Diet drinks or foods may actually promote weight gain and trigger diabetes because the brain misreads the number of calories present and reduces metabolism, a new study suggests.
Researchers at Yale University in the US discovered that the body stops burning energy from food if there is a ‘mismatch’ between food sweetness and calories.
In nature, sweetness signals energy and the greater the sweetness the more calories are available, so the brain has evolved to expect the two to come together. When they do not, the brain can become confused, thinking there are fewer calories to burn.
This research should be enough to convince you that artificial ingredients, whether they be in food or drink, can screw up your system
Tam Fry, National Obesity Forum
The scientists say it could help explain previous studies that have suggested that artificial sweeteners can increase blood sugar levels and possibly trigger diabetes.
“A calorie is not a calorie,” said senior author Dana Small, Professor of Psychiatry at Yale University School of Medicine.
“The assumption that more calories trigger greater metabolic and brain response is wrong. Calories are only half of the equation; sweet taste perception is the other half.
“Our bodies evolved to efficiently use the energy sources available in nature. Our modern food environment is characterized by energy sources our bodies have never seen before.
“When sweet taste and energy are not matched less energy is metabolized and weaker, or inaccurate, signals are sent to the brain. Either one of these effects may affect metabolic health.”
For the new study, scientists scanned the brains of 15 people when they were drinking diet drinks, and compared them to regular beverages. They also monitored how much energy was burned by the body.
They found when there was a ‘mismatch’ between sweetness and calories - as is often the case with diet drinks or foods because they are not as sugary - the calories fail to trigger the body’s metabolism. Reward circuits in the brain also did not register that calories had been consumed, which could lead to eating more.
Commenting on the paper, Dominic Dwyer, Professor of Psychology at Cardiff University, said: “What the paper does imply, correctly in my view, is that mismatches between calories and sweetness interfere with metabolism of calories in a way that could have negative impact on weight gain, diabetes, heart disease etc. but that determining the link between the unprocessed calories and metabolic health needs future work.
“The most important implication is namely the fate of calories consumed in the mismatch conditions.
“These are not efficiently metabolised at the time of ingestion and thus processed later and/or stored either of which could drive weight gain and interfere with metabolism.”
Tam Fry, of the National Obesity Forum, added: "This research should be enough to convince you that artificial ingredients, whether they be in food or drink, can screw up your system even though they may sound healthy.
"They may be free of calories but not of consequences and diabetes is only one of them. "
However other British experts were more skeptical about the findings and warned people to stick to drinking water if they were concerned about artificially sweetened drinks.
Naveed Sattar, Professor of Metabolic Medicine at Glasgow University, said: “There is currently no strong evidence that diet drinks are necessarily bad for you whereas there is stronger and consistent evidence for sugar sweetened drinks being linked to higher diabetes risk.
“Overall, my advice to people drinking sugar-rich drinks would be to replace with water but that if this is not possible, diet drinks are still a better choice to prevent tooth decay.
“Whether diet drinks also help weight loss or other benefits is uncertain and requires proper long term trials which are currently lacking.”
Tom Sanders, Professor emeritus of Nutrition and Dietetics, at King's College London, added: “The statement that a calorie is not a calorie is gobbledegook. Calories are a measure of the energy value of food. The remark is as stupid as saying a pound of feathers is lighter than a pound of lead.
“The claim is not supported by the observational evidence on people who are long-term consumers of artificial sweeteners.
“Furthermore, an analysis of trials of replacing sugar sweetened drinks with artificially flavoured drinks show that there is some weight loss. Weight gain is certainly is not caused by drinking artificial sweeteners.”
The research was published in the journal Current Biology.