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Will diet advice cause more problems in the long run?

Raj Persaud
BSc MSc MB BS MPhil FRCPsych
Consultant Psychiatrist  The Maudsley Hospital London
Gresham Professor for Public Understanding of Psychiatry

One of the most mysterious and puzzling findings from the latest scientific research into those trying to lose weight has been that dieting seems paradoxically to lead to longer-term weight gain.

A new and uniquely comprehensive investigation conducted by Dr Dianne Neumark-Sztainer, an epidemiologist at the School of Public Health at the University of Minnesota, appears to come up with a surprising answer to the conundrum of if and how does "dieting" cause longer-term weight gain.

The study, an exceptional one in terms of following up over 2,500 young people who were trying to lose weight over five years, was conducted by several colleagues from the University of Minnesota and is unusual in exploring in greater detail than hitherto possible why trying to lose weight seems to lead to weight gain and also whether this is just a myth or rooted in reality.

In fact at least four scientifically respectable studies have previously established that "dieting" is not only generally unsuccessful, it seems to make things worse, and indeed predicts weight gain, and actually seems to be a significant cause of obesity in its own right. For example, the Minnesota team previously conducted a five-year study of eating and weight in young people, and found those who reported dieting were at nearly twice the risk of being overweight five years later.

Adolescents who furthermore used particularly unhealthy weight control techniques, such as skipping meals or using diet pills, were at three times the risk of being overweight in five years time.

The researchers were careful in their investigation to make allowances in their study for competing explanations, like their findings could be explained as the result of overweight adolescents having excessive food and weight preoccupations and reporting increased dieting behaviours. In other words, it wasn't just the already overweight becoming more overweight with time as might be expected.

It appeared instead that it was the impact of "going on a diet" regardless of how overweight you already were that turned out to be the crucial risk factor in terms of causing future obesity.
This now repeated finding from scientific research that dieting predicts future weight gain over time is bewildering, in that "dieting" should surely be expected to be associated with healthier eating and physical activity patterns that would lower weight in the longer term.

But the research into genuine longer-term successful weight loss has found a pattern of behaviours such as having breakfast, increasing fruit and vegetable intake and physical activity, which actually has not been associated in the longer term with those "on a diet".

In contrast, "dieting" is more often implemented on a short-term basis, and it is possible that dieting actually sets the scene for future dangerous eating and physical activity patterns.
The Minnesota team points out the danger is those who keep obsessing about dieting trying inevitably to restrict their dietary intake, which merely leads in the longer term to increased feelings of hunger and therefore binge overeating.

"Dieting" actually increases the risks of binge eating, which is definitely linked to longer-term weight gain, and this could be the key mechanism by which diets lead to longer-term obesity. This theory has been referred to by nutritionists as "Dietary restraint theory", which argues that over-relying on mentally controlling eating inevitably leaves dieters vulnerable to uncontrolled eating when the huge emotional effort invested in such mental control is interrupted by stress or exhaustion or any other event.

The Minnesota team concludes that it's the tendency to not introduce longer-term healthy lifestyles into our lives and the tendency instead to go for the "quick fix", which explains why dieting produces weight gain in the longer term.

Now of course nurses, like many health professionals, advise many, if not the majority, of their patients to lose weight - this new research suggests that we all need to be very careful with how we phrase our advice and evaluate its impact on the patient. It's entirely possible that badly framed or worded advice in the end produces the opposite effect to that desired.

Neumark-Sztainer D, Wall M, Haines J, Story M, Eisenberg ME. Why does dieting predict weight gain in adolescents? Findings from Project EAT-II: A 5-year longitudinal study. J Am Diet Assoc 2007;107:448-55.