Weight loss myths – separating fact from fiction

Some widely held beliefs about weight control exist despite a lack of supporting evidence, or even contradicting evidence. These weight loss "myths" can be counterproductive by promoting inaccurate recommendations, and diverting attention away from useful, evidence based strategies.

A team of researchers identified seven popular weight loss myths that they have dispelled in a recent article published in the New England Journal of Medicine. Following is a summary of their findings.

1. Myth - Small sustained changes in energy intake or expenditure will produce large, long-term weight changes

Fact - Small changes that are adhered to over the long-term will have a cumulative effect on weight over time. Examples of small lifestyle changes includes walking an extra ten minutes each morning, or drinking one less glass of soft drink a day.

However, calculations predicting that these changes will accumulate indefinitely fail to take into consideration individual variations in the way the body responds to changes in kilojoule intake and energy expenditure. For example, the loss of body mass alters the energy requirements of the body, meaning you burn off less kilojoules for a given task compared to when you were heavier. This could mean that the impact of small, sustained changes is smaller than expected.

2. Myth - Setting realistic goals for weight loss is important, because otherwise people will become frustrated and lose less weight

Fact - There is no research to suggest that ambitious goals have a negative effect on program completion or weight loss. In fact, studies have shown that more ambitious goals are sometimes associated with better weight-loss results. For example, two studies designed to boost weight-loss by altering unrealistic goals and creating more realistic weight-loss expectations did not help the subject lose any extra weight.

3. Myth - Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss

Fact - You may have heard that fast weight loss leads to fast weight re-gain. But research has shown that faster and greater initial weight loss is associated with lower body weight over the long-term (greater than one year). While it's unknown why some overweight people experience a greater level of initial weight loss compared to others, a recommendation to lose weight more slowly might actually interfere with the ultimate success of a weight-loss attempt.

4. Myth - It is important to assess a person's diet readiness, or stage of change when they seek out treatment for weight-loss

Fact - A person’s diet readiness does not predict the magnitude of weight loss or level commitment to a treatment program. Five studies that specifically evaluated stages of change showed no conclusive evidence of sustained weight loss. According to the researchers, anyone who voluntarily chooses to lose weight is at least minimally ready to engage in the behaviours required to lose weight.

5. Myth - Physical education classes play an important role in reducing or preventing childhood weight problems

Fact - Physical education classes have not been shown to reduce or prevent excess body fat in children. A number of studies that promoted extra physical activity were ineffective in reducing measures of fatness. The researchers note that a certain a level of physical activity would most likely be effective in reducing or preventing childhood weight problems, but whether that level is plausible in a conventional school setting is unknown.

6. Myth - People who are breast-fed are less likely to be overweight later in life

Fact - Trials involving more than 13,000 breast-fed children who were followed for more than six years provided no compelling evidence of an effect on levels of body fat. According to researchers, breast-feeding status no longer appears to be a major determinant of an increased risk of suffering weight problems. However, it is important to note that breastfeeding has other important benefits for the infant and mother and should be encouraged.

7. Myth - Having sex burns lots of kilojoules

Fact - The energy expenditure of sexual intercourse can be estimated by calculating variables such as the intensity of activity, body weight and duration. For most people, this translates to a similar kilojoule burn to that achieved by walking at a moderate pace (approximately 4 km per hour). Given that the average bout of sexual activity lasts about 6 minutes, it won't account for much kilojoule use.

References available on request