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 (which I plan to review here in the next few weeks), author Lierre Keith notes that she suffered from severe depression as a vegan partly because “there are no good plant sources of tryptophan.”
While it’s true that meat is higher in tryptophan than plants, a well-balanced vegan diet is almost guaranteed to provide more than enough of this amino acid. The Institute of Medicine—the group that sets nutrient recommendations for Americans—established an RDA of 5 milligrams of tryptophan for every kg of healthy body weight. Since protein from plant foods is slightly less digestible than animal protein, vegan protein and amino acid needs are about 10% higher than for omnivores. So vegan tryptophan requirements are around 5.5 milligrams per kg of body weight.
For example, a 130-pound vegan woman would require around 325 milligrams of tryptophan per day.
Here is the math (rounded to whole numbers):
130 pounds divided by 2.2 = 59 kg
59 x 5.5 = 325 milligrams of tryptophan
I did a rough calculation of a very bare-bones kind of vegan diet based on the recommendations in my food guide. It included these foods:
1 cup oatmeal
2 slices whole wheat bread
2 tbsp peanut butter
½ cup beans
½ cup hummus
1 medium baked potato
½ cup of brown rice
½ cup soymilk
2 cups steamed broccoli and leafy greens
3 servings of fresh fruit
3 teaspoons added fat (oil or margarine)
This comes to just under 1500 calories (which is actually too low for our sample 130 pound woman) and nearly 23% of the calories come from foods—fruits and fats—that don’t provide any protein. But it still provides more than 170% of the tryptophan requirement for our 130-pound reference woman.
So, yes, vegans can get plenty of tryptophan. It is certainly true that some vegans could have marginal intakes if they are not including protein-rich foods like beans and nuts in their diet. I favor higher protein intakes for vegans for a variety of reasons, including bone health. But even if you fall a little short regarding these recommendations for protein-rich foods, you’ll get enough tryptophan.
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.
So, bottom line: A healthy vegan diet that includes minimum recommendations for grains, legumes/nuts and vegetables will provide plenty of tryptophan—more than you need, actually. And if you suffer from insomnia, drink a glass of sweetened vanilla soymilk. Whether or not this has any true sleep-inducing properties is doubtful—but it’s at least as good as cow’s milk.