If you enjoyed a nice, cool glass of milk with your breakfast this morning you are a mutant.
According to a recently published University College London study, published Aug. 28 in PLoS Computational Biology, the official journal of the International Society of Computational Biology, most adults worldwide cannot digest milk into adulthood, and the ability to do so is the result of a genetic mutation.
The human body produces an enzyme called lactase in order to break down lactose, a milk sugar, in milk said Doug White, a faculty member in the department of nutrition and food science at Auburn University.
"If the enzyme lactase is not present then the body cannot digest the lactose," White said. "This results in nausea, gas, vomiting or diarrhea."
All people have the gene necessary to produce lactase, that gene is simply not expressed throughout adulthood said Robert Keiss, a professor of nutrition at Auburn University and a nutrition specialist for the Alabama Cooperative Extension System.
"We all have the gene, it's just not expressed in adulthood," Keiss said. "Over time the gene becomes quiet."
The researchers in University College London's genetics, evolution and environment department found that people who produce lactase for their entire life do so because of a genetic mutation. These people are said to be lactase persistent.
Americans or Europeans may not realize how uncommon the ability to drink milk is. This is a direct result of the origin of the lactase persistence mutation.
The study said the mutation most likely occurred 7,500 years ago in central Europe when the practice of dairying began.
Rex Dunham, a professor of fish genetics, genetic engineering and aquaculture at Auburn University, said this theory makes perfect sense.
"It's the purpose of mutation, genetic variation to adapt to surroundings," Dunham said. "The mutation would be eliminated if it was not advantageous."
White said genes have specific variations, or markers, in them allowing researchers to track how the gene spreads.
"You can see how certain populations are related," White said. "It's almost like migration."
Outside of Americans and Europeans, the ability to digest milk is quite rare.
Roughly 50 percent of Mediterranean people, 25 percent of African people and zero to five percent of Asians and Native Americans have this ability, White said. This means about 60 percent of the world's population is lactose intolerant.
Keiss said he thought more people were lactose intolerant.
"I would have thought it would be about 75 or 80 percent," Keiss said. "You have to remember, being able to drink milk is pretty rare outside of America or Europe."
Keiss said certain cultures having an inability to process certain foods is not uncommon.
"Native Americans and Asians don't produce alcohol dehydrogenase, the enzyme used to process alcohol," Keiss said. "Because they cannot process the alcohol they become excessively intoxicated very quickly."
Not all people who are lactose intolerant are violently allergic to lactose.
"There are varying degrees of it," Keiss said. "Some can handle it, some can't."
White said the typical reaction of a lactose intolerant person varies so much that some people who can't drink milk could probably eat aged cheese or yogurt because those items have enzymes in them that assist the body in digestion.
But what about those who cannot drink milk at all? Keiss said they should reach for a vegetable.
"Milk is definitely the best source of calcium," Keiss said. "But if you can't drink milk you can get calcium from green, leafy vegetables or fish with bones in it."
Both White and Keiss also said functional foods, food with nutrients added to them, make it easier for people to get all the vitamins and minerals they need.
"Milk is still definitely the best though," Keiss said.
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