We have discussed about serotonin in our previous blogs. Serotonin is a key neurotransmitter in the brain that regulates food intake & feeling of satiety. Availability of Serotonin & increased serotonergic activity in the brain is linked to reduced food intake & greater satiety. Depletion of Serotonin in the brain is associated with overeating, overweight, weight gain & increased consumption of calorie dense foods. Serotonin relays nerve signals in the brain & central nervous system. It is active in brain networks that regulates sleep, mood, appetite & eating behaviour. Besides, it also plays an important role in the digestive system where it helps control movement of intestines, immune system & secretion of enzymes.
Tryptophan is an essential amino acid that is used to build protein & make serotonin. Tryptophan is converted into molecules known as kynurenines which impacts various neurons in the brain & influence behaviour. Kynurenines impact activity, function & survival of neurons in the brain. Changes in the level of kynurenines is said to be linked with changes in learning & memory. It is also linked with regulation of eating behaviour.
Since tryptophan is an essential amino acid, our body cannot make it & has to be taken from outside food. Some sources of tryptophan include:
- Chicken & Turkey
- Beef
- Tofu
- Salmon
- Eggs
- Soybeans
- Milk
As a matter of fact, Tryptophan metabolism impacts our eating behaviour:
- Tryptophan is made into serotonin which in turn regulate food intake & satiety
- Tryptophan is broken down into kynurenine in the kynurenine pathway. Kynurenines directly impact neural activity in brain circuits that regulate energy intake. If more tryptophan is broken down into the kynurenine pathway, then less tryptophan is available to make serotonin what impacts our food intake & satiety.
Kynurenine produced kynurenine pathways are capable of changing activities of neurons in the brain. Increased amount of kynurenine in the bloodstream is linked to food craving, specifically craving of carbohydrate. Higher blood levels of kynurenines also suggest increased breakdown of tryptophan in the kynurenine pathway which essentially means that less tryptophan is available to make serotonin, thereby resulting in increased food craving.
APOA2 is a gene that encodes protein apolipoprotein A2. Apolipoprotein A2 is an essential component of HDL lipoprotein particles that transport fat into the bloodstream to be metabolised into the liver. APOA2 gene apolipoprotein A2 are involved in metabolism of amino acids which included metabolism of tryptophan & branched chain amino acids(BCAA).
SNP of APOA 2 gene created two different alleles/variants : “C allele” & “ T allele”. Those with CC genotype( as compared to TT & CT genotype) are more likely to have altered metabolism of tryptophan with high intakes to saturated fat. This increases risk of overeating among people having CC genotype of APOA2 gene.
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