May 2, 2012 -- Whether we like or loathe the smell of a frying pork chop may depend on our genes, a new study shows.
The study, published in the journal PLoS ONE, is one of the first to show how genes may shape our food choices.
"People who are instinctively vegetarian or vegan or instinctively heavy meat-eaters, it could definitely have some sort of underlying biological component to it," says Kara Hoover, PhD, a biological anthropologist and assistant professor at the University of Alaska Fairbanks. She was not involved in the current research.
"When you consider that our food preferences are driven by flavor, which is the intersection of taste and odor, with a heavier emphasis on odor, clearly genetic variation in humans is going to make a difference in how we prefer food," Hoover tells WebMD.
How Genes Influence Smell
People detect odors thanks to tiny chemical receptors that sit on nerve cells inside the nose. In total, we have genes for about 400 different smell receptors that help sense about 10,000 different odors.
Some of those receptors detect the steroid androstenone, which is found in high concentrations in male pigs.
Farmers have known for some time that uncastrated male pigs can produce meat with a strong odor, so most commercially raised animals in the U.S. are castrated to get rid of the smell, which is known as boar taint.
Previous research found that people who have two copies of a gene that helps sense androstenone -- scientists think that's about 70% of the population -- are able to smell the chemical. These people can have a mixed reaction to the pork.
"For those who are very sensitive to it, it's really disgusting. It's a sweaty, urine-like odor," says researcher Hiroaki Matsunami, PhD, an associate professor of molecular genetics and microbiology at Duke University in Durham, N.C. "For others, you can smell it, but it's not as bad. Those people say it smells fragrant, chemical, or sweet."
In contrast, people with only one copy of the gene or who carry another gene variant for the receptor aren't as bothered by the aroma of androstenone. They find the odor to be weak or unnoticeable.
Genes and Food Preference
In the new study, researchers wondered whether a simple smell test could predict who carries the single copy of the gene, and whether the gene influences the sniffer's perceptions of cooked meat.
It wasn't an entirely academic question. Europe is considering banning a practice that allows farmers to control the amount of androstenone in pork by castrating male pigs. Farmers are worried that consumers will turn their noses up at meat that contains higher levels of the hormone.
For the study, researchers recruited 23 healthy participants: 13 average eaters and 10 trained "sensory assessors," people with sensitive noses that can reliably pick out certain smells.
First, researchers added purified androstenone to two of three cups of water. People were asked to smell each cup and pick out the one that was different. If they were right, researchers classified them as sensitive. If they were wrong, they were considered insensitive.
Next, researchers had the study subjects eat cooked ground pork that had varying levels of androstenone added to it. They kept the levels within the range that might be naturally found in meat.
People were asked to rate the smell and the taste of the meat samples.
Next, researchers tested their genes. They found that all the people who could smell the androstenone had two copies of the gene needed to pick up the scent. These folks were also more likely to rate the taste of the pork with added androstenone as bad.
And everyone who had one copy of the gene could not smell the hormone. They were more likely to say the pork tasted good.
Still, "for those who cannot [initially] smell androstenone, if you try to smell this chemical every day for three weeks, about half of these non-smellers can acquire the ability to smell it," Matsunami says.
That suggests the ability to smell things isn't driven entirely by genes, but also by experience.
But, "it's a gene that's certainly influencing this preference, and I think people need to consider that fact," he says.