I was watching the BBC program “The Men Who Made Us Fat” and was startled to hear the gentleman being interviewed say that a recent study confirmed children are no less active today than they were 30 years ago. He said that the rise in obesity is not a result of decreased activity, but of changes in what and how we eat. (I believe this but it was odd hearing someone of authority say it.)
I’ve made this point several times, referring to government’s (e.g. Michelle Obama’s “Let’s Move” campaign1) and industry’s attempts to shift focus away from the food we eat, towards the activity we’re supposedly not getting, as the reason we’re overweight. It’s a ploy. It blames the individual instead of having to confront the real culprit – the monolithic food industry, a significant player in the US’s emerging status as “corporate oligarchy“.
I don’t know the study upon which his claim was made, but I found this:
Fatness Leads To Inactivity, But Inactivity Does Not Lead To Fatness: A Longitudinal Study In Children, Archives of Disease in Childhood, April 2010
This was a prospective cohort of 202 children in the UK over 7 to 10 years. Cross-sectional studies repeatedly find a link between obesity and inactivity, but they can’t (by nature of study design) determine what caused what. A prospective study like this can determine direction of causality because it looks at changes over time.
Physical activity (PA) was measured using Actigraph accelerometers. The children wore the accelerometers for 7 consecutive days at each annual time point. Two components of PA were analysed: the total volume of PA and the time spent at moderate and vigorous intensities. Body fat per cent (BF%) was measured annually by dual energy x ray absorptiometry.
Results: BF% was predictive of changes in PA over the following 3 years, but PA levels were not predictive of subsequent changes in BF% over the same follow-up period.
Conclusions: Physical inactivity appears to be the result of fatness rather than its cause. This reverse causality may explain why attempts to tackle childhood obesity by promoting PA have been largely unsuccessful.
This study cited other similar studies done on adults which found the same thing:
“Cause must precede effect, and longitudinal studies that measure fatness and activity levels at baseline and long-term follow-up can use the rule of temporality to investigate the dominant direction of causality. Four studies have carried out this kind of analysis in adults.
All four adult studies reported a significant inverse association between baseline fatness and follow-up PA but not between baseline PA and follow-up fatness, suggesting that fatness leads to inactivity but that inactivity does not lead to fatness.”
“All four found that a higher body mass/fat consistently increased the odds of becoming sedentary, whereas being sedentary rarely increased the odds of becoming obese.”
It’s the food:
“If childhood fatness is not the result of physical inactivity, the implication may be that excess energy intake underlies fatness and inactivity.”
The image of the “couch-potato” child who is obese because he is sedentary runs deep in Western consciousness. However, the possibility that the reverse obtains, that his fatness is the cause rather than the result of his inactivity, has far-reaching implications. Although there may be many benefits to PA, the findings of this study, coupled with the limited success of PA interventions aimed at improving BMI, imply that public health strategies may need to target energy intake to curb the year-on-year rise in childhood obesity.
I am surprised when I hear intelligent people say if you exercise more you’ll lose weight. I shouldn’t be surprised though, it just means the food industry has been successful in pushing their message, diverting attention from the real reason Americans are overweight.
Exercise is great for the circulatory system, the lymph, the lungs, the mitochondria … many parts of the body. But if you want to lose weight and live a long, healthy life, you’ll have to change your diet. As Shaun says, “You can’t run from a bad diet.”