Side effects of the keto diet
Is a ketogenic or keto diet harmful? Suitability depends on the person. Keto-adaptation changes fuel use, but sporting performance benefits are not guaranteed. Headaches, constipation, fatigue and cramps can occur in the early stages; palpitations or significant symptoms should not simply be dismissed as normal adaptation. Some symptoms settle, but persistent or worsening problems need review.
Fluid and electrolyte changes can contribute. Needs vary with body size, training, sweating and conditions. The original suggestion of 2–4 litres of water daily with extra salt is not a universal prescription and can be unsuitable in some medical conditions. Avoid both dehydration and excessive fluid or salt intake.
“Keto flu”
“Keto flu” is a nickname for symptoms reported during a dietary transition, not an infectious illness. Changes in fluid balance, food intake and fuel availability may contribute.
Reported symptoms include fatigue, headache, irritability, poor concentration, dizziness, nausea, low motivation and cravings. A glass of salted water is not a proven universal remedy, and a teaspoon of salt can be excessive.
Do not automatically respond by increasing fat or waiting indefinitely. Review energy intake, hydration and whether the approach is appropriate. Persistent or severe symptoms warrant clinical advice.
A gradual transition over one or two weeks may be more manageable for some people, but it does not remove contraindications or guarantee safety.
Bad breath
Acetone, one of the ketone bodies, can contribute to a distinctive breath odour. It does not prove the diet is well planned. Bad breath may settle after several weeks. If it persists, review oral health and the diet. The original example of moving from 20–30 g/day to 50–60 g/day of carbohydrates illustrates changing restriction, not a universal treatment. Fruity breath with illness or symptoms of ketoacidosis needs urgent assessment, especially in diabetes.
Physical performance and the keto diet
Performance can fall during the initial weeks of carbohydrate restriction. Adaptations in fat use take time, but studies lasting 1–2 weeks are not the only evidence available. Even after adaptation, increased fat oxidation does not establish improved performance, particularly at higher intensities.
Appropriate hydration is important, but it cannot compensate for every effect of low carbohydrate availability.
Muscle mass and strength
Very brief strength efforts rely heavily on phosphocreatine, but repeated sets also use glycolytic energy. It is too strong to say that strength development is always unaffected by keto.
For hypertrophy, adequate energy, protein and effective training matter. Carbohydrate availability can support training volume. Comparisons do not justify claiming that high-carbohydrate diets always build more muscle or that keto independently causes greater fat loss at equal calories.
Keto diet contraindications and precautions
Ketoacidosis
Ketoacidosis is a dangerous accumulation of ketones with blood acidity, distinct from ordinary nutritional ketosis. It is a medical emergency, particularly relevant to diabetes and some medicines, including SGLT2 inhibitors.
Type 1 diabetes
Insufficient insulin can allow uncontrolled ketone production and diabetic ketoacidosis. Do not start a ketogenic diet or alter insulin doses independently. Insulin remains essential, and any dietary change needs specialist supervision.
Type 2 diabetes
Discuss carbohydrate restriction with your diabetes team before starting. Medicines may need adjustment, and SGLT2 inhibitors can increase ketoacidosis risk even without very high blood glucose.
Breastfeeding
Lactation increases nutritional demands. The original reference to around 30 g/day of carbohydrate in milk does not establish a safe keto intake. A target of 50 g/day or adding 2–3 pieces of fruit is not a validated safety rule. Restrictive ketogenic diets during breastfeeding require medical advice because lactation ketoacidosis has been reported.
Liver problems
Some dietary approaches may help selected liver conditions, but this does not make keto suitable for all liver disease. Seek medical advice before starting.
Gout
Uric acid may rise during early ketosis, potentially triggering gout in susceptible people. Experimental findings involving beta-hydroxybutyrate do not prove that a ketogenic diet prevents gout attacks. Discuss the approach if you have gout or hyperuricaemia.
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These are examples, not a complete contraindication list. Keto is not suitable for everyone. Seek advice before starting if you have a medical condition, take medication, are pregnant or breastfeeding, or have a history of disordered eating.
The following recipes may fit some lower-carbohydrate plans, depending on quantities and the complete day’s intake:
Griddled salmon with steamed cauliflower, broccoli and carrots
Ingredients
- Salmon 120 g
- Broccoli 80 g
- Cauliflower 80 g
- Carrot 60 g
- Table salt 1 g
- Olive oil 5 g
- Black pepper 1 g
Method
- Clean and chop the cauliflower, broccoli and carrot.
- Steam in a steamer or Lékué container until tender.
- Meanwhile, griddle the salmon until cooked through.
- Serve with olive oil, salt and black pepper.
Figures per serving
Calories: 293
Protein: 38% | Carbohydrates: 22% | Fat: 40%
Pan-fried pork loin with apple and onion
Ingredients
- Pork loin 100 g
- Apple 80 g
- Table salt 1 g
- Black pepper 1 g
- Olive oil 7 g
- Red onion 50 g
- Dried rosemary 1 g
Method
- Wash and cut the apple into wedges and the onions into slices.
- Cook the onion on a griddle or in a frying pan with oil.
- When it begins to brown, add the apple wedges.
- Season the pork loin and cook in another pan over high heat, ensuring it is cooked safely.
- Once everything is ready, plate and serve.
Figures per serving
Calories: 324
Protein: 26% | Carbohydrates: 19% | Fat: 56%
Salmorejo with Serrano ham and hard-boiled egg
Ingredients
- Ready-made salmorejo 250 g
- Diced Serrano ham 60 g
- Hard-boiled egg 60 g
Method
- Serve the chilled salmorejo in a glass or bowl.
- Add the diced Serrano ham.
- Chop the hard-boiled egg and add it. Enjoy! :)
- TIP: For crisp ham, microwave on kitchen paper for around 1 minute, checking frequently.
Figures per serving
Calories: 426
Protein: 28% | Carbohydrates: 17% | Fat: 54%
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For a personalised nutrition plan, explore our subscriptions at INDYA – Sports Nutritionists.
Further reading
Beta-hydroxybutyrate and urate crystal-induced gout in experimental research
Effects of a ketogenic diet on strength, power and hormonal profiles in resistance-trained men
