The question of whether the One Meal A Day (OMAD) diet induces ketosis is common, bridging intermittent fasting and metabolic science. OMAD is an aggressive form of time-restricted eating, and ketosis is a specific metabolic state. The answer depends heavily on the interplay between the fasting duration and the composition of the single meal. Understanding the body’s fuel-switching mechanism is necessary to grasp how often OMAD can lead to the production of ketones.
Defining One Meal A Day
The One Meal A Day (OMAD) protocol is an extreme version of intermittent fasting, characterized by a 23:1 schedule. This means a person fasts for approximately 23 hours and consumes all daily calories within a single one-hour eating window. During the extended fast, only non-caloric beverages like water, black coffee, or plain tea are permitted. The primary physiological effect of this long fast is the depletion of the body’s stored sugar.
The body initially relies on glucose from the last meal for energy. Once that is used, the liver and muscles begin breaking down their stored form of glucose, known as glycogen. This process of glycogenolysis provides fuel for roughly 12 to 24 hours, depending on the individual’s activity level and glycogen stores. By consistently fasting for 23 hours, the OMAD schedule ensures that these glycogen reserves are significantly diminished daily.
The Metabolic State of Ketosis
Ketosis is a metabolic state where the body shifts its primary energy source from glucose to fat. This occurs when carbohydrate intake is severely restricted or during prolonged periods without food. When glucose is unavailable, the liver begins to process stored body fat and dietary fat.
The liver converts fatty acids into compounds called ketone bodies, specifically beta-hydroxybutyrate (BHB), acetoacetate, and acetone. These ketones are released into the bloodstream to be used as an alternative fuel source by the brain, heart, and muscles. A person is considered to be in nutritional ketosis when blood ketone levels, specifically BHB, reach a concentration of approximately 0.5 millimolar (mM) or higher.
The Critical Link: Fasting Duration and Ketone Production
A 23-hour fast, as mandated by the OMAD protocol, is sufficient to initiate the metabolic switch toward fat burning. As the body’s glycogen stores become depleted, insulin levels drop substantially, signaling the body to begin lipolysis, or the breakdown of fat. This reduction in insulin is the primary hormonal trigger for the liver to start producing ketone bodies.
For most people, the first detectable rise in blood ketones occurs between 12 and 24 hours of continuous fasting. Therefore, a daily 23-hour fast places a person right at the threshold of ketone production. While this duration may not lead to the deep or sustained ketosis seen in multiday fasts, it triggers a daily cycle of early ketogenesis. The consistent depletion of glucose stores ensures that the body spends a significant portion of its time in a state of heightened fat oxidation.
Meal Composition as the Controlling Factor
While the 23-hour fast provides the necessary metabolic trigger, it does not guarantee the maintenance of ketosis. The single meal consumed during the one-hour window determines if the ketogenic state is sustained or terminated. If the OMAD meal is high in carbohydrates, the body will use that influx of glucose to rapidly refill the liver and muscle glycogen stores.
A high-carbohydrate meal causes a significant spike in blood glucose and a large release of insulin. This insulin surge is a powerful signal to the body to halt fat breakdown and ketone production, effectively pulling the person out of ketosis. To maintain the metabolic state of ketosis, the single meal must be low in carbohydrates and contain moderate amounts of protein. By consuming minimal glucose-generating macronutrients, the body can continue to rely on fat and ketones for fuel, extending the benefits achieved during the fast into the eating window.