Published October 20, 2026
In this blog post, we’ll cover fatty liver disease. Specifically, we’ll discuss why it’s a health problem worth paying attention to, how many people are affected, what percentage doesn’t even know about it, and how you can measure your liver fat. And make sure to read to the end, when I’ll share some simple tests everyone can do fairly easily to help you estimate whether you may be carrying too much liver fat.
What Is Fatty Liver Disease, and Why Is It a Health Problem?
Fatty liver disease occurs when excess fat builds up inside the liver. Ideally, a healthy liver should not store meaningful amounts of fat, but liver fat clearly becomes a clinical problem when it accounts for 5% of the organ’s total weight, or more. And in fact, in many people with fatty liver disease, 15, 20, or even 25% of the liver can consist of fat that shouldn’t be there.
When liver fat is elevated, we either call it alcoholic fatty liver disease if alcohol abuse is a plausible cause. If the patient is not consuming excessive amounts of alcohol, we call it non-alcoholic fatty liver disease, or NAFLD, which has recently been renamed metabolic dysfunction-associated steatotic liver disease, or MASLD. For more detail on how the different forms of fatty liver disease are defined in clinical practice, see the figure below.
Now, elevated liver fat is not a good thing because it causes insulin resistance in these liver cells, and that’s why it’s a major risk factor for type 2 diabetes. Specifically, the risk of developing type 2 diabetes is more than doubled in people with fatty liver disease compared to those without excessive fat accumulation in their livers, according to a meta-analysis (study of studies) that considered 19 observational cohort studies..
Fatty liver disease can also trigger inflammation, tissue scarring, and long-term liver damage, eventually leading to steatohepatitis, which simply means that the excess fat has caused chronic inflammation in the liver. Non-alcoholic steatohepatitis is also called NASH, and typically affects 20-30% of those with fatty liver disease. And this can then progress further as the liver gets more and more damaged, to fibrosis and potentially cirrhosis.
Liver cirrhosis is end-stage liver disease. It’s usually not reversible, and quite possibly fatal. And the risk of developing liver cirrhosis is 4.7-FOLD higher in people with fatty liver disease compared to people without a fatty liver.
On top of that, fatty liver disease is also a risk factor for liver cancer. That’s one of the really bad kinds of cancer, with a 5-year survival rate of around 20% or less, depending on where you live and, of course, depending on how early it’s caught. And the risk of developing liver cancer is at least 3.5-FOLD higher in people with fatty liver disease compared to those without.
And I argue that the real risks are much higher.
Because these data are based on one of the cohorts in which only about 2% of the entire population was clinically diagnosed with NAFLD. So do you see a problem here? Based on the data we reviewed earlier, the actual prevalence of NAFLD is at least 10-fold higher in these European countries, which means that 90+% of people with NAFLD were not diagnosed and were included in the control group that was assumed to not have NAFLD. And if now you have a lot of people in this control group that actually have NAFLD, that would make it harder to detect a difference in disease incidence between NAFLD and controls, and the associated disease risks weaker, right? In other words, it would be fair to assume that if we had perfect data and everyone was correctly diagnosed so we could categorize them appropriately for this analysis, the risk increase with NAFLD for both liver cirrhosis and liver cancer would be even higher than these analyses show. So even though 4.7-fold and 3.5-fold increased risk is already pretty bad, I wouldn’t be surprised if the real increase in risk were much, much higher.
The same is probably true for the increased risk of type 2 diabetes in patients with vs. without NAFLD. Again, if most patients cannot be correctly categorized because the vast majority of patients with NAFLD haven’t been diagnosed, the observed associations will be diluted by higher risks in ‘controls’ categorized as non-NAFLD but who actually have NAFLD. Further, researchers in most of the 19 observational studies the meta-analysis drew on adjusted their statistical models for major risk factors for type 2 diabetes, which is reasonable. However, one of these risk factors was insulin resistance, and one could argue that insulin resistance is not an independent risk factor or confounder in the relationship between NAFLD and type 2 diabetes risk, but a mediator, because NAFLD is a key cause of insulin resistance. So, again, if we were to compare insulin sensitive people without NAFLD with insulin resistant people with NAFLD, then the difference in type 2 diabetes risk would likey be substantially greater than demonstrated by the currently available studies.
How Common Is Fatty Liver Disease?
Several studies have looked at data of patients in different health care systems in the US and Europe, and found that about 1-2% of adult patients have been diagnosed with fatty liver disease. That would suggest this is a fringe problem affecting a very tiny minority.
However, that couldn’t be further from the truth. Because even though only 1-2% of adults have been DIAGNOSED with fatty liver, when researchers pick a random sample of adults and actually look at their livers, they find that the percentage of adults with fatty liver disease is more like 25, 30, or 35%.
A comprehensive meta-analysis looked at the prevalence of NAFLD worldwide. Let’s start with North America, where they found that across 19 studies, the estimated prevalence varied between 25.9% and 37.1%, averaging around 31.2%. So it’s a reasonable conclusion that about 1 in 3 adults in North America have fatty liver disease. Comparing these population-level figures to the 1% to 2% that have received a formal clinical diagnosis indicates that more than 90% of individuals with the condition may remain undiagnosed in North America.
Similar patterns appear globally. In Western Europe, clinical diagnoses sit near 1%, while the true prevalence approaches 25%. Regional estimates are higher elsewhere, including Latin America at about 44.4% and the Middle East and North Africa region at 36.5%.
So this is a VERY COMMON and VERY SERIOUS ISSUE, and on top of that, a vastly underdiagnosed one. So you definitely want to know whether or not you have fatty liver disease, so that you can get rid of that excessive liver fat. Because the good news is that fatty liver disease is fully reversible in almost all cases. That’s in contrast to advanced liver disease, such as liver cirrhosis, which is usually not reversible.
So how do you find out whether you have too much fat in your liver?
How To Measure Liver Fat Content
There are three main methods to measure liver fat content.
The first approach is a liver biopsy. While a biopsy allows direct tissue inspection for fat deposition, inflammation, and even advanced liver disease, such as fibrosis, it is an invasive procedure with inherent clinical risks. Additionally, because the doctor removes only a tiny piece of this very large organ, a tissue biopsy may not represent the entire liver, so results are typically reported in broader categories. So from a liver biopsy, your doctor may tell you only that you have mild fatty liver disease, or severe fatty liver disease, rather than exact percentages of liver fat. Liver biopsies, while long considered the gold standard, also show a surprising lack of reproducibility, even from the same biopsy sample.
Because of these downsides, two other methods are becoming well established.
The second method on our list is an abdominal MRI scan that lets us measure fat content across the entire liver. This method is officially called magnetic resonance image-derived proton density fat fraction (MRI-PDFF). The major benefits of MRI are that it’s non-invasive and allows us to accurately quantify fat content across the entire liver. So from an MRI scan, you’ll get an exact percentage, and that way you can also use it to detect even small shifts in liver fat content. That’s why most randomized controlled trials use MRI scans to detect changes in liver fat content in response to an intervention. The biggest downsides are the need for access to very expensive equipment and the high cost per scan.
And lastly, the third method is ultrasound. More precisely, it’s better to talk about ultrasound-based methods because, depending on the equipment used, there are different approaches. One that is used a lot in clinical care is the FibroScan, which can estimate liver fat content. So from a FibroScan, the doctor can categorize the patient’s liver fat content rather than provide a precise percentage, similar to what you can do with liver biopsy data. However, new, specialized ultrasound machines now allow quantitative assessment of liver fat, and this ultrasound data correlates quite strongly with MRI-based methods. This new technology has different names depending on the manufacturer of the ultrasound machine, but generally you want to ask for quantitative ultrasound to measure liver fat. This technology has currently been validated for the quantification of liver fat content, but I think it holds promise as well for the quantification of pancreatic fat, which is a key determinant of beta-cell dysfunction.
If we were just interested in liver fat measurement, MRI scan and quantitative ultrasound would be our methods of choice. However, in someone with fatty liver disease, a doctor may also want to assess whether advanced liver disease that can result from excessive fat accumulation, such as fibrosis, may be present. All of these methods can also provide insight into pathological changes in the liver, such as scarring and fibrosis, but to varying degrees. So I recommend that if you think you are at risk of having fatty liver disease, you discuss the best fit for your situation with your doctor, because that will also depend on which options are locally available and what is covered by your health plan.
Well, how can you tell whether you may be at risk of having fatty liver disease?
How To Estimate Whether You May Have a Fatty Liver
So how do you or your doctor know whether you should have one of these specific tests done to assess the fat content in your liver?
One method is the Fatty Liver Index, which uses your body mass index, or BMI, your waist circumference, your blood level of GGT – that’s a liver enzyme – and your fasting triglycerides. The Fatty Liver Index was created by Bedogni and colleagues, and is based on the idea that all of these tend to be elevated in people who have a fatty liver. One downside of this tool is that it can’t estimate your liver fat percentage. It only estimates which category you are in: likely negative for fatty liver disease, likely positive for fatty liver disease, or inconclusive. But that can be very useful because if the estimate is negative based on your data, then it would be very unlikely for you to have fatty liver disease, whereas you can seek further clinical evaluation if your results come back inconclusive or positive. A positive result in this estimation tool should not be seen as a diagnosis, but as a strong indication to seek further clinical testing.
Another issue with the fatty liver index is that it requires all of these data, which may reduce its usefulness. In other words, if you don’t have data on your blood GGT, the tool will not return an estimate. I developed a similar tool, the Insulin Resistance Syndrome Poster, because it also helps assess whether you have what I call Insulin Resistance Syndrome, with visceral and liver fat accumulation as central features. Those of you who have seen prior content on this website may have seen this poster before. However, after reading the Fatty Liver Index paper I just discussed, I actually updated the poster to now include blood GGT.
A note on the choice of liver enzyme. Several other liver enzymes are commonly used to monitor liver disease, such as ALT and AST. AST is not particularly specific or sensitive for detecting changes in liver fat, but ALT or the ALT/AST ratio could well have been included on the poster in place of GGT. In general, the literature shows that both ALT and GGT are similarly sensitive to changes in liver fat in both adults and children. Including both ALT and GGT would be redundant, and the choice for GGT was made because it is part of the established Fatty Liver Index and more strongly predictive of an elevated type 2 diabetes risk than ALT and generally strongly predictive of a wide range of chronic diseases. Because the objective of the Insulin Resistance Syndrome Poster is to help detect subtle shifts in cardiometabolic risks associated with the accumulation of excess visceral and ectopic fat, including biomarkers with strong links to cardiometabolic disease risks was a priority.
Of note here is that changes in ALT, the ALT-to-AST-ratio, and GGT within the normal range are clearly and strongly associated with liver fat accumulation. This suggests that the normal ranges used in clinical practice are too wide and include values that are clearly associated with a pathological state, fatty liver disease. Blood concentrations in these liver enzymes that are above the normal range are more clearly indicative of advanced stages of liver disease, such as fibrosis or cirrhosis.
If you are curious whether you may suffer from fatty liver disease and whether you should bring this topic up with your doctor for further testing, consider downloading the updated version of the poster. Then find the right one for your sex and race, because the cut-offs for some of the biomarkers vary a bit depending on both sex and racial background.
The one above is the version for non-white women, for example. Then try to get as many of these eight biomarkers measured as you can. Ideally, you’ll have data on all eight, but if you can get only seven or six, then that’ll also give you some insights.
OK, now you enter your data using a dot wherever your data fall. Let’s do this together. Let’s assume a non-white woman completes this poster in the way shown below.
All of her data points fall into the green areas of these bars. This would suggest that this woman has a low risk of carrying excess fat in her liver and also in her visceral fat depots. That is because in almost all cases where someone develops a fatty liver, most or all of these values are at least slightly elevated. So let’s assume that the woman in our example gains a bunch of weight over 3-4 years, and now she has developed mild to moderate fatty liver disease. What the research data suggest is that these values would shift to the right as liver fat content increases, as illustrated in the figure below.
And then if she continues on that trajectory and she develops a severe fatty liver, the data points would shift further to the right, like in the example below.
She is now also quite insulin resistant, with a HOMA-IR between 3 and 4, and her fasting glucose is elevated, so she is probably prediabetic. That’s not a coincidence: in this syndrome, as excess visceral and ectopic fat accumulates, insulin resistance, low-grade inflammation, and changes in blood lipids, blood pressure, and blood sugar often follow. Note that it’s not always this clear. What you want to look for is shifts into the orange or red portions of these bars for at least some of the biomarkers. That could be alarming, even if not all markers change in the same way.
Now, one important point is that this is not a clinical diagnostic tool, because it hasn’t been validated. So you cannot and should not use it to diagnose a condition. What I hope this tool will help you do is learn about the relationship between visceral and ectopic fat accumulation and these biomarkers, all of which are also risk factors for cardiometabolic disease. I also hope this blog post and poster will inspire and motivate further discussions with your doctor about excess visceral and ectopic fat, and to also consider whether a clinical assessment of the fat content in your liver may be indicated. If you find that some or many of your markers are in the orange or even red portions of these bars, I urge you to bring this up with your doctor for proper evaluation.
Even if you currently are still young, lean, and healthy, completing this poster every year or two can be really helpful to detect shifts in the wrong direction early. So you don’t have to wait until you have severe fatty liver disease, but maybe you can start to wonder what’s going on when some or most of these markers start moving into the orange portions of these bars.
One additional point. Any one of these markers can be elevated for any number of reasons, so what you want to do is consider all of them together. In people who do not have a fatty liver, most or all of these markers are usually in the green parts of these bars, like in the example we discussed earlier. In people with mild to moderate fatty liver, you’ll often find most of these markers clearly shifted to the right, into the orange portions of these bars. And in people with severe fatty liver, some or many of these markers can be found in the red portions of these bars.
Again, here is the link to download the Insulin Resistance Syndrome poster.
Conclusions
What I hope you will take away from this blog post is that fatty liver disease is now extremely common, affecting between 25% and 44% of the adult population in countries for which we have data. We also have data suggesting that upwards of 90% of patients with fatty liver disease do not know that they have it! That’s insane!
Fatty liver disease isn’t something to take lightly. It’s a major risk factor for type 2 diabetes and advanced, potentially terminal liver disease. So, the #1 thing I hope you take away from this blog post is that you take action to determine whether you may have fatty liver disease. Complete the Fatty Liver Index form online, or complete my Insulin Resistance Syndrome poster, and if your data suggest that you may carry excess liver fat, bring this up with your doctor as soon as you can for proper clinical evaluation. And if you are worried about having a liver biopsy, let that not prevent you from taking action. Just discuss your worries and preferences with your doctor: with MRI and quantitative ultrasound, we now have very good, non-invasive methods to quantify liver fat and also to detect advanced liver disease.
Finally, a big, big thank you to the Patrons enabling me to make this content freely available to a global audience. If you’d like to support Nourished by Science, you can do so here by becoming a patron on Patreon with a regular monthly donation, or a one-time donation here.
Let me know below if you have any questions or comments.
Take care.
References
- European Association for the Study of the Liver (EASL), European Association for the Study of Diabetes (EASD), and European Association for the Study of Obesity (EASO). EASL-EASD-EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD). Journal of Hepatology 2024; 81: 492-42.
- Mantovani et al.; Nonalcoholic fatty liver disease and risk of incident type 2 diabetes: a meta-analysis. Diabetes Care 2018; 41: 372-82.
- Hagstrom et al.; Natural history and progression of metabolic dysfunction-associated steatotic liver disease. Lancet Gastroenterology and Hepatology 2024; 9: 944-56.
- Alexander et al.; Risks and clinical predictors of cirrhosis and hepatocellular carcinoma diagnoses in adults with diagnosed NAFLD: real-world study of 18 million patients in four European cohorts. BMC Medicine 2019; 17: 95.
- Younossi et al.; The global epidemiology of non-alcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH): a systematic review. Hepatology 2023; 77: 1355-47.
- Rodriguez et al.; Discrepancy in metabolic dysfunction-associated statotic liver disease prevalence in a large Northern California cohort. Gastro Hep Advances 2025; 4: 100630.
- Alexander et al.; Real-world data reveal a diagnostic gap in non-alcoholic fatty liver disease. BMC Medicine 2018; 16: 130.
- Kim et al.; Liver biopsy in the real world-reporting, expert concordance and correlation with a pragmatic clinical diagnosis. Alimentary Pharmacology and Therapeutics 2021; 54: 1472-80.
- Panagiotopoulos et al.; Proton density fat fraction for diagnosis of metabolic dysfunction associated steatotic liver disease. Hepatology 2026; 83: 127-41.
- Fraczek et al.; Non-invasive tests as a replacement for liver biopsy in the assessment of MASLD. Medicina (Kaunas) 2025; 61: 736.
- Ahmed et al.; FibroScan’s evolution: a critical 20-year review. Journal of Ultrasound 2025; 28: 295-304.
- Ozturk et al.; Quantitative hepatic fat quantification in non-alcoholic fatty liver disease using ultrasound-based techniques: a review of literature and their diagnostic performance. Ultrasound in Medicine and Biology 2018; 44: 2461-75.
- Website to calculate the Fatty Liver Index. Accessed on October 18, 2026.
- Bedogni et al.; The fatty liver index: a simple and accurate predictor of hepatic steatosis in the general population. BMC Gastroenterology 2006; 6: 33.
- Xuan et al.; Elevated ALT/AST-ratio as a marker for NAFLD risk and severity: insights from a cross-sectional analysis in the United States. Frontiers in Endocrinology 2024; 15: 1457598.
- Sanyal et al.; Profile of liver enzymes in non-alcoholic fatty liver disease in patients with impaired glucose tolerance and newly detected untreated type 2 diabetes. Indian Journal of Endocrinology and Metabolism 2025; 19: 597-601.
- Fraser et al.; Alanine aminotransferase, gamma-glutamyltransferase, and incident diabetes. Diabetes Care 2009; 32: 741-50.
- Koenig and Seneff. Gamma-glutamyltransferase: a predictive biomarker of cellular antioxidant inadequacy and disease risk. Disease Markers 2015; 2025: 818570.
- Chen et al.; Gamma-glutamyl transpeptidase elevation is associated with metabolic syndrome, hepatic steatosis, and fibrosis in patients with nonalcoholic fatty liver disease: a community-based cross-sectional study. Kaohsiung Journal of Medical Science 2021; 37: 819-27.
- Maduri et al.; Association of fatty liver with serum gamma-glutamyltransferase and uric acid in obese children in a tertiary care centre. BMC Pediatrics 2025; 25: 144.
- Schneider et al.; Liver enzymes, race, gender, and diabetes risk: the Atherosclerosis Risk in Communities (ARIC) Study. Diabetes Medicine 2013; 30: 926-33.