Plant-based milk and cow's milk not always nutritionally equal, study says

Stock image of plant-based milks such as almond in a row
Check the labels on plant-based milks for added sugars and calcium and vitamin D supplementation, a new study said. Photo credit: Getty Images

By Sandee LaMotte of CNN

The plant-based milk market is exploding, offering beverages made from seeds, nuts, legumes, grains and blends of those ingredients, often marketed as ready replacements for the traditional choice of cow's milk.

However, not all of those plant milk options are fortified to meet the levels of various nutritional ingredients contained in dairy, according to a new unpublished study presented Monday in Boston at Nutrition 2023, the annual meeting of the American Society for Nutrition.

The study analysed nutrition labels and ingredients for 233 plant-based milk products from 23 different manufacturers and found only 28 of the beverages had as much or more protein, vitamin D and calcium as cow's milk.

"About half were fortified with vitamin D, two-thirds were fortified with calcium, and nearly 20 percent had protein levels similar to cow's milk," said lead study author and registered dietitian Abigail Johnson.

"I'm not seriously concerned about this as it's easy to get these nutrients from other sources, and cow's milk certainly isn't perfect and infallible," said Johnson, who is assistant professor and associate director of the University of Minnesota School of Public Health Nutrition Coordinating Center in Minneapolis. "But if a consumer thinks plant-based milks are a one-to-one substitution for dairy, many of them are not."

In fact, plant-based milks bring healthy options dairy cannot, said nutrition expert Christopher Gardner, a research professor of medicine at the Stanford Prevention Research Center in California who has analysed alternative milks.

"My initial response to the 'Oh my gosh, plant milks aren't as nutritious as cow's milk' is that it's bunk," said Gardner, who is also clinical director of the Stanford Diabetes Research Center. "None of the plant milks have cholesterol, they all have very low levels of saturated fat, and some of them have fibre.

"Dairy milk has cholesterol, has saturated fat and does not have fibre," Gardner added. "And when it comes to dairy and calcium, three-quarters of the world is lactose intolerant, and they get their calcium elsewhere."

In addition, there are milk alternatives that are good options for people aiming to reduce their calorie intake. Some are "quite low in calories, and considerably lower than low-fat milk, so if someone is looking for a white beverage that is low in calories, that may be a reason to look for a milk alternative," said leading nutrition researcher Dr. Walter Willett, a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health in Boston.

"Furthermore, for those concerned about climate change, the milk alternatives will be a better option, and in the long run, we can't have human health without planetary health," said Willett, who is also a professor of medicine at Harvard Medical School.

Read milk labels for specific nutrients

Johnson and her team maintain a massive database of nearly 20,000 food and nutrients labels at the University of Minnesota that is often used by outside researchers for nutrition studies. Due to the expansion of alternative milk products in the marketplace, the database needed updating, and the team began to research the plant-based milks as they were added.

"We found milks made from pistachio, oat, walnut, hazelnut, almond, hemp, flax, cashew, rice - which has been around for a long time - and coconut. This is not coconut milk in the can, but coconut milk in the alternative section of the supermarket," Johnson said.

After analysing the labels, the researchers found 170 of the 233 alt-milk options were fortified with calcium at levels similar to the average 300 milligrams of calcium per 8-ounce glass found in dairy milk. Those same 170 products were also fortified with similar levels of vitamin D as dairy. (Cow's milk doesn't contain vitamin D naturally, so it is always added.)

Specifically, 76 percent of the oat-based milks, 69 percent of the soy-based products, and 66 percent of almond-milk alternatives were fortified with both calcium and vitamin D, according to the study.

"The key takeaway is if you're consuming these because of a specific nutrient, you need to be reading the label because the products are so different from each other," Johnson said.

Calcium and vitamin D, along with potassium and dietary fibre, are considered "dietary components of public health concern" for the general population, according to the 2020-2025 Dietary Guidelines for Americans.

Saturated fats in different kinds of milk

The analysis also looked at levels of saturated fats in alt-milks compared with dairy. Saturated fat increases the body's production of low-density lipoproteins, or LDL ("bad") cholesterol, which can build up inside the arteries and raise the risk of heart attack or stroke.

"Most of the plant milk products fall between the level of 1 percent and skim milk in terms of saturated fat," Johnson said.

Whole milk contains 4.5 grams of saturated fat in every 8-ounce glass; 2 percent milk has 3 grams; 1 percent milk has 1.5 grams; and skim milk has almost 0.3 grams, according to Milk Facts, a website sponsored by the dairy industry.

"Although not covered in this report, soy milk has a good amount of essential fatty acids, both N-6 (omega-6) and N-3 (omega-3), compared to highly saturated fat in cow milk," Willett said. "Thus, soy milk will have a better effect on blood cholesterol levels and will likely be preferable for risk of cardiovascular disease."

Both omega-6 and omega-3 fatty acids are essential for health and must be obtained from food because they cannot be synthesised in the body.

Fibre, added sugars and protein

Johnson and her team also looked at the amount of fibre in plant-based milks. The average American only consumes about 15 grams of fibre a day; however dietary guidelines recommend obtaining 25 to 30 grams of fibre a day from food, not supplements.

"If you were consuming 3 cups of plant milk products throughout the day, you might reach half of your fibre needs," Johnson said. "As a person who studies the microbiome, however, I wouldn't recommend plant-based milk products for fibre yet. I would still suggest people go directly to legumes, whole grains, fruits and vegetables."

Cow's milk is naturally a bit sweet due to a naturally occurring sugar called lactose. Oat milk is similar, in that enzymes break down starches and other complex sugars into maltose, a natural form of sugar. Other plant milks may not be naturally sweet, and Johnson found a few brands used added sugars to compensate.

"About a third of the plant-based milk products have sugar or added sugar in quantities that's more similar to a flavoured milk like a strawberry or chocolate milk," Johnson said. Chocolate milk, for example, contains 25 grams of sugar, twice the amount of sugar as 1 percent milk, while strawberry milk has 29 grams.

Next, the team analysed protein levels. Only 38 of the 223 milk alternatives had a protein level greater than or equal to the 8 grams of protein typically found in every 8-ounce glass of dairy milk, the study found.

"On average, plant-based milks contain about 2 grams of protein," Johnson said.

"The best sources of protein were soy and pea-based milks and milk blends with protein levels between 6 to 10 grams per 8-ounce serving."

That's not particularly worrisome, according to Willett. Most Americans get "plenty of protein from many sources, so this is usually less of an issue," he explained.

"It is (also) interesting that the amount of calcium and protein are much lower in human milk than in cow milk," Willett added. "As human milk is usually considered the ideal form of nutrition, is there reason to believe that cow milk should be the gold standard?"