Carb intake

How many carbs depends on what else you are eating

Carbohydrate is the macro with the least fixed requirement, which is exactly why it works best as the remainder. Protein is set from your bodyweight because it protects tissue. Fat has a floor because it carries vitamins and essential fatty acids. Whatever energy is left over is carbohydrate — and that is not a demotion, it is the flexibility. The macro calculator does all three at once.

The 130 g minimum, and what it actually is

The adult reference intake for carbohydrate is 130 grams a day. It is worth knowing precisely what that number means, because it is routinely misused in both directions. It is an estimate of the glucose the brain uses, set as a requirement figure. It is not a safety threshold, and eating below it is not dangerous — the body makes glucose from other sources when it has to, which is the entire mechanism low-carb diets run on.

So this page flags when you go under it rather than refusing. Plenty of people eat below 130 g deliberately and are fine.

Low-carb and keto: 20, 50, 100 and 150

These boundaries are conventions rather than findings, and the sources quoting them do not entirely agree. Roughly: under 20 g of net carbs reliably produces ketosis for most people; under 50 g does for some; 50 to 100 g is meaningfully low-carb without ketosis; and 100 to 150 g is what most people mean casually by "cutting carbs".

Net carbs are total carbohydrate minus fibre, on the reasoning that fibre is largely not absorbed. It is a useful working figure and a slightly fuzzy one — enter the fibre you actually eat above and the page will work it out.

Carbs for training: 3 to 10 grams per kilogram

These are the only carbohydrate numbers with properly derived evidence behind them, and they are nothing like the percentages. Sports nutrition guidance puts typical needs between 3 and 10 g per kilogram a day, going up to 12 for extreme prolonged activity, with endurance athletes commonly in the 6 to 10 range. Those figures are shown above against your weight — a 75 kg person training two hours a day lands somewhere around 450 to 750 g, which is far more than any percentage-of-calories approach would produce.

If you are training that much and cutting carbohydrate hard at the same time, that conflict is the thing to resolve first.

Fibre and sugar matter more than the total

Two people eating 250 g of carbohydrate a day can be eating entirely different diets. The targets worth holding are 14 g of fibre per 1,000 calories — never below about 25 g, and UK guidance asks for 30 — and free sugars under 10% of calories, ideally under 5%. Those two numbers say more about the quality of a diet than the carbohydrate total ever will.

Where to be careful

If you take insulin or a sulfonylurea, cutting carbohydrate sharply can cause hypoglycaemia, and dose changes have to be agreed with whoever prescribes them before you change how you eat — not after. Carb counting in type 1 diabetes is clinician-led. Pregnancy and breastfeeding need more than the adult minimum, so low-carb targets do not apply. Very low intakes also tend to be low in fibre and in several micronutrients, which takes some planning to avoid.