The underlying theory of blood type diets is that people with different blood types digest lectins differently, and that if people eat food that is not compatible with their blood type, they will experience many health problems.
Leptin is a potent stimulator of the immune system. Leptin receptors on monocytes cause the release intracellularly of STAT3 which cause the monocytes to release IL-6, IL-12 and TNF alpha. The IL-6 goes to the liver and increases production of CRP.
Leptin is a hormone that plays a crucial role in appetite and weight control. It is thought to have at least two major functions. First, it crosses the blood-brain barrier and binds to receptors in the appetite center in the brain, regulating brain cells that tell you how much to eat. Second, it increases sympathetic nervous system activity, which stimulates fatty tissue to burn energy.