The ketogenic diet is a high‑fat, moderate‑protein, very low‑carb approach that shifts your body into ketosis—burning fat for fuel instead of glucose. It's been around for decades, originally used to treat epilepsy, but it's now one of the most popular weight loss and metabolic health strategies.
The first week is the toughest because your body is switching fuel sources. If you feel low energy or headachy, it's usually electrolytes—add salt and drink more water. This guide will walk you through everything you need to know to start keto the right way.
Normally, your body runs on glucose (sugar) from carbohydrates. When you cut carbs to under 50g per day, your liver starts breaking down fat into molecules called ketones. These ketones become your new fuel source.
This metabolic state is called ketosis. It's not dangerous—it's actually how humans survived famines for thousands of years. Your brain can run perfectly well on ketones, and many people report clearer thinking and more stable energy once they're fully adapted.
It takes about 2-7 days to enter ketosis, depending on how strict you are with carbs and how active you are. Exercise speeds up the process by depleting glycogen stores faster.
Fat: 70–80% of daily calories (your primary fuel source)
Protein: 15–25% of daily calories (enough to preserve muscle, not so much that it converts to glucose)
Net Carbs: 5–10% of daily calories (usually 20–50g per day, depending on your size and activity level)
For a 2000-calorie diet, that's roughly 165g fat, 100g protein, and 25g net carbs. If you're smaller or less active, you'll eat less total food but keep the same ratios.
Step 1: Find your basal metabolic rate (BMR) using an online calculator. This is how many calories you burn at rest.
Step 2: Multiply by your activity factor (1.2 for sedentary, 1.5 for moderately active, 1.7 for very active). This gives you your total daily energy expenditure (TDEE).
Step 3: Subtract 300-500 calories for weight loss, or eat at maintenance if you're already lean and doing keto for health or performance.
Step 4: Set protein at 0.8-1g per pound of lean body mass. This prevents muscle loss.
Step 5: Set net carbs at 20-30g to guarantee ketosis.
Step 6: Fill the rest with fat. Fat is the lever you adjust based on hunger and results.
Proteins: Beef, pork, chicken, turkey, salmon, tuna, eggs, bacon, sausage (check for added sugar)
Fats: Butter, olive oil, avocado oil, coconut oil, MCT oil, heavy cream, cheese
Low-Carb Vegetables: Spinach, kale, broccoli, cauliflower, zucchini, asparagus, bell peppers
Dairy: Full-fat cheese, cream cheese, sour cream, Greek yogurt (plain, watch the carbs)
Nuts & Seeds: Almonds, macadamias, pecans, walnuts, chia seeds, flaxseeds (in moderation—they add up)
Beverages: Water, black coffee, tea, sparkling water, bone broth
Grains: Bread, pasta, rice, oats, cereal, crackers
Sugar: Candy, soda, juice, desserts, honey, maple syrup
Starchy Vegetables: Potatoes, sweet potatoes, corn, peas, carrots (small amounts okay)
Most Fruits: Bananas, apples, oranges, grapes (berries in small amounts are fine)
Processed Foods: Chips, cookies, fast food, anything with hidden sugars or seed oils
Low-Fat Products: They're usually high in sugar to compensate for flavor. Always choose full-fat.
In the first 3-7 days, you might feel tired, headachy, irritable, or foggy. This is called the "keto flu," and it's not actually the flu—it's just your body adjusting to burning fat instead of sugar.
The real culprit? Electrolyte loss. When you cut carbs, your body dumps water and electrolytes (sodium, potassium, magnesium). If you don't replace them, you feel awful.
How to fix it:
Sodium: Add 1-2 teaspoons of salt to your food or drink it in broth. Aim for 5000mg per day.
Potassium: Eat avocado, spinach, salmon. Aim for 3000-4000mg per day.
Magnesium: Take a supplement (magnesium glycinate or citrate). Aim for 300-400mg per day.
Do this, and the keto flu is usually mild or non-existent. If you still feel bad after a week, you're either not eating enough fat or you're still eating too many carbs.
Week 1: Water weight drops fast (2-5 pounds). Energy may dip mid-week. Cravings for sugar are strong. Focus on electrolytes.
Week 2-3: Entering ketosis. Energy stabilizes. Hunger decreases. Mental clarity improves. Some people feel amazing, others still adapting.
Week 4-6: Fat adaptation begins. Your body gets better at burning fat for fuel. Exercise performance returns to normal (or better).
Week 8+: Fully adapted. Stable energy, no cravings, mental clarity, consistent fat loss (if that's your goal).
1. Not eating enough fat: If you're hungry all the time, you're under-eating fat. Fat is not optional—it's your fuel. Add butter, oil, or cheese to every meal.
2. Eating too much protein: Excess protein can convert to glucose via gluconeogenesis, which can kick you out of ketosis. Stick to 0.8-1g per pound of lean mass.
3. Hidden carbs in sauces and condiments: Ketchup, BBQ sauce, and salad dressings often have sugar. Read labels. Stick to mustard, mayo, hot sauce, and ranch.
4. Not tracking anything: Especially in the beginning, eyeballing portions will sabotage you. Track everything for at least the first month.
5. Ignoring electrolytes: This is the #1 reason people quit keto. If you feel bad, add salt. If you still feel bad, add more salt.
6. Giving up too soon: Week 2 is the hardest. Push through. By week 4, it gets way easier.
Physical signs: Fruity breath (from acetone, a type of ketone), increased urination (at first), decreased appetite, stable energy.
Testing methods: Urine strips (cheap, not very accurate), blood ketone meters (accurate, expensive), breath analyzers (moderate cost, decent accuracy).
Honestly, you don't need to test. If you're eating under 30g net carbs per day, you're in ketosis. The signs will be obvious: hunger drops, energy stabilizes, and fat loss happens.
For the first 2-4 weeks, your performance might dip. Your muscles are learning to burn fat instead of glycogen. Once you're adapted, endurance athletes often perform better on keto because fat is a more efficient fuel for long efforts.
Strength training works fine on keto. Some people notice a slight decrease in max strength or explosive power, but it's usually minor. If you're a competitive athlete doing high-intensity work, you might benefit from a targeted ketogenic diet (TKD) where you eat 15-30g of fast-acting carbs before training.
You're eating too many calories: Keto makes it easier to eat less because fat is satiating, but you can still overeat. Track your food.
You're eating too many "keto treats": Almond flour cookies, keto bars, and fat bombs are still calorie-dense. They're fine occasionally, but don't make them daily staples.
You're not actually in ketosis: Hidden carbs in sauces, nuts, dairy. Track everything for a week and see where the carbs are sneaking in.
You're not sleeping enough: Sleep affects cortisol and insulin. Aim for 7-9 hours per night.
You're stressed: Chronic stress raises cortisol, which can stall fat loss. Manage stress with exercise, meditation, or just taking breaks.
Q: Can I do keto long-term?
A: Yes. Many people stay keto for years with no issues. Others cycle in and out. Do what feels sustainable for you.
Q: Will I lose muscle on keto?
A: No, as long as you eat enough protein and lift weights. Keto is muscle-sparing.
Q: Can I eat fruit on keto?
A: Small amounts of berries (strawberries, blueberries, raspberries) are fine. Avoid bananas, apples, and tropical fruits.
Q: What if I cheat?
A: You'll get kicked out of ketosis, but you can get back in within 1-2 days by eating strict keto. Don't beat yourself up—just get back on track.
Q: Do I need to count calories on keto?
A: Not necessarily, but if you're not losing weight, start tracking. Some people naturally eat less on keto, but not everyone.
Q: Can I drink alcohol on keto?
A: Yes, but stick to low-carb options: vodka, whiskey, gin, dry wine. Avoid beer, sugary cocktails, and sweet wines.
Keto is simple in theory—eat fat, moderate protein, very low carbs—but the details matter. Track your macros, prioritize electrolytes, and give your body time to adapt. The first two weeks are the hardest, but once you're fat-adapted, it gets much easier.
Use our calculator to track your daily net carbs, and don't overthink it. Stick to whole foods, avoid processed junk, and trust the process. Results take time, but they will come.