Ketogenic eating arrived in popular culture as a weight-loss method, which has obscured what it actually is. It was developed in the 1920s to control seizures in children, it worked, and it is still used for that today in cases where drugs fail. A diet that stops seizures is doing something more fundamental than shifting a number on a scale.
What crossing the threshold changes
Below roughly fifty grams of carbohydrate a day — lower for some people, higher for the well-trained — the liver begins producing ketones in quantity. The brain, which cannot run on fat, runs on these instead, and it does so at a steadier rate than it runs on glucose.
Three consequences follow, and they are the reason the diet does what it does. Insulin stays low, so stored fat is continuously available rather than locked away. Appetite falls, not through willpower but because the fuel supply stops fluctuating. And the energy supply to the brain becomes level, which is the most plausible explanation for the effects seen in epilepsy and reported anecdotally in mood and concentration.
Where the evidence is strong and where it is not
- Strong: seizure control, glycaemic control in type 2 diabetes, weight loss over six to twelve months, triglyceride reduction
- Reasonable: fatty liver, appetite regulation, metabolic markers in insulin resistance
- Early: neurodegenerative conditions, migraine, some psychiatric applications — mechanistically coherent, thin in human trials
- Overstated: cancer treatment, where the metabolic argument is interesting and the clinical evidence does not yet support it
Doing it badly is the norm
Most people who report that keto did not work for them were not in ketosis. Carbohydrate creeps in through sauces, tomato, onion and 'low-carb' products. Protein is set too high, and excess protein is partially converted to glucose. Or the diet becomes processed food with the sugar taken out, which misses the point entirely.
Clean keto is meat, fish, eggs, butter, olive oil and vegetables that grow above ground. Dirty keto is the same macros assembled from packets, and it will produce the ketones without much of the benefit.
The first fortnight
Nearly everything people describe as keto flu is sodium and water loss. Low insulin makes the kidneys excrete sodium faster, and the resulting headache, fatigue and light-headedness get blamed on the diet. Three to five grams of sodium a day from unrefined salt, plus magnesium in the evening, removes most of it.
Who should be careful
- Anyone on insulin or a sulfonylurea, where glucose falls faster than the dose adjusts
- Anyone on blood pressure medication, for the same reason
- People without a gallbladder, who may need help digesting the fat load
- Type 1 diabetes, where ketogenic eating is possible but requires real supervision
None of these are reasons not to do it. They are reasons to have the conversation with a doctor before week one rather than after a problem.
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