By Dr Michael Klentze, Thanyapura Integrative Health Centre
A Performance Boost From Taste of Carbohydrates
In addition to recognizing the usual five “tastes” – sweet, sour, salty, savory, and bitter – the human tongue may have a sixth sense that can sense carbohydrates, according to new research.
In humans, information about the taste of food is perceived by taste receptors on the tongue. Signals from the receptors are transmitted to the organs of the brain that govern our sense of taste.
In the new study, published in the journal Appetite, New Zealand researchers discovered that simply having carbohydrates in your mouth can improve physical performance. The study volunteers carried out tasks after rinsing their mouths with three different fluids. Two of the fluids were artificially sweetened, but only one contained carbohydrates. The third fluid was neither sweetened nor carb-loaded.
The researchers found that after tasting the carbohydrate-loaded fluid, the volunteers showed a 30 percent increase of activity in certain brain areas, especially those which control vision and movement. It seems that that our tongue is able to signal the arrival of “fast energy” food to the brain. So it’s no wonder that low-carb diet products are considered unsatisfying to the appetite, while on the other hand carbohydrates drinks perk up athletic performance very quickly.
How Sweeteners Can Make You Fat
So, what about artificial sweeteners? Experiments generally have found that a sweet taste, whether delivered by sugar or artificial sweeteners, enhances human appetite. In some studies, aspartame-sweetened water – but not aspartame capsules – was found to stimulate hunger more than glucose or water.
Aspartame, acesulfame potassium, and saccharin are all associated with a heightened motivation to eat, and led to the study volunteers selecting more items on a food preference list. Aspartame had the most pronounced effect, possibly because it does not have a bitter aftertaste. The findings suggest that the calories contained in natural sweeteners may trigger a response to keep the overall energy consumption constant.
What Drives The Desire To Eat
The sense of “reward” that we feel after eating food shares circuitry in the brain with other pleasurable activities, such as sex and intoxicating drugs like alcohol. Food reward consists of two components: a “sensory” or hedonic component – the pleasure we feel from food that tastes good – and a “post-ingestive” component, which we feel after eating enough food. The reward system is controlled by the neurotransmitter, dopamine: if dopamine levels rise, we feel happy as we experience the psychological “reward”. Dopamine levels are also crucial for the recognition of the food stimulus and the feeling of satisfaction after eating food with a pleasant taste.
But artificial sweeteners do not activate the food reward pathways in the same way as natural sweeteners. Their lack of calories generally eliminates the post-ingestive component of the food reward process, so that sweetness without caloric content offers partial, but not complete, activation of the food reward pathways. At the same time, the activation of the sensory component may contribute to an increased appetite.
Animals seek food to satisfy an inherent craving for sweetness, even in the absence of energy need. The lack of complete satisfaction of this urge, possible because of the failure of artificial sweeteners to activate the post-ingestive component of the food reward system, seems to fuel food seeking behavior. As a result, the reduction in reward response from artificial sweeteners may contribute to obesity.
How To Lose Weight, Even If It’s Hot Outside
I am frequently asked if fat can burn calories, or if the fat that you eat is simply stored in the body. Fat can burn calories if we convert the yellow fat into brown fat (Brown fat protects against the cold — animals use it for hibernation). Brown fat is used by the body to burn fatty acids in a way that increases mitochondrial activity, even while you sleep.
In preliminary studies it has been shown that the browning of yellow fat which creates a tissue known as “beige” fat, which helps generate heat and burn calories. But how can we do do this? Cold temperatures are the only known stimulus that can increase beige fat mass or brown fat mass. It seems that exposure to cold activates immune cells called macrophages, which use a cytokine called Interleukin-4 to convert yellow fat to beige fat.
Researchers have found that animals even living in 30 degrees heat can convert fat to brown or beige fat when they receive Interleukin-4 – and that the energy expenditure was 30-times higher than without the Interleukin-4!
Another research group found that when a protein called PGC-1 is produced in muscles, it can prompt adipose tissue to brown. A hormone called Metrnl is also produced in muscles after exercise and also with cold exposure, and researchers have found that Metrnl also browns white fat in mice. Mice given gene therapy that boosted production of Metrnl also had better glucose tolerance, suggesting an anti-diabetic effect, and lost a small amount of weight. Metrnl also increased the numbers of certain types of macrophages and the amount of Interleukin-4 in the fat tissue.
The idea that you might be able pharmacological manipulate a person’s energy expenditure by “browning their white fat” is certainly an attractive idea, and it’s a different way of thinking about obesity.
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9. SCIENCESHOT, Thursday, June 5, 2014
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About the Author
Tom Topham holds a 1st class honours degree in Sports Science (Human Performance) from Brunel University, England. He also comes from a triathlon background, competing as an age-grouper and holds a level 2 triathlon coaching qualification.