Why artificial sweeteners make us eat more
Greg Neely wondered what was going on in his body when he drank diet soft drink.
The associate professor at the University of Sydney’s Charles Perkins Centre noticed that the drink seemed to make him feel hungry.
Previous studies have suggested that artificial sweeteners may increase appetite and cause cravings.
However, no one really understood why it happens.
So Neely, who has spent 15 years researching fruit flies, decided to find out.
In the comprehensive new study, published in the journal Cell Metabolism, Neely and his colleagues found that when fruit flies were consistently given a diet containing artificial sweetener, they consumed 30 per cent more kilojoules when their diet returned to naturally sweet food.
“In the fruit fly system the taste was coming up from the tongue to the centre of their brain which was sending a sweetness message, but then within those neurons there was also a gauge of the energy that they’re receiving and basically, the energy wasn’t matching up to the sweetness for a long period of time,” Neely explains of the response to artificial sweeteners.
“The animal’s brain then adapts – sweetness is higher than the actual energy so it recalibrates in the brain and then they’re going to want more sweetness.
“After what should have been a sufficient meal, they felt they hadn’t eaten enough – they were in a semi-fasted state… this fasting response activated changes that increased hunger.”
They also found that artificial sweeteners caused hyperactivity, insomnia and decreased sleep quality – behaviours associated with a semi-fasting state.
Neely says that disparate findings in certain other studies may be down to the design.
“There are lots of association-type population studies on this stuff and they’re set up really differently… it’s hard to mix them all together,” he says, adding “there is more evidence suggesting [sweeteners] are doing something.”
The researchers replicated their findings in mice.
“We’re seeing a cross-file from insects to mammals,” Neely says. “It suggests that the response could be conserved all the way to humans, but it’s a lot harder to do these sorts of studies in humans.”
The research on artificial sweeteners and its general effect on human health has been inconclusive and often contradictory.
This is often because, as Neely points out, they are observational and making associations rather than proving cause and effect.
The only certainty is that too much sugar, artificial or natural, is unhealthy.
Neely says his research is a reminder that artificial sweeteners might be ‘kilojoule-free’ but they still make their mark in our bodies.
“One message is that the’re not doing nothing – they’re having an impact on animal’s brains and presumably our brains,” he says.
“If you’re const overloading your brain w high-levels of sweetness, it might change something in the way you regulates your food intake.”
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