I have come across the word "leptin" a lot recently and instead of just skimming over it and knowing it is vaguely related to weight, I thought I'd do a bit more research.

Leptin (from the Greek word leptos [1] meaning thin) is a hormone that helps control appetite and metabolism. In a normal weight person, when body fat increases, leptin levels rise [2] which signal the brain that it needs to speed up metabolism and decrease appetite. According to Leo Galland, M.D. [3], author of The Fat Resistance Diet [4], when folks are overweight the leptin message gets lost and the body cannot regulate its fat stores.

New research indicates that inflammation, [5] a condition in which your immune system is kicked into overdrive, may lead to weight gain and make losing more difficult. Doctors think inflammation interferes with leptin production. So from a nutritional perspective you should eat inflammation fighting foods that are high in omega-3 fatty acids. [6]

Simply put, leptin is part of the complicated chemical process that helps regulate weight.