Research in rats has found that artificial sweeteners may contribute to weight gain by confusing the body’s ability to control appetite and recognise when it will soon be full.

Study author, Susan Swithers, an associate professor of psychological sciences at the Ingestive Behaviour Research Institute at Purdue University, said, ‘We found that the rats that were getting artificially sweetened yogurt gained more weight and ate more food. The take-home message is that consumption of artificially sweetened products may interfere with an automatic process. We often will stop eating before we’ve been able to absorb all of the calories that come from a meal. One of the reasons we might stop eating is that our experience has taught in the past that, ‘After I eat this food, I’ll feel this full for this long’.

The researchers said that, although they cannot be certain, the weight gain may be explained by the shortfall between the taste indicating that calories are coming, and the actuality of that taste being followed by a lower caloric intake. This may confuse the body’s digestive system, causing it to not increase its metabolic rate by as much the next time the flavour is tasted.

Two groups of rats were fed yoghurt sweetened with either glucose (a sugar) or saccharin (artificial sweetener). The rats that consumed the saccharin-sweetened product ate more overall and increased more in weight. Swithers also noted that the body temperatures of the fatter rats also did not rise as much as it did among the other rats, and said, ‘That might be a kind of measure of energy expenditure, suggesting not only are the animals eating more calories, they may be expending or burning up fewer calories’.

Although it appeared that the rats bodies were ‘learning’ that the sweet taste did not mean more calories and were therefore consuming more to counteract this, there is dispute about whether such behaviour would translate to humans. President of the trade group Calorie Control Council, Lyn Nabors, said that the research had ‘no basis in science’ and ‘no relation to the human experience whatsoever’.