Body Mass Index and Subjective Well-Being in Men and Women

A susceptibility to eating disorders
emerged among women.

FinnTwin16, a nationwide longitudinal study of health behaviors in twins and their families, has provided valuable information about overall health and eating disorders as well. Nearly all live twin births during 1975 to 1979 were identified in a central population registry of Finland. When these twins were 16, 17, and 18, and 22 to 28 years of age, they filled out self-report questionnaires on a range of topics. One topic involved body mass index (BMI, kg/m2) and subjective well-being.

Dr. Milla S. Linna and colleagues at the University of Helsinki and Helsinki University Hospital noted that while a higher BMI is believed to be related to poorer well-being, there has been little information about the effects of lower BMIs among young adults or how an eating disorder might affect their well-being.

To explore these questions, Dr. Linna and researchers used data from the fourth wave of FinnTwin16 questionnaires sent to the study twins. The authors included data from 2415 males and 2825 females 22 to 28 years of age (BMC Public Health. 2013; 13:2431). The authors’ questionnaire assessed a variety of health behaviors and included scales on subjective well-being, as well as a built-in screen for eating disorders developed earlier by one of the authors (Int J Eat Disord. 2006; 39:754).

BMIs were calculated based on self-reported heights and weights. For descriptive purposes the authors classified persons with BMIs <18.5 kg/m² as underweight and those with BMIs >30 kg/m² as obese. In addition, they applied gender-specific Z-scoring of BMI in all analyses.

Women had lower scores on well-being

BMIs. Men had a mean BMI of 23.9 kg/m² and women a mean BMI of 22.2 kg/m². About 1% of men were underweight, while 7% of women were underweight, or had BMIs less than 18.5 kg/m². Obesity was relatively rare (4%) among these young adults. In contrast, dieting was common: 42% of women and 24.4% of men reported intentionally losing more than 11 lb at least once. BMI varied considerably when evaluated by eating disorder: the mean BMI for women with a past history of anorexia nervosa (AN) was 21.2 (32 women); 23.6 in women with bulimia nervosa (BN; 37 women); 20.1 with 9 women with a past history of AN and BN (9 women), and 26.2 in the 11 women with binge eating disorder (BED).

Subjective well-being. Overall, women reported lower levels of well-being than did men. Lean men tended to have lower levels of subjective well-being than did obese men, but this could not be attributed to a diagnosed eating disorder, since only 5 men had lifetime histories of AN and 2 had lifetime histories of binge eating disorder (BED). Women with a lifetime history of an eating disorder and their healthy twin sisters as well reported lower levels of subjective well-being. Subjective well-being also tended to be lower among women with eating disorders, and women with lifetime diagnoses of both AN and BN had extremely high levels of distress.

Differences among men and women

Among men, there was an inverse, U-shaped relationship between BMI and subjective well-being. This was constant across all other indicators of psychological health; the highest levels of subjective well-being were found among overweight men. In the current study, estimates of the optimal BMI in terms of subjective well-being in men varied from 26.1 to 28.9 kg/m². The authors surmised that being in the “overweight” category might be beneficial for young men’s psychological health, partly because men usually have a higher proportion of lean muscle mass compared to women. BMI does not differentiate between fat and muscle tissue, so having a BMI in the overweight range did not necessarily imply an excess fat tissue.

Overall, women reported lower levels of subjective well-being than men, and women with lifetime DSM-IV eating disorders had a U-shaped relationship between BMI and life satisfaction. Interestingly, a similar effect was noted in the twin sisters of women with a lifetime eating disorder who did not report any psychopathology related to eating or weight. In fact, the optimal BMI for subjective well-being appeared to be in the overweight range: 26.4 to 29.0 kg/m²; this was true even after excluding women with BED from the analysis.

The authors suggest that the relationship between BMI and subjective well-being can be attributed to a susceptibility to eating disorders in women. This might imply that body weight might play a greater role in the relationship between subjective well-being among these women compared to women without a susceptibility to eating disorders. Another explanation would be that when being exposed to mental distress, women who are more susceptible to developing an eating disorder more readily react by either losing or gaining weight.