The quantity of several micronutrients is available for cow's milk. Similar information is, however, not available for most nondairy beverages. Amongst micronutrients, we were able to compare only calcium and vitamin D content in cow's milk and nondairy beverages. It was noted that most nondairy beverages are supplemented with equal or greater amounts of calcium and vitamin D compared with the cow's milk (Table 1). Nondairy beverages provide 30% to 45% RDA of calcium and 25% to 20% RDA of vitamin D for toddlers and young children (Tables 2 and 3). Figure 2A and B shows calcium content in all products compared with RDA in toddlers and young children, respectively. Nondairy beverages with equal content of fortified micronutrients, however, cannot be considered as nutritionally equivalent to cow's milk as the bioavailability of the fortified products vary in different beverages.
Nondairy beverages primarily derived from plants that contain the word “milk” are increasingly available (6).
Our results show that the commonly available nondairy beverages are derived from almond, cashew, coconut, hazelnut, hemp, oat, rice, and soy. Many manufacturers add the word “milk” to their product's name, suggesting a healthy beverage that would provide an advantage to their product. We show that these beverages manufactured differ from cow's milk in nutritional content. Inappropriate substitution with these beverages increases the risk of nutritional deficiency (6,7). The quantity of several nutrients in cow's milk has been described in detail (9). Similar data for most of the nondairy beverages is, however, not available. Therefore, it is difficult to compare all the nutritional constituents with cow's milk. Another matter of concern is the bioavailability of the fortified nutrients in the nondairy beverages. The physical state of the substance in the fortified beverage and its interaction with the food matrix are important determinants of absorbability (12). There is, however, no information about the bioavailability of fortified nutrients in nondairy beverages. These issues raise concerns over the trend toward increased consumption of nondairy beverages among children.
Protein is an essential structural component of cells and also plays an important role in functions of various enzymes, hormones, nucleic acids, and other molecules essential for life (13). The most important aspect of a protein from a nutritional point of view is its quality. Protein quality is based on the amino acid composition, digestibility, bioavailability, and specific protein-derived components (13,14). Several methods of evaluating protein quality have been used in the past such as biological assays (Biological Value, Net Protein Utilization, Protein Efficiency ratio), chemical assays (Chemical score, Amino Acid Score), and mixed assays such as protein digestibility–corrected amino acid score (15). In 2011, FAO Expert Consultation on Protein Quality Evaluation in Human Nutrition recommended a new protein quality measure DIAAS to replace protein digestibility–corrected amino acid score. DIAAS is defined as DIAAS % = 100 × [(mg of digestible dietary indispensable amino acid in 1 g of the dietary protein)/(mg of the same dietary indispensable amino acid in 1 g of the reference protein)] (11). DIAAS is based on true ileal amino acid digestibility determined for each amino acid individually, and lysine availability estimates, using nontruncated scores. In calculating DIAAS, the ratio should be calculated for each dietary indispensable amino acid and the lowest value designated as the DIAAS (11).
Rutherfurd et al reported DIAAS values for the individual amino acids in milk protein concentrate, soy protein isolate, rice protein concentrates, and various other proteins in growing rats. Based on the present study, the soy protein isolate has a DIAAS value >100% for most individual indispensable amino acids when calculated using the amino acid requirement pattern for the 0.5- to 3-year-old child. The nutritive value of soy protein is limited by lower content of methionine and cysteine with lowest DIAAS value of 90.6% (16). Fortification with methionine significantly improves nutritional quality of soy-based products (15). Addition of methionine to soy infant formula has shown benefits. Adding methionine to soy protein consumed by adults with an adequate nitrogen intake, however, has no significant effect on the nutritional value (17). Soy protein also contains endogenous inhibitors of digestive enzymes and lectins. These inhibitors and lectins are either inactivated by heat treatment or eliminated by fractionation during food processing to improve the nutritional quality of soy-based products (17). Rutherford et al also reported that the lowest DIAAS for rice protein isolate is 37.1% when calculated using the amino acid requirement pattern for the 0.5- to 3-year-old child (16).
Cow's milk has >100% DIAAS value for all the indispensable amino acids with lowest DIAAS of 118% (11,16). The high protein quality in cow's milk arises both from its nutritional value and from its physiological properties (14). Cow's milk also contains proteins with biological activities including enzymes, immunoglobulin, bactericides, hormones, mediators, and growth factors (14,18). We could not compare the protein quality in other nondairy beverages, except soy and rice protein, because the information about DIAAS and the amino acid composition in those products is not available. This raises unanswerable questions about the protein quality of those products.
Carbohydrate and Fat Content
Fat content in cow's milk is energy dense and a rich source of cholesterol and saturated fatty acids (19) and is thought to be important for the developing brain. After 2 years, a switch to low-fat or fat-free milk is recommended to reduce saturated fat intake (20–22). Newer studies, however, suggest that a high intake of dairy fat can be associated with a lower risk of developing central obesity while a low intake of dairy fat can be associated with a higher risk of central obesity (23). One recent pediatric study showed that consumption of low-fat milk was associated with increased risk of overweight/obesity between 2 and 4 years of age (22). Although nondairy beverages are low in saturated fats, most of the products contain energy equivalent to milk, which is derived mostly from sugars and other carbohydrates.
Several micronutrients including vitamins and minerals are essential for growth and development. Nine shortfall nutrients identified in the 2015 Dietary Guidelines Advisory Committee report are vitamin A, vitamin D, vitamin E, folate, calcium, magnesium, potassium, fiber, and iron for the premenopausal females. Among these shortfall nutrients, calcium, vitamin D, fiber and potassium were classified as nutrients of public health concern because their under consumption is linked to adverse health outcomes (24).
Calcium is essential for healthy bones and teeth. It also has several vital functions within cells predominantly as a second messenger (25). Most of the nondairy beverages are fortified with calcium (Fig. 2A and B). Adding calcium to a product, however, does not guarantee nutritional equivalence with other products containing similar amounts of calcium because the bioavailability of calcium varies significantly in fortified beverages (12). Cow's milk provides more than half of the RDA for calcium in a typical diet of toddlers and young children. Cow's milk has a high content of calcium and that calcium is highly bioavailable (14). Other milk constituents such as lactose and casein phosphopeptides are known to increase the intestinal permeability for calcium salts and increase intestinal absorption, respectively (14,18).
Magnesium, a cofactor for several enzyme systems that regulate diverse biochemical reactions, is required for energy production, and membrane transport. Soy and hemp-based beverages are good sources of magnesium. Zinc is essential for the function of several enzymes and plays a role in DNA repair, cell growth and replication, gene expression, and protein and lipid metabolism. Cow's milk is a good zinc source and the zinc is more bioavailable than nonmilk sources (18).
Cow's milk is a rich source of vitamins including riboflavin, vitamin E, vitamin A, folate, thiamin, niacin, vitamin B6, and vitamin B12. It contains higher amount of riboflavin compared with other products. Fortified cow's milk is also a key dietary source of vitamin D in early childhood. Replacing cow's milk with nondairy beverages could put children at unnecessary risk of complications from low dietary vitamin D. Severe rickets has been described in children who did not drink cow's milk (6).
Nondairy milk beverages are perceived to be healthy but the products available vary remarkably in their nutritional profiles; most have low protein, mineral, and vitamin content and the quality of the protein is less than cow's milk. If these products are portrayed as substitutes for cow's milk in the diets of young children, then protein content and bioavailability of the nutritional additives need to be considered by manufacturers and consumers.
The present study presents information on nondairy beverages in a way that they can be compared with dairy milk, the preferred beverage for children recommended by the American Academy of Pediatrics, the Centers for Disease Control, the US Department of Agriculture and provided in WIC packages unless there is a medical contraindication to its use.
The present study does have limitations. The first is the local nature of the survey for the products. The Web sites for all the products, however, indicate they are distributed nationally. Each and every product were not assessed, because the number is overwhelming. The focus was on the product labeled as “original” in the major categories identified. The Web pages of the manufacturers did not contain complete information and because of this, important attributes, such as protein quality and nutrient bioavailability could not be assessed for all the products. In conclusion, cow's milk plays an important role in the diet of toddlers and young children as it is a rich source of nutrients primarily protein, fats, vitamins, and minerals. Cow's milk should not be removed from the diets of young children unless there is a medical indication to do so. In that circumstance a dietitian can review the entire diet to be sure, it satisfies the nutrient requirement. It is also important that nondiary beverages should not be considered a nutritional substitute for cow's milk until nutrient quality and bioavailability is established.
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Keywords:© 2017 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology,
cow's milk; nondairy beverages; nutrition; protein quality