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Introduction :
This question of why rice makes one sleepy has been in the spotlight for many years. But what triggers this sensation of sleep, particularly after eating rice? Has it something to do with any compound which rice contains, Or is it something present in all grains with varying concentrations and its concentration is highest in rice?
Mechanism
Let’s understand the mechanism of how sleep is induced in our body through the food that we consume.
Studies conducted to understand macronutrients or micronutrients which induce sleep in individuals have shown that Tryptophan is the amino acid that is the main neurotransmitter and precursor for serotonin and melatonin 1.
Now, foods with a high GI index (usually high in carbohydrates) increase the serum ratio of Tryptophan and large neutral amino acids ratio (LNAA). Once there is an increase in glucose levels in the blood, the pancreas detects this increase in glucose and releases insulin in the blood system. The insulin is thought to mediate the transport of Tryptophan into the brain. The increased levels of LNAA lead to increased uptake of LNAA into the muscle. This leaves the Tryptophan to be taken up into the brain of the individual1.
Once the Tryptophan enters the brain, it undergoes a biosynthesis cycle for its conversion into serotonin and then into melatonin. Now the melatonin which is synthesised induces sleep behaviour in the brain of the person. It leads to the sensation of sleep experienced after consuming food.
What is the connection between rice and sleep?
As we have discussed in the above paragraphs, foods high in Carbohydrates increase the tendency of sleepiness with an increase in tryptophan levels. So, why is rice only the culprit one may ask?
Basically, the more the Glycemic index ( the ability of the food to increase the blood sugar level in the blood)2 of the food, the more capacity it has to increase the blood glucose. It leads to an increase in insulin secretion and resultantly increases the levels of melatonin in the brain.
Among the grains which we consume, Rice has the highest Glycemic index. Consuming rice increases insulin levels proportional to the glucose level, leading to easy transport of tryptophan into the brain for melatonin synthesis. Thus, when one consumes rice he or she may feel sleepy due to the mechanism explained above.
The solution that one can incorporate
So the solution that one can incorporate into their diet is the addition of more proteins when they consume rice. A protein-rich diet has been shown to decrease the levels of Tryptophan and LNAA in the blood. Thus, lowering the uptake of tryptophan into the brain and the synthesis of melatonin in the brain.
If one experiences sleepiness after consuming rice at lunch, hampering their work performance, they can include protein-rich sources in the diet. Including foods such as chicken, fish, and meat in their diet, reduces the tryptophan to LNAA ratio. It decreases the uptake of tryptophan into the brain for melatonin synthesis.
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