Liver Enzyme Interpretation in Athletes: Why AST and ALT Rise With Training, GGT as the Alcohol vs Training vs Supplement Disambiguator, and the Hepatotoxic-Supplement Differential in the Sports Nutrition Intake

A 27-year-old CrossFit competitor arrives at intake with a hepatic panel drawn at a routine primary-care physical two weeks earlier. His AST reads 78 U/L, his ALT reads 62 U/L, his alkaline phosphatase reads 82 U/L, his GGT reads 24 U/L, his total bilirubin reads 0.7 mg/dL, and the primary-care note flagged the AST and ALT elevation with a recommendation to abstain from alcohol for six weeks and repeat the panel. His self-reported alcohol intake is one to two drinks per week. His training week has held at twelve sessions across the past six months — five to seven CrossFit metcons, three to four heavy strength sessions, and two to three olympic-lifting technique blocks — and he has been in a self-directed body-recomposition attempt for the past four months on a supplement stack he did not disclose to his primary care physician. The stack: 5 g creatine, 3 g beta-alanine, a pre-workout containing 400 mg caffeine, a fat-burner containing green tea extract at 500 mg EGCG per dose, a SARM (RAD-140) at 10 mg/day cycled three months on, and a proprietary "liver support" blend containing milk thistle, NAC, and TUDCA. He is in your office because he wants a second opinion before he abstains from alcohol he barely drinks, and because he suspects the panel is reading something other than what his physician assumed.

The standard hepatic panel — AST, ALT, ALP, GGT, total and direct bilirubin — was calibrated against a general-population reference distribution where the AST and ALT elevation signal is dominantly hepatic. In the trained-athlete population that distribution shifts. Skeletal muscle contributes substantially to circulating AST, and to a lesser extent ALT, on the timescale of hours to days after a heavy training session; the athlete panel drawn 24 to 72 hours after a squat session, a metcon, or an eccentric-heavy training day routinely returns AST and ALT elevations that are entirely skeletal-muscle-derived and reflect the training pattern, not hepatocyte damage. The primary-care read that assumes hepatic origin and treats the elevation as an alcohol-first differential misclassifies the case.

Layer on the supplement stack the athlete did not disclose. SARMs and other anabolic-androgenic compounds are directly hepatotoxic; green tea extract at high daily EGCG doses is associated with idiosyncratic drug-induced liver injury; some pre-workout stacks contain undeclared substances with hepatic effects; a "liver support" blend containing TUDCA in the athlete's own read is prophylaxis for the anabolic exposure he is running, which the primary-care panel does not surface. The alcohol-first differential misses each of these.

Most sports-RD intakes do not run a structured liver enzyme workup. The panel arrives from primary care, the AST and ALT flag drives a reflexive alcohol conversation, the supplement inventory does not get taken to the depth it needs, and the case gets managed as a lifestyle-modification problem when the actual clinical picture sits in the intersection of training-load, skeletal-muscle contribution, hepatotoxic supplement exposure, and (in a subset of cases) genuine hepatic pathology that the AST-ALT elevation is finally surfacing.

This post is the liver enzyme workup I run when the standard panel returns AST or ALT elevated in an athlete and the primary-care assumption of hepatic-alcohol origin does not fit the picture. The six-dimension interpretive frame, the GGT differential that separates alcohol-driven from training-driven from supplement-driven elevation, the CK and AST-to-ALT ratio overlay that quantifies the skeletal-muscle contribution, the hepatotoxic-supplement inventory the intake must catch, the four-quadrant clinical matrix, the medical-coordination triggers, the common counseling mistakes, and the SOAP pattern that documents the case defensibly.

Why the standard hepatic panel under-flags the athletic case

Three structural reasons.

AST is not liver-specific. Aspartate aminotransferase is expressed in skeletal muscle, cardiac muscle, kidney, brain, and erythrocytes in addition to hepatocytes. Trained athletes running high-volume eccentric or high-intensity training routinely present with AST elevations two to four times the upper limit of the sedentary reference range, driven by skeletal-muscle turnover on the timescale of the training week. The elevation reads on the standard panel as hepatic dysfunction; the underlying source is a bicep, a hamstring, and a quadriceps in a training block that just finished a hard week. The panel drawn within 72 hours of an eccentric-heavy session, a race, or a metcon carries a substantial skeletal-muscle contribution the sedentary reference range does not anticipate.

ALT is more liver-specific but not exclusive. Alanine aminotransferase is more liver-specific than AST but is still expressed in skeletal muscle at meaningful levels. Trained athletes routinely present with ALT elevations up to two times the upper limit of the sedentary reference range that are skeletal-muscle-derived, and the AST-to-ALT ratio is one of the disambiguating variables — a ratio above 2:1 in the athletic setting with normal GGT is more consistent with skeletal-muscle origin than with hepatic origin in most clinical presentations, though the classic alcoholic-hepatitis pattern also runs an AST-to-ALT ratio above 2:1 and the differential requires the co-marker read.

GGT is the differential. Gamma-glutamyl transferase is not expressed at meaningful levels in skeletal muscle. A GGT elevation in the setting of AST and ALT elevation points meaningfully toward hepatic origin — the classic pattern for alcohol-driven liver injury, for hepatotoxic supplements, for bile-duct obstruction, or for NAFLD. A normal or low GGT in the setting of an AST-ALT elevation shifts the differential meaningfully toward the skeletal-muscle contribution as the dominant driver. The primary-care read that flags AST and ALT without integrating the GGT read is under-differentiated.

The six-dimension liver enzyme workup

Dimension 1: Read AST and ALT against GGT, not in isolation. The GGT read is the single most valuable disambiguating variable in the athletic case. A normal GGT — under approximately 40 U/L in most reference ranges, calibrated to the athlete's sex and lab-specific range — in the setting of AST and ALT elevation shifts the differential heavily toward the training-and-skeletal-muscle contribution as the dominant source. An elevated GGT in the same setting shifts toward hepatic-origin differentials: alcohol exposure, hepatotoxic supplement exposure, bile-duct disease, NAFLD, viral hepatitis, or medication-induced injury. The 27-year-old CrossFit competitor with AST 78, ALT 62, GGT 24 has a normal GGT and a strong signal for skeletal-muscle origin as the dominant contributor — the workup does not stop there, but the alcohol-first differential the primary-care read produced is not the leading hypothesis on the integrated panel.

Dimension 2: Read against creatine kinase and the training-load overlay. Creatine kinase is the direct read on skeletal-muscle turnover. A CK elevation — into the 400 to 2,000 U/L range routinely in the trained athlete on a heavy training block, and into the 5,000 to 50,000+ range in the rhabdomyolysis case — surfaces the skeletal-muscle contribution to the AST-ALT elevation quantitatively. The ratio of the CK elevation to the AST-ALT elevation, integrated against the training-load pattern in the 72 hours preceding the draw, tells the skeletal-muscle-contribution story. The CrossFit competitor with a heavy metcon three days before the draw and an unmeasured CK is missing a key variable; the workup that orders CK on the follow-on can quantify what fraction of the AST-ALT elevation is training-derived.

Dimension 3: Read the AST-to-ALT ratio integrated with the clinical picture. The AST-to-ALT ratio has classical pattern associations that inform but do not diagnose the case. Above 2:1 with elevated GGT and clinical alcohol exposure fits the alcoholic-hepatitis pattern. Above 2:1 with normal GGT and heavy recent training fits the skeletal-muscle-derived pattern. Roughly equal or ALT-dominant patterns with elevated GGT can fit NAFLD, viral hepatitis, drug-induced liver injury, or a supplement-driven case. The ratio is a pointer, not a diagnostic — read it against the GGT, the CK, the training pattern, the alcohol history, and the supplement inventory.

Dimension 4: Read against the supplement and medication inventory. The most under-executed component of the athletic liver enzyme workup is the direct supplement inventory. The intake needs to capture: every prescription and over-the-counter medication (acetaminophen dose and frequency in particular, statins, methotrexate, NSAIDs at high chronic dose), every sports supplement (protein powders, pre-workouts, fat-burners, thermogenics), every ergogenic aid (SARMs, prohormones, anabolic-androgenic steroids, growth-hormone releasers, peptides), every herbal product (green tea extract high-dose, kava, garcinia cambogia, black cohosh, chaparral, comfrey, germander, pennyroyal, some ayurvedic preparations), every "liver support" product (which paradoxically may signal the athlete's own suspicion of hepatic exposure), and any recreational substance use. The intake conversation needs to be direct, non-judgmental, and specific — asking generically about supplements produces a partial inventory in the majority of cases. The hepatotoxic-supplement differential is discussed at length below.

Dimension 5: Read against the alcohol history overlay. Alcohol history should be captured with a validated screening tool (AUDIT or AUDIT-C at minimum) and cross-referenced against the GGT read. Elevated GGT in the setting of self-reported low alcohol intake warrants a direct conversation about under-reporting, particularly in populations where competitive weight or performance stigma discourages disclosure. Normal GGT in the setting of self-reported moderate alcohol intake is broadly consistent with the reported pattern. The trained-athlete case with low alcohol intake, normal GGT, and elevated AST-ALT should not be managed with a reflexive alcohol-abstinence recommendation as the primary intervention — the pattern does not fit.

Dimension 6: Read against the metabolic and body-composition overlay. Nonalcoholic fatty liver disease is the most common cause of chronic hepatic enzyme elevation in the general population and is not eliminated as a differential in the athlete just because the BMI is normal. Waist-to-height ratio above 0.5, visceral adiposity on DEXA, elevated triglyceride-to-HDL ratio, elevated fasting insulin or HOMA-IR, and the clinical or family-history risk for metabolic syndrome all belong in the read. The athlete on a body-recomposition attempt with rising insulin resistance and elevated AST-ALT is not out of the NAFLD differential just because he trains hard and looks lean. The [insulin resistance workup](/blog/insulin-resistance-workup-in-athletes) sits adjacent to this workup and should run in parallel where the metabolic picture warrants it.

The four-quadrant clinical decision matrix

The six dimensions collapse into a four-quadrant matrix that drives the action plan.

Quadrant 1: AST and ALT elevated, GGT normal, CK elevated in a pattern consistent with recent heavy training, AST-to-ALT ratio above 2:1, no hepatotoxic supplement exposure, low alcohol intake, no metabolic-syndrome flags. The pattern is consistent with skeletal-muscle-derived enzyme elevation from training. Document the integrated read, repeat the panel at 72 hours off heavy training, and confirm resolution. This is the CrossFit competitor's most likely case pending the supplement-inventory read.

Quadrant 2: AST and ALT elevated, GGT elevated, CK not disproportionately elevated for training load, AST-to-ALT ratio variable, hepatotoxic supplement exposure present, or alcohol history warranting attention, or metabolic-syndrome flags. The pattern is consistent with hepatic-origin enzyme elevation from supplement, alcohol, or metabolic-syndrome contribution. The intervention pathway is discontinuation of the identified hepatotoxic exposure (supplement or alcohol), address of the metabolic-syndrome drivers, and repeat panel at four to twelve weeks depending on the clinical picture. Coordinate with the primary-care team on the panel trajectory.

Quadrant 3: AST and ALT markedly elevated (above five times the upper limit of the reference range), or acute hepatocellular pattern, or clinical jaundice, or synthetic-function markers (albumin, INR, bilirubin) abnormal, or the picture suggests acute drug-induced liver injury. Urgent medical evaluation. The sports-RD role is to surface the supplement, medication, and substance history to the medical team and to withdraw the suspected offending agents while the medical workup runs.

Quadrant 4: Ambiguous panel, mixed signals, or the training-vs-hepatic differential cannot be resolved on the initial workup. Order the extended follow-on — CK, LDH, GGT if not already run, fasting lipid and insulin panel, viral hepatitis serology if indicated by history, ceruloplasmin and iron studies if indicated by history, and a repeat panel at 72 hours off training. Coordinate with the primary-care physician on the extended workup.

The hepatotoxic-supplement differential

The single largest under-caught driver of unexplained liver enzyme elevation in the athletic intake is the undisclosed hepatotoxic supplement. The high-frequency offenders the intake must directly ask about:

SARMs, prohormones, and anabolic-androgenic steroids. RAD-140, ostarine, LGD-4033, ligandrol, and other selective androgen receptor modulators, as well as oral anabolic-androgenic steroids and prohormones, are directly hepatotoxic with the C17-alpha-alkylated compounds carrying the highest risk. The pattern is typically a hepatocellular or mixed injury, often with an AST-to-ALT ratio near or below 1:1, elevated GGT, and possibly elevated bilirubin. The athlete cycling any of these compounds needs to be surfaced as an exposure regardless of the current cycle-on-or-off status. Prompt discontinuation is the intervention; medical co-management is warranted for meaningful elevations.

Green tea extract at high daily EGCG doses. High-dose green tea extract, particularly at daily EGCG doses above 800 mg and in the fasted state, is associated with idiosyncratic drug-induced liver injury. The pattern is variable but hepatocellular is most common. Discontinuation is the intervention; the herbal-supplement inventory should catch this.

Fat-burner and thermogenic stacks. Multi-ingredient fat-burner formulations frequently contain green tea extract at high doses, yohimbine, synephrine, and undisclosed ingredients that may include hepatotoxic compounds. Full-ingredient disclosure is often not available; the recommendation is discontinuation while the workup runs.

Herbal products with known hepatotoxicity. Kava, chaparral, comfrey, germander, pennyroyal, black cohosh (idiosyncratic), and several traditional Chinese and ayurvedic preparations carry hepatotoxicity signals. The intake needs to ask specifically about herbal and traditional-medicine use, as these are frequently not surfaced under the umbrella of "supplements."

Peptides and growth-hormone releasers. Injectable and orally available peptide products, including MK-677 (ibutamoren), various growth-hormone-releasing peptides, and BPC-157 and related compounds, sit in an unregulated space where product purity, dosing, and hepatic effects are not well characterized. Surface as exposures in the intake and coordinate with the medical team.

High-dose acetaminophen. Chronic use of acetaminophen at daily doses above three grams, or acute high-dose use for injury or headache management, produces predictable dose-dependent hepatotoxicity. Athletes managing chronic pain frequently under-report the true acetaminophen dose. Direct-question the pattern in every workup.

Iron supplementation without indication. Chronic iron supplementation in athletes without documented iron deficiency, particularly in male athletes with underlying hemochromatosis susceptibility, produces iron-overload hepatotoxicity on a long timescale. The iron panel — ferritin, transferrin saturation — should sit adjacent to the liver enzyme workup where the picture warrants.

Multi-ingredient protein-adjacent formulations. Protein powders themselves are not hepatotoxic at normal use, but multi-ingredient formulations may contain herbal or ergogenic additives with hepatotoxicity signals. Full ingredient disclosure is warranted for every regularly used product.

The supplement-inventory conversation is the highest-value clinical action in the liver enzyme workup that primary-care physicals routinely miss. The [supplement reconciliation protocol](/blog/supplement-reconciliation-in-sports-nutrition-intake) is the framework for the depth this needs.

When to refer to medical

Five signals warrant medical referral beyond the dietetic workup.

Any acute presentation with jaundice, right-upper-quadrant pain, encephalopathy, or abnormal synthetic-function markers (albumin, INR, bilirubin). Urgent medical evaluation regardless of the AST-ALT read.

AST or ALT above five times the upper limit of the reference range, or a rising trajectory across serial draws. Medical workup for the extended differential — viral hepatitis serology, autoimmune hepatitis panel, iron studies, ceruloplasmin, hepatic imaging.

Elevated GGT with alcohol history warranting the extended alcohol-use-disorder workup. Coordinate with primary care on the AUDIT-based screening and follow-on.

Suspected drug-induced liver injury from a prescription medication (statin, methotrexate, isoniazid, others) or from a hepatotoxic supplement. Medical review and coordination on the discontinuation or substitution plan.

Persistent enzyme elevation on repeat panel four to twelve weeks after the initial identified drivers have been addressed. The functional-workup non-responder warrants the structural workup.

Common counseling mistakes

Reading AST and ALT in isolation and calling the case hepatic dysfunction. The skeletal-muscle contribution in the trained athlete is meaningful and routinely dominant. GGT is the differential; the workup that skips it cannot separate the sources.

Prescribing alcohol abstinence reflexively on the AST-ALT elevation without the GGT read. The trained athlete with low alcohol intake and normal GGT does not need alcohol abstinence as the primary intervention. The recommendation misreads the case and undermines the athlete's trust in the workup.

Failing to run the direct supplement inventory. The generic "any supplements?" question produces a partial inventory. Direct-question SARMs, prohormones, anabolic steroids, pre-workouts (with ingredient list), fat-burners, herbal products, and peptides. Non-judgmental and specific.

Missing the CK follow-on. CK quantifies the skeletal-muscle contribution and is a cheap add-on that resolves substantial ambiguity in the athletic case.

Missing the metabolic-syndrome differential in the lean-appearing athlete. NAFLD is not eliminated by a normal BMI. The waist-to-height, insulin, and lipid panel should sit adjacent to the read.

Delaying medical referral on Quadrant 3. The acute hepatocellular pattern, the jaundice case, and the synthetic-function-abnormal case need medical evaluation now, not after a dietetic trial.

Endorsing "liver support" supplements as an intervention. Milk thistle, TUDCA, NAC, and other "liver support" products do not have consistent evidence of benefit in the absence of a specific clinical indication, may signal the athlete's own suspicion of ongoing hepatotoxic exposure, and can complicate the diagnostic picture. The intervention is discontinuation of the offending exposure, not supplementation over the top of it.

Where this lands in the SOAP

Subjective section format:

Liver Enzyme Workup (panel reviewed YYYY-MM-DD):

• AST: [X U/L, x ULN]
• ALT: [X U/L, x ULN]
• AST-to-ALT ratio: [calculated]
• ALP: [X U/L]
• GGT: [X U/L or NOT ORDERED — flag]
• Total bilirubin: [X mg/dL]
• Direct bilirubin: [X mg/dL if abnormal]
• Albumin: [X g/dL]
• INR: [X, if ordered]
• CK: [X U/L or NOT ORDERED — flag]
• LDH: [X U/L, if ordered]
• Lipid panel, fasting glucose/insulin: [as indicated]

Training context:

• Draw timing relative to last hard session: [X hours]
• Training-load pattern past 7 days: [narrative]
• Recent eccentric-heavy, metcon, or race-effort sessions: [narrative]
• Body-composition trajectory past 3 months: [narrative]

Supplement and medication inventory:

• Prescription medications: [full list, doses]
• Over-the-counter (acetaminophen dose/frequency in particular): [list]
• Sports supplements (protein, creatine, beta-alanine, pre-workout with ingredients): [list]
• Ergogenic aids (SARMs, prohormones, AAS, peptides, GH releasers): [direct-question inventory]
• Herbal products (green tea extract, kava, herbal blends): [list]
• "Liver support" or hepatic-protective products: [list — signal for underlying exposure]

Alcohol history:

• Self-reported servings per week: [X]
• AUDIT or AUDIT-C score: [X]
• Cross-referenced against GGT: [narrative]

Metabolic-syndrome overlay:

• BMI / waist-to-height ratio / DEXA VAT: [values]
• Triglyceride-to-HDL ratio, fasting insulin, HOMA-IR: [values]
• Family / personal history of NAFLD, T2D, metabolic syndrome: [narrative]

Symptom and history:

• Jaundice, RUQ pain, pruritus, dark urine, pale stool: [narrative]
• Fatigue, malaise, appetite change: [narrative]
• Viral hepatitis risk factors, family history of liver disease: [narrative]

Quadrant: [1-4 from clinical matrix]

Clinical impression: [statement integrating AST-ALT with GGT, CK, AST-to-ALT ratio, training pattern, supplement inventory, alcohol history, metabolic overlay]

Action: [supplement discontinuation / CK follow-on / repeat panel timing / medical referral / observation]

Follow-up: [recheck date, plan, escalation triggers]

Assessment integrates the six-dimension read and assigns the case to a quadrant. Plan documents the differential, the supplement or lifestyle intervention, the medical-coordination communications, and the recheck cadence. See [SOAP notes for sports dietitians](/blog/soap-notes-for-sports-dietitians) for the broader documentation framework.

The dietetic intervention in the compensating case

The Quadrant 1 skeletal-muscle-derived case does not warrant a dietetic intervention beyond the recheck-off-training protocol. Educate the athlete on the training-derived enzyme elevation, the resolution timeline, and the future-panel timing recommendation to draw 72+ hours off heavy training when possible.

The Quadrant 2 supplement or lifestyle case responds to three intervention levers in most presentations.

Discontinuation of the identified hepatotoxic exposure. The single-highest-yield action. Full-stack discontinuation of SARMs, prohormones, anabolic steroids, high-dose green tea extract, kava, and other identified offending agents. Complete removal of undisclosed multi-ingredient formulations pending clarification of the ingredient list. Non-judgmental and specific.

Address of metabolic-syndrome drivers where present. NAFLD contribution responds to caloric intake calibrated to the body-composition and insulin picture, carbohydrate quality (see the insulin resistance workup for the framework), body composition improvement where warranted, and alcohol reduction where the pattern warrants.

Repeat panel at four to twelve weeks with expected trajectory documented. The intervention needs the empirical validation the panel provides. Movement toward normalization on serial draws confirms the identified drivers; failure to move warrants the extended workup and the medical coordination.

Where platform tooling helps

The bottleneck in the liver enzyme workup at scale is the multi-system integration — the AST and ALT read against GGT, the CK follow-on integrated with the training-load pattern, the direct supplement inventory across a stack that may include SARMs and multi-ingredient formulations, the metabolic-syndrome overlay, the alcohol-history integration, the differential across skeletal-muscle-derived, hepatic-supplement-driven, alcohol-driven, and NAFLD contributions, and the recheck cadence across serial panels. The intake that runs the integration by hand drops it on busy weeks; the CrossFit competitor's case gets managed as an alcohol-abstinence recommendation when the actual differential runs through his undisclosed supplement stack.

The leverage is a liver enzyme workup module that ingests AST and ALT, prompts for GGT and CK follow-on where not ordered, calculates the AST-to-ALT ratio, prompts for the structured supplement inventory across the categories most under-caught (SARMs, prohormones, herbal products, "liver support" as a signal), integrates the training-load pattern in the 72 hours before the draw, captures the alcohol history against the GGT read, surfaces the four-quadrant decision matrix, pre-populates the SOAP documentation, tracks the recheck cadence, and manages the medical-coordination communications where escalation is warranted. The RD's job is the clinical judgment and the conversation with the athlete, not the spreadsheet.

The chart trail is defensible — every interpretation tied to the integration context that justified it, every referral documented with the pattern that drove it, every dietetic and lifestyle intervention paired with the differential reasoning behind it.

The bottom line

Elevated AST and ALT on a primary-care panel in a trained athlete is not automatically hepatic dysfunction. Skeletal muscle contributes meaningfully to both enzymes on the timescale of hours to days after heavy training, and the panel drawn within 72 hours of an eccentric or high-intensity session in a training-loaded athlete routinely returns AST and ALT elevations that are entirely skeletal-muscle-derived. The primary-care read that assumes hepatic origin and treats the elevation as an alcohol-first differential misclassifies the case.

The workup that catches the real cases reads AST and ALT against GGT, orders CK to quantify the skeletal-muscle contribution, calculates the AST-to-ALT ratio in the clinical context, runs the direct supplement inventory across the categories most under-caught, captures the alcohol history and cross-references against GGT, integrates the metabolic-syndrome overlay, and assigns the case to a four-quadrant matrix that drives the intervention pathway. The Quadrant 1 skeletal-muscle case gets the recheck-off-training confirmation. The Quadrant 2 supplement or lifestyle case gets the identified hepatotoxic exposure discontinued and the metabolic-syndrome drivers addressed. The Quadrant 3 acute case gets the medical referral early. The Quadrant 4 ambiguous case gets the extended follow-on.

The 27-year-old CrossFit competitor with the AST 78, ALT 62, normal GGT, undisclosed SARM cycle, high-dose green tea extract, and self-directed "liver support" stack is not the alcohol-abstinence case the primary-care panel produced. He is a Quadrant 2 case where the alcohol conversation is not the first-order intervention, and where the workup that runs the supplement inventory catches what the alcohol-first read misses. The intake that reads AST and ALT and stops does not.

[Calsanova's Dietitian plan](/signup?role=dietitian) ships a liver enzyme workup module with GGT and CK prompts, structured supplement-inventory capture across SARMs and hepatotoxic-herbal categories, training-load overlay integration, alcohol-history integration against the GGT read, four-quadrant decision-matrix surfacing, and pre-populated SOAP documentation with medical-coordination communications built in. The clinical judgment stays with the RD; the integration stays off the spreadsheet.