People who abandon plant-based diets often say that they suffered from depression as vegans. One common belief is that vegans can’t get adequate tryptophan, an essential amino acid. Tryptophan is needed to make the neurotransmitter serotonin and low levels of serotonin are linked to depression. In the book The Vegetarian Myth, author Lierre Keith notes that she suffered from severe depression as a vegan partly because “there are no good plant sources of tryptophan.”
This is an absolute myth.
In fact, there are many plant sources of tryptophan which have much more of the amino acid than turkey. And, compared to some omnivores and lacto-ovo vegetarians, we vegans may even have the edge when it comes to converting tryptophan to serotonin. According to preliminary research in both adolescents and adults, depression is more common among people with lactose intolerance. The theory is that undigested lactose in the intestines interferes with tryptophan metabolism, leading to low serotonin levels. So people with mild undiagnosed lactose intolerance who still consume some dairy foods could actually be at higher risk for depression.
This is all especially interesting since cow’s milk is touted as a soothing food and a remedy for sleeplessness based on its alleged high content of tryptophan. But a cup of cow’s milk actually has around the same amount of tryptophan as a cup of soymilk or ½ cup of black beans. Foods like legumes also provide the carbohydrates that are needed for tryptophan to get into the brain.
Tryptophan is so powerful that LEF magazine goes as far as saying,
“Tryptophan supplementation simply makes people nicer!”
The reason tryptophan is so powerful is because the body uses it to make serotonin, our “happy hormone” which regulates mood. Because some serotonin gets converted into melatonin, it is also associated with helping sleep. It is impossible to supplement with serotonin itself (even antidepressants don’t boost serotonin production levels; they just prevent serotonin from being absorbed so its effects last longer). You can, however, take tryptophan in order to naturally boost serotonin levels. Some of that serotonin is then used to make melatonin, which helps regulate sleep.
To give you an idea of how powerful tryptophan supplements are, consider these study results. In one study where 1000mg of tryptophan supplements was given to “quarrelsome” adults 3x per day, the subjects became more agreeable. When aggressive 10-year old boys were given 500mg of tryptophan supplements per day, they stopped getting so angry when provoked. By contrast, low levels of tryptophan are shown to induce depression, irritability, aggression, and other mood problems. As for sleep, even small amounts of tryptophan are shown to increase the quality of sleep and alleviate insomnia. (Source)
If you read through the tryptophan studies, you’ll see that all of the amazing benefits of tryptophan are linked to taking tryptophan supplements, and not natural sources of tryptophan from food.
But what about all those hyped-up claims that turkey helps you sleep? The real reason people feel sleepy after Thanksgiving probably has nothing to do with turkey and tryptophan, but rather because they ate too much. When you eat a lot of carbs (especially sugary ones like dessert), it produces a surge of serotonin in the brain which can make you feel happy and sleepy. Plus, your body has to use a lot of energy to digest all of those calories you consumed, which puts you into a coma-like stupor. Consider that the average Thanksgiving dinner has 4,500 calories. That is a lot for your body to digest!
In reality, when you eat tryptophan foods, most of that tryptophan is getting incorporated into tissue proteins or converted into other substances like niacin (source). Tryptophan from foods simply isn’t very good at getting to our brains.
As Scientific American explains, when you eat tryptophan foods, the tryptophan does get into the blood. To get to the brain, it needs to be transported by special proteins across the blood-brain barrier. The problem is that other amino acids are also competing for these transport proteins. The other amino acids are more adept at getting to those transport proteins and tryptophan has a hard time getting from the blood to the brain.
How to Get More Tryptophan from Food
Since tryptophan competes with other amino acids to get to the brain, eating tryptophan foods aren’t going to have a dramatic effect on your mood or sleepiness. But there is an interesting exception: Eating tryptophan foods with carbohydrates can help more tryptophan get to the brain.
When you eat carbs, your body produces insulin. Insulin causes some amino acids to be absorbed into tissues, but it doesn’t have much of an effect on tryptophan. As a result of the insulin, there are fewer competing amino acids and more tryptophan from foods can get to the brain. The American Nutrition Association points to numerous studies which show that eating tryptophan foods as part of a low-protein high-carb diet can improve mood and sleep (vegetarians seem to have an edge here). There are also some cofactors which can help convert tryptophan into serotonin. (Source 1, Source 2)
Finally, we now know that cytokines degrade tryptophan. Cytokines are pro-inflammatory proteins involved in the immune response. They are released when we are sick, and also in response to certain foods, like saturated fats and trans fats. There are some proven ways to reduce cytokine levels, including getting more Omega 3, eating antioxidant-rich foods, reducing saturated fat intake, and getting more fiber. Again, vegans seem to have an edge here. This might be another reason veganism is linked to better mood.
Simply eating foods high in tryptophan isn’t going to help mood or sleep. To get the most of tryptophan from food, you need to:
Reduce cytokines levels which degrade tryptophan (eat more antioxidants and fiber, avoid saturated and trans fats)
Good Sources of Tryptophan
It is time we ruled out turkey as a good source of tryptophan. As Dawn Jackson Blatner, RD, LDN points out, turkey doesn’t have any more tryptophan than other types of poultry. Pretty much any good source of protein is going to have tryptophan – but that doesn’t mean the body can use the tryptophan from these protein sources.
For example, dairy products like milk have lots of tryptophan but they also contain lots of pro-inflammatory cytokines which will degrade tryptophan. Most animal-based proteins are loaded with saturated fat and lacking in fiber and vitamin C, which also makes it difficult for the body to use tryptophan for serotonin and melatonin production.
So, to the surprise of many, the best tryptophan foods are likely those found in plants.
Unlike animal products, plants are rich in anti-inflammatory healthy fats, fiber, antioxidants and also often contain the tryptophan cofactors. Here are some of the best tryptophan foods which will have health benefits beyond just boosting your mood and helping you sleep.
(Turkey is included as a basis of comparison)
Source of Tryptophan
Tryptophan (per 100gram serving)
Turkey, young hen
Sesame seeds or tahini
Spirulina and chia seeds also happen to be rich in numerous other nutrients, so you might want to consider adding these superfoods to your diet regardless of whether you think you need tryptophan.
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