Fatty Liver Disease: Causes, Symptoms, and What the “New” Term MASH Means
Fatty liver disease is one of the most common changes affecting the liver and is frequently discussed in the context of metabolic disorders. For a long time, it was considered more of a marginal issue or a consequence of obesity — today, it is increasingly recognised as an independent medical condition.
The terminology used to describe the disease has also changed. Terms such as “non-alcoholic fatty liver disease” are increasingly being replaced in the scientific literature by new designations. In particular, the terms MASLD and MASH reflect this shift in understanding. And behind these changes lies more than a simple renaming.
When the Liver Becomes Fatty: What Role Does Metabolism Play?
Fatty liver is diagnosed when fat accumulates in liver cells. This condition is referred to as “hepatic steatosis” and may be part of a disease process that also includes inflammatory changes. However, it can also exist without inflammation. Fatty liver is closely linked to metabolic alterations.
These include in particular:
· insulin resistance
These factors are closely associated with the development of the disease and shape its current classification (Powell et al., 2021).
Symptoms of Fatty Liver Disease: Why the Condition Often Goes Unnoticed in Its Early Stages?
Fatty liver disease can occur without clearly recognisable symptoms. When symptoms do appear, they are usually non-specific and cannot be clearly attributed. As a result, the condition is often detected incidentally during medical examinations (Westfall et al., 2020; Powell et al., 2021).
Renaming Fatty Liver Disease: MASLD and MASH Explained
In the scientific literature, the previous term “non-alcoholic fatty liver disease” (NAFLD) has been replaced by a new terminology. The earlier term essentially defined the disease by exclusion — referring to fatty liver not caused by significant alcohol consumption. This approach has increasingly been criticised because it did not place the actual cause — metabolic dysfunction — at the centre.
Against this background, a new terminology was introduced in 2023 as part of an international consensus. The central new term is MASLD, which stands for “Metabolic dysfunction-associated steatotic liver disease.”
This shifts the focus significantly: the disease is no longer defined by what it is not, but by what characterises it — a metabolic dysfunction that is often associated with related conditions.
Within this spectrum, different disease courses continue to be distinguished. A key concept here is MASH, which stands for “Metabolic dysfunction-associated steatohepatitis” (Rinella et al., 2023).
(Rinella et al., 2023)
This inflammatory form is clinically relevant because it is associated with an increased risk of progressive liver damage (we will discuss this in more detail a little later).
Fatty liver is also often associated with obesity (severe overweight). However, this view is too simplistic. People who appear slim or physically fit can also be affected — a phenomenon previously described as “lean NAFLD” and now referred to as “lean MASLD.” This once again highlights that it is not body weight alone that matters, but the underlying metabolic state. Even individuals of normal weight may have metabolic alterations that contribute to the development of fatty liver disease (Sato-Espinoza et al., 2024).
The renamings therefore represent more than linguistic adjustments. They reflect a shift in understanding.
Treatment of Fatty Liver (MASLD and MASH): The Whole Picture Matters
This approach in alternative medicine highlights the limitations of conventional medicine, which often focuses on individual risk factors, while the underlying metabolism as a whole may be considered less comprehensively.
Alternative approaches place different priorities: the focus is on measures that directly influence metabolism and can stabilise it in the long term.
This includes targeted dietary adjustments, e.g. by reducing the intake of energy-dense and highly processed foods (such as ready-made meals), and by achieving a more balanced overall composition of the diet — including higher protein intake and increased consumption of unsaturated fatty acids. The goal is to normalise energy balance and reduce metabolic stress.
At the same time, factors such as insulin sensitivity, lipid metabolism and energy utilisation are emphasised, as they are closely linked to the development of fatty liver disease. Another central approach is the systematic inclusion of lifestyle factors.
These include in particular habits such as
o physical activity / level of daily movement
o the management of sedentary behaviour
… all of which have a direct influence on metabolism and can therefore also affect the underlying mechanisms of fatty liver disease (as these publications show: Nicolai Worm: „Menschenstopfleber – Die heimliche Volkskrankheit Fettleber“, 2013; EASL–EASD–EASO, 2016; Chalasani et al., 2018).
This approach is consistent with the modern classification of fatty liver disease as a metabolically driven condition (MASLD), in which the liver — as mentioned — is not considered in isolation, but in the context of the entire metabolism (Powell et al., 2021; Rinella et al., 2023).
Prognosis: How Dangerous Are MASLD and MASH?
Not every case of fatty liver (MASLD) leads to severe disease.
The key factor is whether and how an inflammatory form (MASH) develops, as this is associated with an increased risk of progressive liver damage.
If the liver is damaged over a prolonged period, it responds with repair processes. During this process, damaged tissue is increasingly replaced by connective or scar tissue, known as fibrosis, which can impair the normal structure and function of the liver (Rinella et al., 2023). However, if fibrosis is detected early, the measures described above may help promote its regression.
Conclusion: “Fatty Liver” — An Oversimplified and Misleading Term
With the new definition introduced in 2023, the perspective on fatty liver disease has shifted significantly: away from a diagnosis of exclusion and towards classification within the context of metabolic processes.
This means that less emphasis is placed on the name of the condition itself, and more on the mechanisms driving it and how its course should be assessed. Ultimately, the decisive factor is whether the disease remains stable or progresses to an inflammatory form — and which factors influence this process.
FAQ — Frequently Asked Questions About MASLD and MASH (Fatty Liver)
1. Why is a slim physique not a reliable protection against MASLD and MASH (fatty liver)?
Because body weight alone is not decisive. Even in individuals of normal weight, insulin resistance, unfavourable fat distribution or other metabolic changes may be present.
2. Can MASLD (fatty liver) exist with normal liver values?
Yes, liver enzyme levels may be normal even when fat accumulation is already present. Therefore, a single laboratory value is not always sufficient to reliably rule out fatty liver disease.
3. What role does abdominal fat play in MASLD and MASH?
Abdominal fat is metabolically active and can promote inflammatory processes as well as insulin resistance. This is why fat distribution may be more important than body weight alone.
4. Is MASH automatically a precursor to liver cirrhosis?
No, MASH does not automatically lead to cirrhosis. However, the inflammatory form increases the risk that fibrosis and more severe liver damage may develop over time.
5. Why is early intervention in MASLD so important?
Because early stages are often more modifiable. Before significant scarring of liver tissue occurs, changes in diet, physical activity and metabolism can be particularly effective.
Further information on the treatment of metabolic diseases can be found in the respective volumes of our “Medizinskandale” series as well as in the volumes of our “Codex Humanus.” The fifth volume has recently been published. Feel free to visit our online shop. Our blog articles also provide additional insights into these and many other topics.
Sources:
· Powell, E. E. et al. (2021): “Non-alcoholic fatty liver disease,” The Lancet.
· Westfall, E. et al. (2020): “Nonalcoholic Fatty Liver Disease: Common Questions and Answers on Diagnosis and Management,” American Family Physician.
· Rinella, M. E. et al. (2023): “A multisociety Delphi consensus statement on new fatty liver disease nomenclature,” Journal of Hepatology.
· Sato-Espinoza, K. et al. (2024): “Update in lean metabolic dysfunction-associated steatotic liver disease,” World Journal of Hepatology.
· Nicolai Worm: “Menschenstopfleber – Die heimliche Volkskrankheit Fettleber,” Systemed Verlag, Lünen, 2013.
· European Association for the Study of the Liver; European Association for the Study of Diabetes; European Association for the Study of Obesity (2016): “EASL–EASD–EASO Clinical Practice Guidelines for the management of non-alcoholic fatty liver disease,” Journal of Hepatology.
· Chalasani, N. et al. (2018): “The diagnosis and management of nonalcoholic fatty liver disease: Practice guidance from the American Association for the Study of Liver Diseases,” Hepatology.