Margit Burmeister
Ann Arbor, Michigan, United States

 

Central European recipes often call for soft cheese, such as the filling of this dish known as Topfenpalatschinken in Austria, cheese blintzes in Israel and the US, and crêpes au fromage in France.

Europeans eat cream, yogurt, and lots of cheese. Middle Eastern and Indian cuisine feature yogurt and a cheese called paneer, but recipes from East or Southeast Asia usually do not include dairy products. Traditional recipes, while being an important part of culture, also reflect the genetic make-up of a people.

After numerous bouts of cramps and diarrhea in my twenties, I was diagnosed as having irritable bowel syndrome. Ten years later, another doctor ordered a stool test and concluded that a parasite, giardia, was the cause of my symptoms and prescribed antibiotics. My symptoms continued, but it was not until my fifties when a DNA profile revealed that I was likely lactose intolerant, a claim soon confirmed with a breath test. I stopped drinking cow’s milk and eating soft cheeses such as those used in the cheese blintzes pictured, and my symptoms resolved.

Why did it take so long to identify this problem? I am of German heritage, with blond hair, blue eyes, and light skin. Most Germans can digest milk and soft cheeses just fine. German recipes routinely call for cream sauces and cheese toppings. I did not fit the genetic stereotype of lactose intolerance; had I been of Mediterranean heritage, where lactose intolerance is more common, I might have been tested for lactose intolerance earlier.

Could it be that our genes determine what we eat? It is likely that genetic mutations, selection, history, and changing cultural and environmental conditions all affect our diet. Lactase is the enzyme that breaks down the milk sugar lactose, allowing newborns to digest their mother’s milk. After weaning, the gene for lactase is usually switched off. Lactose intolerance, then, is actually the normal state of genetic affairs in humans and in all other mammals.

If you drink milk after the lactase gene has been switched off, certain bacteria in your gut do the work of digesting lactose. The gases generated from these bacteria may cause stomach upheaval. But what happened that made many humans, such as most Germans, able to continue to drink milk and eat soft cheeses as adults?

About 9,000 years ago in Northern Europe, human hunter gatherers became farmers. They raised goats and cows, and thus had access to plenty of milk. By chance, a mutation appeared that inactivated the off-switch for the lactase gene. This made the lactase gene active in adults, so that people with this mutation could easily continue to digest milk. Such people had a selective advantage for survival, as they could use milk as a clean, readily available source of food and drink. Hence, pretty quickly, on an evolutionary scale, this mutation spread and became more and more common. Scientists see strong evidence for selection in DNA surrounding this mutation.¹ Nowadays, most northern and central Europeans, as well as people in North Africa, the Middle East, Russia, and India and Pakistan carry this mutation,² and include milk and dairy in their daily diet.

Amazingly, when Africans became farmers, several different mutations in the same gene happened in parallel, were similarly selected for, and also spread quickly.³ As a result, more than a third of all humans, in contrast to all other mammals, can digest lactose as adults.⁴ Lactase mutations are among the strongest and best documented cases of evolutionary selection in humans. But the ability to digest lactose is not common to all humans. People of East and Southeast Asian ancestry do not carry lactase mutations and are lactose intolerant, probably because humans had already migrated to East Asia before this advantageous mutation arose. They will suffer stomach upsets from consuming dairy products; therefore cuisine from China, Japan, and Korea does not usually call for milk or soft cheese.

Lactase persistence is by far the best studied case of a genetic variant affecting diet, but there are many others. Malaria, for example, a disease common in the Mediterranean and other tropical areas, is caused by parasites that multiply in human red cells. Around the Mediterranean, fava beans are commonly eaten. These beans contain a factor that stresses red blood cells in such a way that the parasites cannot survive well, protecting against malaria. British colonists in India found that drinking quinine (as in bitter lemon) had similar preventative effects. But evolution also found another solution: mutations in a gene called G6PD that makes males less susceptible to malaria, and is common in Africa and the Mediterranean. Carriers of this mutation usually have no symptoms until eating fava beans, when the “double up” on malaria protection causes a form of hemolytic anemia.⁵

Our bodies cannot make the essential vitamin B12—it is generated by microorganisms and is only available in animal products, or in small quantities by pickling. Vegan diets lack vitamin B12. This may be the reason why in China, where meat was historically expensive, pickled vegetables became a staple with morning rice, and highly fermented “stinky tofu” is considered healthy to eat. In the south of India, where vegetarianism is much more prominent than in the north of India, the use of pickled vegetables is also more prevalent. Some researchers believe the use of kimchi and other fermented vegetables may contribute to the longevity of Okinawans.

The evolutionary reasons for some genetic variants that affect diet are still unknown. Many East Asians experience a “flushing” response when drinking alcohol, resulting not only in a pink face, but also unpleasant sensations of nausea and increased heart rate. This reaction is triggered by a build-up of a toxic chemical, acetaldehyde, due to mutations in two genes that encode alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). ADH and ALDH mutations also show the tell-tale signs of evolutionary selection,⁶ consistent with their high prevalence in East Asians. Why these loci were selected for, and why only in East Asians, is still unknown. Because of these unpleasant reactions to alcohol, there was traditionally much less of a drinking culture in East Asia compared to Europe. This has changed in recent years, when drinking alcohol has become part of Japanese and Chinese business culture. Socio-cultural selection against the flushing-inducing ADH/ALDH variants in East Asian leadership circles may be occurring. Genes, as well as social and cultural influences, will continue to influence personal and cultural dietary choices.

 

References

1. Bersaglieri T, Sabeti PC, Patterson N, et al. Genetic signatures of strong recent positive selection at the lactase gene. Am J Hum Genet. Jun 2004;74(6):1111-1120.
2. Gerbault P, Liebert A, Itan Y, et al. Evolution of lactase persistence: an example of human niche construction. Philos Trans R Soc Lond B Biol Sci. Mar 27 2011;366(1566):863-877.
3. Tishkoff SA, Reed FA, Ranciaro A, et al. Convergent adaptation of human lactase persistence in Africa and Europe. Nat Genet. Jan 2007;39(1):31-40.
4. Storhaug CL, Fosse SK, Fadnes LT. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. Oct 2017;2(10):738-746.
5. Luzzatto L, Nannelli C, Notaro R. Glucose-6-Phosphate Dehydrogenase Deficiency. Hematol Oncol Clin North Am. Apr 2016;30(2):373-393.
6. Okada Y, Momozawa Y, Sakaue S, et al. Deep whole-genome sequencing reveals recent selection signatures linked to evolution and disease risk of Japanese. Nat Commun. Apr 24 2018;9(1):1631.

 

---

 

MARGIT BURMEISTER, Ph.D., trained in biochemistry at the Free University Berlin and the Weizmann Institute of Science in Israel and received her Ph.D. in Biology from the Ruprecht Karl’s University of Heidelberg for work at the European Molecular Biology Laboratory. She did postdoctoral training at the University of California San Francisco in gene mapping before becoming faculty in four departments of the University of Michigan. Her research has pin-pointed many genes involved in human Mendelian neurological disorders. She has studied gene x environment interactions related to addictions and depression. She collaborates across Europe, Turkey, and China, where she teaches regularly.

 

Summer 2018  |  Sections  |  Food