What Is the Ketogenic Diet?
The ketogenic diet is a high-fat, moderate-protein, very low-carbohydrate nutrition strategy designed to shift the body’s metabolism away from glucose and toward fat as its primary fuel source. Although it has surged in popularity for weight loss and metabolic health, the ketogenic diet originated as a therapeutic intervention for epilepsy nearly a century ago. Today it is also used clinically for insulin resistance, type 2 diabetes, neurological disorders, cancer metabolic therapy and cognitive performance. Understanding how the diet works and how to measure ketosis accurately allows people to use it more safely and effectively.
How Ketosis Works
Under normal circumstances the body prefers glucose, from carbohydrates, for fuel. When there is plenty of glucose, insulin rises to allow glucose into cells for fuel. Fat is typically stored in the presence of insulin which is why it’s known as the “fat storage hormone”. When glucose levels drop along with insulin, such as between meals, overnight, or during prolonged modest exercise, the body reverses the process and mobilizes stored fat for fuel. This does not typically lead to significant ketone production.
A ketogenic diet restricts carbohydrate intake so dramatically that the body changes over to fat as the primary fuel source. Along with this the liver begins converting fatty acids into ketone bodies, primarily beta-hydroxybutyrate (BHB), acetoacetate, and acetone. Carbohydrate intake generally must stay below 20–50 grams of net carbs per day to maintain this metabolic state. Fat becomes the main caloric driver, usually composing 70–80% of total energy intake, while protein stays moderate at roughly 15–20% of calories. When carbohydrates fall to very low levels, insulin drops accordingly, allowing fat mobilization and ketone production to accelerate. As ketone levels rise, the brain and muscles shift from glucose dependency to ketone utilization, producing many of the cognitive and metabolic benefits associated with ketosis.
A point on fat versus ketones. Fat is the primary fuel, not ketones per se. Fat is the underlying energy source being mobilized and oxidized. Ketones are a secondary fuel created from fat. Ketones act as a clean, high-octane, portable, water-soluble fuel derived from fat. They exist so tissues that cannot burn fat (especially the brain) have something to use during carbohydrate scarcity. Without ketones, starvation or ultra low-carb diets would be dangerous.
Intermittent fasting, such as going more than 10-12 hours after the last meal, shifts the body to fat burning and encourages this metabolic flexibility. It leads to a light ketosis. Fasting for 24 hours or so might lead to moderate ketosis while >48 hours of fasting will lead into a deep ketosis.
“Metabolic flexibility” is a related topic, which means being able to shift between fuel sources of glucose and fat efficiently. By avoiding excess carbohydrates, especially high glycemic foods and the excess insulin that comes with them, we encourage our body to naturally switch into fat burning mode. This is a good thing!
Core Foods of a Ketogenic Diet
A typical ketogenic plate focuses on healthy fats such as avocados, olive oil, nuts, seeds, coconut products, butter, and ghee. Protein sources include eggs, poultry, fish, meat, tofu, certain cheeses, and Greek yogurt. Low-carbohydrate, low starch vegetables, also referred to as “above the ground” vegetables, such as leafy greens, broccoli, cauliflower, zucchini, mushrooms, cabbage, and asparagus provide fiber and micronutrients without pushing carbohydrate totals too high.
Foods that undermine ketosis include grains, breads, pastas, rice, potatoes, beans, lentils, most fruits, and sugary foods. For many individuals, the most common mistake is unintentionally consuming too many carbohydrates from sauces, snacks, or “healthy” foods such as quinoa or legumes. Staying mindful of hidden carbs is essential.
“Net carbohydrates” is a bit confusing as it refers to the portion of carbs in food that actually raises blood sugar and insulin. They are calculated by subtracting fiber and certain sugar alcohols (such as erythritol or allulose) from the total carbohydrate count, because these components are not digested into glucose and therefore do not affect ketosis or metabolic state.
Net carbs represent the usable, digestible carbohydrates that impact energy balance, appetite, and ketone production, making them a practical measure for people following ketogenic or low-carb diets. By focusing on net carbs rather than total carbs, individuals can include high-fiber vegetables, nuts, seeds, and other nutrient-dense foods while staying within carbohydrate limits that support stable blood sugar and metabolic flexibility.
The Keto Transition and Electrolyte Balance
One of the defining challenges of transitioning into ketosis is electrolyte imbalance. As insulin drops, the kidneys excrete more sodium and water. This shift contributes to what many call the “keto flu” with fatigue, headache, lightheadedness, and muscle cramps that often appear during the first week. Increasing sodium intake, maintaining hydration, and supplementing magnesium and potassium can dramatically reduce these symptoms. Once the body adapts, most people report improved energy, reduced hunger, more stable blood sugar, and enhanced mental clarity.
Why Measure Ketosis?
We strongly advise getting a blood ketone monitor, such as KetoMojo, Precision Xtra, etc. While many people adopt a ketogenic diet for weight loss or metabolic health, others pursue deeper levels of ketosis for therapeutic reasons. We also observe patients thinking they are in ketosis yet they are not, so the monitor is confirmation. Although urine ketone strips and breath acetone meters offer rough estimates, blood ketone testing is the gold standard for assessing true metabolic ketosis. Blood monitors measure circulating beta-hydroxybutyrate (BHB), which reflects the body’s actual ketone availability.
Understanding Blood Ketone Ranges
Blood ketone levels fall into predictable ranges:
0.0–0.4 mmol/L: Not in Ketosis. Glucose remains the primary fuel, typical of a standard diet.
0.5–0.9 mmol/L: Light Nutritional Ketosis. Common after a fast or early in keto adaptation.
1.0–1.5 mmol/L: Moderate Ketosis. A strong and sustainable zone for weight loss, metabolic improvement, and appetite control.
1.5–3.0 mmol/L: Therapeutic Ketosis. Used in clinical protocols for epilepsy, neurological disorders, migraines, and metabolic cancer support. Ketones dominate brain fuel use in this range.
3.0–5.0 mmol/L: Very High Ketosis. Usually associated with prolonged fasting or very strict carbohydrate restriction. Not necessarily more beneficial than moderate therapeutic levels.
>5.0 mmol/L: Excessive Ketosis. May indicate prolonged fasting or metabolic imbalance. Individuals with type 1 diabetes or those using SGLT2 inhibitors should exercise caution due to ketoacidosis risk.
Factors That Influence Ketone Levels
Ketone levels alone do not determine fat loss. High readings show ketone production, not necessarily fat burning. Eating large amounts of dietary fat can elevate ketones but may slow weight loss if caloric intake is excessive. Conversely, as individuals become keto-adapted, cells use ketones more efficiently, sometimes lowering blood levels even while ketosis remains active.
Daily fluctuations are normal. Ketones tend to be lowest in the morning and higher later in the day, especially after fasting or physical activity. Protein intake also impacts ketone levels; too little protein leads to muscle loss, while excessive protein may slightly raise glucose through gluconeogenesis. Most individuals succeed with moderate protein intake around 0.6–1.0 grams per pound of lean mass.
Vegetarian Approaches to Keto
The ketogenic diet can also be adapted for vegetarians. Ovo-lacto vegetarian keto, which incorporates eggs, cheese, yogurt, nuts, seeds, and low-carb vegetables, is very achievable. Vegan keto is possible but requires more attention to protein sources like tofu, tempeh, nuts, seeds, and low-carb plant proteins. The guiding principles remain unchanged: low carbohydrates, moderate protein, and high-quality fats.
We recommend the book Keto-tarian, by Dr. Will Cole, a functional medicine practitioner. It combines the principles of a ketogenic diet with a mostly plant-based approach, offering a hybrid model that aims to give the metabolic advantages of ketosis without relying on heavy animal fat consumption.
The Wahls Protocol, by Dr Terry Wahls, is another good nutrition book I recommend, focused more on nutrition for helping lower inflammation and/or help autoimmune conditions, but she too submits ideas on a more plant forward ketogenic diet.
Personalizing Ketosis for Your Goals
The ketogenic diet is a flexible metabolic tool. Mild to moderate ketosis is usually sufficient for weight loss and metabolic health improvements. Therapeutic ketosis may be appropriate for individuals addressing specific neurological or metabolic conditions. Monitoring blood ketones allows customization of the diet to match personal goals while ensuring safety and effectiveness.
By understanding both the dietary framework and the physiology behind ketone measurement, individuals can tailor the ketogenic diet to their needs, whether they seek improved energy, weight loss, cognitive enhancement, or targeted clinical benefits.
Author
Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine. He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions. He is founder and medical director of the Integrative Medicine Center of Western Colorado (www.imcwc.com) and Bellezza Laser Aesthetics (www.bellezzalaser.com). Call (970) 245-6911 for an appointment or more information.
