It turns out there is another molecule called vasoactive intestinal polypeptide (VIP), which works alongside leptin. VIP is produced by a number of tissues, including the gut, the pancreas, and two important regulatory systems in the brain, the pituitary gland and the hypothalamus. Studies show that when animals don’t have enough VIP, their blood sugar, insulin, and leptin all become elevated and the animals crave sweets.13
