Almost 15% of American adults suffer from depression,1 a condition that can affect how a person thinks, feels, and handles daily activities. Depression research is ever-evolving. And new data points to intake of proline, an amino acid, as a factor in developing this prevalent and often misunderstood disorder.2
Specifically, researchers from the Girona Biomedical Research Institute (IDIBGI) and Pompeu Fabra University (UPF) in Barcelona, Spain, found that higher intake of proline is linked to depression development. The results of this study were published in Cell Metabolism last month.2
What Is Proline?
The proteins in our bodies are made of various combinations of 20 specific amino acids, nine of which are considered "essential." The body can’t make these nine amino acids on its own, and we need to take them in through our diet.3
Proline is an amino acid that is non-essential, meaning that our bodies can make adequate amounts during most phases of our lives. However, during times of stress, healing, or growth, this amino acid becomes essential as our requirements exceed the amount that our bodies can make.4
Proline-rich Foods
Proline is primarily found in many animal-sourced foods. "The most important sources of proline are gelatin and the skins of animals," Dr. José-Manuel Fernández-Real, director of the Department of Medical Sciences at the University of Girona, and one of the lead investigators of the study, told Verywell, adding that these foods are rich in collagen, which is a natural source of this amino acid.
In fact, proline constitutes about 10% of total amino acids in collagen.5 As such, foods containing collagen, like bone broth, chicken wings (with the skin), pork rinds, and gelatin are rich sources of this amino acid.
Most meats, fish, and dairy foods contain proline as well.
New Developments in the Diet/Depression Link
Although existing data shows that the microbiota-gut-brain axis, or the communication link between the brain and the gut, plays a role in the development of depression, the research available is not particularly strong. Plus, it tends to focus on major depression instead of all levels of severity.2
To learn more about whether diet plays a role in developing depression, the IDIBGI researchers classified approximately 100 subjects into three categories: non-depressed, mildly depressed, and major depressed. From there, they analyzed whether there was a relationship between their depression diagnosis and their gut microbiome composition.
Using an analysis of amino acid called metabolite profiling, researchers were able to most strongly associate proline in the body with depression scores.
To see where this proline was coming from, researchers relied on questionnaires that included information about participants' diets. Once again, proline was the dietary factor with the strongest impact on depression.
Fernández-Real told Verywell that the results were quite surprising. "The intake of proline was the most associated item with the depression score in apparently healthy subjects," he said.
After additionally identifying the proline/depression link in mice, researchers sought to corroborate their findings by transplanting human subjects' gut bacteria into mice. The mice who received the bacteria highest in proline showed more depressive symptoms.
The final step of the study involved fruit flies. Like the mice, the flies who received proline-rich bacteria exhibited signs of depression.
Fernandez-Real noted that the research team did observe that some subjects with a high intake of proline were not depressed.
"These subjects had a gut microbiota that metabolized proline and ‘protected’ them from a high proline in plasma," he said.
Should You Avoid Proline To Reduce Your Depression Risk?
Based on these results, it makes sense to want to rid your kitchen of any food that contains the proline amino acid to keep your depression risk at bay.
Not so fast, advises Liz Shaw, MS, RD, CPT, nutrition media authority and author at ShawSimpleSwaps.com, told Verywell.
"Science is always evolving, and while I appreciate the emphasis researchers are placing on identifying underlying mechanisms of depression and other mood disorders, I do feel it's hard to take this research and make bold recommendations to the general public about proline rich foods," she said.
Shaw added that many foods rich in proline, including meats, fish, and dairy, are full of crucial nutrients for proper growth, development, and immune support.
"Before we recommend clients give up foods that are culturally part of their diet, I think more research is needed, especially regarding the role genetics and a history of mood disorders plays into [depression development] as well," she said.
How to Reduce Depression Risk
If cutting out all meat, fish, and other proline-containing foods is out of the question for you, or if you want to wait until more research is available before you eschew your cheeseburgers and shrimp stir fry, there are plenty of other ways that people can reduce their depression risk.
Although there is no one surefire way to ensure that you will not develop this condition, the National Institute of Aging recommends the following tactics to help prevent depression:6
Participate in physical activity on a regular basis
Follow a low sodium diet
Get 7-9 hours of sleep every night
Maintain social interactions
If you are experiencing symptoms of depression, it is important to take a proactive approach and discuss this with your health care provider. There are methods to treat this condition, and sharing concerns is the first step to management.