Fat cells are part of the endocrine system, and, as I've discussed before, they have the power to influence the degree to which muscle cells prefer glucose versus fats as an energy source. They exercise this control by releasing two signaling peptides: leptin and adiponectin. Adiponectin promotes glucose consumption by the muscles, and it also acts directly on the fat cells to encourage them to take up glucose and convert it to fat. Leptin, on the other hand, stimulates the muscles to prefer fat consumption over glucose consumption.
Statistically, children with ADHD have an abnormally efficient glucose metabolism rate, i.e., for the same amount of insulin, blood sugar levels drop more quickly after a meal than in other children. This observation suggests that their fat cells have arranged a set point of a high adiponectin to leptin ratio, such that the muscles prefer glucose over fats, and fat cells are predisposed to convert glucose to fat. The glucose levels drop more quickly because the muscles and fat cells are using more of it.
Anorexics, children who intentionally starve themselves, are known to have extremely efficient glucose metabolism (tend towards hypoglycemia) and also to have a high ratio of adiponectin to leptin concentrations . This strategy maximizes availability of fatty acids to the heart and brain. It is curious that anorexia is much more common in girls, and ADHD is much more common in boys.
Researchers at Harvard Medical School suspected that there might be an association between anorexia and ADHD. To test this hypothesis, they compared girls with ADHD against a control group to see whether the ones with ADHD were predisposed towards anorexia (ADHD and Anorexia). The results showed that girls with ADHD were 3.6 times more likely than the control group to develop an eating disorder. I have come to believe that anorexia is a technique to combat ADHD that girls are able to adopt, whereas boys do not have enough fat cells to carry out the task of converting glucose to fat. Ritalin is well known to reduce appetite, and long term use can lead to an anorexia-like condition. It may well work, in part, because it achieves this ultra-thin state, thus conserving fats by minimizing the consumption of fat by cells that can get by on glucose.