Genes that help digest food
Ask most people what they think of when they eat, and genetics is not likely to be the first answer. Well, there is a record of human diets in our DNA. From the sugars in milk to starch to fibers — the ability to eat certain food is determined by genetics. Eating also changes genes.
I really enjoyed writing the column this week for Hindustan Times which you can read here. You can find additional sources at the end of this section as well.
First, the "paleo" diet is a misnomer. It is a myth is that our Paleolithic ancestors did not eat grains or other starchy foods. In fact, starch was part of the diet of humans who lived in the Sahara when it was green, over 120,000 years ago!
Starch is very important to human diets. We have amylase in our saliva (in addition to the amylase made by the pancreas), so we can break down starchy food in our mouth into sweet sugars. Modern humans have up to twenty copies of the gene for it, while Neanderthals and apes had only a few. Not only that populations that have more amylase gene copies, and consequently, more amylase in their saliva are inclined to eat more starchy food. Starch is important culturally, and so its vilification is unfortunate. By all means control the amount you eat and avoid processed food, but starch isn’t a poison, eating it makes us human. Even domesticated animals (like dogs) have more copies of amylase than wild ones (like wolves) because they ate human food.
Second, consider lactase, the enzyme that breaks down lactose. All children have lactase but only around one-third of adults globally can digest lactose because they can make the lactase enzyme. The rest are lactose intolerant. The actual percentage varies by population but there's history here too.
Modern humans have been around for approximately 200,000 years. Most of this time our ancestors were hunter-gatherers. Then about 10,000 years ago, our ancestors started to grow crops, domesticate animals, and settle down. Cows were important to certain farmers and pastoralists.
Imagine then that crops have failed 9,000 years ago and there's a famine. Communities face starvation. Those who survived on cow’s milk were able to weather famine better. They passed on this feature to their descendants. Others who were intolerant faced the symptoms of lactose intolerance along with starvation and were more likely to die.
But here’s the truly wild thing. Lactose tolerance in adults rose not once but TWICE in totally different parts of the world- in Europe and in Africa. The mutation that keeps the lactase gene turned on into adulthood is different in African and European populations.
Finally, there's fibre- the insoluble material that we can't digest ourselves but have to rely on the mobile bank of genes in our gut microbiome to digest for us. We can’t just think of our own genes when we consider what we eat, we have to think of the genes of the good microbes in our gut. We have less than 100 different carbohydrate digesting genes, and the microbes in our gut have over 16,000!
Nearly all of us eat plants. Most plant material can't be digested by our own cells. But eating fibre helps prevent obesity, type 2 diabetes, and heart disease. Most of us can digest fibre through enzymes produced by gut microbes.
So, what should you eat to feed your good gut microbes? Fruits, whole grains, legumes, and vegetables. Or summed up in author Michael Pollan’s pithy words — “Eat food. Not too much. Mostly plants.”
There are a lot of wonderful things we're learning about the food our ancestors ate. Your genome is the code for your life and also an anthropological archive and a museum of natural history.
Here are related links that you might find interesting:
How ancient people fell in love with bread, beer and other carbs. This is a wonderful long-read at Nature that I loved reading when it came out last year.
Obesity and and weight loss are much more than calorie counting. This is a free-to-access article I wrote for Science Reporter last year that has quite a bit of information on the gut microbiome.
Convergent adaptation of human lactase persistence in Africa and Europe. This is a landmark paper in Nature Medicine on how lactase persistence arose independently twice.
Africans’ ability to digest milk co-evolved with livestock domestication. An article in Smithsonian on the spread of lactase genes through migration routes in Africa.
Lactase persistence across the Americas from Europe. A recently published scientific article in Frontiers in Genetics.
And finally, I have to mention this great video on the evolution of lactase persistence by the Howard Hughes Medical Institute.
That’s it for now.
Anirban