I go on about amino acids a lot. Sorry about that! If you click here you will be logged into Focus eLearning (come straight back!), then if you click here you will be taken to a nice page about how the digestive enzyme pepsin breaks a protein molecule in your food down into individual amino acids. You can see that the shape of the pepsin molecule is important for it to do its job properly. If proteins get too hot they change shape and stop working. At the bottom of the menu to the left it says Activities. If you click this there are lots of games/labelling exercises to do. They are worth looking at even if they go very slightly further into things than we have done in class.
That is just bonus content – the main event is down below!
Tryptophan is an amino acid. Amino acids are the building blocks from which proteins are built (amino acids get mentioned a few times on the blog). The amino acid sequence needed to make about 24,000 proteins is written into your genetic code – each gene codes for one distinct protein.
Humans can use 20 different amino acids for protein building. 11 of these can be made within the human body from other molecules but 9 amino acids cannot be made and so humans must get these from their diet. Tryptophan is one of these essential amino acids. It is a very common component of a wide range of the proteins commonly found in eggs, fish, meat and cheese.
You can buy tryptophan in pure form as pills in health shops and pharmacies. It is not really possible for anyone to suffer from ‘tryptophan deficiency‘ because to get to that state you would have to be so starved of protein that you would be severely malnourished. The tryptophan is sold as a supplement (to boost existing levels in the diet) and as a remedy for insomnia (not being able to sleep), depression and premenstrual mood changes. I think it is fair to say that mostly the evidence for tryptophan as a remedy for these conditions is weak, and probably little more than anecdotal (ie “it worked for a friend of mine so it might work for me”). However, a recent study has suggested that it might help to improve sleep quality.
The reason I thought of tryptophan for this post is that there is an urban legend about turkey making you sleepy. The logic seems to go something like this…
- People feel drowsy after their Christmas/Thanksgiving meal
- The meal contains turkey meat
- Turkey meat contains tryptophan
- Tryptophan plays a role in serotonin production in the brain
- Serotonin makes you sleepy
- Therefore tryptophan in turkey meat makes you sleepy
It is certainly true that people feel drowsy after a big meal but the evidence suggests that this is more likely to be due to high levels of carbohydrate. There is a condition known as postprandial somnolence – which seems to be triggered by two factors. One is the mass of food in your intestinal tract triggering a response from your nervous system. The other is caused by insulin, the hormone that controls levels of glucose in your blood. When there is a lot of glucose in your blood (after a meal with lots of carbohydrate) your pancreas produces the hormone insulin. Insulin encourages your body to store any glucose that isn’t immediately needed. A by-product of this process is that the brain absorbs more tryptophan from the blood than usual. (The reason why this happens is quite complicated but it is well established that it does happen.) The tryptophan is then converted to serotonin. Serotonin is a hormone associated with feelings of happiness and contented sleepiness.
Another explanation for the grogginess felt after a big meal is that the body diverts your blood supply to concentrate on the digestive system, reducing its flow to the brain and other organs – hence the tiredness. It is nicely explained in the following video (about Thanksgiving rather than Christmas but the idea is the same.)
The effects of supplements can be tested by conducting clinical trials. This is when the medicine is tested on real people rather than on mice or other animals. A group of subjects is split into several groups. One group will get the treatment, another will get a placebo (an inactive treatment that looks exactly like the real thing) and in the best trials another group will get the best current treatment available. These experiments are often called randomised controlled trials (or RCTs for short). There are a number of important factors when doing an investigation like this to ensure that the results are meaningful.
1. Sample size – The experiment needs to be conducted with lots of participants. Often, the more the better. This way you are far more likely to find out how the treatment will behave in the general population.
2. Randomisation – Your test subjects must be split into different groups randomly so that there can be no bias about who gets which treatment.
3. Blinding – This means that neither the patient nor the experimenter knows who is getting the different treatments.
4. Good controls – The treatment must be compared with a control to show that it is something in the medicine having an effect not some other factor. The best trials will compare the treatment to the currently best available medicine to show that it is not just ‘better than doing nothing’ but better than the current best treatment.
None of this is designed to put you off your Christmas turkey. The Daily Mail has reported on a survey about European eating habits on Christmas Day, ranking the UK as having the unhealthiest meal. The French come top of the list with the Czech Republic coming second. The comments at the bottom of the article are hilarious with lots of furious Czechs insisting that they don’t eat healthily at all. I could not find a reference to who had done the survey so it is possibly all just made up to fill space in the paper!
Questions…
- What is a gene?
- Christmas lunch is usually high in carbohydrate. Name a food rich in carbohydrate?
- For what does your body use carbohydrate?
- Suggest a vitamin needed by humans and a good dietary source of it.
- Name a mineral we need from our food. What benefit does the mineral provide?
- Apart from insulin, name one other important chemical released by the pancreas?
- Insulin is a hormone. Name another hormone.
- What is meant by the phrase “a controlled experiment“?
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