In short: the ketogenic diet drastically reduces carbohydrates and increases fat to induce ketosis, a state in which the body uses fat as its primary energy source. It can promote weight loss and better blood sugar control in the short to medium term, but it carries risks (nutritional deficiencies, increased LDL cholesterol, possible kidney strain) that make it important to follow it for limited periods and under medical supervision, with adequate intake of minerals like potassium, magnesium, and calcium.
What is the ketogenic diet?
The ketogenic diet, commonly known as the keto diet, is a way of eating aimed at reducing carbohydrate intake and increasing fat intake, putting the body into a metabolic state known as ketosis. In recent years, this diet has gained increasing popularity.
There are several approaches to the ketogenic diet, each varying in caloric content and macronutrient ratios, including carbohydrates, fats, and proteins.
The primary goal of this diet is to induce ketosis, a process through which the body burns fat for energy. Ketosis is believed to promote weight loss and bring health benefits, such as lowering blood sugar and improving cholesterol levels.
What is ketosis?
Ketosis is a state in which the body uses fat as its primary energy source, producing molecules called ketones.
Normally, the body relies on carbohydrates for energy, with insulin responsible for storing blood sugar (glucose) for this purpose. When carbohydrate intake is reduced, insulin levels drop, triggering a series of metabolic changes.
Initially, glucose is stored as glycogen in the muscles and liver, available for use when needed. After a few days of low carbohydrate intake, these stores are depleted, and the body begins using stored fat as its primary energy source. Fat breakdown produces free fatty acids, which are converted in the liver into ketones that the body can then use as fuel.
Intense physical activity can accelerate the depletion of glycogen stores, causing the body to enter ketosis more quickly.
How does the ketogenic diet work?
By reducing carbohydrate intake in the diet, insulin production also decreases, which can have significant health benefits, especially for people who consume excessive amounts of high-glycemic-index carbohydrates.
Despite weight loss, low blood sugar, and high blood ketone levels, some studies have raised concerns about the long-term effects of the ketogenic diet. A study conducted on rats showed that sustained adoption of a keto diet for 60 days caused side effects such as metabolic acidosis, anemia, and reduced levels of antioxidant enzymes in the blood.
These results indicate that, although the ketogenic diet may offer initial benefits, it's essential to carefully weigh the potential risks and monitor long-term health while following this eating regimen.
Classic ketogenic diet
The classic ketogenic diet (known as cKD) has been used since 1921 to treat epilepsy in children. This type of diet is called "classic" because it was the first to be developed and used. The cKD provides a normal caloric intake but is high in fat and low in carbohydrates, and is used worldwide to treat drug-resistant epilepsy, meaning when conventional medications don't work.
The cKD has demonstrated anticonvulsant effects, helping to prevent or reduce seizures by shifting the primary calorie source from carbohydrates to fats. In practice, the diet consists mainly of fats, with a limited amount of protein and carbohydrates. A common ratio is 4 parts fat to 1 part protein and carbohydrates combined.
Variants of the ketogenic diet
- High-fat and high-protein ketogenic diet (such as the Atkins diet)
- High-fat and normal-to-low-protein ketogenic diet (such as the modified Atkins diet used to treat drug-resistant epilepsy)
- Low-fat and normal-protein ketogenic diet (such as VLCKD, used to treat obesity)
Ketogenic diet: the extremely low-calorie variant
A very common variant of the ketogenic diet is the very-low-calorie ketogenic diet (VLCKD), suggested as a dietary strategy for managing obesity.
This type of diet is characterized by a low carbohydrate intake, under 50 grams per day, and a moderate amount of protein, usually around 1-1.5 grams per kilogram of ideal body weight. Fat intake is around 15-30 grams per day. It's important to note that this diet provides a very low caloric intake, usually between 500 and 800 calories per day, aiming to promote ketosis and weight loss through calorie restriction and carbohydrate elimination.
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Contraindications of the keto diet
In recent years, the ketogenic diet has gained considerable popularity, especially among those looking to lose weight and reduce insulin resistance, in both type 1 and type 2 diabetes.
However, concerns arise regarding long-term effectiveness for weight loss and potential adverse effects on kidney function and blood cholesterol levels, due to increased protein and fat intake.
Particularly in diabetes, increased intake of animal protein, but not plant protein, has been associated with insulin resistance and increased health risk. Foods high in animal protein also contain other nutrients, such as saturated fats, heme iron, and nitrites, which could contribute to these findings. High-protein diets are also linked to compounds produced by gut microbiota fermentation of proteins, which may include pro-inflammatory metabolites.
Adverse effects
In the short term, it's common to experience some symptoms during the transition to a ketogenic diet: easy fatigue during exercise, reduced mental energy, increased hunger, sleep disturbances, muscle cramps, constipation, bad breath, nausea, and stomach pain. Most of these symptoms tend to subside after the first few days of adaptation, and adequate fluid and electrolyte intake can help counter some of them.
Long-term adverse effects include:
- Nutritional deficiencies: keto diets are highly restrictive and can lead to nutritional deficiencies with inadequate intake of essential vitamins, minerals, and phytochemicals.
- Digestive problems: high-fat, low-fiber diets can cause digestive issues, such as constipation, diarrhea, and bloating.
- Kidney stones: a diet high in fat and low in carbohydrates can increase the risk of developing kidney stones.
- Heart disease: it can increase the risk of heart disease due to its high content of saturated fats and lack of fiber.
- Muscle loss: rapid weight loss on a ketogenic diet can lead to muscle loss, negatively impacting athletic performance.
- Cognitive decline: the effects of low-carbohydrate diets on brain metabolism could potentially lead to cognitive decline.
It's important to note that, while the ketogenic diet may offer benefits in improving fat utilization capacity, especially in endurance sports, some authors suggest that high-level athletic performance may not be optimal without adequate carbohydrate intake. This shows how important it is to carefully assess individual needs and find a balance between adapting to ketosis and the specific demands of physical activity.
What does the most recent research say (2025-2026)?
According to PubMed, a narrative review published in 2026 in Nutrients confirms that the ketogenic diet can improve glycemic control and insulin sensitivity in people with obesity and type 2 diabetes, partly by reducing insulin requirements and supporting pancreatic beta-cell function; the same review, however, notes that combining the diet with certain antidiabetic medications (particularly SGLT-2 inhibitors) requires medical supervision due to the risk of euglycemic diabetic ketoacidosis, and observes significant effects of the diet on the gut microbiota (DOI: 10.3390/nu18122004).
A second review from 2025, published in Cell Biochemistry and Biophysics, reaches a balanced conclusion: the ketogenic diet produces short-term benefits for weight, blood sugar, and lipid profile, but its long-term safety and sustainability (beyond 12 months) remain to be evaluated with caution, given cardiovascular risks, possible kidney strain, micronutrient deficiencies, and changes to the gut microbiota. The authors describe it as a useful short-term tool for selected individuals under clinical supervision, rather than a universal solution (DOI: 10.1007/s12013-025-01878-0).
When is the ketogenic diet not recommended?
According to recent studies, women should cautiously avoid the ketogenic diet during pregnancy and breastfeeding, as a negative effect on cognition has been observed in rodents exposed to ketosis from early life through young adulthood. No adverse effects on neurological development have been found, however, in children who have used a ketogenic diet to treat epilepsy.
Groups of people for whom a ketogenic diet may not be advisable include:
1. People with severe liver or kidney disease: the ketogenic diet can affect lipid and carbohydrate metabolism and may not be safe for those with liver or kidney problems.
2. Pregnant or breastfeeding women: the body has specific nutritional needs that may not be adequately met by a ketogenic diet.
3. People with eating disorders: calorie restriction and focus on specific food groups could worsen issues for those suffering from disorders such as anorexia or bulimia.
4. Individuals with certain medical conditions: some conditions, such as type 1 diabetes, may require more careful dietary adjustment, and a ketogenic diet may not be suitable for everyone.
Ketogenic diet pros and cons
The ketogenic diet involves a strict limitation of carbohydrates, while allowing a generous intake of fats, including saturated fats. It has generated considerable interest, with many supporters and just as many detractors.
While it can lead to rapid and significant weight loss and improvements in biomarkers, such as reducing glycated hemoglobin in patients with type 2 diabetes, it can also cause a significant increase in "bad" LDL cholesterol, a fact that makes many doctors hesitant to recommend it.
Two studies conducted in humans have highlighted potential harmful effects of ketone bodies. In a population-based cohort study of individuals aged 54 ± 12 years, a positive correlation was found between circulating ketone bodies and all-cause mortality. The increase in mortality was also linked to an increased liver fat index, an indicator of non-alcoholic fatty liver disease, with this relationship partly mediated by circulating ketone bodies. Another study reported a dose-response relationship between increased ketone body concentrations and a 50% increase in all-cause mortality among white and black Americans.
Although the ketogenic diet has traditionally been considered beneficial for weight and glucose control, with few side effects and good adherence and tolerance even in older adults, concerns remain about its health consequences. The main issue concerns the variation among ketogenic diet versions and the differing effects of their essential components.
How long can you follow the ketogenic diet?
According to most authors, the ketogenic approach should be understood as a time-limited eating regimen. Long-term adherence to a ketogenic diet can be challenging.
Although this diet has shown positive results in inducing rapid and sustained weight loss in obese individuals for up to two years, it's essential to fully understand its clinical impact, safety, tolerability, effectiveness, treatment duration, and long-term prognosis after discontinuation. The duration of the ketogenic diet can vary considerably, from a minimum of 2-3 weeks up to 6-12 months, according to the National Library of Medicine.
During this period, it's crucial to carefully monitor kidney function: given the changes in water metabolism and diuresis associated with reduced glycogen levels, it's advisable to increase fluid intake to maintain water and electrolyte balance. General guidelines recommend drinking at least 8 glasses of water per day, though individual needs may vary based on body weight, physical activity, and climate.
Many questions remain unanswered regarding the long-term effects of the ketogenic diet, especially after discontinuation: only a better understanding of these aspects will allow for more precise and safer guidelines for adopting and maintaining the diet over the long term.
How to reintroduce carbohydrates without gaining weight
When deciding to reintroduce carbohydrates after losing weight on a ketogenic diet, it's advisable to consult a dietitian for personalized guidance. Reintroduction should be gradual and well-planned to avoid sudden blood sugar swings and other side effects.
1. Start slowly: add small amounts of complex carbohydrates, such as starchy vegetables (sweet potatoes, squash, carrots) and whole grains (brown rice, quinoa, spelt). Start with one serving per day and carefully monitor your response.
2. Choose the right carbohydrates: favor foods made from non-genetically-modified raw materials, such as pasta, bread, and baked goods made with ancient durum wheat varieties, which tend to have a less drastic impact on blood sugar levels than refined and ultra-processed products.
3. Monitor your body's response: observe how it reacts to the introduction of carbohydrates, paying attention to symptoms of discomfort, energy, weight, and fat mass, and adjust the amount of carbohydrates accordingly.
Should you take supplements during a ketogenic diet?
During a ketogenic diet, it's essential to ensure adequate intake of all necessary micronutrients. In particular, it's advisable to increase intake of alkalizing minerals such as potassium, magnesium, and calcium, through fortified foods or supplements, such as our Day Up. 👇
This helps balance the potentially higher ketone production, which can have an acidifying effect on the body. Ensuring sufficient intake of these minerals is important to maintain balance and health during the ketogenic diet.
Some nutrients, readily available in grains such as wheat, may be limited during the ketogenic diet, causing side effects such as headaches, brain fog, fatigue, irritability, nausea, difficulty sleeping, and constipation, commonly known as "keto flu." This is a set of symptoms related to reduced blood sugar levels and the body's adaptation to producing ketones as a primary energy source; they usually disappear within a few days or weeks as the body adjusts to the new diet.
Ketone levels considered safe
To maintain safe ketosis levels, it's advisable to keep ketone levels in the range of 1.5-3.0 mmol/L, as recommended by researchers Stephen Phinney and Jeff Volek. These levels can be monitored through urine and blood tests, although urine measurement may not be highly precise and may not necessarily reflect blood ketosis levels, which is considered a more accurate method.
What should you eat on the keto diet?
"It's very important to know which foods you'll be eating before you start and how to incorporate more fat into your diet," says Kristen Mancinelli, RD, author of The Ketogenic Diet: A Scientifically Proven Approach to Fast, Healthy Weight Loss, based in New York City.
Protein
Ketogenic diets are not high in protein (they focus on fat), so it should be consumed in moderation.
Freely: grass-fed beef, fish (especially fatty fish like salmon), dark meat chicken.
Occasionally: bacon, lower-fat proteins like skinless chicken breast and shrimp (add a sauce for some fat instead of eating them plain).
Never: processed meats with added sugar (check the label), meat marinated in sugary sauces, fish or chicken nuggets — often high in sodium, which can raise blood pressure.
Oils and fats
Freely: extra virgin olive oil, avocado, avocado oil.
Occasionally: sunflower oil, safflower oil, corn oil, butter, whole milk, coconut oil.
Never: margarine, trans fats.
Fruits and vegetables
Freely: avocado, leafy greens such as spinach and arugula, celery, asparagus.
Occasionally: leeks, spaghetti squash, eggplant, raspberries, lemon, tomatoes.
Never: potatoes, corn, raisins.
Nuts and seeds
Freely: walnuts, almonds, flax seeds, chia seeds.
Occasionally: cashews and pistachios.
Never: sweetened nut butters, sweetened seeds, chocolate-covered nuts.
Dairy
Freely: feta, parmesan.
Occasionally: whole ricotta, whole Greek yogurt.
Never: milk, sweetened low-fat yogurt, ice cream.
Sweeteners
Occasionally: xylitol, stevia, erythritol, artificial sweeteners.
Never: agave, honey, maple syrup, white and brown sugar.
Condiments and sauces
Freely: guacamole, mayonnaise (with no added sugar).
Occasionally: raw garlic, tomato sauce with no added sugar, balsamic vinegar.
Never: barbecue sauce, ketchup, honey mustard.
Beverages
Freely: water, unsweetened almond milk, bone broth, plain tea.
Occasionally: black coffee, unsweetened sparkling water, zero-calorie drinks.
Never: fruit juice, lemonade.
Herbs and spices
Freely: pepper, thyme, oregano, paprika.
Occasionally: ground ginger, garlic powder, onion powder.
Never: no herb or spice is off-limits; generally they're fine in small quantities to flavor food.
Ketogenic diet for vegetarians
Meat is a staple of the ketogenic diet, but that doesn't mean the diet is off-limits for vegetarians. Many have found ways to adapt the menu and food list to a meat-free lifestyle. Here's what a typical day on the keto diet looks like for vegetarians:
- Breakfast with protein powder or protein pancakes made from eggs and protein powder
- Snack: sliced cucumber with sheep's cheese or ricotta with sunflower seeds
- Lunch: a large salad with avocado, vegetables, seeds, and nuts, or an egg omelet with herbed goat cheese and pesto
- Dinner: zucchini noodles (zoodles) with pesto and tofu; sautéed vegetables with tempeh; or spinach salad with cashew-crusted tofu, grilled zucchini, cubed feta, and high-polyphenol extra virgin olive oil
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Frequently asked questions
Q: How many calories do you eat on the ketogenic diet?
A: It depends on the variant: standard versions maintain normal calorie intake, while VLCKD (very low calorie) provides only 500-800 kcal per day. In all cases, carbohydrates remain under 50 g/day.
Q: How long does the ketogenic diet last?
A: It should be understood as a time-limited regimen: from a minimum of 2-3 weeks up to 6-12 months according to the National Library of Medicine, not as a permanent way of eating.
Q: What are the main risks of the ketogenic diet?
A: Nutritional deficiencies, increased LDL cholesterol, possible kidney strain, kidney stones, muscle loss, and, according to a 2025 review, long-term cardiovascular risks that require clinical supervision.
Q: Does the ketogenic diet cause faster weight loss than other diets?
A: In the short term, yes, often quite rapidly, but long-term sustainability is limited: adherence tends to decline, and the most recent literature (2025-2026) describes it as a useful short-term tool for selected individuals, not a universal solution.
Q: Who should not follow the ketogenic diet?
A: Pregnant or breastfeeding women, people with severe liver or kidney disease, those with eating disorders, and people with conditions such as type 1 diabetes that require more careful dietary management.
Q: Are supplements needed during the ketogenic diet?
A: It's advisable to increase intake of alkalizing minerals such as potassium, magnesium, and calcium, to balance ketone production and reduce the risk of nutritional deficiencies typical of a highly restrictive diet.
Sources
Nutrients 2026;18(12):2004. doi: 10.3390/nu18122004 — Ketogenic Diet in Obesity and Diabetes: A Narrative Review (An Y. et al., PubMed/PMC13304935)
Cell Biochem Biophys 2025;84(1):75-98. doi: 10.1007/s12013-025-01878-0 — The Ketogenic Diet in Obesity Management: Friend or Foe? (Alum E.U. et al., PubMed)
Front Nutr. 2024;11:1322509. doi: 10.3389/fnut.2024.1322509 — Ketogenic diet and behavior: insights from experimental studies
Cureus. 2023 Mar;15(3):e36720. doi: 10.7759/cureus.36720 — Metabolic Effects of Ketogenic Diets and Their Utilization in Obesity Management: A Systematic Review
J Nutr Metab. 2020;2020:3642035. doi: 10.1155/2020/3642035 — Long-Term Ketogenic Diet Induces Metabolic Acidosis, Anemia, and Oxidative Stress in Healthy Wistar Rats
Nutrients. 2023 Dec;15(23):4998. doi: 10.3390/nu15234998 — The Ketogenic Diet in the Prevention of Migraines in the Elderly
Review Atherosclerosis. 2020 Jan;292:119-126. doi: 10.1016/j.atherosclerosis.2019.11.021 — The ketogenic diet: Pros and cons
