Nutritional ketosis is generally defined as blood β-hydroxybutyrate (BHB) levels of 0.5 mmol/L or higher. In most clinical and dietary contexts, levels between 0.5–3.0 mmol/L are observed and associated with metabolic adaptations. The lower end of this range (~0.5–1.0 mmol/L) is sometimes referred to as light ketosis, while higher levels (~1.0–3.0 mmol/L) are often considered more optimal for clinical outcomes. Individual responses, however, vary widely.

In therapeutic settings such as epilepsy or certain metabolic disorders, higher ketone concentrations (often 3.0–5.0 mmol/L) may be used under medical supervision.

Diet and exercise can influence ketone dynamics. For example, aerobic activity tends to increase ketone production and utilization, while high-intensity or anaerobic exercise may temporarily lower circulating ketones. Additionally, the composition of fats and carbs in recent meals will impact the ability to reach certain thresholds.

Ketone monitoring can be a helpful tool to guide nutrition or therapeutic strategies, but it should not become a source of stress. Importantly, individuals with type 1 diabetes, reduced insulin reserve, renal impairment, or other significant conditions should only pursue ketosis under professional guidance to avoid complications such as ketoacidosis.