What’s in the Dairy Case? Oat, Pea, and Coconut Milks: Plants in Cows’ Clothing?

Written by: Lauren Milligan Newmark, Ph.D. | Issue # 78 | 2018

They say there is a lid for every pot. If you’ve recently stood in front of your local grocery store’s dairy case, overwhelmed by the different types of “milks” currently available, you may wonder if there isn’t also a milk type for every shopper. Grains, beans, nuts, and even fruit are being transformed into beverages that can be poured over cereal, whipped up in a latte, and used for dipping chocolate chip cookies.

The plant-based milk substitute market has exploded over the last 10 years, quickly becoming a multi-billion dollar industry in the U.S. and around the globe [1, 2]. This growth has been fueled in part by consumers believing these milk substitutes are as nutritious as (or even more nutritious than) cow milk [3], a perception that is strongly influenced by the use of the word milk in the product name and their very placement next to cow milk in the dairy aisle. Add in claims on the packaging regarding calcium and vitamin D fortification, and it is not hard to see why people would think that anything cows can do, plants could do better.

But consumers should proceed with caution—just because these drinks look, feel, and act like cow milk does not make them nutritional equals. Two previous SPLASH! milk science update contributions discussed how soy and almond milk beverages measured up to cow milk. Read on to find out the nutritional benefits and shortcomings of oat, coconut, rice, pea, and banana (yep, banana) milk.

The Milky Way

Grocery stores have aisles dedicated to water and juice, so if a beverage is found in the dairy case it suggests this product has properties more similar to cow milk than these other drink choices. But how do plant milk manufacturers transform cereals, nuts, beans, and fruit into something that resembles cow milk in appearance and texture?

The first hurdle requires turning a solid into a liquid, and the second requires making that liquid as creamy and milk-like as possible. First, plant parts are extracted in water to make what is best described as a slurry—small plant pieces suspended in water. These small solid pieces must then be strained out. At this point in the process, oat and rice (and other cereal-based) milk makers add in enzymes to break down the natural starches into smaller sugars, which function both to help make the product easier to digest and to sweeten the drink [4]. Some plant milks, such as pea milk, have a slightly different order of operations. Instead of milling with water, yellow peas are milled into flour, the fiber and starch are removed, and the remaining pea protein flour is then blended with water [5]. Either way, the straining process leaves the solids behind, which is ideal for making a smoother tasting drink but also may result in throwing out key nutrients. For example, most of the protein from nuts remains in the solid particles rather than the strained liquid. This explains why a serving of nut milk (like almond and cashew) is so much lower in protein than a serving of nuts.

At this stage, the plants may have been successfully transformed into liquids, but they are more similar in texture and viscosity to water than milk. To make them milky, the next steps (of some but not all brands of plant-based milks) include homogenization, which uses high pressure to break down fat particles into smaller particles, thereby making them more evenly disbursed throughout the liquid; emulsifiers, which help to keep these smaller particles dispersed throughout the solution; and finally, thickening agents, which are added to achieve a creamier consistency. This is also the stage where many of the milks are fortified with vitamins and minerals, namely vitamin D and calcium, to try and match their composition in cow milk [1-4]. Some milks are also fortified with vitamin B12 [2], a vitamin in short supply in vegan and vegetarian diets.

Coconut milk beverage has the opposite problem of cereal- and legume-based milks. Strained coconut meat actually produces a liquid (called coconut milk, no beverage at the end) that is too creamy to be a cow milk substitute but is ideal for making curries and soups. Coconut milk beverage is essentially diluted coconut milk, but also undergoes homogenization, can have added emulsifiers, and many brands are calcium and vitamin D fortified.

Matching milk texture is important but so is looking like milk. To this end, a recent study [1] ascribed a whiteness index (WI) to assess how well various plant-based milks approximated the color of cow milk. Cow milk has a WI of 81.89, and the closest plant-based milks were soy milk and coconut milk (with ratings between 67 and 75 depending on brand and flavor) [1]. Not surprisingly, cashew, almond, and brown rice milk had much lower scores (in the 50s) [1]. If whiteness is indeed a factor is selecting a milk substitute, some plant milks have a natural advantage over others.

Inside the Carton

A comparison of cow milk with plant-based milks is essentially a comparison of cow milk with calcium and vitamin D-fortified plants, as these milks are nothing more than plants, water, and perhaps added sweeteners. Transformation into milk does not increase a plant’s protein or micronutrient content, which is where most plant-based milk substitutes come up short when compared with cow milk. It seems surprising, then, to learn that a survey found half of respondents believed plant-based milk substitutes to be nutritionally superior to cow milk [3].

Part of the misconception may come from confounding healthy with nutrient-rich foods. Plant-based milks (like the plants from which they are derived) are certainly important functional foods, or nutriceuticals—foods that provide health benefits beyond their nutrients [6]. Their transformation into beverages may even increase their intake by consumers, thereby making important contributions to the health of the population. But when you do a side-by-side comparison of what is actually inside the cartons [e.g, 1–4,7], plant-based milks are not a suitable nutritional substitute for cow milk.

Oat milk

Oat milk, like the oats from which it is made, is low in fat and calories and high in iron, folic acid, and fiber. Oats are actually a good source of protein as well; one 8-ounce serving of oat milk has about half the protein (approximately 4 grams) of cow milk (approximately 8 grams). However, the digestibility and protein quality of oat protein is lower than that for whey and casein, the proteins in cow milk (a trend that holds true for all nondairy milks, with the exception of soy) [1–4].

Oat fiber is present in oat milk and has been demonstrated to lower cholesterol, specifically low-density lipoproteins (LDL), also known as the bad cholesterol [4,8,9]. Oat fiber has also been demonstrated to lower the glycemic index (a measure of how quickly glucose enters the bloodstream after eating a food) of oat-based foods, including oat milk [1, 8]. Drinking oat milk is thus a way to drink your whole grains rather than eat them.

Rice milk

If anyone has ever been on an elimination diet, they are well aware that rice is the first food you get to start adding back in because it is one of the leading hypoallergenic foods. Rice milk offers the same benefit, and is often recommended for people with cow milk protein allergy who may also react to soy and nut milks. It should not, however, be used as a milk substitute for infants and toddlers with allergies without other major dietary interventions because it is so low in protein (rice milk has less than 1 gram of protein per 8-ounce serving) [10]. Rice milk lacks calcium and must be fortified, and has carbohydrate as the primary energy source. This means the milk has a naturally sweet taste but also means that it is probably more similar to juice than to milk.

There is also a unique concern with rice milk: arsenic levels [1,7,11]. Rice accumulates arsenic as it grows, and the toxin does make its way into rice milk. Levels of inorganic arsenic (which is the more toxic form) in several brands of rice milk were found to exceed the current EU and U.S. standards for arsenic levels in drinking water [11], suggesting that regular consumption could pose health risks, particularly in pregnant women and young children.

Pea milk

Pea milk is one of the most recent plant-based milk substitutes to emerge on the shelves of the dairy case. Pea milk is similar to soy milk in boasting a high protein content, with some pea milks advertising even higher protein levels than cow milk. But don’t forget to think about protein quantity. Pea protein is not a complete protein, which means it does not provide all of the essential amino acids, and thus should not be the only protein source in the diet.

The list of the nutritional benefits of peas is quite long, and these benefits pass on to pea milk: iron, vitamin C, antioxidants, vitamin K, and fiber are all quite high. Peas are also naturally very low in sugar and fat, which means the majority of energy in pea milk is provided by protein, which does not get filtered out in the milk- making process, as is the case for many nut milks [2]. Peas are naturally low in calcium, vitamin D, and vitamin B12 and are usually fortified with these nutrients as a result. Indeed, many brands boast having more calcium than cow milk. But what is on the nutrition label and what makes its way into your bloodstream may be two very different numbers. The short-chain fatty acids present in cow milk, but missing from pea milk (and other plant milks), enhance calcium absorption in the intestines.

For those with a cow milk protein allergy or on a vegan diet, pea milk offers many of the same nutritional benefits of cow milk. However, protein quality and calcium bioavailability should still be kept in mind when making this nutritional swap; pea milk may come close to cow milk but could still leave consumers with nutritional deficits.

Coconut milk beverage

Coconut milk beverage is a diluted form of coconut milk; the former is found in refrigerated cartons in the dairy case and the latter is usually found in cans in the international food section of the grocery store. Coconut milk is made by grating and squeezing the meat of the coconut, resulting in a thick and creamy white liquid (hence the name “milk”). Coconut milk beverage shares some, but not all, of the nutrients found in coconut meat. For example, coconut milk beverage provides medium-chain fatty acids. Some studies have shown that these fats improve heart health by raising the good cholesterol, high-density lipoproteins (HDL) and lowering LDL [7,12]. Indeed, these fats are the main energy source of coconut milk beverage, as there is little protein (<1 gram per 8-ounce serving). Recently, coconut milk has been marketed as a blended drink with almond milk. Although still low in protein, the addition of almond milk provides consumers with heart-healthy unsaturated fats as well.

Banana milk

Apparently even bananas are getting in on the milk act. Whereas other fruits are blended with water and marketed as juice, bananas’ creamy consistency must lend itself better to a plant-based milk substitute. Depending on the brand, bananas may be combined with grains and seeds, or even soybeans (and potentially some thickening agents and emulsifiers) to create a potassium-rich, vegan milk alternative. The addition of ingredients such as chia seeds and soy beans increases the milks omega-3 fats and protein content but also begs the question of why it is called banana milk when the majority of the nutrition, save for potassium, comes from added plants? Why not banana-flavored soy milk (as they already offer strawberry, vanilla, and chocolate)?

Your Crowded Dairy Case

Although this may seem like plenty of nondairy milk options, this article only touches on the most popular (or unusual, as is the case with banana milk). Hemp milk, sesame milk, peanut milk, quinoa, amaranth, and even potato milk are available in organic food sections and even some large grocery store chains, making it hard for consumers to find cow milk in a section labeled “dairy.” The sheer variety of plant-based milks and the different options (unsweetened, vanilla, and even coffee creamers) may allow consumers to tailor their plant-based milk to their specific dietary needs (e.g., nut allergy, low sugar). As they continue to grow in popularity, there is a critical need to educate the public on each plant-based milk’s nutritional benefits and their shortcomings compared with cow milk. The perception that they are as nutritious as cow milk has the potential to result in nutritional deficiencies, particularly if these milks are used to replace cow milk in growing children and adolescents.

References

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