How what you eat impacts your sleep.
You’ve probably heard of melatonin, often referred to as the sleep hormone. Melatonin is produced in a part of the brain called the pineal gland from another hormone serotonin. This is where things can get confusing because serotonin isn’t only synthesised in the brain and it has several roles in the body. It is important to differentiate between these and understand how what you eat impacts your sleep.
Serotonin has to be produced endogenously from tryptophan. In other words, it is synthesised by the body. Tryptophan is an essential amino acid, meaning that we can’t produce it, we must ingest it as part of protein foods. Tryptophan is found in significant quantities in turkey, chicken, salmon and lentils. Very good quantities are found in soybeans, milk, some seeds like pumpkin and sesame seeds and also oats. Milky bedtime drinks will provide tryptophan. There are also good quantities in bananas and peanuts which is why you often hear of people having peanut butter and banana on toast or oatcakes to help them sleep.
Tryptophan does not occur in foods alone. Protein foods consist of a spectrum of amino acids. When we eat the protein food it is digested and broken down into the individual amino acids hence releasing the tryptophan. In cells called enterochromaffin cells of the small intestine, the tryptophan can then be synthesised to serotonin. This serotonin produced in the gut is used for gut motility and nutrient absorption. 90% of the serotonin we produce from tryptophan is found in the gut and used in this way.
Serotonin metabolism in the gut does not aid in the production of melatonin and sleep. Serotonin itself cannot cross the blood-brain barrier and tryptophan must pass into circulation to enter the brain where it can then be converted to serotonin and subsequently melatonin. Gut health and the gut microbiota has an important role to play as some microbes degrade tryptophan making it less available to enter general circulation. Providing the gut microbiota with complex carbohydrates for fermentation has been shown to reduce tryptophan degradation by gut microbiota and therefore more is available to enter circulation.
In proportion to the quantity of protein within a food, the tryptophan content is generally only around 1%. The tryptophan needs to be transported into the brain by a carrier which is also used by several other amino acids. Tryptophan needs to compete with these amino acids for the carrier yet only makes up a small proportion of the amino acids in circulation.
When we eat tryptophan foods with a carbohydrate source the associated insulin release from eating the carbohydrate allows the competitive amino acids to enter muscle cells thereby leaving the transport protein available for tryptophan. Tryptophan can then enter the brain. Some tryptophan foods contain carbohydrates so can be particularly beneficial for sleep; the milky bedtime drink, oats and banana are all carbohydrate sources. When including carbohydrates in the diet remember to focus on complex sources rather than simple sugars that are abundant in processed foods and drinks.
You’re probably wondering with all the obstacles to tryptophan reaching the brain how we ever manage to produce melatonin and have restful sleep. The body is remarkable and given the right tools will perform physiological functions effectively. It is important to include tryptophan foods and complex carbohydrates within the diet as well as optimising gut health and the microbiome. Transporting tryptophan to the brain, however, is only part of the story. We still need to synthesise melatonin and this is impacted by dietary and lifestyle factors that we will cover in other blogs.
This should help you understand how what you eat impacts your sleep.
There are many tools useful in monitoring your sleep. The Oura Ring provides a guide allowing you to make lifestyle changes to improve sleep quality.
If you want to learn even more about how what you eat impacts your sleep, watch our webinar ‘Healthy Eating for Sleep’.