Does our genes have a role to play in compulsory overeating?

Lot of us end up eating more than our body requires due to our inclination towards specific foods- Some people are fond of sweets while others like spicy foods? This overeating trait in every individual depends upon their genetic predisposition. Today we are going to discuss how our genetic makeup impacts our satiety & appetite level.

Endocannabinoid system is ournerve signalling system found in our brain, spinal cord , peripheral nervous system & digestive tract. This signalling system has a role to play in various functions & processes that take place in our body including memory, mood, stress response, pain, inflammation, appetite & eating behaviour( overeating), fertility digestion & energy balance. Needless to mention there that our gut bacteria also has a role to play since it directly coordinates & communicates with our brain through the vagus nerve.

Let us discuss the Endocannabinoid system in detail. It has the following components:

1. Cannabinoid receptors-CB1 & CB2
2. Endocannabinoid
3. Enzymes that break down Endocannabinoids

Cannabinoid receptors are found on the surface of nerve & other cells. There are two major types of Cannabinoid receptors-CB1 & CB2. CB1 are generally found in the central nervous system( brain & spinal cord) where they are located on the surface of neuron endings. When CB1 receptors are activated, they can alter the release of neurotransmitter- dopamine which changes nerve activity. It actually inhibits release of neurotransmitters from presynaptic neurons( These neurons send messages by releasing neurotransmitter chemicals upon receiving a signal to react).This essentially means less neurotransmitters activate the postsynaptic neuron, thereby changing nerve activity. It is because of these changes in nerve activity that explains the impact of Endocannabinoid system on mood, appetite, eating behaviour & stress response

CB 2 receptors are normally found in cells & tissues of the immune system where they play an important role in regulating inflammation. The impact of Endocannabinoid system on eating behaviour & appetite is mediated through CB 1 receptor. Understanding the impact of this receptor helps us understand why some people have more knack for overeating.

Endocannabinoids are molecules naturally produced by your body that activate cannabinoid receptors. Two Endocannabinoids produced by our body are Anandamide (AEA)  & 2-arachidonoylglycerol (2-AG). In the central & Peripheral nervous system, these Endocannabinoids are produced by our nerve cells.

Endocannabinoids are produced from lipids by postsynaptic neurons: Once released, endocannabinoids travel back across the synapse and bind to cannabinoid receptors on the presynaptic neuron. This inhibits neurotransmitter release and alters nerve activity. This is known as retrograde signalling.

Besides, the Endocannabinoid system also includes enzymes used to break down endocannabinoid molecules. These enzymes are important since they assist in terminating action of endocannabinoid on nerve activity. One of the key enzyme is FAAH that breaks down Anandamide (AEA)  & to lesser extent 2-arachidonoylglycerol (2-AG).

Anandamide binds more closely to CB 1receptor found in central nervous system. By binding to this receptor & altering nerve activity in various brain circuits, this molecule is said to play an important role in memory, appetite, pain, emotional & feeling.

Let us discuss how the Anandamide & Endocannabinoid system impacts our eating behaviour!

Activation of the Endocannabinoid system is said to stimulate appetite & promote food intake. A lot of us experience a common behaviour called Munchies which is characterised by increasing appetite & a strong inclination to eat foods that are high in fat, salt & sugar. This is said to result from activation of CB 1 receptors which stimulate brain circuits that promote food intake.

Anandamide (ANA) produced naturally by our body activates CB 1 receptor in the endocannabinoid system & as a result drives consumption of high fat palatable food. Given the wide distribution of CB 1 receptors in our body, there are various ways in which Anandamide stimulates eating/overeating which are discussed below:

1. Anandamide enhances smell & taste perception: CB1 receptors are present on smell sensing & taste sensing nerves in nose, mouth & brain. Activation of these sensors by Anandamide may enhance sensitivity to food odours & neural response to sweet tastes. This will drive us to ask more for high palatable foods.
2. Anandamide activity in gut drives for demand for more high fat foods: Anandamide acting on gastrointestinal tract indirectly influences brain areas that regulate food intake so that we increase our intake of fat over other nutrients. As such activation of CB 1 receptor by Anandamide in the gut leads to secretion of Ghrelin ( the hunger hormone) that stimulates our eating behaviour, enhances taste perception & increases rewarding value for high fat foods.
3. Anandamide stimulates the brain circuit that promotes appetite & food intake: Hypothalamus in our brain regulates appetite, satiety & food intake. Special neurons in brain circuits have CB1 receptors on their surface. When these receptors are activated by Anandamide, it suppresses our appetite & increases food intake.
4. Anandamide enhances pleasurable aspects of food: Our brain has a reward system that the mediates the pleasurable aspects of stimuli such as food, sex, and drugs, and drives our motivation to obtain these stimuli. This reward system becomes activated both in response to eating food and to the anticipation of food from cues such as sights, smells, certain social situations.By binding to CB1 receptors in these brain areas, anandamide alters the activity of our neural reward system, thereby increasing the rewarding and pleasurable aspects of food.

Compulsory overeating refers to collection of uncontrollable eating behaviours such as eating food in large amounts, eating despite not being hungry, eating impulsive & binge eating. Given the stimulating impact of Anandamide, CB 1 receptor & endocannabinoid system activation on food intake, high anandamide levels & overactivity of endocannabinoid system can lead to overeating. The enzyme FAAH- Fatty acid amino hydrolase responsible for breaking down endocannabinoid in the central nervous system. By breaking down FAAH terminates the action of Anandamide on CB 1 receptors & prevents changes in nerve activity.

FAAH enzyme is decoded by FAAH genes. A SNP of the FAAH gene changes DNA code from letter C to A giving rise to two alleles  “ C” & “A”. The A allele codes for Enzyme that can be easily degraded & as such results in low level FAAH activity. Due to this people with A allele breakdown endocannabinoid  less effectively resulting in a high amount of Anandamide in our bloodstream levels. Therefore people with A allele of FAAH has high risk of attracting Obesity.

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