̽��ֱ�� of Cambridge - milk

Opinion: Why some humans developed a taste for milk and some didn’t

Anonymous — Fri, 11 Mar 2016 15:22:47 +0000

Imagine a dinner party somewhere in Italy to which, as it turns out, my dad has been invited. On the menu tonight is a sliced tomato, basil and mozzarella salad, pasta with a creamy mushroom sauce topped with parmesan cheese, and Italian gelato ice cream to finish. However, except for the sliced tomatoes and basil, my dad cannot eat anything on offer and is destined to leave the party hungry. My dad is, as I am, ethnically Chinese – and, like the majority of Chinese folk, lactose intolerant.

Although the inability to drink and eat dairy products (or more specifically the inability to digest lactose, the type of sugar found in milk) is commonly called “lactose intolerance”, this is actually a misnomer. All humans are lactose tolerant in early life because we are mammals. Most humans only switch to being lactose intolerant in the transition to adulthood.

But if so many adults struggle to digest dairy, why did we start drinking the milk of other animals in the first place? Well, with the domestication of large mammals, in particular cows, sheep and goats, people began to realise that animals could provide nutrition from more than just their meat. In fact, drinking its milk greatly increases the amount of calories available from an animal during its life-span. Couple this with the subsequent development of cheese making, which allowed for the nutrients available from milk to be preserved in compact and portable form and, voila, a new rich and renewable source of food was available to nascent herding communities.

̽��ֱ��ability to digest dairy products as adults is likely to be adaptive owing to its increased nutritional benefits (sugars, as well as fat, protein and calcium) and milk’s role as an important drinking source in arid regions. Considering the symptoms of lactose intolerance, which include water loss from diarrhoea, individuals who had acquired the genetic adaptation of “lactase persistence” and could therefore metabolise dairy products, would have had a very strong selective advantage in areas where herding of cattle, sheep and goats occurred.

Herd mentality

So powerful was the selection pressure in herding societies to be able to consume milk and its related products, that the trait of lactase persistence actually emerged independently at least three times; in northern Europeans, emanating from what is now Denmark, and in two geographically distinct African populations.

Map of lactase persistence. Royal Society, CC BY

̽��ֱ��incredible thing is that although the adaptation in the three cases involved different genetic changes, they all influence the same gene, lactose dehydrogenase, required for metabolising lactose into glucose.

Chicken, pigs and tofu

A key question is how have most other peoples around the world, such as Chinese folk like my dad, continued to thrive without this ability to digest lactose as adults? Certainly the climate in much of East Asia would not have precluded the herding of cattle.

In lieu of viable milking herds, alternative sources of easily renewable protein were identified. For instance, chickens were first domesticated in China. Chickens provided a key protein source, not only from their meat – but also from their eggs, which are, like milk and cheese, a rich, portable and renewable food source. Chickens are also far smaller and have a shorter lifespan compared to large mammalian species, making production less complicated.

Crucially, one of the key crops domesticated by the Chinese – in addition to rice, of course – was the soya bean, which also has a very high protein content. Soya beans are a versatile crop and are the source ingredient for tofu and also soya milk. In much of East Asia today, chickens and pigs (also first domesticated by the Chinese) form the bulk of the meat consumed – and this is supplemented by a large number of soya-related products, including tofu, soya milk, fermented soya beans, and a dizzying array of different soy sauces.

Decaf soya latte

I spent a significant period of my childhood in Singapore, where fresh milk was almost non-existent, and although powdered milk was available, everyone drank soy milk. These days, of course, soy milk is big in the West, too – it is perceived by some to be healthier than cow’s milk as it has less fat and natural sugars and it is now widely available in all major supermarkets and in most coffee shops as a replacement for milk.

There’s a widespread belief in certain sectors of society that lactose intolerance is an indication that humans were not supposed to drink milk as adults. And certainly in some parts of the world, where this is the norm rather than the exception, this is certainly the case. But there’s no denying that the ability to digest cow (and goat and sheep and camel) milk and its products gave some humans the edge in the survival stakes and helped them thrive in early agricultural societies.

̽��ֱ��author will be giving a talk: Starch, milk and alcohol, as part of the Cambridge Science Festival which runs until March 20.

Giles Yeo, Principal Research Associate, director of Genomics/Transcriptomics, MRC Metabolic Diseases Unit, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Giles Yeo (MRC Metabolic Diseases Unit) discusses the origins of lactose intolerance.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

March of the superbugs

admin — Wed, 13 Feb 2013 09:38:50 +0000

Every so often, research laboratories and hospitals testing patients for the superbug methicillin-resistant Staphylococcus aureus (MRSA) have come across an oddity: a strain that appeared to be MRSA because it was resistant to antibiotics but one that tested negative with the ‘gold standard’ molecular test. ̽��ֱ��quirky cases were so infrequent that they were usually filed away for future analysis or disregarded. Until, that is, PhD student Laura Garcia-Alvarez from Cambridge’s Department of Veterinary Medicine had the tenacity to look a little further at a bacterial strain she had spotted in cows’ milk.

MRSA first appeared in 1961 and epidemic strains of this difficult-to-treat bacterium have since spread worldwide in hospitals and the community. In the farming world, MRSA causes bovine mastitis – an infection of cows’ udders – affecting both animal welfare and milk yields.

Garcia-Alvarez was working with Dr Mark Holmes on bovine mastitis when she came across one of the ‘curious anomalies’. ̽��ֱ��strain was resistant to antibiotics but in the standard molecular test was negative for the presence of mecA – the gene responsible for methicillin resistance. She had the isolates retested and then sequenced at the Wellcome Trust Sanger Institute.

It turned out that she had discovered a new strain of MRSA. Its antibiotic resistance is carried not by mecA but by mecC, a gene that is so genetically dissimilar to mecA that it can’t be picked up by the standard molecular test used to define MRSA but only by DNA sequencing.

As Holmes and Garcia-Alvarez began to spread the information to colleagues around Europe, it soon became clear that this phenomenon was not confined to cows: others had found the unusual samples in humans. “We started to get calls from hospitals and research groups who had come across a small number of human MRSA strains that behaved differently,” said Holmes. “Within a few weeks, we had a further 50 isolates. This meant that what we were looking at was a human problem too.”

Garcia-Alvarez, who at the time was a student on the Department’s postgraduate training in infectious disease dynamics programme, described how finding the same new strain in both humans and cows was worrying, although no cause for immediate alarm: “Pasteurisation of milk will prevent any risk of infection via the food chain. In the wider UK community, less than 3% of individuals carry MRSA – typically in their noses – without becoming ill.”

“Nonetheless,” added Holmes, “MRSA presents a major challenge to the control of infectious diseases. Finding a new strain – studying its prevalence, how it confers antibiotic resistance and how it’s transmitted – can tell us enormous amounts about the origins and evolution of antibiotic resistance.”

New understanding

Since the discovery, Holmes’ team has been investigating the prevalence of the strain in human and animal populations – and the potential for passing the strain between species – in partnership with Cambridge’s Department of Medicine, the Sanger Institute and the Moredun Research Institute (Scotland), and funded by the Medical Research Council.

One of their first steps was to develop a better genetic test, one that also detected the new strain. ̽��ֱ��timing was fortuitous. Moves to help hospitals identify MRSA more quickly have resulted in the development of automated systems based on genetic testing. Because the standard genetic test does not detect the new strain, the scientists have now developed a protocol that will pick up both strains.

Moreover, their recent research has shown that additional MRSA strains have emerged that possess other mechanisms of antibiotic resistance: “We’ve found about 40 human MRSA isolates that don’t have a mecA or a mecC gene, and we are trying to establish why these are resistant to methicillin-family antibiotics. In retrospect, it was incredibly lucky that the original isolate we investigated happened to have a genetic variation in a known gene that could be picked up by whole genome sequencing.”

To identify how mecC confers antibiotic resistance, Holmes collaborated with Professor Alexander Tomasz at Rockefeller ̽��ֱ��, New York. They discovered that the gene is more resistant than mecA to cefoxitin (one of the newer classes of antibiotics): “Inappropriate use of antibiotics in human and veterinary medicine has favoured the selection and growth of antibiotic-resistant microorganisms,” explained Holmes. “Our finding suggests that an increased use of this drug may have driven emergence of the new strain.”

“We also now know that the new strain is found in almost every species that we’ve studied, including domestic cats and dogs, wild rats, deer, a rabbit, a common seal, sheep and a chaffinch. ̽��ֱ��bacterium may have lost factors that restricted it to certain species, or gained pan-host virulence factors that make it better able to colonise multiple species. We need to know how and why this has happened to understand the emergence of bacterial pathogens from animals and their dissemination into human populations.”

Now, their latest research has tracked transmission of the superbug, providing the first direct evidence of transmission of the new strain between livestock and humans.

̽��ֱ��researchers capitalised on a growing trend to use increasingly rapid and affordable DNA sequencing for tracking the transmission of pathogens. This technique is helping scientists to look for differences at the level of single letters in the genetic code as a means to map the direction of infection – from patient to patient, and from one animal species to another. ̽��ֱ��team investigated two cases of mecC MRSA in Danish farmers. ̽��ֱ��strains circulating in the farmers’ livestock and those isolated from the patients only differed by a small number of letters – strong evidence that the farmers had acquired their infections from their animals, in one case a sheep and in another a cow.

“ ̽��ֱ��ability to confirm animal-to-human transmission in virtual real time using this technology can’t be underestimated,” said Holmes. “High-throughput DNA sequencing is going to revolutionise clinical microbiology by enabling targeted epidemiological follow-up and infection control.”

Nearing the precipice

Mastitis is the most common infectious disease of dairy cattle, affecting the welfare of cows and, according to one estimate, costs the UK dairy industry around £170 million per year. Its control and treatment relies on the use of millions of doses of therapeutic and prophylactic antibiotics every year. “Our research on MRSA is pointing to the fact that although we are not on the precipice of having the whole system collapse through selection of bugs that are even more resistant or having husbandry systems that make it impossible to eliminate them, we are closer to the precipice than we would like to be,” said Holmes. “As it is, S. aureus is considered impossible to eliminate in dairy herds – you have to live with it once you’ve got it. “Farmers and veterinarians are in a constant battle to improve the health of dairy cows, yet farming cannot be sustained at these levels if it is generating these types of resistance. Moreover, we can’t predict how these bacterial strains will evolve – they could become more resistant, more virulent or better able to jump between species.”
Holmes views the interface between veterinary medicine and human medicine as crucial to understanding infectious diseases such as MRSA: “There is very little research on S. aureus mastitis in cows in comparison to research into it as a human pathogen, and yet now we’re beginning to see exactly the same organism being found in people and in cows. This means that we should be thinking about the epidemiology of disease control and the development of antibiotic resistance in both species. Understanding how new strains emerge will help us to understand the growing public health problem of antibiotic resistance.”

For more information, please contact Louise Walsh at the ̽��ֱ�� of Cambridge Office of External Affairs and Communications.

Scientists who recently discovered a new strain of superbug have now tracked its transmission between animals and humans.

We can’t predict how these bacterial strains will evolve – they could become more resistant, more virulent or better able to jump between species

Mark Holmes

JelleS on flickr

Cow

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Yes

Indians and Europeans share a milky past

ns480 — Fri, 09 Sep 2011 10:09:02 +0000

̽��ֱ��Cambridge team, in association with fellow researchers at CCMB Hyderabad, UCL, ̽��ֱ�� of Tartu, Harvard and ̽��ֱ�� of Chennai, were studying genetic changes that allow some 32 per cent of the world’s population to be lactase persistent – able to digest lactose, the sugar in milk. To their surprise they found the same mutation, with the same origin, at high frequency in Europe and India.

̽��ֱ��team’s study may also help scientists’ understanding of evolutionary processes such as biological adaptation and how culture and economic developments affect human biology. Its authors say the study has shown that with a little kick from natural selection, genes can spread far, wide and fast.

Lactase persistence is common in Europe, the Middle East and some parts of Africa and India – areas where domesticated cattle are widespread - but either rare or absent in most other parts of the world.

When someone who is not lactase persistent drinks milk they will often suffer symptoms such as abdominal pain, bloating, nausea and diarrhoea – otherwise known as lactose intolerance.

While all babies produce the gut enzyme lactase, essential for the digestion of lactose in milk, the production of the enzyme is usually shut down some time before adulthood.

Although once thought of as normal, lactase persistence was found in the 1960s to be an unusual trait in humans and seems to be completely absent from other mammals whose lactase production diminishes significantly after being weaned and is never resumed.

̽��ֱ��focus of the Cambridge-led study was India – the world’s largest producers and consumers of milk. ̽��ֱ��team looked at nearly 2,300 DNA samples from across the Indian subcontinent from all major language groups and geographic regions – the first study of its kind.

Previous studies had shown that lactase persistence had evolved at least four times in the last 10,000 years, independently in Europe, the Middle East and Africa. However, little was known about its genetic causes in India, until now.

Cambridge’s Dr Irene Gallego Romero, the lead author, said: “India was an unknown quantity. But since lactase persistence had evolved independently in the Middle East and Africa, and because cattle had been domesticated independently in India around seven or eight thousand years ago, we were expecting to see uniquely Indian genetic causes.”

̽��ֱ��vast majority of lactase persistent Europeans carry a mutation -13910T, that has been shown to have been strongly favoured by natural selection among people with supplies of milk to hand. It seems to have originated somewhere in Europe around 7,500 years ago. ̽��ֱ��mutation seems to be absent from samples of early central European farmer’s skeletons who lived around the time that domestic cattle, sheep and goats arrived there.

“To our surprise we found that the -13910T mutation was also common in India – especially in those populations with a tradition of milk drinking,” said Dr Toomas Kivisild of Cambridge ̽��ֱ��, senior author of the study.

“Not only that, but by looking at nearby genetic regions we could show that the Indian -13910T has the same origin as that found in Europeans; that it could lead back to the same few people who may have migrated between Europe and India.

However, that raises the question of why there are few instances of lactase tolerance in between.

Professor Mark Thomas of UCL, a co-author, said: “Genetic data doesn’t support some sort of large migration of people from Europe to India in the last 10,000 years. What’s more likely is that just a few migrants carried this mutation to India, and then it spread quickly.”

̽��ֱ��study also revealed large differences in the distribution of -13910T in India with many southern and eastern populations – especially those who do not practice pastoralism – having near zero frequencies.

̽��ֱ��study team speculate that the spread of the lactase persistent gene variant was highly dependent on the mobility of cattle keepers and the extent to which they reproduced with people who did not keep cattle.

In India, reproductive isolation between castes, tribes and religions can be strong. ̽��ֱ��study group suggest such isolation may have also been common historically when lactase persistence was spreading.

This work was supported by the UK-India Education Research Initiative (grant number RG47772), the European Commission Seventh Framework Programme Internal Training Networks (LeCHE, grant number 215362-2), the European Union Seventh Framework Programme Ecogene (grant number 205419), the European Union Regional Development Fund through a Centre of Excellence in Genomics award and a Bhatnagar Fellowship from Council of Scientific and Industrial Research, Government of India.

Cambridge ̽��ֱ�� researchers have discovered that lactose tolerant milk-drinkers in India and Europe could be related to the same person who lived at some point in the last 10,000 years.

To our surprise we found that the -13910T mutation was also common in India – especially in those populations with a tradition of milk drinking.

Dr Toomas Kivisild

kakie; from Flickr Creative Commons

milk

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Yes