
In addition, blood was collected three times from every participant to measure the levels of three dairy-derived fats: first at the outset of the study in 1992, again six years later, and for the last time 13 years later.
Higher levels of the three fats — pentadecanoic acid, heptadecanoic acid, and trans-palmitoleic acid — were considered good signs that a participant had been consuming substantial amounts of whole-fat dairy.
As it turned out, none of the three dairy-derived fatty acids could be linked with the risk of death from any cause, or to a higher risk of developing cardiovascular disease (CVD).
Instead, high blood levels of one of the three fats — heptadecanoic acid — were linked to a lower risk of death from heart disease, and a 42% reduction in the risk for stroke.
According to Dr. Otto, these findings suggest that current dietary guidelines should be revised: “Consistent with previous findings, our results highlight the need to revisit current dietary guidance on whole fat dairy foods, which are rich sources of nutrients such as calcium and potassium.”
And she made an important point: “Our findings not only support, but also significantly strengthen, the growing body of evidence that suggests that dairy fat, contrary to popular belief, does not increase risk of heart disease or overall mortality in older adults.”
Study #2: Canadian report links milk to reduced death and heart disease rates
Scientists from Canada’s McMaster University just reported the results of an evidence review the covered very large numbers of people (Dehghan M et al. 2018).
The data they analyzed came from the Prospective Urban Rural Epidemiological (PURE) study, which was designed to examine the impact of urbanization on the risk for cardiovascular disease and key risk factors: such as obesity, hypertension, pre-diabetic syndrome, and unhealthy blood-fat profiles.
The PURE study included 136,384 participants aged 35-70 years in 21 countries, not including the United States or Canada.
The participants’ typical diets were recorded at the start of the study using country-specific food questionnaires, and they were followed up for up to 12 years, and an average of 9.1 years.
And the results linked consumption of about three servings of dairy (milk-based) foods daily to lower rates of cardiovascular disease (CVD) and related deaths, compared to lower levels of dairy consumption.
The results also linked consumption of three servings of whole-fat dairy daily to lower rates of death and cardiovascular disease, compared with those who consumed less than one-half serving per day.
As lead author Mahshid Dehghan put it, “Our findings support that consumption of dairy products might be beneficial for mortality and cardiovascular disease, especially in low-income and middle-income countries where dairy consumption is much lower than in North America or Europe.”
For the purposes of this study, one serving of dairy was deemed equivalent to an 8-oz glass of milk, a cup of yogurt, a half-ounce slice of cheese, or a teaspoon of butter.
Participants were grouped into four categories: no dairy, less than one serving per day, one to two servings per day, and (high-intake) more than two servings per day.
Compared to the no-intake group, the high intake group had lower rates of:
• Deaths from all causes (3.4% vs. 5.6%),
• Non-cardiovascular death (2.5% vs. 4%)
• Death from cardiovascular causes (0.9% vs. 1.6%)
• Major cardiovascular disease (3.5% vs. 4.9%)
• Stroke (1.2% vs. 2.9%).
And, compared to those who consumed less than 0.5 servings of whole-fat dairy per day, higher intake was associated with lower rates of:
• Death from any cause (3.3% vs. 4.4%)
• Major cardiovascular disease (3.7% vs. 5)
The authors said that we need to determine why dairy foods would reduce the risk for cardiovascular diseases — and as the results of the Boston-Texas study showed, some saturated fats appear beneficial to cardiovascular health.
Milk products also provide potentially beneficial compounds, including specific amino acids, unsaturated fats, vitamins K1 and K2, calcium, magnesium, potassium, and — in the case of fermented dairy foods like yogurt — beneficial probiotic microbes.
Two limitations of the study were that it relied on people’s responses to diet questionnaires, which are not entirely reliable, and the fact that the questionnaires were administered at the outset of the study, while people’s diets can change over time.
The weaknesses that stem from those limitations were somewhat mitigated by the very large size and long duration of this study.
The PURE study was funded by more than 50 organizations, including the PHRI (Population Health Research Institute) of McMaster University and Hamilton Health Sciences, the Heart and Stroke Foundation of Ontario and Canada, and the Canadian Institutes of Health Research (CIHR).
Study #3: Milk fat may help deter diabetes
Evidence that dairy fat may help reduce the risk for diabetes has been growing steadily.
We reported on some of that evidence in Full-Fat Dairy – Especially Yogurt – May Deter Diabetes, Dairy May Deter Diabetes, and Does Milk Help Deter Diabetes?.
Now, an international research team led by scientists from Britain’s University of Cambridge and Boston’s Tufts University have published results of an evidence review covering 16 “prospective cohort” studies from 12 countries (including seven from the United States) that involved a total of 63,682 participants (Imamura F et al. 2018).
Each of those epidemiological studies probed the relationship between dairy fat and the risk of type 2, “adult onset” diabetes.
The authors explained why they presumed dairy fat might not be a risk for diabetes: “While dairy fat contains [saturated] palmitic acid that could increase risk of [type 2 diabetes], it also contains several other types of fatty acids ...”. (Which of course include the three fats found beneficial in the Boston-Texas study.)
They analyzed the participants' blood to look for markers of dairy fat consumption and compared those with the risk for developing type 2 diabetes.
As in the Boston-Texas study, the UK-Boston team’s analysis of the 16 studies linked higher levels of three fatty acids found in milk to a 30% lower reduced risk of developing type 2 diabetes, compared to the participants with the lowest blood levels.
As lead researcher Dr. Fumiaki Imamura said, “Our results provide the most comprehensive global evidence to date about dairy fat biomarkers and their relationship with lower risk of type 2 diabetes. We hope that our findings and existing evidence about dairy fat will help inform future dietary recommendations for the prevention of lifestyle-related diseases.”
The researchers noted that their findings could not distinguish between different types of dairy products, which may exert different effects on metabolic factors related to diabetes.
That seems likely, especially when it comes to fermented milk foods like yogurt, kefir, cottage cheese, and aged cheese.
Study #4: Low-fat fermented dairy linked to lower heart risk, non-fermented to higher risk
Earlier this year, researchers from Finland investigated whether fermented and non-fermented dairy products had different impacts on the risk of coronary heart disease (CHD).
Their study analyzed data from the 20-year Kuopio Ischaemic Heart Disease Risk Factor Study, which involved 1,981 men, aged 42-60 years (Koskinen TT et al. 2018).
The new analysis included only participants who were free of CHD at the outset of the study, who were eating relatively large amounts of dairy foods.
During the original study, the participants completed four-day diet diaries to determine their average intakes of various foods, including various kinds of dairy foods.
After adjusting the results to account for the effects of factors known to influence the risk for CHD, those who were eating the most fermented dairy products were 27% less likely to have developed CHD.
In contrast, those who were eating the most non-fermented dairy products where 52% more likely to have developed CHD.
Those who were eating the most low-fat fermented dairy products — such as yogurt or sour cream — were 26% less likely to develop CHD.
And the analysis found no link to higher or lower risk of CHD among those who were eating the most high-fat fermented dairy foods and low-fat or high-fat non-fermented dairy products.
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