A new study conducted by researchers at the University of Kansas School of Medicine suggests that most research articles reporting weight loss studies fail to indicate crucial patient characteristics that may bias the results.

The team led by Cheryl Gibson found that over 90 percent of diet studies did not adequately and comprehensively describe their subjects, making them almost impossible to interpret accurately.

The researchers analysed 231 articles reporting studies of the effects of diet restriction, diet restriction and exercise, or exercise only, on weight loss; as well as research studies on body composition, fat distribution, metabolism and aerobic fitness.

The analysis included articles from 1966 to 2003 that reported studies of obese adult participants.

The team focused on how the articles reported subject characteristics, using the Consolidation of the Standard of Reporting Trials Characteristics (CONSORT) as a guide. The CONSORT statement is a list of 21 elements, recommended as essential for a study to be valid, by a panel of clinical investigators, epidemiologists, biostatisticians and journal editors.

The characteristics the researchers chose to concentrate on were age, gender, general health, medication use (other than drugs taken to control obesity), ethnicity and postmenopausal status. It has been shown that all of these characteristics affect weight and can alter the effect of diet and exercise on weight loss.

The researchers also examined whether the sample size at the beginning and at the end of the study was indicated, by gender. “Without knowledge of the number of subjects who were lost to follow-up, readers are unable to judge the effectiveness of a clinical treatment or ascertain whether or not a research finding has practical significance” the authors said.

Their results show that medication use was the least indicated of the characteristics, as 92per cent of the articles missed it out. The subject’s health status was ignored by 34per cent of the studies.

Ethnicity was not indicated in 86per cent of the studies, and the subject’s age was not reported in 11per cent of the studies. 8per cent of the studies failed to report the postmenopausal status of their participants, and 4per cent did not indicate gender.

“We found major shortcomings in the reporting of subject characteristics. Many studies did not report variables that may explain some of the variance in outcomes [...] and reveal poor adherence to published standards of reporting,” they concluded.