Monday, July 27, 2009
Is lactose intolerance natural?
First, what is lactose intolerance? Our major source of lactose is milk (cow, goat, sheep and human) or yogurt. It is not found in hard cheese or butter. At birth, we have a digestive enzyme called lactase to break down lactose in breast milk to its constituent sugars, glucose and galactose, which are then absorbed into the blood.
By the age of 5 years, in many people on the planet their lactase enzyme is no longer produced and they can’t digest lactose. In this case large amounts of lactose can cause intestinal cramping because gut bacteria convert the lactose to gas and lactic acid. Not comfortable. They are now lactose intolerant. (Note here: lactose intolerance is not an allergy).
The human genome reveals more
Geneticists have been able to check DNA from around the world and married their findings to history, enabling to explain why many of us can drink milk later in life without problems. Around 10,000 years ago humans kept cattle as a beast of burden and a source of meat. The ability to handle lactose doesn’t seem to be in anyone around this time. A DNA mutation soon after allowed some people to be able to drink milk well past their 5th birthday and into adulthood.
Clearly, being able to drink cow milk was a benefit during times of food shortage. The mutation then became more dominant in parts of Europe through to northern India. It is thought the mutation occurred independently in parts of Arabia when the camel became domesticated and camels’ milk entered the diet.
Rapid spread of mutation
Studies of DNA from skeletal remains in central Europe show that about 80% of people in that area had the mutation for tolerating lactose about 7000 years ago. That is a rapid spread of a mutation, strongly suggesting that it offered a survival advantage, according to a new book The 10,000 Year Explosion – How Civilization Accelerated Human Evolution by Professors of Anthropology Cochran and Harpending.
In fact, being able to tolerate lactose in the diet, allowed the expansion of the Indo-Europeans, tracked by both the spread of lactose tolerance and the Indo-European languages (eg Spanish, English, Hindi, Portuguese, Russian, German, French). Put another way, if your native language was Indo-European in origin, then there was a good chance you could handle lactose over the last 7000 years or so.
Dairy produce better than meat for survival
Dairy farming generates about five times as many Calories (kJs) per area of farming when compared to raising cattle for slaughter. You can quickly see the advantage here. More Calories per hectare means a greater number of people fed, meaning more warriors to defend the land or occupy other lands. Dairy farmers were more mobile and less reliant on seasonal cereal crops, so this helpful mutation meant that both a common language and a survival advantage travelled widely.
It also explains why eastern and southern Asia, Japan, parts of Africa and the indigenous folk of Australia have both a very different language background and the inability to handle lactose after being weaned.
What does it all mean?
Some of us are designed to drink milk and others aren’t. The answer lies in evolution and genetic changes and not in ideology. Milk is a great source of calcium and riboflavin. Calcium can also be found in hard cheese, which has no lactose, and calcium fortified soy drinks. If you enjoy cow milk, I suggest that a reduced-fat milk is your better choice as most of them (in Australia) have more calcium than in regular milk. Well, I’m a dietitian, I had to say that!
Reference: The 10,00 Year Explosion by Gregory Cochran & Henry Harpending, Basic Books, New York 2009