Fat Metabolism

I attended a couple of veterinary meetings last year about obesity because there is a new drug to treat obesity in dogs. Obesity is a hot topic of research in humans and animals. What they have found is that fat tissue does not just lie around and store fat. It is a very metabolically active tissue that produces lots of hormones and inflammatory mediators like interleukins and prostaglandins. Antiinflammatories such as ibupofen are antiprostaglandins - so trying to treat painful joints while the fat keeps pumping out more prostaglandins makes treating these conditions in obese patients more difficult. These contribute to the development of inflammatory diseases - most notably osteoarthritis, but in people may account for the fact that obese people are also more prone to things like autoimmune diseases. The arthritis is not worse because of the mechanical forces of excess weight which seems logical- it is actually that fat creates the inflammation itself. The fat itself also contributes to insulin resistance - regardless of diet, and it contributes to resistance to the hormone Leptin which signals satiety, so we eat more when we're fat BECAUSE of the fat already there. We always think of obesity as causing problems because of the mechanical forces of the weight and the diabetogenic diet that created it in the first place. But once the fat is there, all other factors being equal, it is busy creating disease through it’s own metabolic actions. 

Incidentally, the new drug for obesity in dogs started as a hopeful drug for humans. It is effective and cheap and works very well for dogs, but alas, it causes severe fatty liver disease in us and cats.