Keto Diet: How It Works, What the Research Shows and Who Should Avoid It
The keto diet (ketogenic diet) is an eating pattern that is very low in carbohydrates and high in fat. It is most often chosen by people who want to lose weight.
In this article you will learn how the keto diet works, what the research actually shows, how to avoid the most common difficulties at the start, and who this diet is not suitable for.
In brief. On a keto diet, people usually eat less than 50 g of carbohydrates per day.1 In the first few months weight often falls faster, but after a year the difference compared with other diets is small.2 Talk to your doctor before you start if you have a chronic condition or take medicines.
How does the keto diet work?
Normally, the body uses glucose from carbohydrates for energy. When carbohydrates are greatly reduced, the liver begins to produce ketones from fat. This state is called ketosis.1
In a typical keto diet, about 70–80% of energy comes from fat, about 10–20% from protein and only about 5–10% from carbohydrates.1
Example. One banana, a bowl of rice or a few slices of bread can already make up a large share of the whole day's keto allowance. That is why on this diet you have to count your carbohydrate sources.
What can you eat?
| Eaten often | Limited | Almost never eaten |
|---|---|---|
| Meat, fish, eggs, cheese, avocados, nuts, oils, non-starchy vegetables | Berries, milk, yoghurt | Bread, pasta, rice, potatoes, sweets, most fruit, sugary drinks |
It is important not only to limit carbohydrates but also to choose good-quality fats: fish, nuts, olive oil and avocados.
What does the research show about weight loss?
In a review of 13 studies, people who followed a very-low-carbohydrate keto diet lost on average about 0.9 kg more after a year or longer than those who followed a low-fat diet.2
What this means for you. The keto diet may help, but it is not a miracle. In the long run, what matters most is which way of eating you can stick to consistently.
In the first weeks, weight falls quickly because the body loses water along with its carbohydrate stores.1 This is not fat loss.
The keto flu and how to avoid it
During the first few days, some people feel tired and may have a headache, irritability or dizziness. This is called the “keto flu”.1
- Drink enough fluids. At the start the body loses more water.
- Don't forget electrolytes. Sodium, potassium and magnesium are lost along with water.1
- Reduce carbohydrates gradually rather than all in one day.
Possible risks
- Constipation. A keto diet is often low in fibre. About 25 g of fibre per day is recommended for adults.3 Eat plenty of non-starchy vegetables.
- Cholesterol. In studies, the keto diet often increased the level of “bad” LDL cholesterol.2 If you follow a keto diet for longer, have your blood tests checked.
- Vitamin and mineral deficiencies. If you give up fruit, grains and legumes, you may run short of some nutrients.1
Do not start a keto diet without consulting a doctor if you:4
- have diabetes and take insulin or other blood sugar-lowering medicines;
- have kidney, liver or pancreatic disease;
- are pregnant or breastfeeding;
- have, or have had, an eating disorder.
In some severe forms of epilepsy, the keto diet is used as part of treatment, but only under medical supervision.4
Selected products for a keto diet
Commercial information. These are products available in our shop. This is not a ranking of effectiveness. Before buying, check the composition and instructions for use on the product page.
Keto Electrolyte Powder, Lemon Lime - 330g - Trace Minerals
Electrolyte powder, with 1000 mg of potassium and 120 mg of magnesium per serving. The potassium content is high, so if you have kidney disease or take blood pressure medicines, consult your doctor first.5
MCT Oil, Pure Liquid - 473 ml - NOW Foods
Medium-chain triglyceride oil from coconut and palm kernel oil: 50% caprylic (C8) and 30% capric (C10) acid. One tablespoon (15 ml) contains 14 g of fat and 130 kcal. Start with a smaller amount, as taking a lot at once may cause digestive discomfort.6
Inulin Prebiotic Pure Powder - 227g - NOW Foods
Inulin powder from blue agave, with 4 g of fibre per teaspoon. Convenient to stir into yoghurt or a drink. Increase your fibre intake gradually.7
40% Low Carb High Protein Bar, Chocolate - 24 x 50g - Weider
Protein bar, with 20 g of protein, 9 g of carbohydrates and 1.2 g of sugar per 50 g bar. Some of the carbohydrates come from the sweetener maltitol, which in larger amounts may have a laxative effect.8
Frequently asked questions
How long can you follow a keto diet?
There is little data on effects beyond a few years.1 If you plan to follow a keto diet for a long time, have your health checked regularly.
Can you exercise on a keto diet?
Yes, but in the first weeks intense workouts may feel harder. We write more about nutrition for people who exercise in the article Supplements for people who exercise.
Do you need supplements on a keto diet?
Not always. First, put together a varied menu with plenty of vegetables. Electrolytes and fibre are most often useful at the start or if your food does not provide enough of them.
Scientific sources
- Harvard T.H. Chan School of Public Health, The Nutrition Source. Diet Review: Ketogenic Diet for Weight Loss. hsph.harvard.edu
- Bueno NB, de Melo ISV, de Oliveira SL, da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr. 2013;110(7):1178–1187. doi:10.1017/S0007114513000548
- EFSA NDA Panel. Scientific opinion on dietary reference values for carbohydrates and dietary fibre. EFSA Journal. 2010;8(3):1462. doi:10.2903/j.efsa.2010.1462
- Masood W, Annamaraju P, Khan Suheb MZ, Uppaluri KR. Ketogenic Diet. StatPearls. Treasure Island (FL): StatPearls Publishing. ncbi.nlm.nih.gov
- Trace Minerals. Keto Electrolyte Powder, Lemon Lime, 330 g. Product label.
- NOW Foods. MCT Oil, Pure Liquid, 473 ml. Product label.
- NOW Foods. Inulin Prebiotic Pure Powder, 227 g. Product label.
- Weider. 40% Low Carb High Protein Bar, Chocolate, 50 g. Product label.
Disclaimer. This article is for information purposes only and does not replace a consultation with a doctor, dietitian or pharmacist. Food supplements are not intended to treat or prevent diseases and are not a substitute for a varied diet and a healthy lifestyle. Before changing your diet or taking supplements, especially during pregnancy or breastfeeding, or if you have a chronic condition or take medicines, consult a healthcare professional.
