Fad Diets and Teenagers: Why Controlling "Calories In" and "Calories Out" Doesn't Work
Articles on fad diets and teenagers abound. Most of these discuss topics that ultimately relate back to calorie control. We want our teenagers to lose weight, so we encourage them to exercise more. We also encourage them to eat less. We look at the psychological underpinnings of obesity and hypothesize that fat teens get fat because their friends are fat, because they play too many video games, and so forth.
Nearly all debates about fad diets and teenagers begin with this assumption that "calories count." Therefore, every solution to teen obesity focuses on calorie control. We want our kids to be thinner, so we dream up ways to get them to eat fewer calories and burn off more calories. This is ultimately because we believe in the Caloric Balance Hypothesis, which tells us that weight changes -- including weight gain associated with puberty -- must be controlled by "Calories In" and "Calories Out."
The Lipophilia Hypothesis says that puberty probably drives changes in insulin levels and/or insulin sensitivity. These changes then alter the constitution of the fat tissue, which in turn alters metabolism and appetite and thus drives a positive caloric balance. Your teen eats more because she's gaining weight; she doesn't gain weight because she's eating more.
So which theory about fad diets and teenagers is right? What does the evidence tell us?
1. Here is one article that seems to imply a lot: "Puberty decreases insulin sensitivity."
The authors write that "puberty associate[s] with decreased sensitivity to insulin that normally is compensated for by increased insulin secretion."
They also say that "insulin sensitivity correlate[s] inversely with body mass index."
These observations jive with Lipophilia.
2. Here is another article that can inform our discussion on fad diets and teenagers: "Growth at puberty."
The authors tell us that:
"The hormonal regulation of... body composition depend[s] on the release of gonadotropins, leptin, sex steroids, and growth hormone. It is very likely that interactions among these hormonal axes are more important than their main effects, and that alterations in body composition and the regional distribution of body fat actually are signals to alter the neuroendocrine and peripheral hormone axis."
So hormones regulate how body fat is distributed and how body fat accumulates in teenagers going through puberty. But if hormones regulate how fat gets distributed, then how can we blame "excess calories" for weight gain? And if we can't blame excess calories, then how can we tell people that eating less and exercising more "works"?
Again, the simplest and most plausible hypothesis for why pubescent teens gain weight must be the Lipophilia Hypothesis – Caloric Balance just doesn't hold up when you look at evidence in our real world.