A 20-year old man in Taiwan went to a dermatology clinic for a strange rash that had developed across his shoulders and chest. The raised, red, and itchy condition had been bothering him for a full month. By this point, he had also developed patches of pigmented skin interlaced with the red rash.
According to a case report in the New England Journal of Medicine, a skin biopsy showed swelling between his skin cells and inflammation around blood vessels, but testing came up negative for other common signs of skin conditions, leaving doctors with few leads. The doctors ultimately came to a diagnosis not by analyzing his skin further but by hearing about his diet.
The man told doctors that two months prior to his clinic appointment—a month before his rash developed—he had switched to a ketogenic diet, which is a high-fat but very low-carbohydrate eating pattern. This diet forces the body to shift from using glucose (sugar derived from carbohydrates) as an energy source to fat instead.
When this happens, the body can go into ketosis. This starts with fat tissue breaking down, leading to the release of free fatty acids. These fatty acids are transported to the liver, where they’re metabolized to acetyl-CoA. Excessive amounts of this molecule gum up metabolic processes and lead to the formation of ketone bodies, primarily acetoacetate and beta-hydroxybutyrate. (A ketone is a specific chemical structure that includes a single bond to two CH3 or R groups with a double bond to an oxygen molecule.) Ketone bodies made in the liver can enter the circulatory system and be used as a source of energy for tissues around the body, particularly the brain.
Ketogenic diets have clinical uses—they’ve proven useful for managing drug-resistant epilepsy and some rare genetic metabolic diseases. Studies have looked at them as possible ways to manage obesity and type 2 diabetes, and there’s interest in their use in cancer metabolism and neurodegenerative diseases, including Parkinson’s disease and Alzheimer’s disease.