A ketogenic diet, when used for treatment-resistant depression, has no greater effect on anxiety, cognitive function, anhedonia, quality of life, or work/social functioning than a matched control diet, indicating that its impact is limited to depression severity.

When the body burns fat for fuel instead of sugar, it produces ketones that change how brain cells communicate using glutamate and GABA. This change reduces feelings of depression but does not affect how the brain handles anxiety, focus, memory, or motivation, because those functions rely on different brain chemicals and circuits that ketones do not touch.