Starting a keto diet means shifting your body’s primary fuel source from carbohydrates to fat. The standard approach calls for eating 70 to 80% of your daily calories from fat, 10 to 20% from protein, and only 5 to 10% from carbohydrates. For most people, that translates to roughly 20 to 50 grams of carbs per day. The transition takes some planning, but the basics are straightforward once you understand what to eat, what to expect in the first few weeks, and how to avoid common mistakes.
What Happens in Your Body on Keto
When you dramatically cut carbs, your blood sugar and insulin levels drop. This signals your liver to start converting fatty acids into molecules called ketones, which your brain and muscles can use for energy instead of glucose. You can enter this state, called ketosis, within the first few days of restricting carbs.
Ketosis and fat adaptation are not the same thing, though. Ketosis can happen overnight if you stop eating carbs. Fat adaptation, where your cells become genuinely efficient at burning fat as a default fuel source, takes about a month or longer of consistent low-carb eating. Sustained fat loss typically kicks in around the four-week mark. The first week or two often involves water weight loss rather than true fat loss, so don’t be discouraged if progress seems to stall after an initial drop on the scale.
Setting Up Your Macros
The simplest way to start is to focus on one number: your daily carb limit. Most beginners aim for 20 to 25 grams of net carbs per day. Net carbs are calculated by subtracting fiber from total carbohydrates. If a food has 10 grams of total carbs and 4 grams of fiber, it has 6 grams of net carbs. For processed foods that contain sugar alcohols (like sorbitol, xylitol, maltitol, or erythritol), subtract half the sugar alcohol content as well.
Once your carb limit is set, fill the rest of your plate with fat and moderate protein. A common mistake is eating too much protein and not enough fat, which can slow the transition into ketosis. Think of protein as a side component and fat as your main energy source. A rough starting point: if you eat 2,000 calories a day, about 1,500 of those should come from fat, 300 from protein, and 200 or fewer from carbs.
Foods to Build Your Meals Around
The core of a keto diet is whole, unprocessed food that’s naturally high in fat and low in carbs. Fresh meat and poultry contain zero carbs. Salmon and other fish are nearly carb-free and provide healthy fats. One large egg has less than 1 gram of carbs. An ounce of cheddar cheese has just 1 gram. Olive oil, butter, and ghee are all carb-free fat sources you can cook with liberally.
For vegetables, stick to those that grow above ground. Leafy greens, broccoli, cauliflower, zucchini, and bell peppers are all relatively low in carbs. Starchy vegetables like potatoes, corn, and sweet potatoes are too carb-heavy to fit. Berries (especially raspberries and blackberries) are the lowest-sugar fruits and can work in small portions. Most other fruits are too high in natural sugar.
For drinks, coffee, tea, and unsweetened sparkling water are all carb-free. If you need a pasta substitute, shirataki noodles contain less than 1 gram of net carbs per serving. Nuts like macadamias and pecans are good snack options, though portions matter since carbs can add up quickly.
What to Cut and What to Watch For
The obvious removals are bread, pasta, rice, cereal, and anything with added sugar. But hidden carbs are the real threat to staying in ketosis, especially in processed and packaged foods. There are at least 61 different names for sugar on food labels, according to researchers at UC San Francisco. Some of the less obvious ones include maltodextrin, dextrose, barley malt syrup, rice syrup, evaporated cane juice, and fruit juice concentrate. If an ingredient list contains any word ending in “-ose” (fructose, maltose, sucrose, dextrose), that’s a sugar.
Sauces and condiments are a common trap. Ketchup, barbecue sauce, teriyaki sauce, and many salad dressings contain significant added sugar. So do “low-fat” versions of yogurt, milk, and other dairy products, which often replace fat with sugar. Read labels carefully for the first few weeks until you learn which brands are safe.
Getting Through the First Week
Most people experience some combination of headaches, achiness, nausea, fatigue, and constipation in the first few days. This cluster of symptoms is commonly called “keto flu,” and it’s caused by the sudden shift in how your body is fueling itself. Your kidneys flush out more water and electrolytes when insulin drops, which is the main driver of these symptoms.
The fix is simple: increase your salt, potassium, and magnesium intake. Add more salt to your food than you normally would. Drink broth or bouillon. Eat potassium-rich keto foods like avocado and spinach. If you’re noticing muscle cramps, weakness, or persistent fatigue, an electrolyte supplement or sugar-free sports drink can help your body adjust more smoothly. Most people feel significantly better by the end of the first week, and the symptoms rarely last beyond two weeks.
Staying well-hydrated is also critical. The water weight you lose in the first few days means you need to actively replace fluids. Aim for more water than you think you need, especially during days three through seven.
A Simple Approach to Your First Week of Meals
You don’t need complicated recipes to start. A practical first week looks something like this: eggs cooked in butter with cheese for breakfast, a salad with grilled chicken, olive oil, and avocado for lunch, and salmon or steak with roasted broccoli and butter for dinner. Snack on cheese, nuts, or hard-boiled eggs if you’re hungry between meals. Many people find their appetite naturally decreases after a few days in ketosis, which makes eating less food feel effortless rather than forced.
Meal prepping on the weekend helps enormously. Cook a batch of protein, wash and chop vegetables, and portion out snacks. The most common reason people break their carb limit in the first week is being caught hungry without a keto-friendly option nearby.
Tracking Ketones
You don’t need to test your ketone levels, but it can be motivating early on to confirm you’re in ketosis. The two main options are urine test strips and blood ketone meters. Urine strips are inexpensive and available at any pharmacy without a prescription. They work well in the first week or two but become less reliable over time as your body gets more efficient at using ketones (leaving fewer in your urine).
Blood meters give accurate, real-time readings of your current ketone levels. They’re more expensive and require finger-prick test strips, but they remain reliable long-term. For most beginners, urine strips are a fine and affordable starting point. If you stick with keto for more than a month and want precise data, upgrading to a blood meter is worthwhile.
Who Should Be Cautious
Keto is not safe for people with conditions involving the pancreas, liver, thyroid, or gallbladder. If you take diabetes medication that lowers blood sugar, those medications may need to be adjusted within a few days of starting keto, since your blood sugar will drop significantly from the dietary change alone. Anyone on blood sugar-lowering medication should work with their doctor before making this switch. Pregnant or breastfeeding women should also avoid strict keto without medical guidance.
For most other healthy adults, the diet is safe to start on your own. The first month is the hardest. Once you’re fat-adapted, cravings diminish, energy stabilizes, and the eating pattern starts to feel like a normal routine rather than a restrictive diet.