As I mentioned in my last post, I’m reading Candace Pert’s fascinating book Molecules of Emotion at the moment, and her theory of the “bodymind” as one integrated, dynamic network is seizing my imagination. She’s a prominent scientist who has worked mostly on peptides, the “molecules of emotion” of her title, which are the means of communication between a number of bodymind systems.
Peptides are made up of amino acids, the building blocks of proteins. There are a number of different amino acids, but there are 8 in particular that we can’t make for ourselves out of other amino acids, and we have to take these in through our food. They do get recycled, and if our diet is inadequate we can sometimes get them from the proteins that make up much of our body’s structure, but ultimately we have to eat them or we won’t have enough.
Because the peptides (and other messenger molecules which keep the body’s systems coordinated) are made from them, a lack of one of these essential amino acids is clearly a problem. Normally this doesn’t occur, of course, since they are common enough that any reasonably normal diet should contain all of them in sufficient quantity. Vegetarians have to be careful, though, and there are some subtleties to be aware of.
photo credit: Tina Keller
As an example, I’ll start with tryptophan, which I came across when researching my Sleeper’s Checklist. Tryptophan is the precursor to the neurotransmitter serotonin and the neurohormone melatonin. Melatonin is thought to be involved in regulating the sleep-wake cycle, while serotonin is well known for its role in mood regulation. Antidepressant drugs apparently relieve depression by affecting the levels of serotonin available in the brain. The exact reason why this relieves depression (and why the antidepressant effects take a couple of weeks to kick in, even though the effect on serotonin is very rapid) is not yet fully understood.
Serotonin is also important in the digestive system for regulating the movement of the intestines, and in fact about 8 or 9 times as much serotonin is found in the digestive system as in the brain. In the brain, it modulates appetite, sexual desire, mood, anger and sleep, among other behaviours and drives. A Swedish study has even suggested a correlation between the density of a particular kind of serotonin receptor in the brain and the likelihood of having had a religious experience.
photo credit: h.koppdelaney
Since serotonin is made from tryptophan, and we can’t make tryptophan, it’s important to have adequate levels of tryptophan intake in our diet – but it’s not just that simple (things seldom are when neurotransmitters are involved). Two other amino acids, phenylalanine and leucine, “compete” with tryptophan to be transported into the brain across the protective membrane which surrounds it (the blood-brain barrier), so not just the absolute amount, but also the ratio, of tryptophan to these other amino acids is important. Also, in some conditions such as lactose intolerance (difficulty digesting dairy products) or fructose malabsorption, tryptophan is not properly absorbed by the gut. Interestingly, fructose malabsorption has been linked to depression.
So what foods help balance the books for tryptophan? Bananas, dates, pineapples, plums and nuts are mentioned in one article on nutrition, depression and sleep. However, an editorial in the Journal of Psychiatry and Neuroscience tends to minimize the contribution of diet to serotonin levels, though it does note some interesting correlations between levels of American corn or maize consumption and homicide rates in countries around the world (corn being relatively low in tryptophan). That article places more stress on changes in thinking, exercise, and exposure to light as non-drug means of raising serotonin levels (and I’ll talk about those more in future posts).
Not just serotonin levels, but the rate of serotonin turnover, seem to be significant in relation to violent behaviour and suicide. Low serotonin turnover, for reasons as yet not understood, correlates with high rates of these behaviours. So it isn’t just how much you have, but how long you’ve had it, apparently.
I was recently reading about another study correlating consumption low-tryptophan foods with aggression, not at a population level but in individuals. Moeller et al. (Tryptophan depletion and aggressive responding in healthy males, published in Psychopharmacology) found in 1996 that healthy young men, after 24 hours of a low-tryptophan diet and having been given a tryptophan-free amino acid mixture, responded significantly more aggressively a few hours afterwards than the same subjects under control conditions. So feeding aggressive or suicidal people on, for example, Diet Coke and corn chips (high in phenylalanine, low in tryptophan) seems like it would be a bad idea.
I’m not going to do the Usual Internet Thing and make a flat-out statement about how eating such-and-such a food will work a miraculous change in your mood because of its tryptophan content, though. The mechanisms are more complex than that. Diet does contribute to mood, and so eating a well-balanced diet that is well adapted for your particular biochemistry and other circumstances is an important contribution to keeping your bodymind in good order, but it’s just not as simple as eating more tryptophan-containing foods in order to feel better.
For further information, I suggest Nutritiondata.com and the World’s Healthiest Foods website, two excellent sources of information about food and health. (Those links lead to pages directly relevant to tryptophan.)
Technorati Tags: nutrition, tryptophan, serotonin, mood
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