Neurochemicals and Hunger Feeding behavior is influenced by complex interactions among several neurochemicals. Fat cells produce and secrete a substance known as leptin, from leptos, the Greek word for "thin" (Zhang et al. 1994). When fat stores are low, levels of circulating leptin will also be low. As shown in Figure 9.16, initial reports that administering additional leptin to obese rodents reduced their weight led many researchers to believe that leptin could be used to treat human obesity. Unfortunately, obese humans already produce large amounts of leptin, but they seem to be resistant to its effects (Friedman & Halaas, 1998). Providing more leptin is unlikely to help obese individuals lose weight.