Abstract

Introduction

Cow’s milk has been widely consumed around the world for hundreds of centuries and acts as an important source of protein. It also acts as a wholesome complete food providing all the major nutrients like fat, carbohydrates and proteins. Further, researchers have shown that the consumption of bovine milk can help the human body by providing wide range of host-defence proteins (Hettinga et al. 2011; van Neerven et al. 2012). This is because various beneficial anti-microbial effects are observed in both human and bovine milks. Especially in the case of infants, it was observed that the consumption of raw cow’s milk has reduced the risk of fever and respiratory infections considerably (Loss et al. 2015). Despite the considerable advantages with the consumption of cow’s milk there are various downsides associated with it. Firstly, the presence of various pathogens like Salmonella spp. and Escherichia coli O157:H7 in milk has been associated to cause wide spread disease outbreaks around the world (Oliver et al. 2009).

Secondly, the cow’s milk allergy is one the most wide spread allergy among infants and children (Vanga et al. 2015c). According to the latest reports, 2.2–3.5% of the infants are allergic to cow’s milk followed by peanuts and tree nuts (Gray et al. 2014; Sicherer and Sampson 2014; Vanga et al. 2015a, b). But, recent studies conducted on a large scale have shown that about 35% of these infants out grow their allergenicity towards milk by the age of 5–6 years; and this may further increase to 80% by the time they reach 16 years (Gray et al. 2014; Santos et al. 2010; Skripak et al. 2007). Another issue widely associated with consumption of cow’s milk is ‘lactose intolerance’. The main source of lactose carbohydrate in humans are human milk and bovine milk (Scrimshaw and Murray 1988). The intolerance is due to the absence or deficiency of the enzyme lactase in the digestive tract and is widely observed in 15–75% of the adults (Bahna 2002; Scrimshaw and Murray 1988). Few studies showed that 80% of people from African origin and 100% people of Asian and American Indian origin are lactose intolerant (Swagerty Jr et al. 2002). Further, other factors like presence of cholesterol and vegetarianism have pushed the people and the food industry to look for alternatives. Few of the researchers have also found a relation between higher risks of cancer being associated with regular consumption of milk both in males and females (Qin et al. 2007; Song et al. 2013). Increasing demand for Vegetarian and Vegan diets all over the world with concern over health and environment are also a major contributing factors (Messina and Reed Mangels 2001; Van Winckel et al. 2011). Thus, the raise in the demand for alternatives to bovine milks has increased over the past few decades. These alternative milks also called ‘non-dairy alternatives’ mainly include soy milk, almond milk, rice milk, cashew milk and coconut milk. Various other sources have also been used to produce these milks, but relatively in minor quantities like hemp, hazelnuts, macadamia nuts, flax and oats. Commercial producers have also successfully introduced blended milks in the market successfully in countries like USA, Canada and UK.

Though, the consumption of bovine milk has been decreasing with a considerable increase in the alternative milks, the amount of research conducted is quite limited on these products with an exception of soy milk (Murugkar 2014, 2015; Stewart et al. 2013). This can be attributed to the fact that soy beans and various soy products have been used for centuries in many parts of the world. But various questions are still to be answered to find advantages to these plants based milk alternatives. Firstly, the ongoing debate on whether these products should be called ‘milks’ or ‘beverage/juice/drink’ should be addressed. The traditional definition of milk is “whitish fluid, rich in fat and protein, secreted by mammary glands of female mammals for the nourishment of their young, and taken from cows, sheep, etc., as an article of human diet” (Dictionary; Van Winckel et al. 2011). Though this definition does not fit the products that are currently sold as ‘milk alternatives’ in most cases their uses are similar to cow’s milk and is used as an article for human diet. Further questions have been raised about the nutritional content and the health advantages of the plant based milks compared to the traditional milks which have to be answered through extensive research. It is only in the past decade that the researchers have tried to understand the importance of these products and their use in management of cow’s milk allergy and intolerance and various other health issues (Sethi et al. 2016).

This review will try to answer these questions by compiling the nutritional aspects and various advantages and disadvantages of consuming plant based alternative milks in comparison to the bovine milk (Fig. 1). This review will help the readers in making an informed decision about introduction of plant based alternative milks in comparison to the traditional bovine milks. This will also aid the researchers in understanding the gaps in research regarding the milks and their health benefits in humans.

The nutritional content has been compiled by using commercial products and the nutritional data obtained from their packaging. The USDA web database has also been used as a source for the nutritional data which helped in cross referring this information depending on the availability of the database (USDA 2015). The data is presented in the format followed by Jaffe (Jaffé 2015). The data was accessed online on each of the organization’s website which reported the nutritional content on bases of consumption quantities of 240 ml. A total of ten plant based milks were initially selected to be analysed. The lower threshold for analysis of the data was put as four i.e. unless there are four independent companies that produce the same kind of product, it will not be considered for further analysis. Only four of the ten initially selected met this requirement, almond milk, soy milk, rice milk and coconut milk. But, it should be noted that only three of the above milks have nutritional content mentioned in the USDA database as of 2015 with an exception of coconut milk. All the major nutrients have been reported for the above 4 plant based alternative milks: carbohydrates, fats, proteins, vitamins and minerals. Among the vitamins and minerals only the ones that are most often mentioned on the label have been selected. It should be further noted that the values of vitamins and minerals are presented as % values. The Dietary Reference Intakes (DRI) values used to calculate the vitamins and minerals from the % values have been obtained from the reports issued by the Food and Nutrition Board of Institute of Medicine, National Academy of science accessed through National Institutes of Health, US Department of Health and Human Services. The final DRI values used were calculated using the averages of recommended intakes for all the males and females from all ages which have been reported in Table 1.

Analysis of plant based alternate milks

Discussion

As already mentioned above, one of the primary reasons for the increased demand for plant based alternative milks is associated with lactose intolerance. This is the condition where patients are unable to digest the lactose sugar due to insufficient amount of lactase enzyme in the digestive tract (Swagerty Jr et al. 2002). The common symptoms reported on consumption of lactose products include bloating, abdominal pain, flatus and watery stool. In some cases, nausea and vomiting are also observed (Lomer et al. 2008). Irrespective of the large portion of population suffering from lactose intolerance, mammalian milk including cow’s milk is widely consumed due to its nutritional content. The mammalian milk has perfect composition of nutrients because it acts as the only source of energy to the neonates of different mammalian species. For example, human milk is a perfect source of nutrition to a newborn infant (El-Agamy 2007). However, when the human milk is not available cow’s milk is usually the substitute used for human consumption because of the nutritional similarities. The nutrient profile of cow’s milk is provided in Table 1. Consumption of 100 g of cow’s milk provides about 64 kcal of energy with 4.65 g of Carbohydrates giving 29% energy, 3.66 g of fat yielding 46% energy and 3.28 g of protein yielding 21% energy. To act as an alternative source of milk, the selected food should have a similar energy distribution as shown above. This energy distribution is much more balanced compared to almonds, rice and coconuts which are used in the manufacturing of alternative milks. From Table 1 it can be calculated that 69 and 76% of the total energies of almonds and coconut come from fats and 89% of the total energy in rice comes from carbohydrates. Further, it has to be noted that the amount of saturated fat in coconut is very high which is generally associated with cardiovascular issues (Siri-Tarino et al. 2010). Rice is a very bad source of proteins and fat as starch is the main source of almost all of its energy. In the case of almonds and soybean, the content of mono-unsaturated fatty acids (MUFA) and poly-unsaturated fatty acids (PUFA) is significantly higher compared to saturated fats. Both, MUFA and PUFA were found to have beneficial health effects in controlling cardiovascular events and cancer formation (Kris-Etherton and Committee 1999; Tapiero et al. 2002; Tavazzi et al. 2008). Considering these advantages and the energy balance, soybean and almonds should be the ideal raw materials for milk preparation in replacing cow’s milk in human diet in terms of the three major nutrients discussed. However, cow’s milk is also a very important source of calcium which is required by the human body for the maintenance of bone health especially during childhood and adolescence (Bowman 2002; Sandler et al. 1985). Numerically, Table 1 shows that the total amount of calcium in 100 g of almonds and soybean is significantly higher than that of milk. But, this would be an improper way to compare these values as the total number of calories from 100 g of almonds and soybean is also significantly higher than that of milk. Hence to rectify this misleading nutritional information, a novel term is introduced ‘weight of nutrient per kcal of energy’ i.e. nutrient density for appropriate comparisons of the nutrient components with respect to the energy yield rather than the mass of the food (Newmark 1987). As per this criteria, milk (1.9 mg calcium/kcal) is found to be a much better source of calcium compared to almonds (0.46 mg calcium/kcal) and soybean (0.62 mg calcium/kcal).

Table 1 also shows the nutritional content of 240 ml of cow’s milk compared with the values reported for plant based milk beverages. The calculation was done using the milk density reported as 1030 kg/m³ (actual rage 1027–1033 kg/m³) (Douglas 1995). The total energy yield of 240 ml of cow’s milk was found to be 158 kcal, where as the average energy yield for the same amount of almond milk, soy milk, rice milk and coconut milk was calculated to be 36.43 ± 6.9, 95 ± 15.16, 133 ± 13.04, 48.75 ± 7.5 kcal respectively. The significantly lower number of calories present in plant based milk beverages is one of the biggest attractions for the increasing demand. The difference is due to the presence of sugars in cow’s milk which is generally present in lower quantities in plant based milks (with an exception of rice milk). The total carbohydrate content in cow’s milk is about 11.5 g in 240 ml. But in the case of plant based milk beverages, the total carbohydrate content was found to be 1.32 ± 0.9, 5 ± 1.83, 1.19 ± 0.56 g in almond milk, soy milk and coconut milk respectively. Conversely, rice milk has the highest quantity of carbohydrates with 25.28 ± 1.7 g which makes it comparable in terms of the total calories available on consumption of a similar volume. Cow’s milk is a food obtained from mammal and hence there is a significant amount of cholesterol present (Jensen et al. 1991). None of the plant based milk beverages would have any cholesterol which is an added advantage and another contributing factor for increasing demand.

The fat content in cow’s milk is about 9.05 g which gives a total energy of 72.4 kcal. Of the 9.05 g of fat in the 240 ml of cow’s milk, about 63% (5.64 g) is saturated fat and 29% (2.62 g) is MUFA. All the plant based milks discussed have lower fat values compared to cow’s milk. But, saturated fats are the lowest in almond milk (0%), followed by 7% in rice milk and 15% in soy milk. In the case of coconut milk, almost all (95%) of the fats reported is saturated. No data is reported regarding MUFA and PUFA. Almond milk with no saturated fats and high quantities of unsaturated fatty acids (86%) seems to be a better alternative among others considering fat as the criteria. Cow’s milk is also a very important source of protein (8.11 g) in human diet and only soy milk is comparable in providing with same amount of proteins (8.71 g) to the human body. But, it should be noted that both cow’s milk allergy and soybean allergy are major issues are associated with proteins present in these products which are primarily responsible for the eliciting allergic reactions (Sicherer 2011; Sicherer and Sampson 2010; Vanga et al. 2015c). Almond milk also provides a limited quantity of protein which is about 1.67 ± 1.63 g. Almond proteins are also responsible for causing allergic reactions in the allergic patients (Vanga and Raghavan 2016).

Calcium in most brands of the plant based alternative milks is added to mimic the levels present in cow’s milk. The levels of calcium range widely between 22–495, 0–385, 22–330 and 44–495 mg in almond milk, soy milk, rice milk and coconut milk respectively. But, further research is needed to establish the consequences of added calcium in the human body. Various other minerals are available in considerable quantities in cow’s milk which include magnesium (32 mg), phosphorous (230 mg) and potassium (373 mg). Most of the alternative milks contain comparable quantities of minerals i.e. at least 50–70%, with an exception of coconut milk with no phosphorous reported and lower amounts of potassium in rice milk and coconut milk. Few brands of soy milk were found to contain even higher amounts of phosphorous and potassium compared to cow’s milk. Cow’s milk is also a very good source of vitamins. But, among alternative milks only soy milk contains comparable amounts of nutrients. The vitamin content of other milks is not reported on the labels meaning they are either not present or present in very minute quantities.

Conclusion

Overall, the review outlines the nutritional differences among various plant based alternative milks and cow’s milk. It is quite clear that nutritionally soy milk is the best alternative for replacing cow’s milk in human diet. But, various issues including the ‘beany flavor’ and presence of anti-nutrients are major hurdles which encouraged people to look for more alternatives like almond milk, etc., Though, almond milk also has a balanced nutrient profile and much better flavor, the nutrient density and the total number of calories are not as rich as that of cow’s milk. Hence, when consuming almond milk care should be taken that various essential nutrients are available through other sources in the diet in appropriate quantities. Rice milk and coconut milk cannot act as an ideal alternative for cow’s milk because of limited nutrient diversity, but they are the options for consumers that are allergic to soybeans and/or almonds. Further research is needed to understand the effect of various conventional and novel processing methods on the nutrient profile, flavor and texture of these alternative milks.

Acknowledgement

Abbreviations

Compliance with ethical standards

References