Can’t Resist Starchy Foods? It May Be in Your Genes

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We seem to be obsessed with food as sport lately: Iron Chef. Food Wars. Throwdown with Bobby Flay. Add all the non-televised cooking competitions and magazine and blog lists declaring the best barbecue, the best pizza, the best donut, and you might think deliciousness could be objectively quantified.

But we know, of course, that taste is highly subjective and, increasingly, researchers are discovering a scientific basis for the differences in how we perceive foods.

The latest is a study from researchers at Monell Chemical Senses Center in Philadelphia, who demonstrated that the amount of an enzyme in an individual's saliva dramatically affected how the person perceived the texture of starchy food. The report was released yesterday in the journal PLoS ONE.

"Differences in starch perception likely influence people's liking for and intake of starchy and starch-thickened foods and thus affect their nutritional status," said study lead author Abigail Mandel, a nutritional scientist at Monell, in a press release.

Amylase is an enzyme that accounts for up to half of the protein in human saliva, and which starts the process of breaking down dietary starch into sugars. The amount of amylase in an individual is genetically influenced and varies widely, depending on the number of copies of the gene a person inherits. Other factors can also affect both the quantity and activity of the enzyme, including stress and circadian rhythms (the "internal body clock" that tells you when it's time to sleep, eat, etc.). There is also evidence that a diet high in starch can signal the body to increase amylase.

The Monell researchers tested how saliva with varying concentrations of amylase worked on starch when mixed in a test tube, as well as how subjects perceived the viscosity of a starchy food after mixing it in their mouths for 60 seconds. They found that subjects who had higher levels of the enzyme perceived a more rapid and dramatic thinning of the starch than those with low levels.

"This means that foods with different starch levels will be perceived very differently by people as a function of how much salivary amylase they produce. What may seem like a thick and resistant pudding or starchy food to some may noticeably thin in the mouths of others," said senior author Paul A. S. Breslin, a Monell perceptual geneticist.

The report noted earlier research that found that populations with a historically high-starch diet had more copies of the AMY1 gene, which determines the amount of amylase in the saliva, than populations with a high-protein diet. The Monell researchers suggested that this could help reinforce the preference for starchy foods in those populations, because amylase activity affects both the perception of a food's creaminess and the release of flavor compounds. Anecdotally, this makes sense to me—my Eastern European ancestors plumped up on all manner of noodles, dumplings and breads, foods I also find hard to resist.

Researchers also hypothesized that the amount of an individual's salivary amylase influences their starch digestion and metabolism. If further research confirms this hypothesis, it would mean that people with high amylase levels would experience an increased glycemic load after a high-starch meal because they rapidly break starch down into smaller glucose molecules. It could help explain why some people develop metabolic diseases like diabetes while others don't.

"In today's state of food excess and high starch ingestion, it is possible that high levels of salivary amylase contribute to the risk of insulin resistance and non-insulin dependent diabetes," said Mandel.

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