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Of course, mice are not men, but changing diet has been shown to change human gut bacteria, and fairly quickly. That suggests it's possible that dietary choices can alter well-being and behavior, Lee said, but researchers aren't yet sure if this complex interplay means that swapping food in or out of one's diet can ease or cure a mental illness.
"We're not at the point where we can use diet as therapy, especially when we're dealing with someone whose mental health issues render them very disabled, because we just don't know enough," Lee said. "I think we're just on the new frontier, and five or 10 years from now we'll know more."
Jacka, president of the International Society for Nutritional Psychiatry Research, echoes these reservations. She notes that nearly all research on the connection between diet and mental health has been limited to animal studies and observational studies in humans.
"We can't say [that] if we improve your diet, you'll feel better," she said. "We have circumstantial evidence that suggests this could be true, but we can't say for sure."
The lack of strong evidence and well-designed studies has led to some resistance to Berk's and Jacka's work. Until recently, "the idea that what you put in your mouth could affect your mental health was met with great skepticism," said Jacka, who recalled colleagues' dismissing the idea as "rubbish." With more studies, though, the research community is beginning to come around, she said.
Even as scientists struggle to understand the link between food and mood, some patients, such as Corbitt, seem to tap into it without intending to.
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"I changed my diet because I had gastrointestinal issues," said a 32-year-old woman with bipolar disorder who lives in San Francisco and asked not to be named because she worries about being stigmatized. Three years ago, at her gastroenterologist's urging, she tried the Atkins diet and found relief — not just from her digestive issues but also from her mental illness, which had at one point nearly derailed her life.