Genetic testing can have implications for use of caffeine in sports nutrition

In a session at the recent meeting of the International Society of Sports Nutrition in Phoenix, Nanci Guest, a PhD candidate at the University of Toronto, presented her ongoing research into how genetics affect how subjects respond to various nutrients.  Guest is also a strength and conditioning coach, and is on the scientific advisory board of the testing firm Nutrigenomix, which she relies on for the genetic tests she uses in her research.

No role in talent identification

First off, Guest put the fear of eugenics to rest.  In other words, if genetic testing becomes the norm, will these tests be used to select children at a young age for various paths in life?  Could the ‘genetically’ smart kids get sent to prep school while the average kids get send to a trade school?  Or in the realm of athletics, can you identify the next Usain Bolt as an infant via an inexpensive genetic test?

At least in the realm of sports performance, Guest said the consensus is that genetic testing is of no value in identifying who is going to grow up to be the strongest or the fastest.  Obviously there are broad population-based trends that are easily observable, such as the predominance of those athletes with West African heritage in shorter sprint distances, and these must have an underlying genetic basis. But there are at present too many factors to consider, including aspects of mental makeup.  But the testing as it exists today can hit targets of more modest scope, such as how an athlete would respond to certain training regimens or nutrient intake profiles.

More evidence for nutrigenomics

“​We​’​ve known for years that genetics has a role in how we respond to training.  Genetic variations are going to result in unique responses.  While we currently don​’​t have the science to use genetic tests in talent identification, there is a role for nutrigenomics,​” ​Guest said.

Guest noted that each human inherits a unique and not necessarily perfectly predictable set of genetic instructions from his or her parents.  When looking at the SNPs (single nucleotide polymorphisms), three variants, or genotypes are possible depending on how the nucleotides are substituted in, for example:  AA, CA, or CC. Guest has conducted research for several years in how these slight variations can affect how subjects respond to specific nutrients.

“​We know this affects how the body utilizes vitamin D, for example. And it affects how the body uses caffeine, too,​”​ she said.

Widely used ingredient

Among sports nutrition ingredients, caffeine is among the most widely used and is in common use in the general population as well.  The ingredient is present in many plants, such as coffee, tea and cocoa, and is easily synthesized as well. While it is common knowledge that caffeine ‘hits’ different people in different ways, knowing how people respond to caffeine in a precise way could have big implications for performance, Guest said.

“​Caffeine is the world​’​s most widely consumed psychoactive substance.  Ninety percent of adults ​[in North America] consume it on a regular basis.  The main effect of caffeine is to block the effects of adenosine resulting in the release of neurotransmitters, primarily dopamine.  You end up with lower perceived exertion in skeletal muscle.  Caffeine has a higher benefit when your are really fatigued. It does show performance improvements in endurance sports, less in stop and go sports and the least benefit of all in short, high intensity sports,​”​ Guest said.  (This last bit of information is curious, given how many pre workout products, aimed at the short, high intensity strength training crowd, rely on caffeine as the main ingredient.)

Genetics determines responses

In a previous study​ presented a couple of years ago at the same meeting, Guest looked into genetic variation and caffeine in a test with trained cyclists over a simulated 40 K time trial.  She examined whether a panel of 25 SNPs in 19 genes that might be related to caffeine metabolism. She did find variations in how the athletes responded to caffeine, with some showing higher heart rates, but these did not translate into a performance increase.

In her more recent research, which she outlined at the meeting but which is in the final stages of being published, Guest did a more elaborate and thorough test, using multiple performance benchmarks including Wingate measurements, a hand grip power test, a vertical jump exercise and a simulated 10K cycling time trial.

For the subjects identified as ‘fast metabolizers’ of caffeine based on their genetic profiles, Guest saw an overall 3.2% increase in performance.  For those who have an average response to caffeine, Guest said she found no benefit. For the slow metabolizers, there was a suggestion that caffeine could actually hurt performance, though the sample size for this last group was too small to say anything definitive in that regard, she said.