When you're trying to lose weight, it feels like sugar is everywhere — and it's never your friend. We all know that reducing sugar intake is one of the best ways to help weight loss. But a new Australian study in both animals and humans reminds us that consuming artificial sweeteners can be just as bad as consuming too much regular sugar. In fact, the artificial stuff can actually increase hunger and result in you eating more.
The study, co-led by the University of Sydney, has revealed for the first time why this happens. The team says they have newly identified a system in the brain that calculates the balance between the sweetness and the energy content of food. Artificial sweeteners, they suggest, alter taste perceptions and so affect the brain's ability to regulate appetite.
"After chronic exposure to a diet that contained the artificial sweetener sucralose, we saw that animals began eating a lot more," says lead researcher Greg Neely from the university's Faculty of Science. "Through systematic investigation of this effect, we found that inside the brain's reward centers, sweet sensation is integrated with energy content. When sweetness versus energy is out of balance for a period of time, the brain recalibrates and increases total calories consumed."
For the study, which is published in the journal Cell Metabolism, fruit flies were exposed to an artificially sweetened diet for prolonged periods — more than five days — while their food intake was monitored. The researchers found that 30% more calories were consumed than when the fruit flies were given food that was naturally sweetened.
"When we investigated why animals were eating more even though they had enough calories," Neely says, "we found that chronic consumption of this artificial sweetener actually increases the sweet intensity of real nutritive sugar, and this then increases the animal's overall motivation to eat more food."
In other words, the body comes to expect to receive a certain amount of energy when it detects a particular level of sweetness — and sucralose is 600 times sweeter than ordinary sucrose. Sweeteners help us lose weight, of course, by delivering all the sweetness with only a fraction of the energy. However, when the sweetness-to-energy ratio doesn't add up, the brain compensates by asking for that missing energy in the form of more food.
Artificial sweeteners are often prescribed as a tool to treat obesity and researchers say billions of people worldwide consume them despite little being known about their full impact on the brain and the way it regulates hunger. The team says theirs is the first study to identify how artificial sweeteners can stimulate appetite via a complex network of neurons that responds to artificially sweetened food by telling an animal it hasn't received enough energy.
Following their studies on fruit flies, the scientists wanted to discover whether artificial sweeteners also increased food intake in mammals. A team led by Professor Herbert Herzog replicated the study using mice, delivering a sucralose-laden diet for seven days. The researchers say the mice also displayed a significant increase in food consumption and that the brain pathways involved in their behavior was the same as in the fruit flies.
"These findings further reinforce the idea that ‘sugar-free’ varieties of processed food and drink may not be as inert as we anticipated." Herzog says. "Artificial sweeteners can actually change how animals perceive the sweetness of their food, with a discrepancy between sweetness and energy levels prompting an increase in caloric consumption."
It was also found that artificial sweeteners promote insomnia, hyperactivity and decreased sleep quality. These are all behaviors, the team say, "consistent with a mild starvation or fasting state." Similar effects on sleep have also previously been reported in human studies. "We were able to functionally map a new neuronal network that balances food's palatability with energy content. The pathway we discovered is part of a conserved starvation response that actually makes nutritious food taste better when you are starving," says Neely.
A study published in Nature in 2015 also looked into the relationship between neural activity and hunger. This earlier study in mice also hinted at the mechanism which makes food taste better when we're hungry and investigated the idea that nature has hardwired us to snack. Again, it seems that the easiest answer for maintaining weight loss is healthy sleeping and eating patterns combined with regular exercise — not to mention weaning ourselves off that need for a sugar fix.