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FOOD & DRINK

GOAT MILK: AN OVERVIEW OF ITS ROLE IN THE HUMAN DIET The smell and taste of goat milk may be unpalatable to some, but its nutritional profile is much the same as cow’s milk. Now that goat milk products are becoming more popular and goat milk-based infant formulas are available throughout the UK, this article examines the general efficacy of goat milk. Animal milks have been used to supplement the human diet for thousands of years. Goats (capra hircus) are thought to have been the first animals that humans have used for their milk and the second animal to be domesticated after the dog. They have the highest yield of milk of any dairy animal in relation to their body weight.1 Apart from coconut and other nut milks (that technically do not meet the definition of ‘milk’) now flooding the supermarket isles, goat milk (also known as caprine milk) is one of the main alternatives to cow’s milk. It is relied upon as a major source of nutrition in many developing countries. In the UK, however, cow’s milk remains the most commonly used milk.2 Goat milk can be purchased in selected supermarkets as skimmed, semi-skimmed, or whole milk, much the same as cow’s milk, retailing at around £1.72 per litre compared to £0.80 for fresh cow’s milk.3 SMELL AND TASTE

You may have noticed that the marmiteesque smell of goat’s cheese is not at all dissimilar to what you would smell standing downwind from a goat. This scent is from three fatty acids: caproic, caprylic and capric acid. These only

become a problem if they are released as free fatty acids from the milk fat by poor treatment of the milk. Goats have scent glands behind their horns that secrete a potently odorous oil that includes the same three fatty acids.1 Fresh goat milk, ice creams, cream, live yoghurts and goat milk-based spreads are available from UK brands. From tasting some goat milk yoghurt myself, I was pleasantly surprised; it is very mild and creamy and I found it to lack the tanginess of cow’s milk yoghurt. The goat scent was almost undetectable. NUTRITIONAL PROFILE

The energy content of whole cow’s milk and goat milk is very similar (see Table 1 overleaf).4

Alice Fletcher Registered Dietitian within the NHS, Countess of Chester NHS Foundation Trust (Community Dietitian)

Alice has been a registered dietitian for four and a half years, working within NHS Community based teams. She is passionate about evidencebased nutrition and dispelling diet myths. In her spare time, Alice blogs about food and nutrition at nutritionin wonderland.com.

REFERENCES Please visit the Subscriber zone at NHDmag.com

Vitamins and minerals • Potassium, magnesium, iron and vitamin A are all slightly higher in goat milk compared with cow’s milk. • Both cow’s milk and goat milk are good sources of iodine (full-fat cow’s milk = 30μg per 100ml). The exact quantity of iodine in goat milk is not known, but is thought to be significant. • Both cow’s and goat milk are poor sources of vitamin D (unless fortified). www.NHDmag.com April 2019 - Issue 143

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FOOD & DRINK Table 1: Macro and micronutrients contained within goat, cow’s and unsweetened soya milk Per 100g*

Goat

Soya

Cow

(unsweetened)

Per 100g

Goat

Cow

Soya (unsweetened)

Energy (kcal)

62

63

26

Iron (mg)

0.12

0.02

0.43

Protein (g)

3.1

3.4

2.4

Zinc (mg)

0.5

0.5

0.3

Fat (g)

3.7

3.6

1.6

Vitamin A (µg)

44

38

Saturated fat (g)

2.37

2.29

0.24

Vitamin D (µg)

0.1

Tr

0.8

Carbohydrate (g)

4.4

4.6

0.5

Thiamin (mg)

0.03

0.03

0.06

Sugars (g)

4.4

4.6

0.2

Riboflavin (mg)

0.04

0.23

0.2

Potassium (mg)

170

157

74

Niacin (mg)

0.8

0.8

0.1

Calcium (mg)

100

120

120

Vitamin B6 (mg)

0.06

0.06

0.03

Magnesium (mg)

13

11

15

Folate (µg)

1.0

8.0

14

Phosphorus (mg)

90

96

48

Vitamin B12 (mg)

0.1

0.9

0.4

Highlighted = lactose content. Contents of table sourced from McCance and Widdowson4

Table 2: Macronutrients of goat yoghurt vs cow’s milk yoghurt Nutrient

Full-fat goat yoghurt per 100ml

Full-fat Greek plain yoghurt per 100ml*

kcal (calories)

105kcal

133

Fat (g)

7.3

10.2

5.0

6.7

4.3

4.8

3.2

4.5

- of which saturates (g) Carbohydrate (g) - of which sugars (g) Protein (g)

5.5

5.7

*Greek yoghurt based on McCance and Widdowson, goat milk yoghurt was not available on this spreadsheet, I have used St Helen’s Farm original natural Goats Milk Yoghurt. 4

• Goat milk contains only 1µg of folate per 100ml, mature breast milk contains approximately 5µg per 100ml and cow’s milk the most at 8μg per 100ml.4 • An interesting study using rats found that consumption of goat milk resulted in greater bioavailability of zinc and selenium and a greater deposit of zinc in key organs compared with both a milk-free diet and one containing cow’s milk. However, much more research is needed.5 Digestibility • Goat milk is higher in medium chain fatty acids than cow’s milk and the fat molecules are smaller. It is theorised that this is one of the reasons why people report finding goat milk easier to digest than cow’s milk.6 • Goat milk forms a softer curd in the stomach compared with cow’s milk.7 20

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• Goat milk contains only 0.2g per 100g less lactose than cow’s milk. • In vitro, when the human digestive system is mimicked, caseins from goat milk have been found to be more efficiently digested compared with caseins from cow’s milk.8,9 • In vitro studies found that although the protein quality does not differ between goat milk formula (GMF), cow’s milk formula (CMF) and human milk, the kinetics of protein digestion of GMF is more comparable to that of human milk than CMF.10 OLIGOSACCHARIDES, GUT HEALTH AND IBD

Human milk oligosaccharides are complex sugars that function as selective growth substrates for specific beneficial bacteria in the gastrointestinal system. Goat milk contains the highest amount of oligosaccharides amongst the milk of domestic animals, and has significant


FOOD & DRINK similarities to human milk oligosaccharides from a structural point of view.11,12 Goat milk oligosaccharides have been found to have anti-inflammatory effects in rats with experimental colitis and may be useful in the management of inflammatory bowel disease. One study published in 2006, looked at 20 rats with artificially induced colitis. They were fed the same diet, but with different sources of fibre, cellulose, or a mixture of goat milk derived oligosaccharides and cellulose (this made up 5% of the diet). Those consuming goat milk oligosaccharides showed less severe colonic lesions and a more favourable intestinal microbiota.13 A similar study published in 2006, found that rats with colitis who were fed goat milk whey (rich in oligosaccharides) lost less weight compared with the control group.14 These results have been repeated once again within a 2017 study using rats, but this appears yet to progress to human studies.15 Interestingly, similar results were also found when goat yoghurt was studied in rats with induced colitis.16 GOAT MILK AND ATOPIC DERMATITIS

The internet is awash with anecdotal reports of goat milk dairy products curing (or at least hugely improving) the severity of atopic dermatitis (AD). The proposed causes of AD vary widely, including soaps, detergents, stress, the weather and sometimes food allergies.17 Dietary manipulation by parents with the premise of improving symptoms has been found to be increasingly practiced.18 One crossover study found ass milk to improve AD’s severity compared with goat milk, which did not find significant improvements.19 Evidence for goat milk holding an advantage over cow’s milk for AD remains largely anecdotal. The incidence of eczema assessed using SCORAD was 14% in a clinical trial of infants randomised to goat milk formula from birth compared to 23% in infants fed cow’s milk formula.29 The difference was not statistically significant as the trial was powered to assess growth outcomes, not allergy, and hence would need to be confirmed in a larger study. IS IT LESS ALLERGENIC?

It has previously been suggested that goat milk could be an alternative for those suffering with

cow’s milk protein allergy (CMPA). Incidence of CMPA in adults is extremely low. The World Health Organisation has estimated it to affect 1.9-4.9% of children.20 More than half of children with IgE-mediated CMPA outgrow their milk allergy by five years of age. Most children with non-IgE-mediated cow’s milk allergy will be milk tolerant by three years of age.21 Goat-milk-based formulas should not be given to infants with CMPA, unless directed by a healthcare professional.22 Some of the proteins in goat milk are sufficiently similar to those found in cow’s milk and may cause cross-reactivity.23 There have been case reports of babies and children who have had severe allergic reactions to goat milk.24,25 A study in 1999, undertaken to ascertain the cross reactivity of milk proteins between different species of mammals, found that IgEs from children who were allergic to cow’s milk, were capable of recognising milk proteins from ewe, goat and buffalo, while none of the children reacted with the more obscure camel milk. Camel milk was also not recognised from circulating IgEs from a child specifically allergic to ewe’s milk. Specific antibovine monoclonal antibodies cross-reacted with proteins from other mammalian species, apart from those of camel. This was thought to be due to phylogenetic differences (camels are not as closely related as the other species24). A later study in 2011 (n=38) found similar results.26 A small study published in 2003, tested 12 patients with cow’s milk allergy for tolerance to goat milk protein through radioallergosorbent assay (RAST), specific IgE, skin prick and challenge tests. Only 25% of the patients showed adequate immediate and late oral tolerance and had negative results of immunological tests for adverse reactions, demonstrating the close cross reactivity between the proteins.24 GOAT MILK FORMULA (GMF)

You may be wondering if GMF has the same scent/taste that we have already discussed; you will be pleased to hear that this can be prevented by careful handling during manufacturing, leaving a neutral scent. The safety and nutritional adequacy of GMFs have previously been questioned. Until March www.NHDmag.com April 2019 - Issue 143

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FOOD & DRINK 2014, it was illegal to market infant formula based on goat milk proteins (GMF). In 2004, the European Food Safety Authority (EFSA) felt that small study sample sizes and the lack of a breast-milk-only control groups meant that the adequacy of GMF could not be confirmed.27,28 However, following on from new evidence since the initial 2004 review, EFSA overturned their position. Two main studies are discussed in the EFSA Report,29 one having taken place in Auckland, New Zealand (a pilot study of 62 infants)30 and a later study in Adelaide Australia (301 infants). The latter randomised, double-blind controlled trial compared growth rates and nutritional status of 200 infants with exclusive feeding of GMF or CMF for at least four months.31 An exclusively breastfed reference group (up to at least four months) was included as a control (n=101). The primary outcomes were body weight, length and head circumference at enrolment and at the indicated time points. The secondary outcomes were markers of nutritional status in blood at the age of four months (haemoglobin, haematocrit, creatinine, urea nitrogen, folate, albumin, ferritin, blood amino acids). There were not any differences in the occurrence of serious adverse events, general health and incidence of dermatitis, or medically diagnosed food allergy. The GMF used in both studies was based on whole milk with a casein whey ratio of 80:20 and was compared with whey adjusted 60:40 CMF. Nutritional outcomes and growth did not differ between GMF and CMF. As a result, GMF was permitted under both EU and UK regulations and is available across the UK. Digestibility of GMF It has been suggested that GMF may be easier for babies to digest, resulting in more frequent and softer stools. A large prospective cohort study of 976 infants from birth to 12 months of age was published in 2011. The study measured (amongst other things) the bowel movements of infants fed breast milk, CMF and GMF. Stool number and consistency were recorded between 0 and four months. The consistency of stools was graded by parents, using an analogue scale with these categories: runny, soft or pasty, soft but well formed, firm and hard. It was found that 22

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more of the infants fed CMF had fewer, but more well-formed bowel motions compared with breastfed infants. The stool characteristics of infants fed GMF resembled those of infants fed breast milk. Ultimately, it looked as though GMF was easier to digest than CMF, with less risk of forming hard stools.32 CAUTION

As with any milk given to babies, apart from breast milk, it must be supplemented with powdered formula to contain all the required nutrition in the correct amounts.33 Case reports detail babies becoming extremely malnourished from a homemade formula recipe based upon goat milk, or from feeding babies goat milk that has not been supplemented. Other morbidities have included severe electrolyte abnormalities, metabolic acidosis, megaloblastic anaemia, haemolytic uremic syndrome and infections.34,35 Now that correctly formulated powdered goat milk formulas are readily available, the risk of parents turning to inadequate homemade recipes should be reduced. SUMMARY

• Fresh goat milk is around twice the price of fresh cow’s milk in UK supermarkets. • Goat milk appears to be more quickly digested compared with cow’s milk and it is marginally lower in lactose (5% less). • Goat milk is not recommended as an alternative for infants with diagnosed CMPA unless directed by a healthcare professional. • GMF based on whole milk with a casein whey ratio of 80:20 provides growth and nutritional outcomes in infants, comparable to a standard whey-based CMF. • GMF is permitted under both EU and UK regulations and is now available across the UK. • Anecdotal reports show switching from cow’s milk to goat milk may help some people who suffer from AD; however, significant evidence within scientific literature is presently lacking. • Goat milk and goat yoghurt may attenuate symptoms in IBD, but research into this area very much remains in its infancy and recommendations for humans cannot be made.

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Goat milk: an overview of its role in the human diet  

by Alice Fletcher

Goat milk: an overview of its role in the human diet  

by Alice Fletcher