Keto and Fatty Liver: What a Randomised Trial Found

Non-alcoholic fatty liver disease, now often called metabolic-associated fatty liver, is exactly what it sounds like: fat accumulating in the liver of people who do not drink heavily. It is extremely common, tracks closely with weight and insulin resistance, and is the kind of quiet condition that does real long-term damage. Because the liver makes fat partly from surplus carbohydrate, a low-carb diet is an obvious thing to test, and one randomised trial tested it well.

The trial

Holmer and colleagues, publishing in JHEP Reports in 2021, randomised 74 patients with fatty liver into three groups for twelve weeks: a low-carb high-fat diet, a 5:2 intermittent-fasting diet, or standard lifestyle advice from a liver specialist. Crucially, they measured liver fat directly using magnetic resonance spectroscopy rather than relying on rough proxies, which makes the results more trustworthy than many diet studies.

What it found

Both diets clearly beat standard advice. The low-carb high-fat group reduced their liver fat by about 7.2 per cent in absolute terms, the 5:2 group by 6.1 per cent, and the standard-care group by only 3.6 per cent. Weight loss followed the same pattern, with both diet groups losing around 7 kilograms against 2.5 for standard care. So a low-carb diet substantially cut liver fat, and did so about as effectively as intermittent fasting, with both leaving general lifestyle advice well behind.

Why cutting carbs hits liver fat

The mechanism is fairly direct. When you eat more carbohydrate than you immediately need, the liver converts some of the excess into fat through a process called de novo lipogenesis, and in fatty liver this machinery is running hot. Cut the carbohydrate, especially sugar and refined starch, and you reduce the raw material the liver is turning into fat, while the accompanying weight loss and improved insulin sensitivity ease the problem further. Lower the input, and the liver gradually clears its backlog.

The honest nuance

This is where a careful read matters, because the trial was not a clean win for low-carb on every measure. While the low-carb diet matched 5:2 for cutting liver fat and weight, liver stiffness, a marker of scarring, improved in the fasting and standard-care groups but not in the low-carb group over this short window. The 5:2 diet also lowered LDL cholesterol and was, on the whole, better tolerated by participants. So the fair summary is that low-carb is highly effective for reducing liver fat, as good as fasting on that count, but it is not uniquely superior, and fasting had a few edges. The researchers’ sensible conclusion was that dietary advice can be tailored to what a person will actually stick to, since both approaches worked.

What it means in practice

If you have fatty liver, the research supports a low-carb diet as a genuinely effective way to reduce it, particularly the sugar and refined-carbohydrate end of your eating, and the weight loss that comes with it helps on every front. It also means you have options: if low-carb does not suit you, intermittent fasting achieved much the same liver-fat reduction in this trial, so the best diet is largely the one you can keep up. Keep an eye on your blood lipids with your doctor, given the LDL difference seen here, and treat fatty liver as something to manage with medical input rather than alone, since it can progress.

The bottom line

In a randomised trial measuring liver fat directly, a low-carb high-fat diet cut it by around 7 per cent in twelve weeks, double what standard advice achieved and on par with 5:2 fasting. Cutting carbohydrate reduces the fat the liver manufactures and drives useful weight loss, which is why it works. It is not the only route, and fasting matched it with a couple of advantages, so the takeaway is that an effective diet for fatty liver is one that genuinely lowers carbs or calories and that you can actually sustain.

This is general information about the ketogenic diet, not medical advice. Fatty liver disease needs medical assessment and monitoring; manage it with your doctor. If you are pregnant, on medication, or managing another condition, speak to a professional before changing your diet.

Source: Holmer M, et al. Treatment of NAFLD with intermittent calorie restriction or low-carb high-fat diet, a randomised controlled trial. JHEP Reports. 2021;3(3):100256. Read it here.