In 1921, Dr Russell Wilder at the Mayo Clinic discovered that a carbohydrate-free diet drastically reduced seizures in children who didn’t respond to medication. Before the keto diet became a weight loss tool, it was saving the lives of neurological patients for decades. Today it’s one of the most popular and most hotly debated ways of eating in the world. Before you decide to try it, get to know the mechanisms, benefits, and real limitations!
Key facts about the keto diet:
- Ketosis is a metabolic state in which the body burns fat instead of glucose as its primary fuel
- Standard keto means around 70-75% of calories from fat, 20-25% from protein, and only 5% from carbohydrates
- Reaching ketosis typically requires 2-4 days of limiting carbohydrates to 20-50 g per day
- Keto flu – headaches and fatigue in the first week – is a temporary adaptation effect
- Not everyone should follow the keto diet – people with liver and kidney conditions need medical advice
What is ketosis?
Ketosis is a state in which the liver produces ketone bodies. Acetoacetate, beta-hydroxybutyrate, and acetone – as an alternative fuel for the brain and muscles. Under normal conditions, the body prefers glucose. When carbohydrate intake falls below a threshold (typically 20-50 grams per day), glycogen stores (glucose stored in muscles and the liver) are depleted within 1-3 days and the body switches to fat metabolism.
Ketone bodies are efficient fuel – the brain uses them readily, as they are more energetically stable than glucose. They don’t cause insulin spikes. Some people in ketosis report greater mental clarity and steady energy levels throughout the day – without the afternoon slump. Dietary ketosis differs from diabetic ketoacidosis, which is a dangerous complication of diabetes. These are two entirely different states.
What does the keto diet look like in practice?
The typical keto macronutrient breakdown is 70-75% of calories from fat, 20-25% from protein, and just 5-10% from carbohydrates – roughly 20-50 grams of carbohydrates per day. For comparison: a single wheat roll contains around 50 grams of carbohydrates, already exceeding the daily limit. Carbohydrates aren’t the enemy of longevity – but limiting them in ketosis has a specific metabolic purpose.
In practice, this means giving up bread, pasta, rice, most fruit, and sweet products. The plate is dominated by meat, fish, eggs, full-fat dairy, nuts, avocado, and non-starchy vegetables. A typical keto day might look like: scrambled eggs with bacon and avocado, chicken salad with olive oil, salmon with broccoli and butter.
What to eat on the keto diet?
Which fats to choose on keto?
The best fats for keto are extra virgin olive oil, avocado, macadamia nuts, and oily fish – rich in mono- and polyunsaturated fatty acids. Saturated fats from meat and butter are acceptable but shouldn’t dominate. Trans fats from processed products are off-limits on any diet, not just keto.
How to put together meals without carbohydrates?
The basis of every keto meal is non-starchy vegetables paired with a source of fat or protein. Spinach, broccoli, courgette, and cauliflower can be combined with eggs, meat, or fish in almost endless configurations. Cauliflower is particularly versatile: it can be blended into “rice”, baked as a “pizza base”, or cooked as a mash.
Foods allowed on keto:
- Meat and fish – beef, poultry, pork, salmon, sardines, mackerel (no breading)
- Eggs and dairy – eggs, cheese, butter, cream, full-fat Greek yoghurt
- Fats and nuts – olive oil, avocado, coconut oil, macadamia nuts, almonds
- Non-starchy vegetables – broccoli, spinach, courgette, cauliflower, peppers, cucumber, salad leaves
- Berries in small amounts – raspberries and strawberries have the lowest sugar content among fruits
The first weeks on the keto diet – effects and challenges
The first 3-7 days on keto are often the hardest. Body, deprived of glucose, loses a lot of water (3-4 grams of water are bound to each gram of glycogen). Hence the rapid initial weight drop and the risk of dehydration. “Keto flu” sets in: headaches, fatigue, irritability, and brain fog. This is an adaptation response, not an illness. It typically passes within a week, once the body efficiently switches to burning ketones.
After 3-4 weeks, most people report stable energy levels, a smaller appetite, and no snacking between meals. Research published in the European Journal of Clinical Nutrition, involving people with obesity, found that a keto diet over 24 weeks lowered fasting glucose by 12%, triglycerides by 39%, and raised HDL cholesterol by 11%. At the same time, research from Harvard Medical School points out that long-term restriction of fibre from wholegrains may increase cardiovascular risk – an important counterpoint when planning keto long term.
Contraindications to the keto diet
The keto diet isn’t right for everyone. People with liver, kidney, or pancreatic conditions should avoid it without medical guidance – fat and ketone metabolism places demands on these organs. People with diabetes taking insulin or glucose-lowering medication may need dose adjustments, as keto drastically reduces insulin requirements – without supervision, hypoglycaemia (a dangerously low blood sugar level) can occur.
Groups requiring particular caution:
- People with diabetes – adjusting insulin dosage requires close medical supervision
- Pregnant and breastfeeding women – carbohydrate restriction may disrupt foetal development
- People with kidney disease – high-protein versions of keto may accelerate kidney damage
- Those with eating disorders – the restrictive nature of keto can intensify a preoccupation with food
- Endurance athletes – keto reduces performance in sports requiring rapid glucose-based energy
Is the keto diet effective for weight loss?
Keto is effective for short-term weight loss, though not for the reasons its advocates often cite. The most important mechanism is appetite reduction – ketones suppress ghrelin (the hunger hormone) and increase satiety. High fat and protein content of meals makes it hard to overconsume calories. The rapid initial weight drop is mostly water loss, not fat. Calorie restriction is a more decisive factor for longevity than any specific eating pattern.
Keto diet and heart health and cholesterol
Keto’s effect on cholesterol depends on individual factors. In most people, triglycerides fall and HDL cholesterol rises – a favourable change for heart health. LDL cholesterol may rise or fall – this depends on the type of fats consumed and the individual’s genetic response. In around 30% of people following keto, an increase in LDL is observed, which requires monitoring. Heart health on keto requires regular blood tests every 3-6 months.
Typical lipid panel changes on the keto diet:
- Triglycerides – drop noticeably in most people, sometimes by 30-40%
- HDL cholesterol – rises, which is beneficial for protecting blood vessels
- LDL cholesterol – unpredictable: depends on genetics and the quality of fats consumed
- Blood tests every 3-6 months – essential when following keto long term
Is the keto diet safe long term?
Keto can be safe long term – but only with proper planning, supplementation, and regular blood tests every 3-6 months. Long-term keto use (more than 2 years) is relatively poorly studied. It’s known that a diet low in fibre from wholegrains and varied vegetables can lead to deficiencies in magnesium, potassium, and B vitamins. The risk of kidney stones is higher on a high-protein, acidic diet. On the other hand, many people with type 2 diabetes follow keto successfully for years under medical supervision.
FAQ: Frequently asked questions about the keto diet
Can you eat fruit on the keto diet?
Most fruit contains too much sugar for ketosis, but raspberries, strawberries, and blackberries in small portions (50-100 g per day) fit within the carbohydrate limit and are acceptable on the keto diet.
How long should you follow the keto diet?
There’s no definitive answer – some people use keto as a 3-6 month intervention, others for years; the key is regular monitoring of health and blood test results, rather than a fixed duration.
Is the keto diet suitable for athletes?
Keto can work for low-intensity endurance sports, but it reduces performance in disciplines requiring short bursts of glucose-based energy, such as sprinting, weightlifting, or team sports.
References:
- Westman, E. C., et al. (2007). The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutrition & Metabolism. https://doi.org/10.1186/1743-7075-4-19
- Kosinski, C., & Jornayvaz, F. R. (2017). Effects of ketogenic diets on cardiovascular risk factors. Nutrients. https://doi.org/10.3390/nu9050517
- Brouns, F. (2018). Overweight and diabetes prevention: is a low-carbohydrate-high-fat diet recommendable? European Journal of Nutrition. https://doi.org/10.1007/s00394-018-1636-y
