For years, many individuals have joked that just looking at food makes them gain weight. Well, maybe the joke was not too far of the mark.... Recent research found that just looking at and smelling food triggers the release of insulin.
In other words, just the sensory cues of food are enough to stimulate receptors in the brain and the nervous system to result in the pancreas secreting insulin. This is what normally happens in healthy individuals - and it's called the cephalic phase of insulin release.
Interestingly, in very overweight (obese) humans and mice, this response can be impaired.
From Science Daily: The mere sight of a meal triggers an inflammatory response in the brain
Even before carbohydrates reach the bloodstream, the very sight and smell of a meal trigger the release of insulin. For the first time, researchers from the University of Basel and University Hospital Basel have shown that this insulin release depends on a short-term inflammatory response that takes place in these circumstances.
In overweight individuals, however, this inflammatory response is so excessive that it can impair insulin secretion.
Even the anticipation of a forthcoming meal triggers a series of responses in the body, perhaps the most familiar of which is the watering of the mouth. But the hormone insulin, which regulates blood sugar, also arrives on the scene even before we tuck into the first mouthful of food. Experts refer to this as the neurally mediated (or cephalic) phase of insulin secretion.
Meal stimulates immune defense
In the past, however, it was unclear how the sensory perception of a meal generated a signal to the pancreas to ramp up insulin production. Now, researchers from the University of Basel and University Hospital Basel have identified an important piece of the puzzle: an inflammatory factor known as interleukin 1 beta (IL1B), which is also involved in the immune response to pathogens or in tissue damage. The team have reported their findings in the journal Cell Metabolism.
"The fact that this inflammatory factor is responsible for a considerable proportion of normal insulin secretion in healthy individuals is surprising, because it's also involved in the development of type 2 diabetes," explains study leader Professor Marc Donath from the Department of Biomedicine and the Clinic of Endocrinology.
Short-lived inflammatory response
Circumstances are different when it comes to neurally mediated insulin secretion: "The smell and sight of a meal stimulate specific immune cells in the brain known as the microglia," says study author Dr. Sophia Wiedemann, resident physician for internal medicine. "These cells briefly secrete IL1B, which in turn affects the autonomic nervous system via the vagus nerve." This system then relays the signal to the site of insulin secretion -- that is, the pancreas.