Ketosis

Understanding ketosis: when your body switches to fat burning

Ketosis is a normal metabolic state where your body burns fat for fuel instead of carbohydrates. When you restrict carbs below roughly 50 grams per day, your liver glycogen stores become depleted and your liver starts converting fatty acids into ketone bodies ^[1]. These ketones — primarily beta-hydroxybutyrate (BHB), acetoacetate, and acetone — become the main energy source for your brain, muscles, and heart. During nutritional ketosis, blood ketone levels typically range from 0.5 to 3.0 millimolar, a state that differs fundamentally from diabetic ketoacidosis, a dangerous condition occurring in uncontrolled type 1 diabetes where ketones can exceed 10-25 millimolar ^[2].

How ketosis affects your brain and cognition

Your brain, which normally relies almost entirely on glucose, can adapt remarkably well to using ketones as fuel. Research shows ketones provide approximately 60-70% of cerebral energy needs during sustained ketosis ^[3]. This alternative fuel source may offer neuroprotective benefits. Studies in patients with drug-resistant epilepsy have demonstrated that ketosis can significantly reduce seizure frequency, which is why the ketogenic diet has been a clinical therapy for epilepsy since the 1920s ^[4]. Many people also report improved mental clarity and focus during ketosis, attributed to the stable energy supply and reduced blood sugar fluctuations.

Metabolic benefits: what the research shows

Beyond being an alternative fuel, ketones function as signaling molecules that influence gene expression and cellular processes. Beta-hydroxybutyrate acts as a histone deacetylase inhibitor and can activate anti-inflammatory pathways throughout the body. Studies indicate ketosis improves insulin sensitivity and helps regulate blood sugar levels. Weight loss on ketogenic diets appears to stem from multiple mechanisms: reduced appetite through appetite-suppressing effects of ketones, increased satiety from higher protein and fat intake, and improved metabolic efficiency ^[5]. Research also suggests ketosis may extend lifespan in animal models, though human longevity data remains limited.

Measuring and achieving ketosis

You can measure ketosis objectively through several methods. Blood ketone meters that measure beta-hydroxybutyrate provide the most accurate readings, with nutritional ketosis defined as 0.5-3.0 millimolar. Urine test strips offer a cheaper but less reliable option, becoming inaccurate once your body adapts and excretes fewer ketones. Breath analyzers measure acetone and provide reasonable correlation with blood levels. To enter ketosis, most people need to restrict carbohydrates to 20-50 grams daily for 3-7 days. The adaptation period, often called the "keto flu," typically lasts 1-4 weeks as your body upregulates enzymes for ketone production.

Safety considerations and who should avoid it

While nutritional ketosis is safe for most healthy adults, certain groups should avoid it. People with pancreatic insufficiency, liver disease, or a history of eating disorders should not attempt ketosis. The diet can raise LDL cholesterol significantly in some individuals, so regular blood work is advisable for long-term adherence. Pregnant women and those with type 1 diabetes require medical supervision if attempting ketosis. Common short-term side effects include fatigue, headaches, and constipation, often remedied by proper hydration and electrolyte supplementation. If you take medications for diabetes or blood pressure, consult your healthcare provider before starting, as doses may need adjustment.