depressed woman laying in bed

Eating a Certain Protein Is Related to Developing Depression : Study

Depression and mental health are some of the most talked-about topics in health today. We are learning more and more about the impact that mental health has on our physical well-being, as well as all of the factors that contribute to mental and emotional wellness. Recent research has shown that there is a specific protein that you likely consume daily that is related to developing depression.

New Study Shows This Amino Acid from Protein May Contribute to Depression

Researchers from Girona Biomedical Research Institute (IDIBGI) and Pompeu Fabra University (UPF) in Barcelona, Spain have found that a diet high in the amino acid proline is linked to an increased risk in developing depression. Proline is a non-essential amino acid, aka a protein that our body makes by itself. This means it is not necessary to get it through the diet unless our bodies are under stress and we require more than what our body can make by itself. Proline is found in gelatin, grass-fed beef, wild-caught fish, pasture-raised chicken, bone broth, cage-free eggs, and organ meats such as liver. (1)

The first thing the researchers did was analyze the amount and type of amino acids in the study participants’ diets. The participants then completed a questionnaire in order to measure their depressive mood. It was with this that the researchers noticed the correlation between diets high in proline and depression. (2) They had 100 participants divided into three categories: Not depressed, mildly depressed, and majorly depressed. (3)

Not The Whole Story

Though they did find an interesting link between high proline diets and depression, not everyone who had a high proline intake had poor mental health outcomes. As the researchers studied further, they found that there is also a link between depression and bacteria, particularly bacterial genes associated with proline metabolism. They realized that the amount of proline circulating in the body depends on the person’s microbiota and how much of that protein they can metabolize.

“The microbiota of patients with high proline consumption but low plasma levels of proline was similar to the microbiota associated with low levels of depression and was enriched in bacterial genes involved in the transport and metabolism of proline,” said Dr. Mayneris-Perxachs, a Miguel Servet researcher at the IDIBGI. Dr. Fernandez-Real added: “These subjects had a gut microbiota that metabolized proline and ‘protected’ them from a high proline in plasma.”

Read: 7 Signs of Loneliness and 17 Things You Can Do About it. 

The Cause Or The Consequence?

The researchers next had to figure out whether or not the proline was a cause of depression or a consequence of it. To study this, they transplanted the participants’ microbiota into mice. The mice who received the microbiota of the participants with high proline levels became more depressed than the mice that didn’t. They also found higher amounts of the gene associated with the transport of proline in the brains of those mice. The researchers said that this could indicate causality.

The team did another similar study in fruit flies. They isolated two types of bacteria from the microbiota associated with proline consumption and added them to the flies’ feed, which they had previously sterilized. These were lactobacillus and enterobacter. The flies that received lactobacillus fared better. They showed more willingness to overcome difficulties that they faced afterward. Those that ingested enterobacter, however, became much more depressed.

Lastly, they repeated the experiment on genetically modified flies. In these flies, the scientists had eliminated the channels that carry proline to the brain. With the proline unable to reach the brain, the flies became highly resistant to depression.

What This Means For Fighting Depression

“These results demonstrate the importance of proline and its influence on people’s depressive mood, which so far had not been taken into account,” explained Dr. Fernández-Real. 

Beyond just looking at proline, the researchers say that this opens the door to further studying the effects of diet on depression. This goes not just for diets that cause depression, but also for diet-based treatments for mental illness.

Keep Reading: A woman with terminal cancer says taking ‘magic’ mushrooms eased her depression and helped her process a miscarriage she had decades ago


  1. Microbiota alterations in proline metabolism impact depression.” Cell. Jordi Mayneris-Perxachs, et al. May 3, 2022.
  2. Researchers Find That Eating a Certain Protein Is Related to Developing Depression.” Sci Tech Daily. UNIVERSITAT POMPEU FABRA. June 2, 2022.
  3. Foods High in Proline May Be Linked to Depression, Study Finds.” Very Well Health. Lauren Manaker MS, RDN, LD, CLEC. June 10, 2022.