Ketogenic Diet: A Review ★★★★☆

By R.Davies, PhD・Diet Atlas
Published on May 05, 2026

The ‘ketogenic’ diet is a high-fat, very low-carbohydrate, moderate-protein diet. The classic ketogenic diet consists of about 70-90% of calories from fat, 6-10% from protein, and only 2-10% from carbohydrates, limiting it to 20-50 grams a day. The very low-carbohydrate intake forces you into a ‘metabolic state’ called ketosis. This is where the liver converts fat into ketones that are used as an alternative source of energy.

The diet was originally developed in the 1920s as a treatment for epilepsy. Since then, it has gained mainstream popularity for its weight loss and health benefits. After about 2–4 days of very low-carbohydrate intake, your carbohydrate stores become depleted, and the body increases the amount of fat it uses for fuel. The liver then starts to produce ketones, which the brain and other tissues use as fuel when carbohydrates aren’t around to use.

The main foods on the ketogenic diet are: fatty meats, fish, eggs, full-fat dairy products, nuts, seeds, oils (particularly coconut and olive oil), butter, avocados, and low-carbohydrate vegetables (e.g., leafy greens and cruciferous vegetables). 

Grains, most fruits, starchy vegetables (e.g., potatoes and corn), legumes, sugar, and most processed foods are banned (or severely restricted). Eating even small amounts of carbohydrates can take you out of ketosis, so you have to pay special attention to the amount of carbs you’re eating.

Pros

The ketogenic diet leads to quick weight loss and metabolic health benefits, particularly for people who’re already obese and/or have type 2 diabetes. The ‘initial’ weight loss on the keto diet (i.e., first 6 to 12 months) is a bit quicker than most other diets. However, after a year, there doesn’t appear to be any weight loss benefits.

The ‘metabolic health’ benefits are also well-documented. People who follow the diet have reported improved blood sugar and blood lipid profiles. People with type 2 diabetes experience substantial improvements in health, sometimes allowing their medication to be reduced (under close medical supervision). The diet also leads to notable increases in the good “HDL” cholesterol and decreases in blood triglycerides (important markers of cardiovascular health).

Beyond the cardiometabolic health benefits, the diet remains an effective treatment for drug-resistant epilepsy. There’s strong evidence suggesting it reduces seizures in both children and adults. Emerging research suggests there are some potential benefits for the gut microbiome, as well as some neurological conditions.

Cons

The diet's very low carbohydrate intake can limit intake of dietary fibre, several vitamins and minerals (e.g., B vitamins, vitamin C, magnesium, and potassium), and other nutrients found in plants and whole grains. Without careful planning (and probably supplementation), this could lead to nutrient deficiencies and increase disease risk.

A common concern is the elevated low-density lipoprotein (‘LDL’) cholesterol that is reported in a lot of people who follow the diet. This raises questions about long-term cardiovascular health risk despite improvements in other blood lipids. 

There are also well-known side effects, sometimes called the ‘keto flu’, which include fatigue, headaches, irritability, constipation, nausea, and muscle cramps. However, these typically stop within days or weeks of following the diet. The more serious potential complications include kidney stones, nutrient deficiencies, and gut problems.

In practice, maintaining the diet can be difficult. The diet's highly restrictive nature, high cost, limited food choices, and social barriers make the diet (relatively) difficult to follow long-term. A lot of people struggle to stay in ketosis without education and support from someone who knows what they are doing.

Bottom Line

The ketogenic diet is effective for short-term weight loss and metabolic health improvements, particularly for people who are overweight, obese, and have type 2 diabetes. However, concerns remain about its effects on cholesterol levels, nutrient content, how easy it is to follow, and long-term health risks.

Sources

Crosby L et al. Ketogenic Diets and Chronic Disease: Weighing the Benefits Against the Risks. Front Nutr. 2021 Jul 16;8:702802. PMID: 34336911

Daley SF et al. The Ketogenic Diet: Clinical Applications, Evidence-based Indications, and Implementation. [Updated 2025 Dec 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499830/

Muscogiuri G et al. Obesity Management Task Force (OMTF) of the European Association for the Study of Obesity (EASO). European Guidelines for Obesity Management in Adults with a Very Low-Calorie Ketogenic Diet: A Systematic Review and Meta-Analysis. Obes Facts. 2021;14(2):222-245. PMID: 33882506

O'Neill B, Raggi P. The ketogenic diet: Pros and cons. Atherosclerosis. 2020 Jan;292:119-126. PMID: 31805451

Patikorn C et al. Effects of ketogenic diet on health outcomes: an umbrella review of meta-analyses of randomized clinical trials. BMC Med. 2023 May 25;21(1):196. PMID: 37231411

Zhou C et al. Ketogenic Diet Benefits to Weight Loss, Glycemic Control, and Lipid Profiles in Overweight Patients with Type 2 Diabetes Mellitus: A Meta-Analysis of Randomized Controlled Trails. Int J Environ Res Public Health. 2022 Aug 22;19(16):10429. PMID: 36012064

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Published: May 05, 2026

Lead Author: R.Davies, PhD | Author Bio

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