Monday, September 19, 2011

Increasing Adolescent Obesity Among Girls: How School Stress is the New Scapegoat When the Skinny Fat Phenomenon and Twinkie Diets Really are to Blame.

Image 1: Was it school stress that cost Michelle Obama her famous "guns" (=muscular upper arms)? Probably not - and despite contrary conclusions in the study at hand, I doubt that it is school stress that leaves our daughters fat, but undermuscled. What do you say?
According to the results of a recent evaluation of the data from the European HELENA trial, school, or rather the stress your children are exposed to within the educational system, may be one of the reasons for the increasing number of obese adolescents (age 12-18 years) - at least if we trust the statistical finesse of Tineke De Vriendt, Els Clays and 10 other scientists who recently published a paper on European adolescents’ level of perceived stress and its relationship with body adiposity in the European Journal of Public Health (DeVriendt. 2011). The study was part of the Healthy Lifestyle in Europe by Nutrition in Adolescence cross-sectional study (HELENA-CSS), the aim of which is to obtain "reliable and comparable data from a selected cohort of European adolescents concerning a broad variety of parameters related to nutrition, health, physical activity and fitness", or in other words, to provide the epidemiological back-bone for the formulation of more or less mainstream hypotheses on "why we are getting sick and obese"... be that as it may, with a sample size that allows for a confidence level of 95% and <0.3 error and 3865 adolescents from more than 10 European cities, the data from the HELENA study is probably the best we can get at the moment and thus you may nonetheless be interested to hear that ...
School-related stress was demonstrated to be a main source of stress in European adolescents, [...and] in adolescent girls (but not in boys), a positive association was observed between their level of perceived stress and measures of general and abdominal obesity.
If you have a closer look at the stress data, expressed on a 6-scale Likert scale from 1 = ‘Not at all stressful’ over  2 = ‘A little stressful’, 3 = ‘Moderately stressful’, 4 = ‘Quite stressful’ to 5 = ‘Very
stressful’ (with 6 indicating ‘Is irrelevant to me’), you will notice that school and the closely related fear of an "uncertain future" are in fact the major stressors in the life of our adolescent children (and you may safely assume that the results won't be very different in the US).
Figure 1: Overview of perceived stressors; values expressed on a Likert-scale from 1 to 5 (data adapted from DeVriendt. 2011)
In that, it is yet interesting to observe that none of the stressors is on average perceived as "quite stressful" or even "very stressful". It is also noteworthy that on 5 out of 10 scales and on the summary scores girls experienced more stress than boys. In view of the scientists previously cited conclusion (of which I do not have to tell you that it is based on one of those sophisticated *cough* statistical models) that only "in adolescent girls (but not in boys), a positive association was observed between their level of perceived stress and measures of general and abdominal obesity", it may thus surprise you to hear that the obesity rate among boys is more than 2x higher than among adolescent girls (cf. figure 2). So how is that?
Figure 2: Body adiposity characteristic of study sample (n=1121) of adolescents from the HELENA trial (data adapted from DeVriendt. 2011)
Well, we all know that even with a perfectly "normal" BMI, you can easily be "skinny fat". A phenomenon of which I feel that it is becoming the norm, not the exception, among adolescent girls, who - after their nth an-apple-a-day diets have lost nothing but muscle and thus have a very high body-fat percentage with a low overall body-weight.

This hypothesis would be confirmed by the regression coefficients of the statistical models from the study, according to which the association of perceived stress with the body fat level of the girls is 7x higher than the association of perceived stress and BMI, which is something that should you make reconsider, whether
  1. body weight and BMI is an important biological measure, at all,
  2. the real "obesity" rate, including skinny fats, among girls is not way higher than the 1.9% reported in the study would suggest, and
  3. in how far school-stress, despite being the "major stressor" in this survey and not a misguided beauty-ideal is to blame for the increasingly unbalanced ratio of lean to fat mass in adolescent girls
The importance of the latter, i.e. a questionably beauty-ideal, in the etiology of (and this would be ironic if it was not so unfortunate) diet-induced obesity could also explain that the pubertal stage the girls were in and not stress or their diet had the greatest "explanatory value" (remember: we are talking of associations here) in regard of their body fat levels (cf. figure 3).
Image 2: Low self-esteem and false beauty-ideals pave the way into disordered eating and life-long misery. Something you want to spare your daughter and son, don't you?
Did you know that according to a 2000 national survey 45% of the girls, but only 20% of the boys from 5th to 12th grade reported to have tried one or more diets at some point in the past (Neumark-Sztainer)? And would you have guessed that 17% did even consider their own eating behavior as already "distorted"? Needless to say that both of these factors showed a high correlation with overweight status, low self-esteem, depression, suicidal ideation, and substance use; and certainly reason enough for you to help our children (girls and boys) not to fall victim to ill-advised beauty-ideals and false dietary recommendations.
And from the fact that the same variable had 7x less predictive value in boys, who obviously do not want to be skinny fat and refrain from Twinkie-style low calorie, low fat dieting, we can with some caution (due to hormonal effects on fat accumulation) conclude that it is not just a time factor, meaning that the older girls have more time to accumulate body fat...
Figure 3: Regression coefficients (=associative strength*100) of stress or pubertal stage with body-fat percentage in adolescent boys and girls from the HELENA trial - mind the logarithmic scaling! (data adapted from DeVriendt. 2011)
Now, what can you do about that? Well, without even knowing you probably have already done something! Assuming that you (just like every other reader of the SuppVersity ;-) are of above-average intelligence, your education has already provided your daughter, but not your son, with a better chance of staying lean than her peers from less educated parents (~80x higher explanatory value than stress!). All that is left now to make absolutely fat-proof, is to tell her that strong, not skinny fat is the new beautiful ;-)