The efforts made in order to lose weight are frequently initiated as a result of knowledge about the dangerous consequences of obesity, such as social stigma and negative effects on health. Nevertheless, this is not always the case due to the fact that a lot of women and girls make attempts to lose weight even in the lack of overweight. Long term weight loss is very often fruitless, due to the fact that body size, shape and weight are strongly genetically influenced.
While weight loss is generally considered to be advantageous, it can also predispose weak individuals to overeating and eating disorders. Hence, the scientists investigated whether intentional weight loss (IWL) is connected with potentially harmful eating habits in a large and representative population-based sample of young adult twins. The major objective of the research was to scrutinize the genetic and environmental contributions to IWL in this unique twin sample and to check whether the genetic liability affecting IWL is completely shared with the genetic liability affecting BMI.
The data used in the study come from the FinnTwin16, a population-based research of five birth cohorts of Finnish twins that were born between 1975 and 1979. The baseline evaluation was carried out by postal questionnaire at the age of 16 years, with follow-up at 17 years and 18.5 years and the fourth wave of data collection taking place at the mean respondent’s age of 24.4 years. This research included 1258 like-sexed twin pairs.
IWL was evaluated in the sample by means of using the following question: ‘How many times during your life have you deliberately lost > 5 kg of weight?’ The responders in the ‘never’ category formed the no-IWL group. Participants responding ‘once’ molded the 1-IWL group, and those responding ‘2 times to 4 times’ or ‘5 times or more’ molded the 2-1W group. On all questionnaires the twins self-reported their existing weight and height, from which BMI at each age was calculated. Waist circumference was measured by the respondents by means of a tape measure that was posted along with the questionnaire. Restrictive eating and overeating were evaluated with the question: ‘Which of the following best describes you?’ The choices were ‘It’s rather easy for me to eat about the amount I require’ (normal eating, reference category); ‘Frequently, I eat more than I really need’ (overeating); ‘I frequently try to limit my eating’ (restrictive eating); and ‘From time to time, I’m on a strict diet, at others, I overeat’ (alternating restricting/overeating). To evaluate eating styles of the participants, a short 12-item questionnaire was expanded: five items evaluated snacking/grazing styles, three evaluated health-conscious eating, two evaluated emotional eating, one evaluated externally cued eating, and one evaluated night eating.
People who had been involved in IWL showed markedly more limiting, overeating, and alternating restricting/overeating than persons in the no-IWL group. Snacking and eating in the evening were typical of women with at least two IWL attempts. Eating in reply to visual and emotional cues was very pronounced in women who had been involved in IWL but much less so in men. IWL was estimated to have a heritability of 38 per cent [95 per cent confidence interval (CI), 19 per cent to 55 per cent] in men, and 66 per cent (95 per cent CI, 55 per cent to 75 per cent in women. The genetic covariance of BMI and IWL was 0.38 (95 per cent CI, 0.28 to 0.47) for men and 0.45 (95 per cent CI, 0.41 to 0.52) for women.
There are also discrete sex differences in eating styles connected with IWL and in the heritability of IWL. The majority of genetic factors influencing BMI are different from those influencing IWL.
