Fundamentals of Human Nutrition/Alcohol metabolism
12.6 Alcohol metabolism
Alcohol Alcohol known as ethyl alcohol or ethanol is produced by the fermentation of different substances like yeast, starches, and sugar (Alcohol). This intoxicating substance is found in many different beverages like wine, liquor, and beer. This substance can be absorbed from two organs the stomach and small intestine and directly absorb into the bloodstream, affecting the central nervous system (Alcohol).
Introduction to Alcohol Metabolism The majority of the alcohol one consumes, about 92-98%, is metabolized by the human body; the other 2-8% is lost through other bodily functions like “urine, sweat, or breath” (HAMS: Harm Reduction for Alcohol). There are two primary pathways in which alcohol can be metabolized: The most significant pathway, which metabolizes the majority of ethanol in the liver, is initiated by the enzyme alcohol dehydrogenase (ADH) (HAMS: Harm Reduction for Alcohol). This system is responsible for breaking down small amounts of alcohol. ADH oxidizes ethanol into Acetaldehyde, a toxin that contributes to the damaging effects of alcohol. Once it is converted, Acetaldehyde enters the mitochondria and is oxidized into acetate (King, 2015). The second pathway of ethanol metabolism is known as the Microsomal ethanol-oxidizing system (MEOS). The activity of this oxidizing system increases with the excess consumption of alcohol and unlike the ADH system, requires energy (HAMS: Harm Reduction for Alcohol).
An In-depth look at Alcohol Metabolism
As mentioned above, the process of oxidative alcohol metabolism can be broken down into four essential steps. These steps are the digestion and absorption of ethyl alcohol, the oxidation of ethyl alcohol to acetaldehyde, further oxidation of acetaldehyde to acetate, and the synthesis of acetyl-CoA from acetate.
According to the National Institute on Alcohol Abuse and Alcoholism’s 2007 publication, there are three main routes for the oxidation of ethyl alcohol to acetate. The first and primary route oxidative route involves the enzyme alcohol dehydrogenase. This enzymatic reaction occurs in the cytosol of hepatic cells and involves the oxidation of ethyl alcohol to acetate with a simultaneous reduction of a Nicotinamide Adenine Dinucleotide (NAD+) by two electrons to its reduced form (NADH). The second route of ethyl alcohol oxidation involves the enzyme catalase, which is located in cell bodies called peroxisomes. In this enzymatic reaction, catalase stimulates the oxidation of ethyl alcohol via a reduction reaction with a hydrogen peroxide molecule (H2O2) to two water molecules (H2O). This once again ultimately yields acetaldehyde. While this pathway facilitates only a small minority of alcohol metabolism, some research suggests that the pathway becomes more preferential when the patient is in a fasted state (Zakhari, 206). The third and final known route of ethyl alcohol oxidation is the Microsomal ethanol-oxidizing system (MEOS). Microsomes are nano sized heterogeneous vesicles that form from components of a cell’s endoplasmic reticulum ("Cellular Component - Microsome," n.d.). These microsomes, or vesicles, contain cytochrome P450 enzymes that assist in the oxidation of ethyl alcohol, especially in patients with a history of chronic alcohol consumption. Cytochrome P450 enzymes work in an energy dependent reaction where an oxygen molecule acts as the electron acceptor, reducing the ethyl alcohol molecule, and Nicotinamide Adenine Dinucleotide Phosphate molecule acts as a reducing agent.
All of the mentioned reactions above contribute solely to the second step of alcohol metabolism, the oxidation of ethyl alcohol to acetaldehyde. According to Zakhari’s 2006 publication, acetaldehyde is a highly toxic and reactive molecule that is believed to be not only a carcinogen, but also may contribute to the addictivity of alcohol consumption. As such, it is of vital importance to quickly oxidize the acetaldehyde molecule to a less toxic acetate molecule. This process is almost entirely governed by the enzyme aldehyde dehydrogenase 2 (ALDH2), which is located in the mitochondria of cells. This enzyme utilizes NAD+ as an oxidizing agent of acetaldehyde to form acetate. It is important to note that there is also an aldehyde dehydrogenase 1 enzyme that is active in the cytosol, however the metabolic activity of this enzyme is extremely small in relation to ALDH2 (Zakhari, 2006).
The final step in the metabolism of ethyl alcohol involves the transformation of acetate into a metabolically useful molecule. This is accomplished by converting acetate into acetyl CoA via the enzyme acetyl-CoA synthetase. Acetyl CoA is a molecule may now go on to perform a number of metabolic activities, such as enter the Krebs cycle, or be used for lipid and cholesterol biosynthesis (Zakhari, 2006).
Physiological Differences that can Affect Metabolism Food- The amount and type of food one has in the Gastrointestinal System (GI tract) can affect the absorption of ethanol. The rate of absorption depends on the stomach and how quickly it can void it contents into the small intestine. This means that the more food one has in his or her stomach will slow the digestion and absorption of this “intoxicating” substance, diminishing its effects (Factors Influencing Alcohol Absorption and Metabolism, 2000). Gender- Women and men metabolize alcohol differently. Women have less body water and lower amounts of active ADH. This increases the amount of alcohol ingested and absorbed by the blood stream, causing women to be more susceptible to alcohols affects (Factors Influencing Alcohol Absorption and Metabolism, 2000).
Adverse Effects of Excess Alcohol Consumption
Depending on the state of the Individual and rate of consumption, alcohol can have short term and long term effects. Some short term effects are: “slurred speech, drowsiness, vomiting, breathing difficulties, impaired judgement, decreased perception and coordination, blackouts, and unconsciousness (Short- & Long-Term Effects of Alcohol). If alcohol is consumed in large amounts, known as binge drinking, it can cause long term effects, including: “unintentional injuries such as a car crash, family problems, high blood pressure, liver disease, and cancer” (Short- & Long-Term Effects of Alcohol).
Fetal Alcohol Syndrome
One of the lasting effects of alcohol consumption is known as Fetal Alcohol Syndrome. This occurs when a woman drinks alcohol during pregnancy. Children affected by this can suffer from physical, behavioral, and learning disabilities (Factors about FASDs, 2015). Some include: “abnormal facial features, small head size, low body weight, poor coordination, difficulty with attention, learning disabilities, vision or hearing problems, and problems with the heart, kidneys, or bones” (Factors about FASDs, 2015).
Alchol. (n.d.). Retrieved August 20, 2015, from http://www.drugabuse.gov/drugs-abuse/alcohol Cellular component - Microsome. (n.d.). Retrieved December 2, 2015, from http://www.uniprot.org/locations/SL-0166 HAMS: Harm Reduction for Alcohol. (n.d.). Retrieved August 20, 2015, from http://www.hamsnetwork.org/metabolism/ Factors Influencing Alcohol Absorption and Metabolism. (2000, October). Retrieved August 20, 2015, from http://pubs.niaaa.nih.gov/publications/aa35.htm Facts about FASDs. (2015, April 16). Retrieved August 20, 2015, from http://www.cdc.gov/ncbddd/fasd/facts.html King, M. (2015, August 18). Ethanol Metabolism. Retrieved August 20, 2015, from http://themedicalbiochemistrypage.org/ethanol-metabolism.php#metabolism National Institute of Alcohol Abuse and Alcoholism. (2007, July). Alcohol Metabolism: An Update. Retrieved December 2, 2015, from http://pubs.niaaa.nih.gov/publications/AA72/AA72.htm Short- & Long-Term Effects of Alcohol. (n.d.). Retrieved August 20, 2015, from http://www.drugfreeworld.org/drugfacts/alcohol/short-term-long-term-effects.html Zakhari, +. (2006). Overview: How is alcohol metabolized by the body? Overview: How Is Alcohol Metabolized by the Body?, 29(4). Retrieved December 2, 2015, from http://pubs.niaaa.nih.gov/publications/arh294/245-255.pdf
Section 12.6- Alcohol Metabolism
The term alcohol actually refers to a group of organic compounds containing a hydroxyl (OH) group. In laymen’s terms, alcohol refers to ethanol, or ethyl alcohol, the byproduct of fermentation, a process in which yeast consumes sugars to produce CO2 and ethanol (Whitney & Rolfes, 2016). When describing alcohol, it is mostly considered to be the intoxicating ingredient in beer, wine, and liquor. Because ethanol is less toxic than other alcohols, and because of the effects it causes, people consume it to obtain those effects. Therefore alcohol is classified as a drug, a substance that modifies bodily functions.
Absorption of Alcohol in the Body
As soon as alcohol enters the body it is immediately absorbed. Unlike foods, which require time in order to break down and absorb nutrients, the effects of alcohol can be felt immediately. Alcohol dehydrogenase begins the breakdown of alcohol in the stomach. It is then passed quickly through the small intestine where absorption takes place before most other nutrients to ensure quick disposal. From the small intestine, the capillaries carry alcohol to every cell in the liver, where most of the absorption takes place (Whitney & Rolfes, 2016). While in the liver, alcohol is metabolized by two enzymes: Alcohol dehydrogenase (ADH), as in the stomach, and aldehyde dehydrogenase (ALDH). ADH first metabolizes alcohol into acetaldehyde and then further metabolizes it into acetate. Acetate is then metabolized into water and carbon dioxide in tissues other than the liver and eliminated from the body (US Dept. of Health and Human Services, 2007).
Effects of Alcohol
According the National Institute on Alcohol Abuse and Alcoholism (n.d.), alcohol affects multiple organs in the body including the brain, heart, liver, pancreas, and immune system. In the brain, alcohol can affect the how the brain works and looks, leading to irrational behavior and the inability to coordinate movement easily and think clearly. Excess alcohol consumption has been shown to affect the heart, both over time and on single occasions, by causing cardiomyopathy (stretching and drooping of heart muscle), arrythimias, stroke, and high blood pressure. Because the liver is the site of most alcohol absorption, the affects of drinking weigh heavily on the liver. Excess drinking can lead to steatosis (fatty liver), alcohol hepatitis, fibrosis, and cirrhosis of the liver. The pancreas creates a toxic substance that can lead to pancreatitis because of alcohol consumption. Finally, alcohol consumption, even on a single occasion, can weaken the body’s immune system, making it more susceptible to diseases like pneumonia and tuberculosis (National Institute on Alcohol Abuse and Alcoholism, n.d.).
Alcohol alert (U.S. Department of Health and Human Services, Comp.) [Leaflet]. (2007). Retrieved from http://pubs.niaaa.nih.gov/publications/AA72/AA72.htm
National Institute on Alcohol Abuse and Alcoholism. (n.d.). Alcohol's effects on the body. Retrieved November 30, 2015, from http://www.niaaa.nih.gov/alcohol-health/alcohols-effects-body
Whitney, E., & Rolfes, S. R. (2016). Understanding nutrition (14th ed.). Stamford, CT: Cengage Learning.
12.6.1 Health Ramifications of Alcohol Use
Individuals all across the globe have become accustomed to drinking alcohol. To some it is a regular, casual activity, while others only partake in the consumption to celebrate special occasions. The subject is controversial, but there are studies that suggest a moderate daily intake of alcohol promotes cardiovascular health. In detail the daily recommended alcohol intake for women is one drink as to men to being two drinks per day (One drink = Beer: 12oz; Wine: 5 ounces; Hard Liquor: 1.5). Alcohol is metabolized in the body primarily through the liver; additionally alcohol can also be metabolized through the stomach, brain, and pancreas. Therefore, consumption of alcohol beyond the daily recommendation increases one’s risk of developing life-altering diseases, simply because alcohol interacts with the human body through various routes.
Short Term Effect
The tolerance of consuming alcohol varies differently each person. In essence, gender, age, body weight, and how fast their body metabolizes alcohol are different factors as to how fast alcohol can affect an individual (What is Moderation, n.d.). Some short-term effects of alcohol can consist of: vomiting, slurred speech, impaired judgment, headaches, distorted vision and hearing, decrease in motor skills, and blackouts (Short- & Long-Term Effects of Alcohol, n.d.). As mentioned before, these different short-term effects vary to each person’s gender and physical condition.
Long Term Effect
When one indulges in too much alcohol, they increase their risk of developing effects (both long-term and permanent). Depending on the gender, physicality, and genetic background of the person, each person will have different reactions to over consumption of alcohol. Some of the various unfortunate long-term effects are cancer of mouth or throat, cardiovascular disease, liver, disease, nervous system, pancreatitis, and birth defect.
Excessive alcohol drinking can contribute to the development to different harmful cancers. The various risk of cancers can include the mouth, throat, colon, liver, even rectum, and breast (Alcohol Alert, 2007). However, the consumption of alcohol is not directly correlated to the development of cancer; diagnosis does not become inherent, the risks are just increased. When alcohol is consumed in the body, its converted into a toxic chemical called acetaldehyde (Alcohol Alert, 2007). This chemical can be a stimulant to the formation of cancer because acetaldehyde can cause the interruption the cells repairing a damaged DNA (How alcohol causes cancer, 2015). Additionally, acetaldehyde causes liver cells to regenerate faster than normal; this can lead to cell alternation that can be a promoter to cancer.
As the liver accounts for being the main source for alcohol to be metabolized, this places the liver in a vulnerable position to being harmfully effected due to its high exposure. Fatty liver is a type of liver disease that’s commonly attained by over consumption of alcohol, which in fact over 90% of regular drinkers develops this type of disease (Alcohol Alert, 2007).
Alcohol metabolism also occurs in the pancreas, which can dangerously expose it to high levels of toxicity byproducts of acetaldehyde (Alcohol Alert, 2007). Like other diseases, overconsumption of alcohol isn’t the only factor to the cause of pancreatitis, but more in addition to dietary habits, smoking, genetic background of how alcohol is metabolized, and the routinely patterns of alcohol intake (Alcohol Alert, 2007).
Women who are pregnant are highly recommended not to consume alcohol. For example, women who consumes alcohol during pregnancy are likely to be exposed to Fetal Alcohol Spectrum Disorder, also known as FADS. All of the toxic chemicals from when the alcohol enters the body to when its been metabolized to acetaldehyde, will cause birth defects. For example, highly exposing the fetus to alcohol can prevent the fetus from receiving essential nutrients through the placenta (Alcohol Alert, 2007). Babies, who are born with FADS, are prone to reach conditions of mental impairment, physical abnormalities, and behavioral problems (What is Moderation, n.d.).
What is Moderation? (n.d.). Retrieved December 2, 2015, from http://www.alcoholscreening.org/Learn-More.aspx?topicID=8&articleID=26 Short- & Long-Term Effects of Alcohol. (n.d.). Retrieved December 2, 2015, from http://www.drugfreeworld.org/drugfacts/alcohol/short-term-long-term- effects.html Alcohol Alert (2007). Retrieved from U.S. Department of Health & Human Services: http://pubs.niaaa.nih.gov/publications/AA72/AA72.pdf How alcohol causes cancer. (2015, March 23). Retrieved December 2, 2015, from http://www.cancerresearchuk.org/about-cancer/causes-of-cancer/alcohol-and- cancer/how-alcohol-causes-cancer