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Absorption of Alcohol into the Blood Stream

The absorption rate of alcohol into the bloodstream depends on many factors, those factors may be the difference in a higher or lower blood alcohol content ("BAC") percentage.



Absorption of alcohol into a person's body occurs through a process known as diffusion. Alcohol need not be digested by the body. Alcohol undergoes no chemical change in the body; rather, it is gradually absorbed into the blood, while it passes through the body's digestive system. The quantity of alcohol present in the blood can then be measured. That measurement is usually expressed as a percentage by weight of a given volume of blood. Most commonly, the percentage is expressed as weight per unit volume or grams per 100 milliliters.

Where does alcohol enter the bloodstream?

With respect to the diffusion of alcohol, although a small percent is diffused into the bloodstream through the stomach wall, most of the alcohol passes through the pylorus, which is the junction of the stomach and the upper section of the small intestine. It then passes into the small intestine where most of it is absorbed. Only about 20% of the alcohol is absorbed through the stomach wall with the remaining 80% occurring in the small intestine. This is partially due to the much greater surface area of the small intestine as compared with the stomach.


The rate of absorption depends on numerous factors, including the amount of food the person has in his stomach. This is true primarily because food causes the pylorus to remain constricted or closed, and the alcohol will not be available for absorption until digestion is complete and the pylorus opens, allowing the food, and the alcohol, to pass into the small intestine. Generally speaking, therefore, foods that take longer to digest, such as fats and proteins, will slow absorption more than less complex foods such as carbohydrates. Stomach emptying is also affected by the time of day, with the speed being faster in the morning.

  • The presence of food will slow down or retard absorption. When a person drinks on an empty stomach, most of the alcohol consumed will be absorbed rapidly, with nearly half consumed within the first fifteen minutes and 90% absorbed within one hour.
  • The kind of food the subject consumes also will affect the absorption rate. This is because some food will pass directly into the small intestine, thereby promoting rapid absorption, while other kinds of food will pass more slowly, slowing down absorption. As a general rule, food containing large amounts of carbohydrates will pass through the stomach rapidly, while those foods containing proteins will pass more slowly. Fats can remain in the stomach for almost a full day.
  • The kind of alcohol.  Any alcohol which is mixed with a carbonated beverage, such as champagne, sparkling wines or any kind of soft drink mixer, will speed the absorption rate.
  • Male or female?  There may be significant gender differences as well, although these have not been thoroughly investigated. It is well-known however that women have more fat and less water as a function of weight than do men, and also, that women have larger livers than do men of equal size and weight.
  • The blood.  When considering the forensic implications of absorption it is also important to understand that there are differences in measurable BAC in arterial blood as compared with venous blood, and these largely depend on whether the BAC is increasing or decreasing.
  • Health, age.  Finally, a person's health can influence the absorption rate. If a person is malnourished or suffering from a disease such as gastritis, the alcohol absorption rate can be significantly affected.

If you've been arrested and charged with a DUI, you need an attorney with an understanding of the blood tests used by the police, hospital, or doctors to determine your BAC.  You may call Shaffer & Engle Law Offices, LLC (717) 268-4287 or email us today.