We present a case of reversible memory loss and brain fog associated with prolonged ketogenic diet use.

Ketogenic diet has gained recognition as a popular weight loss strategy however, it has been associated with various adverse effects including nausea, headache, fatigue and dizziness. It has also been hypothesized to negatively impact memory and cognition through several mechanisms including decreased glucose availability, altered synaptic function, and potential neurotoxic effects of ketone bodies.  The available data on long-term neurocognitive effects, however, remains scarce.

A 48 year old woman presented with two year history of gradually worsening memory loss and brain fog. She described word finding difficulty and impaired ability to recall details of conversations or events. Formal cognitive testing showed deficits in attention, anterograde memory, and executive functions such as task-switching and planning. Labs including vitamin B12, folate, TSH, comprehensive metabolic panel, CRP, and ESR were unremarkable. Of note, she had adhered to a strict ketogenic diet for weight loss continuously for the past two years. She discontinued the ketogenic diet and within two months noticed significant improvement in her memory and cognitive function. Repeat cognitive testing was normal.