Via medicalxpress.com: free radicals crucial in surpressing appetite.

After the mice ate, the team saw that the neurons responsible for stopping overeating had high levels of free radicals. This process is driven by the hormone leptin and glucose, which signal the brain to modulate food intake. When mice eat, leptin and glucose levels go up, as does free radical levels. However, in mice with diet-induced obesity, these same neurons display impaired firing and activity (leptin resistance); in these mice, levels of free radicals were buffered by peroxisomes, preventing the activation of these neurons and thus the ability to feel sated after eating.

Complex systems always have trade-offs like this.