Alcohol Metabolism Changes Considerably After Gastric Bypass Surgery

It is important for anyone handling the defense of drunk driving cases to have a basic understanding of how alcohol enters and is eliminated in the bloodstream.  This is broadly referred to as alcohol metabolism.  This knowledge can sometimes be pivotal in determining and resolving issues of dispute in a typical drunk driving case, and when death or serious injury is involved, alcohol metabolism can be the major focus of a defense.

Very simply speaking, alcohol metabolism is a function of three things: alcohol consumption, distribution and elimination.  The amount of alcohol consumed will ultimately control the upper range of a driver’s possible peak bodily alcohol content (BAC).  As a rule of thumb, an alcoholic beverage can raise a driver’s blood alcohol level by .02 to .025 per unit of alcohol.1  (One unit being a 12 oz beer or 1.5 oz of 80- proof liquor).

However, provided the alcohol enters the body through the normal course, the stomach will act as the gatekeeper before the alcohol reaches the blood stream.  Once in the blood stream, the alcohol is (relatively) quickly distributed throughout the body.  When a person drinks on an empty stomach the alcohol rapidly reaches the small intestine and then the bloodstream.  When the stomach is full, the alcohol will take much longer to reach the small intestine.  Once in the bloodstream, elimination takes place primarily in the liver.  An enzyme known as alcohol dehydrogenase is responsible for breaking down or neutralizing the alcohol, but can only do so in a fixed amount per hour.  This fixed amount does not change with the amount of alcohol present.

Persons who have had great difficulty managing their weight might consider gastric bypass surgery as a way to encourage weight loss.  This surgery involves radically reducing the size of the stomach, and might involve creating two stomach pouches that are both attached to the small intestine.  In addition to reducing the stomach size, the movement of food and liquid through the stomach also changes.

Gastric bypass surgery results in alcohol moving much more quickly from the stomach into the small intestine.  Because 80% of beverage alcohol is absorbed in the small intestine, this surgery results in a much higher peak BAC than with the equivalent amount of alcohol consumed before the surgery.  Additionally, there is far less gastric alcohol dehydrogenase available for the approximately 20% of initial metabolism of alcohol which normally occurs in the stomach.

Due to these anatomical and physiological changes, drinking after gastric bypass surgery is similar to drinking on an empty stomach, but creates an even higher peak BAC because there is almost no opportunity for the alcohol to begin to break down before entering the bloodstream.  An even better comparison would be to look at the differences in oral consumption verses intravenous consumption.  Because a gastric bypass patient has so little stomach left after surgery, alcohol enters the bloodstream almost as if it was injected by a needle.

This is borne out by the scientific research.  According to one study, alcohol metabolism was significantly different between the bypass patients and the control group who had no stomach surgery.  The bypass patients had a greater peak alcohol level, and it also took them longer to reach zero or no alcohol.  The difference in peak BAC is significant.  The bypass patients were at .08 or unlawful when the control group only had a BAC of just .05.2  This is a nearly 40% difference!

By way of example: assume a driver has consumed a six pack of typical American beer.  This would be six units of alcohol, and would collectively have the capacity to raise a normal person’s peak BAC to about .12-.15.  Thus, with gastric bypass increasing this by 40%, the same amount of alcohol would now create a peak BAC of .168 to .210.  In thinking about these numbers, bear in mind that this does not include any elimination during the drinking spree and before the test was given.  Average elimination rates for adult males is .015 per hour and adult women .018 per hour.

This considerable difference between peak alcohol levels is especially problematic for the “social drinker.”  As can be seen from the example, an average drinker can consume 3 beers and still be below the legal limit whereas a bypass patient could be far above it after the same 3 drinks.  This is why another research study3 suggested that the “higher Cmax (peak BAC) in bypass patients after drinking small amounts of alcohol could have negative consequences when skilled tasks are performed such as driving a motor vehicle.”  Furthermore, “the effects of alcohol on performance and behavior are more pronounced when BAC is rising and near Cmax.”4

As a general intent crime it would be difficult to argue that an unusually high and unlawful bodily alcohol level owing to gastric bypass surgery is a legally exonerating fact.  However, gastric bypass surgery certainly might play into whether or not a person expected to be drunk driving after a relatively small amount of alcohol.  Also, where a death or serious injury is involved this information and knowledge could be pivotal in either the defense or the sentencing.

Defense attorneys handling alleged drunk driving cases where the driver has had gastric bypass surgery should carefully review the facts and interview the client to determine if there still might be a legally or factually sufficient defense.  This is especially true where the facts suggest drinking in close proximity to driving where there might be a rising blood alcohol defense.  It is also very important to carefully review the discovery where an accident or death occurred as in those cases the prosecutor may try to rely on a back-estimation of the alcohol level (also known as retrograde extrapolation) to establish the BAC at the time of the driving.  Be aware that these calculations might also be impacted by bypass surgery.

by Patrick T. Barone

Patrick T. Barone is an adjunct professor at Cooley Law School where he teaches "Drunk Driving Law and Practice."  Mr. Barone is also the co-author of two books on DUI-related issues, including Defending Drinking Drivers (James Publishing), a well-known and highly respected multi-volume national legal treatise.  He is a frequent lecturer on trial practice and drunk driving defense tactics. He can be contacted on the web at:


1. See Jones & Holmgren, Age and gender differences in blood-alcohol concentration
in apprehended drivers in relation to the amounts of alcohol consumed, 188 Forensic
Sci Int’l 43 (2009).
2. Hagedorn, Does Peak BAC Alter Alcohol Metabolism? Surgery for Obesity and Related Diseases, 3 (2007) 543-548.
3. Klockhoff, Faster Absorption of Ethanol and Higher Peak Concentration in Women after Gastric Bypass Surgery, Br J Clin Pharmacol, 2002 December 54(6): 587-591.
4. Id.