Tryptophan, Milk and Depression

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.

 

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22 Responses to Tryptophan, Milk and Depression

  1. Adam September 2, 2010 at 2:11 pm #

    Thanks for this. I think there are a couple of other points worth mentioning. Keith's writings about tryptophan are primarily based on Julia Ross's book The Mood Cure, which actually does mention numerous plant sources of tryptophan, so she's really being dishonest in claiming what she does.
    Moreover, there is some doubt that dietary tryptophan actually increases serotonin levels. From a literature review: "Although purified tryptophan increases brain serotonin, foods containing tryptophan do not. This is because tryptophan is transported into the brain by a transport system that is active toward all the large neutral amino acids and tryptophan is the least abundant amino acid in protein. There is competition between the various amino acids for the transport system, so after the ingestion of a meal containing protein, the rise in the plasma level of the other large neutral amino acids will prevent the rise in plasma tryptophan from increasing brain tryptophan. The idea, common in popular culture, that a high-protein food such as turkey will raise brain tryptophan and serotonin is, unfortunately,  false." (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077351/?tool=pmcentrez )

    • Ginny Messina September 2, 2010 at 3:37 pm #

      Thanks, Adam. I know that there is competition among the amino acids and this is one reason why high-protein foods are supposedly not a good way to increase serotonin levels. But, there are also older studies suggesting a link between diets low in tryptophan and symptoms of depression. Admittedly, though, there are lots of questions about this and I'm glad to have the NCBI article. 

      Regarding Keith's references, this is one of the things that really bugged me–the fact that she uses popular books rather than primary sources, making it next to impossible (or at least laborious) to trace her assertions back to the actual research. I didn't look to see if she actually even quoted those books accurately. I appreciate your careful research on this!  

    • Elizabeth March 8, 2013 at 10:37 am #

      Just because tryptophan is the least abundant amino acid does not mean it will not make it into the brain. Tryptophan supplements have been vital in aiding sleep for the Parkinson’s patient under my care and her neurologist recommended a small glass of warm milk to aid sleep because the warmth helps release the tryptophan. I believe it is hardly a myth that we feel better after meals with high tryptophan content. We are not mice and unfortunately none of us can actually measure whether the tryptophan we eat actually makes it into the brain of a living person. Definitive statements against are not scientific as you really have no idea. I spent 15 years doing scientific work, ultimately obtaining a PhD in Biochemistry from a major university and have cared for a PD patient for the past 22 years and tryptophan works better than any drug in producing sleep and preventing daytime sleepiness.

  2. Elaine Martin September 2, 2010 at 2:14 pm #

    Dear Ginny,
    Your beginning sentence is confusing. Shouldn't it read "People who abandon meat-based diets…" ? Just wondering. E

    • Ginny Messina September 2, 2010 at 3:29 pm #

      Elaine, I was talking about ex-vegans, who abandon their plant-based diet and go back to eating animal foods. Some say that they suffered from depression while eating only vegan foods and that it went away when they started eating meat again. Sorry for the confusion!

  3. D. September 2, 2010 at 3:15 pm #

    Great post, Ginny. It's nice to see another hype-fueled vegan myth busted by science!

    • Ginny Messina September 2, 2010 at 3:28 pm #

      Thank you!

  4. beforewisdom September 2, 2010 at 4:41 pm #

    When Keith's book came out a few months ago, I saw a youtube of a local news show where she made this fictional claim.  FWIW, I think it might be useful to have a URL, so that she can't back pedal later.

    Reading the reviews of her book on Amazon is amusing.  
    A number of people giving the book a high rating will write one or two types of comments.
    he first is that they loved her book, thought she was right on, but she made this, that and the other factual error.   IMO, the essence of a non-fiction book is that you can rely on it to give you facts.  If it has the facts wrong, then it is a failure as a book.
    The second type of positive comment is that they loved her book, she is right on about vegan diets and vegans, but boy oh boy she is Keith wrong about this other group of people, other subject which the comment author is a fan of.   
    In other words, the people who like Keith's book like it because she is telling them what they want to hear and if the facts are off, well that is unfortunate.
    Bleh!
     

  5. beforewisdom September 2, 2010 at 4:43 pm #

    If someone is going to take time to read Keith's book, please borrow it from Interlibrary Loan and don't put any more money in her pocket.   Also, you might want to consider contributing to this wiki dedicated to debunking her book:
     
    http://www.vegetarianmyth.com/

    • Ginny Messina September 2, 2010 at 4:48 pm #

       I bought a used copy on amazon.com. My library doesn't have it and I didn't want to do anything to encourage them to buy it! Will take a look at the wiki.

  6. beforewisdom September 3, 2010 at 5:29 am #

    Thank you for writing this article.  
    Lierre Keith doesn't have the academic credentials or research experience to write about the variety of subjects covered in her book.   Her claims are laughable to the experts who are educated in those fields, so they feel justified in not bothering to reply to her mistaken claims.   Yet, many people want to believe what Keith has to say, are gobbling it up and spreading Keith's misinformation.
    Every reply by an expert who unlike Keith, has credentials, education and experience in the subjects they write about will help slow Keith's dangerous misinformation down.

    Thank you again for writing this article.

  7. Joanne September 3, 2010 at 11:15 pm #

    Researchers found the vegetarians reported diets significantly lower in EPA and DHA, the omega-3 fatty acids that we get from eating fish, and which many studies have found are a key factor in improving both physical and mental health. So they expected to find the vegetarians would have higher incidences of issues like depression, anxiety, and mood problems. Instead, they found the opposite result. Vegetarians scored lower on depression tests and had better mood profiles than their fish- and meat-eating peers.
    http://www.rodale.com/vegetarian-diets
     
     

  8. Liz September 13, 2010 at 6:09 pm #

    Hi, i am very curious to read your review of Keith's book, which I also recently read. I have dabbled in and out of a vegan diet for years, and her book brought up so many questions. Especially disturbing is her take on grains and human health. Tell me more! what should i believe??
    gracias,
    Liz

  9. Tracy October 19, 2010 at 11:54 am #

    Thanks for the post. I think lack of tryptophan does cause problems for some newbie vegans who don't know they need to be focusing on ways to get it.
    As for the Vegetarian Myth, I can't bring myself to read it, it sounds like a pretty outlandish treatise from an outlandish person, from what I have heard. I'm glad someone is taking the time to analyze it. =)

  10. cyrell October 24, 2010 at 3:36 am #

    I had depressions before i went vegan and the new diet helped me greatly….also because i have Crohn´s disease and people with this illness suffer more likely depressions then healthy people.
     
    Maybe it has also to do with malnutrion because this conditions makes it harder to get all nutrients.
    But with me turning to a vegan diet my symptoms dropped and i rarely suffer anything. I also do not need medication…great, isn´t it?

  11. Nicole November 20, 2010 at 6:47 am #

    Ginny – what are the options for tryptophan sources for a vegan who's allergic to both soy and nuts?  My husband is allergic to most nuts (except for cashews and the occasional walnuts) and soy milk, though he doesn't have a problem with tofu.  He's also allergic to most fruits, but all vegetables are fine. Thx!

    • Ginny Messina November 21, 2010 at 11:53 am #

      Nicole, does your husband eat other kinds of beans? He can actually get plenty just from regular beans and grains. Oats are especially rich in tryptophan.

      • Nicole November 22, 2010 at 8:34 am #

        Ginny: yes, I can get him to eat beans (mostly because I do all the cooking!)  We've both started eating  more oatmeal, though it's quick oats and not whole oats because we both dislike the texture of whole cooked oats as oatmeal (though combining 1/2 whole and 1/2 quick might be a better idea).  We do eat wheat, rice, spelt, and quinoa, though we need to eat more of the latter two.
        I'm happyto hear about beans being a source – I've been trying to get them into more of our meals lately.
        Thanks for the tips! :)

  12. TheTastyVegan January 30, 2011 at 12:52 pm #

    Thanks for another excellent post on vegan nutrition!

    I jsut wanted to mention that, Cyrell, your Crohn's symptoms may very well be connected to the fact that the digestive system also has a quite elaborate nervous system associated with it that responds to neurotransmitters like serotonin independent of the brain's response to the same substances.  So a nervous and dysfunctional digestive system can be both a cause and effect of absorption issues. 

    Some good vegan sources of tryptophan from the USDA charts include:
    spirulina, chia seeds, pumpkin seeds, parsley, tahini, sesame seeds, oatbran 

    Obviously you'd need to eat a lot of parsley though as this is based on dry weight I think!  Somr alternatives to legumes and pulses for tryptophan though for those who are allergic/intolerant.

    The other interesting thing about tryptophan is that it can be converted into serotonin in the blood stream and serotonin cannot pass the blood-brain barrier so if this happens the tryptophan/serotonin actually has no effect on neurotransmitter levels.  This can, in fact, be a serious problem and cause serotoninergic syndrome if someone has too much serotonin in their system.  One of the things I find strange is that a lot of supplements containing 5-HTP (5-hydroxytryptophan) also contain B6, which, while needed to convert tryptophan to serotonin in the brain could lead (possibly) to earlier bloodstream conversion making the supplement actually ineffective or dangerous.  I've tried to find any research on this and noone seems to have done any! Have you come across this in your reading Ginny? Anyone else?  It does worry me, particularly if considering suggesting a 5HTP suppl to someone for migraines or depression (or even appetite regulation/weight loss).

    On a side issue, I was wondering if you could point me to the page(s) on the site where you discuss higher protein intake to benefit bone health? I admit it's not something I've studied too closely but I thought one of the considerations with high protein intakes was that it can have an acidifying effect on the blood which can then actually leach calcium from the bones to rebalance things (I may be getting this the wrong way round…but it's Sunday and I'm too lazy to do my own research on this one!).

    Thanks for the info, as always, very informative! I might get round to borrowing that Keith book sometime but I'm slightly afraid to pollute my mind with such obvious propagandist nonsense… seems she's just trying to match her ethics to her lifestlye choices in a rather backwards fashion.

    Cheers,
    Leigh
    Some references for all you fellow nutritionnerds out there:

     
    Badawy, A.A., (2002), Tryptophan metabolism in alcoholism, Nutr Res Rev, Vol.15, No.1, pp.123-52.

    Németh, S., (1977), The effect of stress on the activity of hepatic tryptophan pyrrolase, of tyrosine aminotransferase in various organs and on the level of tryptophan in the liver and plasma of rats, Physiol Bohemoslov, Vol.26, No.6, pp.557-63.
     

    Inamdar, A.R., Kurup, C.K., Ramasarma, T., (1972), Effect of hypobaric stress on enzymes of tryptophan metabolism, Biochem J., Vol.127, No.3, pp.509-14.

  13. clara March 20, 2011 at 2:43 am #

    "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."
     
    Could you maybe tell me the source of this finding? This is really interesting to me and I would love to read more about it!  Thank you for your kindness!

  14. Amy WO March 22, 2011 at 11:25 am #

    Thank you for this post!  I have been a vegetarian for 20 years and just made the switch to a vegan diet a few months ago. I really can't believe how much better I feel- better mood, less "brain fog." I have always been a pretty unhealthy veggie, though, so I'm sure it's at least partly due to getting the sugar and refined carbs out of my diet.
    I look forward to browsing your site. Thanks for providing a great resource!

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