Understanding the Fatty Liver Index (FLI)
A validated screening algorithm that predicts fatty liver without ultrasound or biopsy
December 2025
Who is this especially useful for?
- ✓Those with central obesity or metabolic syndrome
- ✓People with elevated liver enzymes (ALT, GGT)
- ✓Anyone with high triglycerides or prediabetes
- ✓Those tracking lifestyle intervention progress
- ✓People wanting to assess liver health without imaging
FLI is particularly valuable for catching fatty liver that standard liver enzyme tests (ALT, AST) miss—up to 80% of cases.
How to find your lab numbers
Locate your triglycerides (TG) in the lipid panel section
Find GGT (gamma-glutamyl transferase) in liver enzymes
Calculate your BMI or have height and weight ready
Measure waist circumference at navel level
Triglycerides and GGT are from standard blood work. BMI requires height/weight. Waist circumference you can measure at home with a tape measure.
The FLI Formula
FLI uses a logistic regression model validated in the Dionysos Nutrition & Liver Study (n=496):
Logit = 0.953×ln(TG) + 0.139×BMI + 0.718×ln(GGT) + 0.053×WC − 15.745
FLI = (e^Logit ÷ (1 + e^Logit)) × 100
Where TG = triglycerides (mg/dL), GGT = gamma-glutamyl transferase (U/L), BMI = body mass index (kg/m²), and WC = waist circumference (cm).
Example Calculation
TG: 150 mg/dL, GGT: 45 U/L, BMI: 28, WC: 95 cm
Logit = 0.953×ln(150) + 0.139×28 + 0.718×ln(45) + 0.053×95 − 15.745
Logit = 4.78 + 3.89 + 2.73 + 5.04 − 15.745 = 0.70
FLI = (e^0.70 ÷ (1 + e^0.70)) × 100 = 67
FLI = 67 → Rules IN fatty liver (≥60)
The silent epidemic
NAFLD affects 25-30% of adults worldwide, yet most cases go undiagnosed because fatty liver is usually asymptomatic until advanced stages. FLI enables early detection using routine blood work.
Research Foundation
FLI was developed and validated in the Dionysos Nutrition & Liver Study using ultrasound-confirmed hepatic steatosis as the gold standard. The algorithm has been subsequently validated across multiple populations worldwide.
How different perspectives interpret FLI
Clinical thresholds vs optimal liver health
Standard Medical
Uses validated dual thresholds for clinical decisions
Hepatic steatosis screening and diagnostic workup
Research Consensus
Aims for metabolically healthy liver
Preventing any significant liver fat accumulation
Metabolic Focus
Views liver as central metabolic organ
De novo lipogenesis, insulin sensitivity, metabolic dysfunction
Interpreting Your FLI
FLI provides a probability score from 0-100 with clinically validated thresholds:
Negative likelihood ratio 0.2. 87% sensitivity for excluding steatosis.
→ No imaging needed unless other clinical concerns
Cannot definitively rule in or rule out hepatic steatosis.
→ Consider ultrasound if clinically indicated
Positive likelihood ratio 4.3. 86% specificity for confirming steatosis.
→ High probability of NAFLD; lifestyle intervention recommended
The Four FLI Components
Each component contributes to predicting liver fat:
Triglycerides
Direct reflection of hepatic lipid export. Elevated TG signals liver is producing excess fat.
Highest weight in formula (0.953 × ln)
GGT
Liver enzyme elevated in steatosis, oxidative stress, and insulin resistance.
Second highest (0.718 × ln)
BMI
Overall adiposity correlates with ectopic fat deposition in liver.
Linear term (0.139 ×)
Waist Circumference
Visceral fat is metabolically active and directly portally drains to liver.
Linear term (0.053 ×)
Why FLI Matters
Non-alcoholic fatty liver disease is the hepatic manifestation of metabolic syndrome:
Better than liver enzymes
Standard ALT/AST tests miss up to 80% of fatty liver cases. FLI captures what traditional tests miss.
Reversible early
Unlike cirrhosis, early fatty liver can be completely reversed. Early detection enables intervention before irreversible damage.
Metabolic hub
Fatty liver isn't just a liver problem—it's central to insulin resistance, type 2 diabetes, and cardiovascular disease.
No imaging required
FLI uses routine blood work + body measurements. No ultrasound, no biopsy, no radiation.
Trackable progress
Monitor improvement objectively over time. See lifestyle changes reflected in your score.
NAFLD Progression Stages
Understanding where you are in the spectrum:
Simple Steatosis
Fat accumulation without inflammation. Fully reversible.
Usually FLI ≥60
NASH
Non-alcoholic steatohepatitis. Fat + inflammation. Still reversible but requires attention.
FLI doesn't distinguish from simple steatosis
Fibrosis
Scarring begins. Partial reversal possible with aggressive intervention.
Requires FIB-4 or imaging
Cirrhosis
Advanced scarring. Irreversible. Focus shifts to preventing complications.
Beyond FLI scope
How to Improve Your FLI
Since FLI combines metabolic markers, improving it requires addressing root causes:
🥗Dietary Changes
Reduce fructose dramatically
De novo lipogenesis (liver fat production) is primarily driven by fructose. Sugar-sweetened beverages are the biggest culprit.
Cut refined carbohydrates
Excess carbs → insulin spikes → liver fat production. Low-carb approaches often produce dramatic FLI improvements.
Consider coffee
Multiple studies show coffee consumption is associated with lower GGT and reduced NAFLD progression.
Increase choline intake
Choline is essential for exporting fat from the liver. Eggs, liver, and beef are excellent sources.
🏃Lifestyle Changes
Lose visceral fat
Even 5-10% body weight loss significantly reduces hepatic steatosis. Waist circumference is the key metric.
Exercise regularly
Both aerobic and resistance exercise reduce liver fat independently of weight loss. Aim for 150+ minutes/week.
Eliminate alcohol completely
While FLI predicts NAFLD, any alcohol stresses the liver. Abstinence accelerates reversal.
Improve sleep
Poor sleep quality is independently associated with NAFLD. Aim for 7-9 hours of quality sleep.
Expected Timeline for FLI Improvement
With consistent intervention, many individuals move from 'rules in' (≥60) to 'rules out' (<30) within 3-6 months. Triglycerides often drop first (weeks 2-4), followed by waist circumference and GGT (months 1-3).
What FLI Cannot Tell You
FLI is a screening tool with specific limitations:
- ⚠FLI predicts steatosis (fat), not inflammation (NASH) or fibrosis (scarring)
- ⚠The indeterminate zone (30-59) requires additional testing for clarity
- ⚠May overestimate risk in heavy alcohol users (elevated GGT from alcohol)
- ⚠Very muscular individuals may have falsely elevated scores (high BMI from muscle)
- ⚠Does not replace imaging when clinical suspicion is high
Key Takeaways
- 1.FLI < 30 effectively rules out fatty liver with 87% sensitivity
- 2.FLI ≥ 60 strongly suggests fatty liver with 86% specificity
- 3.The four components: triglycerides, GGT, BMI, waist circumference
- 4.NAFLD is reversible with diet and lifestyle changes—especially early
- 5.Track FLI every 3-6 months during active intervention
- 6.Monitor HOMA-IR alongside FLI for complete metabolic picture
References
- 1.Bedogni G, Bellentani S, Miglioli L, et al. The Fatty Liver Index: a simple and accurate predictor of hepatic steatosis in the general population. BMC Gastroenterology. 2006;6:33. PMID: 17081293
- 2.Gastaldelli A, Kozakova M, Højlund K, et al. Fatty liver is associated with insulin resistance, risk of coronary heart disease, and early atherosclerosis in a large European population. Hepatology. 2009;49(5):1537-1544. PMID: 19291789
- 3.Vilar-Gomez E, Martinez-Perez Y, Calzadilla-Bertot L, et al. Weight loss through lifestyle modification significantly reduces features of nonalcoholic steatohepatitis. Gastroenterology. 2015;149(2):367-378. PMID: 25865049
- 4.Younossi ZM, Koenig AB, Abdelatif D, et al. Global epidemiology of nonalcoholic fatty liver disease—Meta-analytic assessment of prevalence, incidence, and outcomes. Hepatology. 2016;64(1):73-84. PMID: 26707365
- 5.Zelber-Sagi S, Nitzan-Kaluski D, Goldsmith R, et al. Long term nutritional intake and the risk for non-alcoholic fatty liver disease: a population based study. Journal of Hepatology. 2007;47(5):711-717. PMID: 17850914
Medical Disclaimer
The Fatty Liver Index (FLI) guide provided on Metabolicum is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.