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Milk – Is it as healthful as we think

Milk – Is it as healthful as we think

Many people include milk in their diet, but few meet the daily recommended quantities. Experts now urge us to rethink these recommendations and explain why milk may not be as healthful as we think.

Dairy milk’s image has taken a bit of a beating, with the likes of oat, almond, and soy milk being hailed as environmentally friendly alternatives.

But for many people of all ages, cow’s milk remains a firm favorite —sloshed over cereal, as a frothy companion to coffee, or enjoyed as a bedtime drink.

The United States 2015-2020 Dietary Guidelines recommend that individuals aged 9 years and over consume 3 cup-equivalents of fat-free and low-fat (1%) dairy products. According to the guideline, put together by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture, this includes milk, yogurt, cheese, and fortified soy milk.

Yet the average amount of dairy that U.S. adults consume is around 1.6 cups each day, far short of the recommended levels.

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Experts writing in the New England Journal of Medicine do not think so. Instead, they call into question the quality of the evidence underpinning these recommendations and suggest alternative sources to provide us with the nutrients necessary for our health.

Strength of evidence is ‘limited’

The debate about milk is, in fact, not a new one.

Back in 2014, Connie M Weaver, emeritus professor and formerly the Head of the Department of Nutrition Science at Purdue University in West Lafayette, IN, wrote an article in The American Journal of Clinical Nutrition highlighting the lack of good quality evidence in support of dairy guidelines.

In her article, which was, in part, funded by Danone Institute International, Weaver alludes to the historical reasons behind milk’s importance to our diet.

“Dairy foods play a central role in most dietary guidance recommendations. They provide a package of essential nutrients and bioactive constituents for health that are difficult to obtain in diets with no or limited use of dairy products,” Weaver writes.

“Since the agricultural revolution, when energy sources shifted from plant foods relatively high in calcium in the diets of hunter-gatherers to cereal crops with low calcium content, the major source of dietary calcium has been milk,” she continues.

Milk has featured in every iteration of the U.S. Dietary Guidelines since its first publication in 1917. Every 5 years, the Dietary Guidelines for Americans Advisory Committee updates the guide, reviewing the available evidence.

Weaver references research that highlights how following a dairy-free diet in the context of a U.S.-style Western diet left adolescents aged 9 –18 years struggling to achieve the recommended intake of calcium.

For the purpose of meeting daily nutrient intake, milk and cheese contribute “46.3% of calcium, 11.6% of potassium, and 7.9% of magnesium in the American diet.”

Yet, when it comes to health overall, Weaver writes, “the strength of the evidence for dairy consumption and health is limited by the lack of appropriately powered randomized controlled trials.”

Human health and the environment

Fast forward to 2020, and a new review article in the New England Journal of Medicine picks up the argument.

Who both hold positions at Harvard T.H. Chain School of Public Health and Harvard Medical School in Boston, MA, discuss the merits of milk. They also pose questions about the possible risk that consuming it may carry.

Both Dr. Willett, a professor of epidemiology and nutrition, and Dr. Ludwig, an endocrinologist, declare no relevant conflicts of interest or industry sponsorship for their article.

Medical News Today asked Dr. Willett why he is interested in studying the relationship between milk consumption and health.

“This is an important topic because milk is one of few foods that are specifically part of dietary guidelines in the U.S. and many other countries, and the recommended amount in the U.S. (3 glasses per day or equivalent amounts of cheese or other dairy products) would make up a large part of an overall diet,” he explained.

“However, studies over the last several decades have not clearly supported the need for such high intakes for prevention of fractures, which has been the main justification, and some concerns about harm have been raised,” he continued. “We thus thought an overview of evidence on risks and benefits would be useful.”

But health is not Dr. Willett’s only concern.

“Also, milk has a heavy environmental footprint, especially greenhouse gas production, and if everyone consumed 3 glasses per day, this would make avoiding extreme globally warming very difficult,” he elaborated. “This should be at least be considered when making decisions about production and consumption of milk.”

Milk studies have ‘serious limitations’

In their article, the professors highlight the contributions that milk may make to the multitude of aspects of our health.

Bone health is probably the most familiar to many people.

Milk is a ready source of calcium, a mineral central to developing and maintaining good bone function. Yet, the studies that set the daily recommendations for how much milk and by extension calcium, we should consume, were very small.

“The basis for the U.S. recommendations for milk consumption derives from studies assessing the balance of calcium intake and excretion in just 155 adults in whom the estimated calcium intake needed to maintain balance was 741 mg per day,” the professors write in their article.

“Beyond small size, these balance studies have other serious limitations, including short duration (2 to 3 weeks) and high habitual calcium intakes,” they continue.

The evidence does not support milk consumption to reduce the risk of hip fractures, they further explain.

On the contrary, they point out that countries with high milk and calcium intake also have the highest hip fracture rates.

The results showed that higher milk consumption leads to an increased risk of hip fractures later in life.

How quickly and how tall we grow are two other examples. Research has established a link between these and milk consumption. Yet, the professors urge caution when drawing conclusions at this point.

“The health consequences of accelerated growth and greater adult height are complex,” they write. “Tall stature is associated with lower risks of cardiovascular disease but with higher risks of many cancers, hip fractures, and pulmonary emboli.”

Weight, heart health, and cancer

Researchers then turned their attention to a host of other aspects of our health that milk consumption may or may not affect.

Several studies have investigated whether milk consumption is beneficial for weight management in adults and children. The professors argue that these showed no “clear effects.”

Moreover, they point out that researchers advice to choose reduced-fat dairy, low-fat milk does not appear to have advantages over whole milk for weight control — and in children, available evidence suggests greater long-term weight gain with reduced-fat milk than with full-fat milk.”

They also argue that the evidence to support a favorable effect of milk on high blood pressure and cholesterol levels is weak and that studies do not support milk as a risk factor for type 1 or type 2 diabetes.

When they looked at cancer, studies showed mixed results. Some studies linked milk consumption to a lower risk of developing colorectal cancer, possibly due to the high levels of calcium found in milk. Other studies, however, pointed to increased rates of breast, prostate, and endometrial cancer.

But when it comes to heart disease, they said that “for persons living in low-income countries where diets are very high in starch, moderate intake of dairy foods may reduce cardiovascular disease by providing nutritional value and reducing glycemic load.”

Recommendation does not ‘appear to be justified’

So, what is the professors’ overall take on milk?

“In our opinion, the current recommendation to greatly increase consumption of dairy foods to 3 or more servings per day does not appear to be justified,” they conclude in the paper.

How much milk a person should consume will, they suggest, depends on individual circumstances.

“If someone is consuming a poor-quality diet high in refined starch and sugar, as is common in many [low-income] populations around the world, milk can fill in some important nutritional gaps,”

“However, if diet quality is otherwise good, the added nutritional benefits of milk will be much less.”

But what does that mean for our calcium and vitamin D intake?

“When consumption of milk is low, the two nutrients of primary concern, calcium and vitamin D (which is of particular concern at higher latitudes) can be obtained from other foods or supplements without the potential negative consequences of dairy foods,” the professors conclude in their paper.

And here is how they propose we can achieve this:

“For calcium, alternative dietary sources include kale, broccoli, tofu, nuts, beans, and fortified orange juice; for vitamin D, supplements can provide adequate intake at a far lower cost than fortified milk.”

Should we drink milk or not?

When MNT asked Dr. Willett whether he thinks people should consider avoiding milk, he explained: “In our review, we concluded that milk is not an essential part of a healthful diet, but consumption of modest amounts is compatible with good health. Thus, we suggested a possible range for health of zero to about 2 servings a day for adults.”

“I think having flexibility is good because different people have different preferences for many reasons,” he continued.

“For environmental reasons, keeping this to about 1 serving a day on average would be important. This is actually not very different from current consumption, which is about 1.6 servings a day; going to 3 servings a day as has been recommended would be a radical change and is not necessary,”

“Milk is deeply woven into the culture of many populations in cold climates because this was a way to provide nutrition year-round when many other foods were not available. In most of the world, people do not consume milk as adults, and it is not essential.”

So, how aware are the general public of the recommended milk guidelines?

“I think most people are aware of the recommendation but not necessarily taking it to heart,” Bjarnadóttir commented. “This recommendation is also special in a way that it can’t apply to everyone. A great deal of the world’s population doesn’t tolerate dairy, and therefore dairy is not a part of their daily routine.”

‘The dose makes the potion’

What kind of research would Bjarnadóttir like to see in the future to help clarify any links between milk and our health?

“There’s already a good amount of research available on milk and dairy, and it’s one of those things that may be hard to study and get concrete results,”

“Milk intake in habitual milk consumers vs. milk intake in people not used to drinking milk or don’t tolerate milk will give very conflicting and unreliable results. There are also many confounding factors to consider, such as micronutrient status and macronutrient intakes,” she continued. “Milk may confer much more benefit to people who have a lower protein and e.g., calcium intake than people who generally have higher intakes.”

“In addition to that, the dose makes the potion. Consuming too much or too little of anything can have poor health effects. “

“For future research, I think we’d get the most reliable information in well defined randomized controlled trials in well established groups of people of differing ages, with differing habitual intakes, and well recorded nutrient statuses,” Bjarnadóttir proposed. “Those results, coupled with longitudinal observation studies in well established groups of people with a set habitual intake of milk, would give us some good data to work with.”

So, does Bjarnadóttir think we should drink milk or steer clear of it?

“Although dairy is not a necessary component of a healthful diet, I think that if you tolerate milk and dairy, they can definitely be healthful additions to your diet. Milk is nutrient-dense, high in protein, and readily available,” she said.

“My recommendations would be to limit your intake to no more than 2 servings per day and emphasize consuming non-sweetened, full-fat dairy, such as yogurt. That being said, if you don’t like or don’t tolerate dairy, there are plenty of other ways to get the nutrients found in milk and live a very healthy life.”

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