How it works
Keto cuts carbohydrate low enough, typically under about 50 grams a day and often 20 to 30 grams, that the liver starts making ketone bodies from fat as an alternative fuel. Most of your calories come from fat, with protein moderate to high. Older clinical versions kept protein low, but lifters commonly eat 1.4 to 2.0 g/kg, and most people stay in ketosis at that level.
Expect an adaptation period in the first one to three weeks. Glycogen stores drop and take water with them (hence the fast early drop on the scale), and some people get fatigue, headaches or weaker sessions, the so-called keto flu. Extra sodium, potassium and magnesium are commonly recommended during this phase. Over time your body gets better at burning fat during exercise, but hard efforts still run largely on carbohydrate.
Foods to emphasize
Foods to limit
Sample day
| Meal | What it could look like |
|---|---|
| Breakfast | Three-egg omelette with spinach, mushrooms and cheese, cooked in olive oil |
| Lunch | Large salad with salmon, avocado, olives, pumpkin seeds and olive oil dressing |
| Snack | Plain full-fat Greek yogurt with a few raspberries and walnuts |
| Dinner | Chicken thighs, roasted cauliflower and broccoli with butter or olive oil |
| Evening | Celery with almond butter, broth with added salt |
What the evidence says
With protein and calories matched, controlled studies generally find that ketogenic and higher-carb diets produce similar fat loss. One tightly controlled metabolic ward study even found slightly more fat loss with fat restriction than with carb restriction over a short period. Some trials in resistance-trained people report similar strength gains but smaller lean mass gains on keto, partly because measured lean mass includes glycogen and water. In an elite race-walking study, a low-carb, high-fat diet raised fat oxidation but hurt exercise economy and wiped out the performance gains seen in the carb-fed groups. Keto looks like a valid adherence tool for some people, not a metabolic advantage.