Ask five people what low-carb means and you get five answers. Researchers don't agree either: a 2024 review of hundreds of papers found that most trials called a diet low-carb at around 100 g of carbohydrate a day or less, while some used 40–60 g. Health services tend to use two simple bands: low-carb is under about 130 g a day, and very low-carb (the "keto" range) is about 20–50 g a day.
For comparison, European dietary guidance (EFSA) suggests that carbohydrates provide 45–60% of your energy. At 2,000 kcal a day that is roughly 225–300 g of carbohydrate. So even "low-carb" eating is a big step down from the usual advice, and keto is a very big one.
Tap the portions you might eat in a day. The numbers are typical values for the portion shown; real products differ, so check labels. Then set your daily energy and see which band you are in.
Low-carb diets can help some people lose weight over the first months, but studies mostly stop at around six months. A 2021 BMJ systematic review in type 2 diabetes found that benefits seen at six months had shrunk by twelve months, and that LDL ("bad") cholesterol had worsened in some trials. In other words, the research is mixed and long-term data is thin, especially for very low-carb diets.
What does tend to matter more than the carb count itself is what replaces the carbs. Swapping sugary drinks and refined snacks for beans, vegetables and whole foods helps on almost any plan. Cutting out fibre-rich foods works against you: EFSA considers about 25 g of fibre a day adequate for adults, and very low-carb eating makes that hard to reach.
If you try a gentler low-carb approach, a small step is easier to keep than a dramatic one. Constipation and bad breath are commonly reported with very low-carb diets and are often temporary. A sensible start looks like this:
Low-carb is a range, not a switch: under about 130 g is "low", about 20–50 g is "keto", and the long-term evidence is still mixed.
This guide is information, not medical advice. If you have diabetes, kidney or liver disease or high blood pressure, are pregnant or breastfeeding, have or have had an eating disorder, or take medication (especially for diabetes or blood pressure), talk to your doctor or a dietitian before cutting carbohydrates. Medication doses can need adjusting, and one NHS hospital trust advises that people with type 1 diabetes should only change carbohydrate intake under dietitian supervision and does not recommend very low-carb diets.