The study is looking at how a nutrient called **leucine** affects the brain and mood in adults with midlife depression. Depression is a mental health condition that can make people feel very sad and lose interest in activities. The study will last for 6 weeks and will include people with depression and signs of inflammation (swelling) in their bodies. Inflammation might be linked to depression through something called the *kynurenine pathway*, which can create harmful substances in the brain. Leucine might help block these harmful substances. Half of the participants will take leucine supplements, while the other half will take another nutrient called lysine for comparison. Researchers will use brain scans and surveys to see if leucine helps improve mood and brain function. This study could lead to new treatments for depression and might even help lower the risk of dementia (memory loss) in those with depression.

• The study lasts for 6 weeks.
• Participants will be divided into two groups: leucine and lysine.
• Participants will undergo brain scans and fill out mood surveys.