Crash dieting 'makes you thick'

Trying to look like this could impair your brain power

A new study suggests that crash dieting reduces mental performance.

The research, details of which were announced at the British Association's Festival of Science in Sheffield, UK, indicates that drastic dieting can impair memory and slow reaction times.

Scientists were already aware that dieting can cause depression and produce negative psychological effects such as low self-esteem and poor self image.

But this study was one of the first to assess how dieting affects mental performance.

One hundred women took part in the study, some of whom were on crash diets and some of whom ate a healthy, balanced diet.

Psychological impairments

The study, by Dr Mike Green, now of Unilever, but who did work whilst at the Institute of Food Research in Reading, used a variety of computer-based tasks to measure their strategic planning skills and response time.

"The impairments to mental functions were not due to underfeeding but the psychological impairments of dieting," he said.

"A good analogy is like the RAM memory in a computer. There is a set amount of capacity to perform tasks and the more programs you run at the same time, the less memory is available for new tasks."

People dieting, particularly crash dieting, can be preoccupied with thoughts of hunger, worries over their body shape and feelings of low self-esteem. These thoughts then hinder any other mental activity, according to Dr Green.

Poor performance

The reaction times of the non-dieters in the study were between 350 and 400 milliseconds. For dieters, these rose to between 450 and 500 ms.

The poor performances only applied to women undergoing rapid weight loss, not those on long-term programmes.

Dr Wynnie Chan of the British Nutrition Foundation said the answer was clear: "What people need to do is eat sensibly, adopt a healthy balanced diet and adopt a much more physically active lifestyle," she said.

Another study reported at the festival suggested that skipping breakfast, a common ploy to reduce food intake, leads to memory being poorer later in the day.

Professor David Benton, a psychologist from the University of Wales in Swansea, also said that those who miss the first meal of the day are less happy that day than those who do not.