Scientists found the reactions of female dieters were 15 to 20 per cent slower than those of non-dieters, and their short-term memory was between 10 and 20 per cent worse than that of women eating what they wanted, the British Association was told yesterday. Mental impairment resulted from anxiety about food rather than deficiency of nutrients caused by fasting, the researchers concluded.
"We found that dieters display poorer memory, an impaired ability to sustain attention over a period of time, and slower reaction," said Michael Green, who conducted the research at the Institute of Food Research in Reading. "We found this is a function of being on a diet per se because when we tested the same people, their performance is impaired when they are dieting but not when they are eating what they want," Dr Green said. "Rather than this being due to the biological consequence of underfeeding and starvation, we think this is due to the psychological consequences of dieting. We found that when we actually try experimentally to deprive people of food for a period of time we do not get these effects."
Eating a chocolate bar failed to improve the performance of dieters; for some people the snack even made things worse, suggesting that food anxiety rather than low blood glucose levels is responsible. The scientists said the findings are the result of a person's preoccupation with food and body shape, their constant thoughts about hunger and a feeling of low self-esteem.
Dr Green suggested that the psychological preoccupations of dieters may be analogous to the limited memory of a computer, with dieters using up limited processing capability within their brains.
"Using the computer analogy," Dr Green said, "if you have one document or program running at any one time that functions well, but if you try to run three or four programs at the same time, the system slows down because there is only a limited capacity to do what is being set.
"It [the effect of dieting] is quite comparable to what you get with anxiety or depression. So there is nothing special about dieting; this is simply what happens with any preoccupying worry," he added. Meanwhile, a second study also found that skipping breakfast was linked to short- term mental impairment, according to David Benton, a psychologist at the University of Wales in Swansea, who studied 832 women to test the idea that fasting has a negative impact on memory.
"The ability to recall a list of words was greatest when tested less than 30 minutes after eating breakfast. Following breakfast, the ability to remember a word list declined progressively over three and a half hours," Dr Benton said.
The researchers found that the memories of women who ate breakfast were significantly better at all periods in the morning than those of the people who had missed the meal. Eating a breakfast also promoted a feeling of well-being, Dr Benton added.