To get into ketosis, you need to eat mostly fat, moderate protein, and very few carbohydrates, typically under 50 grams of carbs per day and sometimes as low as 20 grams. That’s less than what’s in a single plain bagel. When you restrict carbs this sharply, your body burns through its stored glucose (glycogen) and starts producing ketones from fat as its primary fuel source. Most people enter ketosis within 2 to 4 days of eating this way, though it can take a week or longer depending on your starting point and activity level.
The Macronutrient Breakdown
Popular ketogenic resources generally suggest getting 70 to 80% of your daily calories from fat, 10 to 20% from protein, and just 5 to 10% from carbohydrates. On a 2,000-calorie diet, that translates to roughly 155 to 178 grams of fat, 50 to 100 grams of protein, and 20 to 50 grams of carbs. Fat isn’t just the majority of your plate; it’s the overwhelming majority. This ratio is what forces your metabolism to shift from burning glucose to burning fat for energy.
Protein matters more than people realize. Too little and you’ll lose muscle. Too much and your body can convert excess protein into glucose, which slows the transition. Staying in that 10 to 20% range gives your body enough to maintain and repair tissue without interfering with ketone production.
Best Fat Sources
Not all fats are created equal. Prioritize sources rich in monounsaturated and polyunsaturated fats: olive oil, avocado oil, sesame oil, and whole avocados. Nuts and seeds are excellent options, particularly almonds, macadamia nuts, hazelnuts, walnuts, pistachios, chia seeds, flaxseeds, and pumpkin seeds. These provide fat alongside fiber and micronutrients.
For omega-3 fats, turn to fatty fish like tuna, mackerel, sardines, and salmon. Coconut oil is another staple because it contains medium-chain triglycerides, a type of fat your liver converts to ketones especially quickly. Butter, ghee, and heavy cream round out the list. Use these liberally in cooking and on vegetables to hit your fat targets without feeling like you’re forcing it.
Which Vegetables to Choose
When your entire carb budget is 20 to 50 grams a day, every gram counts. Leafy greens are your safest bet. A cup of raw kale has just 1 gram of carbs, almost all of it fiber. A cup of raw spinach has about 1 gram, and a cup of lettuce has 2 grams with 1 gram of fiber. You can eat generous portions of these without making a dent in your carb limit.
Cruciferous vegetables work well too, though you need to watch portions a bit more carefully. A cup of raw broccoli has 6 grams of carbs (4 net after subtracting 2 grams of fiber). A cup of raw cauliflower has 5 grams total, 3 net. Cabbage comes in at 5 grams per cup with 2 grams of fiber. Brussels sprouts run about 6 grams per half cup cooked, with 2 grams of fiber. Celery, cucumber, asparagus, and squash are also good low-carb choices.
One real concern with keto is fiber intake. One study found that people on ketogenic diets averaged only 6.4 grams of fiber per day, far below the recommended 28 grams. Loading up on leafy greens and cruciferous vegetables, plus chia and flaxseeds, helps close that gap.
Protein Without Overdoing It
Good protein sources for ketosis include eggs, fatty cuts of meat, poultry with the skin on, and fatty fish. These naturally pair protein with fat, making it easier to hit both targets simultaneously. Full-fat cheese, Greek yogurt (in small amounts), and cottage cheese also work, though dairy carbs can add up if you’re not tracking.
A practical approach: build each meal around a fat source and a protein source, then add low-carb vegetables. A plate might look like salmon cooked in olive oil with a side of spinach sautéed in butter, or chicken thighs with roasted broccoli topped with cheese.
What to Drink
Water is the obvious choice, but you have more options than you might think. Coffee and tea are nearly carb-free. Black and green tea contain less than 1 gram of carbs per cup. Add heavy cream or unsweetened plant-based creamer instead of regular milk or sweetened creamers. Avoid sugar, honey, and standard flavored syrups.
Sparkling water, especially unflavored or naturally flavored versions, is a solid choice. Unsweetened almond milk, coconut milk, and macadamia nut milk all work, but only the unsweetened varieties. Even small amounts of lemon and lime juice are fine for adding flavor. If you drink alcohol occasionally, hard liquors like vodka, whiskey, rum, and tequila are naturally carb-free. The lowest-carb beers have 2 to 3 grams of net carbs per bottle.
Watch for Hidden Sugars
Packaged foods marketed as “keto-friendly” sometimes contain ingredients that can spike your blood sugar. The CDC identifies several common names for added sugar you should scan ingredient labels for: cane sugar, turbinado sugar, corn syrup, high-fructose corn syrup, rice syrup, molasses, caramel, honey, agave, and any juice concentrate. Any ingredient ending in “-ose” is a sugar, including glucose, fructose, maltose, dextrose, and sucrose. Words like “glazed,” “candied,” “caramelized,” or “frosted” also signal added sugar.
Managing Electrolytes During the Transition
The “keto flu,” that stretch of fatigue, headaches, and muscle cramps in the first few days, is largely an electrolyte problem. When you cut carbs, your kidneys excrete more sodium and water than usual. Low sodium is the most common culprit behind feeling terrible during the transition.
Aim for 4 to 6 grams of sodium per day (more than double the standard dietary guidelines, but appropriate for very low-carb eating). Salt your food generously and consider broth or bouillon. For potassium, target 3.5 to 5 grams daily through avocados, leafy greens, and nuts. Magnesium should be 400 to 600 milligrams per day, found in pumpkin seeds, spinach, and dark chocolate (in small amounts). Getting these electrolytes right from day one can prevent keto flu entirely for many people.
How to Know It’s Working
Nutritional ketosis is defined as blood ketone levels between 0.5 and 3.0 mmol/L. You can measure this with a blood ketone meter, which is the most accurate method. Urine strips are cheaper but become less reliable over time as your body gets more efficient at using ketones. Breath meters offer a middle ground.
Physical signs that you’ve entered ketosis include reduced appetite, a metallic or fruity taste in your mouth, increased thirst, and more frequent urination. Some people notice sharper mental clarity after the initial adjustment period. If you’re eating under 50 grams of carbs daily and keeping fat high, most people reach measurable ketosis within 2 to 4 days. Physical activity speeds this up by burning through glycogen stores faster, encouraging your liver to ramp up ketone production.