What Is the Keto Diet?
A simple guide to what keto is and how it works. Learn the basics of the ketogenic diet without the hype or confusion.
The ketogenic diet—or “keto”—is a very low-carb, high-fat way of eating. It changes how your body uses energy by shifting it from burning carbs to burning fat.
When carbs are low enough, your liver turns fat into ketones. These ketones fuel your body and brain instead of glucose. This is called ketosis.
Think of keto as flipping your body’s fuel switch—from sugar to fat.
How Ketosis Works
Most people rely on carbohydrates for energy. But on keto, you limit carbs (usually to under 50g net per day), and your body runs out of stored glucose within 2-4 days. So it switches to burning fat.
In ketosis, your body:
- Breaks down fat into molecules called ketones (specifically beta-hydroxybutyrate, acetoacetate, and acetone)
- Uses ketones for energy instead of sugar—your brain can get up to 70% of its fuel from ketones
- Lowers insulin levels, which may support fat burning and blood sugar control
- Increases fat oxidation, meaning you burn more fat throughout the day
How to know you’re in ketosis:
| Method | What It Measures | Ketosis Range |
|---|---|---|
| Blood ketone meter | BHB in blood | 0.5–3.0 mmol/L |
| Urine strips | Acetoacetate | Moderate to large |
| Breath meter | Acetone | 10–40 ppm |
Blood meters are most accurate. Urine strips work well at first but become less reliable over time as your body gets better at using ketones.
Research shows ketosis can help regulate hunger hormones, reduce appetite, and improve insulin sensitivity—especially in people with overweight or type 2 diabetes 12.
The Keto Adaptation Timeline
Your body doesn’t flip a switch overnight. Here’s what to expect:
| Timeframe | What’s Happening |
|---|---|
| Days 1-3 | Glycogen depletes, you may feel tired or foggy |
| Days 4-7 | Ketone production ramps up, “keto flu” may peak |
| Weeks 2-4 | Energy improves, cravings decrease |
| Weeks 4-12 | Full fat-adaptation, exercise performance returns |
Most people enter nutritional ketosis within 2-7 days of eating under 50g carbs. Full fat-adaptation—where your body efficiently uses fat for all activities—takes 4-12 weeks.
Keto Macros: What You Eat
Keto isn’t just about eating fat. It’s about shifting your macronutrient balance:
| Macro | Percent of Calories | What That Means |
|---|---|---|
| Fat | 70–75% | Avocados, olive oil, butter, meat |
| Protein | 20–25% | Eggs, poultry, seafood, beef |
| Net Carbs | 5–10% | Leafy greens, broccoli, berries |
Most people aim for 20–50g net carbs per day (total carbs minus fiber).
Learn more in our Keto Macros Guide.
What You Can and Can’t Eat
Foods to Eat Freely
| Food Category | Best Choices | Net Carbs (per serving) |
|---|---|---|
| Proteins | Beef, pork, chicken, fish, eggs | 0g |
| Healthy Fats | Olive oil, avocado oil, butter, ghee | 0g |
| Above-ground veggies | Spinach, kale, broccoli, cauliflower | 1-3g |
| Full-fat dairy | Cheese, heavy cream, sour cream | 0-1g |
| Nuts & seeds | Macadamias, pecans, walnuts | 1-2g |
| Berries (limited) | Raspberries, blackberries | 3-5g per ½ cup |
Foods to Avoid Completely
| Food Category | Why to Avoid | Net Carbs (per serving) |
|---|---|---|
| Grains | Bread, pasta, rice, oats | 20-45g |
| Sugary foods | Candy, cookies, soda | 20-60g |
| Starchy vegetables | Potatoes, corn, peas | 15-30g |
| Most fruits | Bananas, apples, grapes | 15-25g |
| Beans & legumes | Black beans, lentils, chickpeas | 15-25g |
| Low-fat products | Often high in sugar to compensate | Varies |
Foods That Seem Keto But Aren’t
Watch out for these sneaky carb sources:
- Keto bars — many contain maltitol, which spikes blood sugar
- Sugar-free candy — often has hidden carbs from sugar alcohols
- Flavored yogurt — even “low-carb” versions can have 10-15g carbs
- Tomato sauce — often loaded with added sugar
- Condiments — BBQ sauce, ketchup, and teriyaki are sugar bombs
For a full list, check out the Keto Shopping List.
Why People Try Keto
Keto isn’t just about weight loss. Here’s why people do it:
- Lose fat without constant hunger — keto naturally suppresses appetite
- Improve energy and focus — avoid blood sugar crashes that cause brain fog
- Lower blood sugar and insulin — especially beneficial for type 2 diabetes
- Support metabolic health — may help with PCOS and other conditions 34
It’s not magic—it works by changing your fuel source and appetite signals.
Who Should Avoid Keto?
Keto isn’t right for everyone. It may not be a good fit if you:
- Have a history of disordered eating
- Are pregnant or breastfeeding without medical supervision
- Take insulin or medications for blood sugar
- Have certain liver or kidney conditions
Talk to your doctor if you’re unsure—especially if you’re managing a medical condition.
Common Keto Myths (Busted)
MYTH: You have to eat sticks of butter. TRUTH: Keto can be done with healthy fats like olive oil, avocado, and salmon.
MYTH: You’ll be in ketosis 24/7 or it doesn’t work. TRUTH: You don’t need to be perfect to see benefits.
MYTH: Keto is dangerous long-term. TRUTH: It depends on how you do it. There’s strong evidence for its safety when done correctly under medical guidance 5.
How to Start Keto (Your First Week)
Day 1-2: Clean out your kitchen Remove temptations—bread, pasta, chips, sugary snacks. Stock up on eggs, meat, avocados, cheese, and leafy greens.
Day 3-4: Keep it simple Don’t try complicated recipes yet. Eat eggs and bacon for breakfast, salad with chicken for lunch, steak with vegetables for dinner.
Day 5-7: Manage the transition You might feel tired or foggy. This is normal. Drink extra water, add salt to your food, and consider an electrolyte supplement.
Week 2 and beyond: Energy should improve. Start tracking macros if you haven’t already, and explore more variety in your meals.
Key Takeaways
- Keto = low carb, high fat, moderate protein (typically under 50g net carbs daily)
- It helps your body switch to burning fat and producing ketones for fuel
- Most people enter ketosis within 2-7 days, but full adaptation takes 4-12 weeks
- It may support fat loss, better energy, and blood sugar control
- It’s not for everyone—consult your doctor if you have medical conditions
What to Read Next
- Keto Macros: How to Track Fat, Protein, and Carbs
- Benefits of the Keto Diet
- Keto Side Effects and How to Avoid Them
- Keto vs. Low-Carb: What’s the Difference?
- Beginner Keto Meal Plan
Sources
National Institutes of Health - Ketogenic Diet and Weight Loss ↩︎
American Journal of Clinical Nutrition - Effects of Ketosis on Appetite and Hormones ↩︎
Harvard T.H. Chan School of Public Health - Keto Diet Overview ↩︎
Cleveland Clinic - What Is the Keto Diet? ↩︎