Nutrition
Low carb & keto
What to eat on keto, what ketosis does and does not do for fat loss, the effect on training performance, and who the diet genuinely suits.
A ketogenic diet restricts carbohydrate far enough — usually below 20 to 50 grams a day — that the body shifts to producing ketones from fat as an alternative fuel. That metabolic state is real and measurable.
Whether it makes you lose more fat than any other approach is a separate question, and the answer is no.
What you actually eat
The food list is more restrictive than most diets and simpler than most people expect.
Freely: meat, poultry, fish and seafood, eggs, hard cheeses, butter, olive and avocado oil, nuts and seeds, avocado, and low-carbohydrate vegetables — leafy greens, broccoli, cauliflower, courgette, asparagus, peppers, mushrooms.
In small amounts: berries, higher-carb nuts like cashews, tomatoes, onions, full-fat dairy.
Not at all: bread, pasta, rice, potatoes, oats and other grains; most fruit; legumes and beans; sugar in any form; and the majority of packaged food.
That last exclusion is doing a lot of the work. A diet that removes bread, pasta, sugar and most convenience food tends to reduce calories whether or not ketosis is involved.
Ketosis is not a fat-loss mechanism
The strongest evidence here comes from metabolic ward studies, where intake is controlled by researchers rather than self-reported.
Under those conditions, matching calories and protein, ketogenic diets do not produce more fat loss than higher-carbohydrate ones. The energy balance determines the outcome; the macronutrient arrangement does not override it.
The dramatic first week is glycogen. Each gram of stored carbohydrate holds roughly three grams of water, so depleting it drops two to three kilograms within days. It is genuine weight and it is not fat, and it returns just as quickly when carbohydrate does.
The training cost is real
This is the honest drawback for anyone who lifts.
Glycogen is the primary fuel for high-intensity efforts — heavy sets, repeated sprints, anything above a moderate pace. Running it chronically low tends to cost reps and make hard sessions feel harder, particularly in the first several weeks.
Some people adapt substantially. Low-intensity endurance work is affected far less, and there are endurance athletes who perform well on very low carbohydrate. But if your training is built around progressive overload in the five to twelve rep range, keto is working against the fuel system that supports it.
Managing the transition
The “keto flu” of the first week — headache, fatigue, irritability, cramps — is mostly a sodium and water problem. When insulin falls, the kidneys excrete sodium, and the symptoms follow.
Adding salt deliberately, and drinking to thirst rather than forcing fluid, reduces it considerably. See the hydration guide for the detail. It is a transition effect, not evidence the diet is working.
Who it genuinely suits
People who find carbohydrate-rich foods hard to stop eating, and who feel noticeably more satisfied on protein and fat. People with certain medical indications, where ketogenic diets have established therapeutic use. And people who simply prefer the food.
Those are good reasons. “It burns more fat” is not one, and anyone who wants the same result with more flexibility can get it from a normal calorie deficit with adequate protein.
Common questions
What foods can you eat on keto?
Meat, fish, eggs, hard cheeses, butter and oils, nuts and seeds, avocado, and low-carb vegetables such as leafy greens, broccoli, cauliflower, courgette and peppers. Excluded are grains, most fruit, legumes, potatoes, sugar and anything made from flour — which is what keeps carbohydrate under roughly 20 to 50 grams a day.
Does keto burn more fat than other diets?
Not once calories and protein are matched. Metabolic ward studies — where intake is controlled rather than reported — find no meaningful fat-loss advantage for ketogenic diets. The rapid early weight loss is glycogen and its bound water, typically two or three kilograms in the first week.
Does keto hurt gym performance?
For high-intensity work, usually yes, at least initially. Glycogen is the primary fuel for hard sets and repeated efforts, and running it low tends to cost reps. Low-intensity endurance work is much less affected, and some people adapt over several weeks.
What is the keto flu?
Headache, fatigue, irritability and cramps in the first week, caused largely by the water and sodium your kidneys excrete when insulin falls. Adding sodium deliberately — salt on food, or broth — reduces it substantially. It is a transition symptom, not a sign the diet is working.
How many carbs can you eat on keto?
Usually 20 to 50 grams a day to maintain ketosis, with the threshold varying between individuals and with activity level. More active people can often eat toward the higher end and stay in ketosis because they use glucose faster.
Is keto safe long term?
For most healthy adults, several years of use has not shown clear harm, though long-term data is limited compared with more conventional diets. Cholesterol responses vary considerably between individuals, so periodic blood work is sensible. Anyone with liver, pancreatic or gallbladder conditions should get medical advice first.
Keep reading
More in diets & patterns.