Obesity is accompanied by many health risks, including diabetes, heart disease and musculoskeletal problems. Small decreases in weight have been associated with decreases in the risk of these adverse health outcomes, however, sustained weight loss is incredibly difficult to accomplish.

It has been well documented that people underestimate their height and weight (see my previous post on parental perceptions of child BMI). However, does knowledge of one’s weight affect willingness to start weight control behaviours? How much does your perceived weight differ from your actual weight? And more importantly, can health care professionals affect starting weight control behaviours?

More after the jump.

NHANES is a US-based, nationally representative sample. Click the picture to go to the official NHANES website

What did they do?

In order to answer these questions, they used the NHANES database. The National Health and Nutrition Examination Survey is an absolutely phenomenal database that contains information on a representative sample of Americans. It consists of an interview on demographic, socioeconomic, dietary and health-related questions, as well as a physical exam and laboratory tests. The program began in the 1960s, and has been an invaluable source of information for many researchers.

To determine their weight status, participants were asked “do you consider yourself now to be overweight, underweight or about the right weight?” They also had their height and weight directly measured.

Participants were asked a series of questions. To determine if they wanted to lose weight, they were asked “Would you like to weigh more, less or stay about the same.” They were then asked if they were doing anything to try and lose weight or to not gain weight. If they said yes, they were asked what they were doing. This was categorized as “diet,” “physical activity” and “other.”

What did they find?

They had 16,720 people available for their analysis. They found that approximately a third of their sample was overweight, and another third was obese (females: 27.6% and 34.1%; males: 39.4% and 31.3% overweight and obese respectively). They also found that 64.3% of their sample wanted to lose weight, with a higher prevalence among women than men (73.2% vs 55.1%). Finally, they also found that of those who perceived themselves as overweight, almost all wanted to weigh less (98.3% of women, 95.2% of men).

Now when it came to actually trying to lose weight, men who viewed themselves as being overweight were 1.39-times more likely to pursue weight control (95% CI: 1.09-1.78). Non significant findings were found for obese men, as well as overweight and obese females.

This was markedly different if a health care professional made the diagnosis of overweight or obese. Women were 2.22-times more likely to pursue weight control (95% CI: 1.69-2.91), while men were 2.14-times more likely to pursue weight control (95% CI: 1.58-2.91).

And what now?

Those diagnosed by a health care professional for being overweight or obese are more likely to start weight control treatment than if they consider themselves overweight or obese. There is also evidence that health care professionals do not educate their patients in safe weight loss practices. The prevalence of obese patients who received advice to lose weight decreased from 44% in 1994 to 40% in 2000 (even though the prevalence of overweight and obesity went up in this time) (Jackson et al., 2005). These findings suggest that health care professionals may be an under-utilized resource that could help patients lose weight in a health manner.

Yaemsiri S, Slining MM, & Agarwal SK (2011). Perceived weight status, overweight diagnosis, and weight control among US adults: the NHANES 2003-2008 Study. International journal of obesity, 35 (8), 1063-70 PMID: 21042327
Jackson JE, Doescher MP, Saver BG, & Hart LG (2005). Trends in professional advice to lose weight among obese adults, 1994 to 2000. Journal of general internal medicine, 20 (9), 814-8 PMID: 16117748