Fasting with a Fatty Liver: What Therapeutic Fasting Does for the Liver

The essentials at a glance

• 20 to 30 per cent of adults in industrialised nations have a fatty liver; among people with obesity the figure is 80 to 90 per cent.
• In an observational study, periodic fasting over roughly 8.5 days lowered the Fatty Liver Index by an average of 14 points.
• Alongside weight loss, the metabolic switch — the shift to fat burning after 12 to 36 hours without food — is considered the key mechanism; every additional fasting day improved the index.
• The Fatty Liver Index is a calculated index based on BMI, waist circumference, triglycerides and GGT, not measured liver fat.
• Weight loss of at least 5 per cent improves fatty deposits and liver values; 10 per cent also improves fibrosis.
• Advanced liver or kidney failure is a contraindication; therapeutic fasting belongs in medical care.

What is a fatty liver, and how do you notice it?

A fatty liver rarely announces itself through pain, and precisely for that reason it is worth meeting it with calm and medical guidance. The medical field has recently reorganised itself: since the summer of 2023, the liver diseases formerly known as NAFLD and NASH are called SLD, MASLD and MASH — steatotic liver disease, metabolic dysfunction-associated steatotic liver disease, and its inflamed form. In every case the underlying basis is the same: fat that settles in the liver cells because more energy is taken in than is used.

The condition is widespread. In the industrialised nations, around 20 to 30 per cent of adults have a fatty liver; among people with obesity it is 80 to 90 per cent. It is encouraged by excess weight, type 2 diabetes, insulin resistance and lack of exercise — in other words, by exactly the metabolic picture that creeps in over years of abundance.

Why the fatty deposits usually go unnoticed

The liver itself feels no pain, and the signs those affected occasionally report are unspecific: fatigue, a feeling of pressure in the right upper abdomen, bloating or sleep disturbances. A simple fatty liver is initially harmless, but it can become inflamed, scar over and progress to liver cirrhosis. The road to cirrhosis is a long one: in about 30 percent of those affected an inflammation develops, only after that can scarring and cirrhosis follow, and the simple fatty change can recede. The finding is therefore a reason to take a closer look, not a cause for panic.

• Blood values: Blood values can point to a fatty liver, but they do not have to be altered.
• Ultrasound: An ultrasound examination can visualise a fatty liver, and the diagnosis is often made on this basis.
• Further clarification: In very rare cases a tissue sample comes into question, and the doctor rules out other causes such as alcohol or viral hepatitis.

What do studies show about fasting and fatty liver?

The most illuminating study on this question dates from 2019. Stefan Drinda and colleagues accompanied 697 fasters, 38 of them with type 2 diabetes, who fasted for an average of 8.5 days according to the Buchinger method, and measured the so-called Fatty Liver Index, or FLI for short. It fell by an average of 14 points, by around 19 points among the participants with type 2 diabetes, and just under half of the participants — exactly 49.9 percent — lost at least 5 percent of their body weight. The longer the fast lasted, the greater the improvement.

What the study achieves — and what it does not

• The FLI is a calculated index based on BMI, waist circumference, triglycerides and gamma-GT, not directly measured liver fat.
• The study was observational and had no control group; it therefore shows an association, not proof of effect in the strict sense.
• The effect does not rest on weight loss alone: the improvement in the FLI correlated with the number of fasting days and with the drop in BMI, and in almost half of the participants with an elevated index a BMI reduction of under 5 percent was already enough to move them into a lower risk category.

The authors name the so-called metabolic switch as the key mechanism: after roughly 12 to 36 hours without food, the metabolism shifts from sugar drawn from the glycogen stores to fatty acids and the ketone bodies formed from them — away from storing, towards mobilising fat. In overweight, insulin resistance and type 2 diabetes, a high insulin level delays this switch. On top of weight loss comes this effect: each additional fasting day increased the chance that an elevated index would improve by 40 percent, so the duration of the fast must be sufficient for the liver to benefit. A week of fasting is therefore not a self-running cure, but an intervention in the metabolism that wants to be well chosen and medically accompanied.

How much weight loss does the liver need for good?

The target marks of the current guidelines are remarkably sober: a weight loss of at least 5 percent already improves the fatty change and the liver values, and at at least 10 percent an incipient fibrosis also improves. What matters is the loss itself, not the path taken towards it. The liver rewards keeping it off, not the initial sprint.

For all fatty liver diseases, lifestyle changes come first in treatment, and a Mediterranean diet is expressly recommended in the German guideline. Medicines such as resmetirom and semaglutide, by contrast, are approved only for a narrowly defined group, namely adults with a liver inflammation, MASH, and scarring at stage F2 to F3.

Alongside weight reduction, a carbohydrate-reduced diet is another important element in the regression of fatty liver. The authors of the fasting study refer to investigations showing that, at the same amount of weight loss, a low-carbohydrate diet lowered liver fat more strongly in the short term than calorie reduction alone — probably through increased fat burning and greater formation of ketone bodies.

For the time after the fast, this means: you decide. Weight reduction in therapeutic fasting is a side effect that only lasts if the diet is maintained afterwards. The rebuilding begins with breaking the fast and should cover about one third of the fasting period; after that, those interested can continue learning to eat with Schlanke Tanne Low Carb, our own house diet, rich in vegetables and protein. How losing weight, muscle mass and the yo-yo effect relate to one another, we have examined in detail under therapeutic fasting and weight.

Who is therapeutic fasting suitable for with a fatty liver?

Whether fasting makes sense with a fatty liver cannot be judged from the findings alone, but only from the whole person. The fasting therapy guidelines of the Ärztegesellschaft Heilfasten und Ernährung name as exceptions that rule out fasting, among others, advanced liver or kidney insufficiency, because the body then lacks the ability to detoxify and excrete, as well as pregnancy and breastfeeding and anorexia.

• Acute illnesses
• Advanced cardiovascular diseases
• Eating disorders
• Pregnancy and breastfeeding
• Severe underweight

Anyone not affected by these limits is medically accompanied at the Tannerhof from the very beginning: with medical history and examination, laboratory values, among them liver and fat values, bioimpedance for body composition, progress checks and a concluding consultation. To support the liver, a hay-flower compress is gladly applied during the fast, which stimulates circulation and gets the liver's metabolism going. What this accompaniment looks like in detail is described on our page on medically accompanied fasting.

For guests with a health concern such as a fatty liver, our doctors recommend a longer fasting duration of at least ten pure fasting days under close accompaniment. The Body Detox Fasting programme is built precisely for this entry: within 8 days (BASIC) or 10 days (ADVANCED), the fasting transition is medically accompanied, with diagnostics at the start and a clear view of how the diet continues afterwards. A fasting week can thus set the regression of fatty liver in motion; it is only completed in the months that follow, in which the maintained weight speaks for the liver.