Carolina Criminal Defense & DUI Lawyer UpdatesThe Limits of Chemical Certainty: The Auto-Brewery Syndrome & DWI Charges
Auto-Brewery Syndrome (ABS) remains a bit of a theoretical curiosity. It represents a measurable biochemical anomaly during which yeast or bacteria residing in the gastrointestinal tract convert carbohydrates into ethanol within the human body. 
Though somewhat rare, it is medically documented, scientifically verifiable in some instances, and possibly legally consequential, at least relative to DUI charges in North Carolina.
ABS reveals the longstanding problems with treating a blood or breath alcohol number as unassailable evidence of impairment, the alleged per se impairment often espoused by prosecutors.
Clearly, chemical testing is the backbone of impaired-driving enforcement. Reason and the common “horse sense” of North Carolina jurors remains the sinew and musculature of our system of justice that helps ensure fundamental fairness, holding the State accountable to its Burden of Proof.
Forensic measurement of a BAC – Blood Alcohol Concentration presupposes that the ethanol detected originated from consumption of an alcoholic beverage. ABS may, in appropriate circumstances, serve as a basis of attacking that assumption.
The presence of endogenous ethanol means the numeric reading is not necessarily proof of voluntary ingestion of EtOH (Ethanol / Ethyl Alcohol) or actual impairment. It raises questions that could reach beyond one case or one defendant, challenging reliability of the State’s evidentiary model and the integrity of judicial fact-finding itself.
The following analysis explores Auto-Brewery Syndrome as both a biological phenomenon and a forensic problem for DWI charges in North Carolina. It draws upon peer-reviewed literature, including Ricardo Jorge Dinis-Oliveira’s 2021 review in Metabolites, and integrates the medical science with North Carolina evidentiary law. The discussion is written for prosecutors, defense counsel, toxicologists, and expert witnesses who understand that science, not rhetoric, should guide the admissibility of evidence.
If you or someone you care about faces an impaired driving charge in the Charlotte metro region, including Mecklenburg, Iredell, Union, Gaston, Lincoln, or Rowan Counties, contact Bill Powers at Powers Law Firm to discuss the case. For select cases, our DWI defense lawyers are available for consultation statewide. Recognized throughout North Carolina for his work in impaired-driving defense and his contributions to legal education, Bill Powers may be reached by TEXT or call at 704-342-4357 to discuss the facts of your case on a confidential basis.
I. Auto-Brewery Syndrome: The Metabolic Mechanism of Endogenous Ethanol
The human gastrointestinal tract is a complex ecosystem of bacteria, fungi, and other microorganisms collectively known as the microbiome. Under normal conditions, this community maintains equilibrium.
Fungi represent less than two percent of its composition and are generally suppressed by bacterial flora. Antibiotics, surgical alteration of the bowel, diabetes, ketotic intermittent fasting, immune compromise, or carbohydrate-rich and absent diets can disrupt this balance.
In ABS, specific microorganisms, most commonly Saccharomyces cerevisiae and Candida albicans, but sometimes Candida glabrata, Candida krusei, or Klebsiella pneumoniae ferment dietary carbohydrates into ethanol through glycolytic and anaerobic pathways.
The process begins with glucose transport across the cell membrane, followed by pyruvate decarboxylation and coproduction of acetaldehyde to ethanol. Humans lack the enzyme pyruvate decarboxylase, which prevents significant endogenous ethanol synthesis under ordinary physiology. Microbial colonization can bypass that limitation.
Normally, trace ethanol produced in the gut is metabolized on its first pass through the liver. Hepatic alcohol dehydrogenase has a low Michaelis constant (Km 0.05-0.10 g/L) and clears ethanol efficiently at low concentrations.
Physiologic endogenous levels are typically less than 0.001 g/L, which is below forensic relevance.
For ABS to produce measurable intoxication, hepatic clearance must be overwhelmed by sustained in-situ fermentation – Bill Powers, North Carolina DWI Defense Lawyer
Scientific literature provides confirmation that such conditions exist in patients with short bowel syndrome, Crohn’s disease, gastrectomy, Roux-en-Y gastric bypass, or chronic obstruction.
Diabetes and prolonged antibiotic therapy have also been associated with dysbiosis-induced ethanol production. The resulting metabolic environment favors yeast proliferation, particularly under acidic gastric pH and carbohydrate excess.
II. Clinical Diagnosis and Auto-Brewery Syndrome
Because the syndrome is relatively rare, the diagnostic and evidentiary threshold is necessarily exacting. A claim of endogenous ethanol production requires substantive proof, not mere anecdotal assertion. The methodological approach may involve a supervised carbohydrate challenge in a controlled medical setting, 24/7 glucose and/or ketone monitoring, and a documented medical record.
A “carbohydrate challenge” ordinarily begins with 24 hours of dietary control to eliminate exogenous ethanol and standardize carbohydrate intake. The subject is then administered approximately 200 grams of glucose under continuous observation. Repeated blood and breath samples are collected at defined intervals, typically at baseline and at 0.5, 1, 2, 4, 8, 16, and 24 hours. All samples are preserved in fluoride-oxalate tubes, refrigerated immediately, and analyzed by headspace gas chromatography using dual columns or mass spectrometric confirmation (the same testing protocol common in North Carolina GC testing for alcohol in DWI charges).
The NC DWI Quick Reference Guide
A positive result is defined as a measurable increase in blood or breath alcohol concentration without any possibility of external consumption. Elevated levels confirm endogenous production. The test should be terminated if BAC levels rise to unsafe ranges. Endoscopy and stool cultures can also help to identify the organisms responsible, and possible antifungal susceptibility.
Even with strict supervision, false negatives are possible if microbial activity fluctuates or if environmental factors such as pH and substrate availability differ from baseline living conditions. For this reason, courts evaluating the evidentiary value of a glucose challenge under Rule 702 might consider repeat testing and corroborating microbiological data.
III. Quantitative Context: Physiologic Versus Pathologic Ethanol
Population studies using gas chromatography have found median concentrations around 0.001 g/L, orders of magnitude below statutory thresholds. These findings confirm that under normal physiology, internal fermentation (in most but not all instances) contributes little to nothing of legal consequence.
Healthy subjects consistently show negligible endogenous ethanol production. That means Auto-Brewery Syndrome as a defense, should be, at best, rare – Bill Powers, Charlotte DWI Lawyer
At the same time, there are documented ABS cases with reported blood alcohol concentrations exceeding 2.0 g/L without ingestion (drinking) an alcoholic beverage.
Such values are extreme but often explainable.
In each confirmed case, the patient exhibited a combination of risk factors, including things like a compromised intestinal anatomy, yeast overgrowth, carbohydrate loading, and diminished hepatic function (liver failure).
From a forensic perspective, the issue is not how frequently these cases occur but whether the possibility invalidates the assumption that every detectable ethanol molecule must originate from drinking.
A single verified mechanism capable of producing forensic-level ethanol internally deserves a cautious review of chemical (BAC reading) evidence.
IV. The Statutory Framework and the Misuse of “Per Se”
North Carolina’s impaired-driving law, N.C.G.S. 20-138.1, is routinely described as a “per se” law.
That terminology is at best imprecise, and at worse, somewhat misleading.
The NC DWI law does not create a true strict liability offense, even though prosecutors often characterize the so-called “.08 or more” provision as such.
The law still requires proof of operation, alcohol presence, and sufficient reliability of the analytical method used to establish the numerical result.
At most it creates a rebuttable statutory inference, not an absolute liability scheme. The finder of fact must still determine credibility, reliability, and whether the State met its burden of proof beyond a reasonable doubt.
The phrase, “shall be deemed sufficient” in the North Carolina Pattern Jury Instruction (N.C.P.I.—Crim. 270.20) reflects a deliberate policy choice that subtly tilts the scales.
It converts what should be an evidentiary inference into something resembling a legislative command to the fact-finder.
In theory, the PJI is meant to track the statute, but that phrasing clearly is not neutral. It tells jurors that a chemical number is sufficient to convict if they find the testing reliable, not merely that they may consider it as evidence of impairment.
The difference is profound.
“Shall be deemed sufficient” reads more like a rule of law than an evidentiary presumption, effectively giving statutory weight to a machine-generated number.
The law establishes evidentiary thresholds (as to the reported BAC) that permit, but do not compel, a finding of impairment based on a chemical number.
The finder of fact determines credibility and weight of all evidence properly admitted at trial.
In practice, that language pressures juries to treat the numeric reading as dispositive, despite Rule 702’s demand for proof of reliability.
A fair instruction would acknowledge that the number is one piece of evidence to be weighed with all others, not an automatic finding of guilt – Bill Powers, DWI Defense Lawyer
The term “per se” originated as a prosecutorial convenience, borrowed from civil regulatory language, and gradually embedded in law enforcement training and appellate shorthand.
It obscures the reality that every chemical analysis is subject to scientific limitations. Breath and blood alcohol results are evidence, not verdicts.
Auto-Brewery Syndrome strikes at the core of that misunderstanding.
If endogenous ethanol production can inflate a BAC reading independent of consumption, the statutory presumption that a particular number equates to guilt collapses.
The statute’s reliability depends on the biological premise that ethanol concentration reflects ingestion and metabolism. Properly proven ABS could serve to break that link.
In practical terms, that means the jury or judge is called to evaluate whether the number reflects the defendant’s physiology rather than voluntary drinking-related impairment.
The evidentiary burden shifts not in law but in logic. The State should be required to prove that the ethanol detected arose from consumption beyond a reasonable doubt.
V. Evidentiary Reliability and Expert Qualification under Rule 702
North Carolina Rule of Evidence regarding 702 Expert Witness testimony aligns with the Daubert standard of scientific reliability.
The rule asks whether the testimony is based on sufficient facts, derived from reliable principles, and applied properly to the case.
ABS – Auto-Brewery Syndrome evidence meets those criteria when presented through competent medical and toxicological experts who adhere to recognized diagnostic protocols.
A properly documented glucose challenge, conducted under supervision, is a reproducible experiment with known error rates.
It is testable, peer-reviewed, and anchored in established microbiological science. The methodology satisfies Rule 702. The dispute lies in its application, not its legitimacy.
When defendants assert ABS without data, courts rightly exclude speculative testimony.
When the defense presents confirmed endogenous ethanol production under controlled conditions, the evidence should be admissible. It directly bears on the reliability of the State’s chemical tests and the ultimate issue of impairment – Bill Powers, DUI Defense Attorney
Judges should distinguish between “my client has ABS” as an argument and Auto-Brewery Syndrome as a demonstrated metabolic fact.
The former is rhetoric, the latter is evidence.
VI. Analytical Artifacts and the Problem of False Positives
Endogenous ethanol production is not the only threat to forensic accuracy.
Post-collection fermentation, improper preservation, or microbial contamination can generate or increase ethanol levels after sampling.
Blood stored without fluoride preservatives, exposed to heat, or delayed in analysis can yield artificially high readings due to in-vitro fermentation – Bill Powers, DWI Defense Lawyer
Improper sampling and storing resulting in endogenous alcohol production mimic ABS in effect but differ in origin.
Both, however, prove the same conceptual point.
Ethanol numbers should not deemed self-authenticating.
Without proper controls, the measurement may represent chemistry occurring outside the body rather than inside it.
Courts evaluating chemical results should therefore consider the total analytical environment.
Preservation method, storage temperature, transit time, and chain of custody can all be key aspects of scientific reliability and therefore determinative of admissibly or irrelevant, inadmissible evidence.
When the State’s evidence lacks documentation of such variables, the reading should not be treated as dispositive.
VII. Medical Treatment and Forensic Corroboration
Auto-brewery syndrome is clinically verifiable
When treated with antifungal medication, dietary restriction, or in some cases fecal microbiota transplantation, patients can show measurable drops in blood ethanol and resolution of symptoms.
The improvement confirms causation and shows that restoring microbial balance reverses the condition.
Patients adhering to low-carbohydrate or ketogenic diets frequently report symptom improvement, which aligns with the underlying fermentation mechanism.
The fact that dietary control can eliminate ethanol production reinforces the argument that metabolism, not alcohol consumption, drives the phenomenon – Bill Powers, NC DWI Defense Lawyer
A documented decline in measurable ethanol following antifungal therapy supports the biological reality of ABS and should serve to undermine the assumption that ethanol concentration alone establishes guilt.
VIII. The Role of the Finder of Fact
The North Carolina Constitution entrusts credibility determinations to the finder of fact.
- Article I, Section 6 (Separation of powers)
- Section 19 (Law of the land; equal protection of the laws), establishes that factual determinations, including credibility of evidence and witnesses, belong exclusively to the jury, not the legislature or executive
- Under Article I, Section 24 of the North Carolina Constitution, the authority to determine the weight and credibility of evidence rests with the finder of fact, not the State or its instruments
When confronted with ABS evidence, the trier of fact should be tasked with the decision of whether the chemical number reflects impairment, voluntary consumption, or pathological fermentation.
The jury instruction on chemical analysis should also therefore frame the result as evidence to be weighed in light of all circumstances, including medical and scientific explanations for its accuracy or inaccuracy.
To treat a number as absolute is to remove the question of guilt from human judgment and vest it in a machine. That is neither law nor science – Bill Powers, Criminal Defense Attorney
IX. Ethical and Policy Considerations
Recognizing ABS does not excuse unsafe driving.
The condition does not grant immunity from responsibility for conduct that endangers others.
It does, however, demand precision in proof.
Dismissing ABS as fiction ignores established microbiological evidence.
At the same time, accepting every claim of Auto-Brewery Syndrome from clients who are looking for any/every reason to avoid a DWI conviction, without scrutiny, would undermine public confidence and your reputation in the well of the bar.
The proper balance lies in measured skepticism supported by data.
When properly tested, ABS represents a scientific fact with forensic implications that the law must accommodate.
The broader policy lesson is humility.
The human body is not a closed system, and metabolism varies.
The State’s reliance on a single chemical measurement as a proxy for culpability should evolve with the science. Legal certainty built upon biological uniformity is unsustainable. It’s also flat out unfair.
X. The Broader Scientific Context
The implications of ABS extend beyond impaired-driving cases.
Endogenous ethanol production has been linked to nonalcoholic fatty liver disease, metabolic syndrome, and alterations in immune response.
Such reported findings reinforce that ethanol can be both a metabolite and a toxin produced within the body.
From a forensic standpoint, the critical insight is that human biochemistry is variable.
The assumption that every positive alcohol reading derives from drinking ignores that variability.
Modern science demands individualized evaluation rather than categorical inference.
Laboratories and law enforcement agencies would be wise to update training to include awareness of endogenous ethanol production, post-collection fermentation, and microbiome variability.
Education reduces misinterpretation and strengthens public trust in forensic testing.
XII. Auto-Brewery Syndrome: From Numbers to Knowledge
Auto-Brewery Syndrome DWI North Carolina is not an academic exercise. It represents a necessary recalibration of how the criminal justice system interprets scientific evidence. The statutory number in N.C.G.S. 20-138.1 is evidence, not destiny.
When chemical testing meets atypical human physiology, the presumption of accuracy should yield to proof. ABS teaches that the intersection of biology and law demands more than mechanical reliance on breath testing machines. It requires judgment informed by science.
Forensic reliability depends on understanding both the chemistry of ethanol and the context in which it appears. The presence of endogenous ethanol, confirmed through rigorous testing, may refute the premise that all intoxication is self-inflicted. The law should respond with the same discipline that science requires: question the assumption, test the hypothesis, and decide only after the data are verified.
That is how truth is determined in a courtroom, and it is how justice needs to remain aligned with reality.
If you’re facing a DWI charge in the Charlotte metro region, including Mecklenburg, Iredell, Union, Gaston, Lincoln, and Rowan Counties, careful legal guidance matters. Cases that involve medical or scientific issues require thoughtful evaluation and experience in both law and forensic science. To discuss a pending case or consult on evidentiary questions, text or call the Powers Law Firm at 704-342-4357. For select cases, Bill Powers is also available for consultation statewide.