Endocannabinoid System Science

Appetite and the Endocannabinoid System

What is hunger?

Hunger is the sensation produced by the body when the stomach is physically empty and blood sugar levels have dropped below a certain threshold. The primary hormones that control the feelings of hunger and satiety (fullness) are called ghrelin and leptin. Ghrelin is produced by the stomach and it produces the feeling of hunger and the physiological effect of salivation.  Leptin is produced after a meal is consumed and it causes one to feel full or satiated.  It is produced by fatty tissue and it triggers the transformation of sugars and carbohydrates into glycogen (fat) for storage rather than glucose (blood sugar) for immediate energy consumption.  Once blood glucose levels drop below a certain level, the stomach releases ghrelin which induces feeding behavior.  Surely hunger is much more complex than this simple explanation however.

How is hunger mediated?

Our bodies maintain a delicate balance of hormones and enzymes that collectively control all of our behavior and bodily function.The feeling of hunger is evolutionarily necessary because without it, we would not feel inclined to consume the amount of food necessary to fuel our activity. The body has several mechanisms which mediate hunger and they all are controlled in some way by the endocannabinoid system. This is why those who consume THC report “the munchies,” or an increase in cravings and appetite.  The activity of THC and other CB1 agonists like anandamide has the net effect of increasing the pleasure derived from food, which increases behavior associated with obtaining and consuming food.  

What is the positive incentive perspective?

The concept of pleasure-based motivation has been prominent since the time of Freud.  His ideas are the basis of our understanding of how the physical brain is connected to the abstract psyche.  The keystone of the freudian school of thought is:

  1. Positive stimuli reinforce the behavior that produced them,
  2. Negative stimuli discourage the behavior that produced them,
  3. Stimuli that simultaneously have positive and negative components permit higher thought and spectral organization.

This relates to hunger because one of the main mechanisms by which we feel hunger and are therefore motivated to eat is the positive reinforcement associated with foods that taste good.For example, sugar tastes good to us because it is readily turned into energy or fat by the body, so it’s digestion is both efficient and highly satisfactory to the needs of the body.  Endocannabinoids are released from neurons that receive a rewarding signal, and they increase the firing rate of the neuron which sent the positive stimulus. By this mechanism, endocannabinoids regulate our hunger drive, and that’s why THC increases appetite: it mimics the effect of the endocannabinoid anandamide, but to a much greater degree.  This is the positive incentive theory of hunger and appetite, and it is a positive feedback mechanism that produces feeding behavior.

What is the set-point theory of appetite?

While the positive incentive theory is certainly backed up by profound evidence, it is not the only mechanism of hunger.  Indeed, appetite serves a very real and vital physiological purpose: the provision of fuel for all of the activities of the body.  When we eat, carbohydrates and amino acids are derived by our stomach from the sugar and protein in the food we consume and delivered into the blood, where the can be delivered to cells and used.  Once the presence of carbs and protein is felt, leptin is released and we feel full. When levels of blood sugar (from carbs) and amino acid (from protein) fall below a certain level, called a set-point, ghrelin is produced by the stomach, and we feel hungry again.

The set-point is derived from a complex combination of many different chemical levels, which are largely controlled by the endocannabinoid system.  The generally accepted role of the ECS in modulating hunger has to do with the cellular response to the better-understood hormones leptin and ghrelin.  When cells encounter these hormones, they have opposing effects on the ECS; ghrelin encourages the release of more endocannabinoids that remind the brain how tasty food is and create a craving, and leptin has the opposite effect, by inducing the uptake of endocannabinoids therefore producing the opposite effect of increased endocannabinoid levels.

Both of these umbrella processes are active in our perception of hunger and they are both vital to the regulation of our appetite and metabolism.  Many disorders of either overeating or undereating are resultant of a hormonal imbalance that triggers the wrong mix of endocannabinoids in the various parts of the brain and body associated with hunger.  For this reason, phytocannabinoids like CBD are highly effective in adjusting our response to the appetite hormones, and through either positive or negative feedback, it actually causes the body to correct the underlying hormonal imbalance, something synthetic pharmaceuticals are unable to claim.