Is dieting good for you?

By this time of year, most New Year’s resolutions to lose weight have long since bitten the dust. But actually, the prospects for successful dieting are never good. Out of every 100 people who diet, only four are able both to lose weight and to maintain their post-diet weight.

When it comes to dieting, most of us are hopeless recidivists. Most of us also refuse to accept such glum news. Our image of what constitutes our correct weight and body size, dictated by a media and public health community obsessed with obesity, continues to drive both women and men to attempt something that is largely impossible. Worse, if there is a health effect of dieting, it may actually be detrimental rather than beneficial.

Research finds that 90 per cent of American high school girls are dieting, despite the fact that many are not overweight or obese. A 2001 study of female high school students by Brigham Young University researchers found that 11 per cent had used laxatives to lose weight, 15 per cent had taken appetite control pills, and nine per cent had made themselves vomit after eating.

Almost half of these girls restricted their food intake to a mere 1,200 calories a day or less. The World Health Organisation defines starvation as a diet of less than 900 calories per day, yet many diets only allow between 950 and 1,200 calories per day.

A recent survey of women’s eating habits found that the median caloric intake is only about 1,600 calories per day, even though the recommended dietary allowance (RDA) for adult women is 2,200 daily calories.

As Jane Ogden of King’s College, London writes in Fat Chance: The Myth of Dieting Explained: ‘For the large majority of women, dieting does not work. Dieting creates more problems than it solves; dieting and overeating become a vicious circle. Dieters never stop dieting, and never stop using the dieting industry.’

The evidence that diets are doomed to failure is extensive. Several studies that have looked at dieting, diet types and weight-loss counselling have concluded that attempts at weight loss are largely unsuccessful, even in highly controlled situations.

In a study that compared low carbohydrate and low fat diets, researchers found that adherence was poor and attrition was high in both groups. Another study that compared self-help diets with commercial diet plans found that after two years the differences in the two groups were negligible.

A review of the major commercial weight loss programs concluded that even the comparatively successful programmes were characterised by ‘high costs, high attrition rates, and a high probability of regaining 50 per cent or more of lost weight in one to two years’.

One shudders to think about the odds of the less successful ones. As the US National Institutes of Health’s review of weight loss programmes put it, ‘Regardless of the products used, successful weight loss… was limited’.

The reasons for such failures are not always found in a lack of willpower. Our metabolic rate conspires against sustained weight loss by decreasing in response to reduced caloric intake so the body can still function.

Some experts suggest that a fortnight of dieting can lead to a 20 percent decline in metabolic rate. This sets up a vicious cycle in which it becomes progressively more difficult to lose each additional pound, as the dieter’s body uses food more efficiently and draws less from its reserve of fat.

The difficulties of dieting are usually put to one side when compared to the alleged health benefits. After all, don’t people who lose weight have a lower risk of heart disease and type-2 diabetes? But those who accept the evidence about the dangers of obesity, based on epidemiological studies, should also be aware that there is equally strong evidence from such studies that dieting is bad for you. A National Institutes of Health conference that reviewed the evidence about dieting concluded: ‘Most studies, and the strongest science, shows weight loss… is actually strongly associated with increased risks of death – by as much as several hundred per cent.’

Dieters have double the risk of getting type-2 diabetes compared to those who are overweight but do not diet. The connection between weight loss and increased risk for an early death is particularly striking in two large studies – the Iowa Women’s Health Study and the American Cancer Society study.

In the follow-up to the American Cancer Society study, researchers found that healthy obese women were in fact better off not losing weight. Healthy women who lost weight had increased mortality risks from cancer, cardiovascular disease, and all other diseases when compared to healthy women who did not diet. A later study found comparable results for men.

Over the past 20 years, more than two dozen studies have found that weight losses of 20 to 30 pounds (between nine and 13 kilos) – the amount most dieters say they want to lose – lead to an increased risk of premature mortality. During the same period, only four studies have found that losing weight increases life expectancy.

Commenting on the gain in life expectancy from such efforts, author and commentator Paul Campos notes that one study ‘found an eleven-hour increase in life expectancy per pound lost… the equivalent of an extra month of life in return for a permanent 50 pound weight loss’.

Rather than lamenting our inevitable fall off the dieting wagon, perhaps we should resolve to take our slightly plump selves as a testimony not to bad health but good health. Let’s raise a well-laden fork to resolving not to think about dieting again until next year.

Patrick Basham and John Luik are co-authors of Diet Nation: Exposing the Obesity Crusade, published by the Social Affairs Unit. They will be launching the book on Thursday 22 March at the Institute of Economic Affairs, London.

Sources:

P Basham, G Gori, and J Luik, Diet Nation: Exposing the Obesity Crusade.

P Campos, The Obesity Myth.

G Foster et al. ‘A Randomized Trial of a Low-Carbohydrate Diet for Obesity’, New England Journal of Medicine (2003) 348: 2082-90.

S French et al. ‘Prospective Study of Intentional Weight Loss and Mortality in Older Women: The Iowa Women’s Health Study’, American Journal of Epidemiology (1999) 149: 504-14.

S Heshka, ‘Weight Loss With Self-help Compared With a Structured Commercial Program’, Journal of the American Medicine Association (2003) 289: 1792-98.

F Hyman, ‘Evidence for Success of Caloric Restriction in Weight Loss and Control’ Annals of Internal Medicine, (1993) 116: 681-87.

National Institutes of Health, Methods for Voluntary Weight Loss and Control Conference, 1992

J Ogden, Fat Chance: The Myth of Dieting Explained

P Nilsson et al. ‘The Enigma of Increased Non-cancer Mortality after Weight Loss in Healthy Men Who Are Overweight or Obese’, Journal of Internal Medicine (2002) 252: 70-78.

J Ogden, The Psychology of Eating

E Pamuk et al. ‘Weight Loss and Mortality in a National Cohort of Adults 1973-1987’, American Journal of Epidemiology (1992) 136: 686-97.

E Pamuk et al. ‘Weight Loss and Subsequent Death in a Cohort of US Adults’, Annals of Internal of Medicine (1993) 119: 744-48S.

F Samaha et al. ‘A Low Carbohydrate as Compared with Low-Fat Diet in Severe Obesity’, New England Journal of Medicine (2003) 348: 2074-81.