Body can sense carbohydrates coming
Auckland University researchers have shown the brain knows energy is on the way to the body, minutes before it gets into the bloodstream.
In an experiment, participants were given artificially sweetened liquid solutions - either with carbohydrate in, or a placebo that had no carbohydrate. The liquids tasted the same.
The study found a 30 per cent increase in task-related brain activity when carbohydrate was present even though the liquid wasn’t swallowed.
"This study provides further evidence of a 'sixth taste sense' for carbohydrate by receptors in the human mouth," Dr Nick Gant from the university's Centre for Brain Research said.
"The mouth signals that energy is on its way which in turn leads to increased activity in key regions of the brain including those that control movement and vision.”
The findings showed a scientific basis for the lack of kick people felt when drinking diet beverages, Gant said.
They could also explain why the "perk up" response noted in athletes after they drank carbohydrate was immediate, even though the body hadn’t had time to absorb it and convert it to energy.
"We may be able to use the experimental platform in this study to help develop functional foods and artificial sweeteners that are as hedonistically rewarding as the real thing.”
The research could also be helpful for patients who could not be fed through their mouths and were missing the signalling phase. The lack of signals could help explain why artificial nutrition therapy was less successful than ingesting food in the normal way, and it could be possible to develop some rinses to provide those signals to the brain.
The mechanism involved sensed energy was coming, Gant said.
Given there was no evolutionary reason for people to spit the carbohydrate out, the body expected energy 10 minutes later when the carbohydrate got into the blood stream.
"When you're doing exercise you're depleting your body's energy. The body makes you slow down a bit at that time. This signals help is on its way so don't bother slowing down."
The study used a unique brain imaging sequence to test the behavioural and neural response of 10 participants doing arm exercises while their mouths were rinsed with the solutions.
The carbohydrate used in the experiment was similar to the type used in sports drinks which were useful for the small portion of the population who were so well trained they could exercise until the point where they needed the extra energy, Gant said.
"Most of us are exercising to lose weight, whereas these drinks have a lot of calories which end up putting on weight."