While little research exists on the effects of alcohol on weight gain, the statistics of concurrent alcohol use with the disease of obesity, and the incidence of alcohol use disorder after bariatric surgery, a body of research is growing. This article is intended to provide an overview on the topic of alcohol as it relates to obesity.
Many are familiar with the harmful effects of chronic alcohol use on the body but are unclear on the mechanism of how this happens. Chronic ethanol intake creates dangerous protein-aldehyde compounds, pro-inflammatory chemical attractants, harmful immune cells, and dangerous free radicals. Even though alcohol itself is toxic to the liver, it also degrades intestinal mucosal barriers, altering the microbiome of the gut and triggering the growth of harmful bacteria. Ethanol is metabolized by both a CYP enzyme pathway and an alcohol dehydrogenase pathway. These pathways require the enzymes NADPH and NAD respectively. As a result of these enzymes being used to degrade alcohol, the body creates free radical reactive oxygen species, which cause more damage. It has been established that the amount of damage to the liver is directly related to the amount and duration of exposure to ethanol, and less related to the type of alcoholic beverage. Drinking just 4-5 standard drinks per day is associated with fatty liver (hepatic steatosis). The normal progression is from steatosis to steatohepatitis (inflamed fatty liver) to hepatic fibrosis (scarred liver). The fibrosis occurs due to the activation of “stellate cells” and a subsequent increase in liver collagen production (Subramaniyan, et al., 2021).
In addition to the isolated effects of alcohol on the liver and overall health, more information is emerging regarding diet and body weight in conjunction with alcohol use. One group of authors demonstrated in mice that the murine equivalent of binge drinking combined with a high-fat diet (HFD) resulted in an increase of overactive immune fighting cells, called neutrophils, that were able to penetrate the liver. As a result, the liver can become more inflamed, contributing to liver injury (Hwang, Ren, & Gao, 2020).
Metabolic syndrome is defined as meeting 3 of 5 set criteria known to be associated with insulin resistance, thus metabolic syndrome is a syndrome of insulin resistance. Park et al. found an increased risk of metabolic syndrome and obesity in Korean men, women, and the elderly who drink more than 14 grams per day as compared to nondrinkers. In people with obesity or abdominal obesity, or those who need to manage their blood pressure, glucose, or triglyceride, drinking just 7 grams of alcohol per day may increase the risk of metabolic syndrome. For reference, 14 grams of alcohol is equivalent to 1 shot of liquor, 5-6 ounces of wine, or 12 ounces of beer (Park EJ, 2022).
Another topic worth mentioning is the increased use of alcohol after bariatric surgery. It is well-established that Alcohol Use Disorder (AUD) may increase after bariatric surgery. For example, one study showed that in their cohort, whereas most individuals reported needing to drink 4 or more alcoholic beverages before feeling the effects of alcohol before surgery, most participants reported feeling the effects of alcohol after 1 drink of ethanol after surgery. This began as early as 5 months after surgery and a large portion of participants reported concurrent food and alcohol intake, ignoring guidelines recommending delaying beverage consumption at least 30 minutes after eating. In Smith et al.’s study, the first alcoholic drinks were approximately 21 weeks after surgery on average, with mean heaviest drink consumption being 71 weeks after surgery, averaging ~26 drinks a week. Interestingly, the amounts of alcohol consumption prior to 6 months before surgery compared to consumption after surgery were very similar. In other words, “Participants generally returned to preoperative drinking frequencies.” Yet despite drinking the same amount, “more individuals sought treatment for alcohol problems after surgery than before, which may reflect that the impact of alcohol use on functioning was more significant following surgery.” In addition, nearly 1/3 of participants met criteria for newly diagnosed alcohol abuse or dependence (Mellinger, et al., 2022).
Despite having no control for comparison, Smith’s study also found that in a population of alcohol use disorder post-surgery, half the participants had a lifetime mood disorder such as depression and 1/5th reported a lifetime eating disorder (Smith, et al., 2018). Another study referenced “Lifetime prevalence of Axis I psychiatric and substance use disorders in bariatric surgery patients may be as high as 73% and 32%, respectively” (Mellinger, et al., 2022). And another stated, “Less Improvement/ worsening mental health, getting divorced (vs. remaining married), starting smoking (vs. remaining a non-smoker), and starting regular drinking (vs. remaining a non-regular drinker) post-surgery were independently associated with a higher risk of post-surgery [alcohol use disorder], illicit drug use, and [substance use disorder] treatment” (King, et al., 2018). Rates of alcohol misuse, abuse, or dependence after bariatric surgery range from 1.3% to 28.4% depending on multiple factors. The top factors known to predict alcohol use disorder were: “being male, younger age, smoking, regular alcohol consumption, pre-surgical [alcohol use disorder] AUD, and a lower sense of belonging.” However, predictors could be affected by other factors such as type of surgical procedure (Ivezaj, et al., 2020).
The surgery associated with the largest alcohol misuse was roux-en-y gastric bypass followed by gastric sleeve (Mellinger, et al., 2022). King et al. stated that “Among adults with severe obesity, undergoing RYGB was associated with increased risk of incident AUD symptoms, illicit drug use, and SUD treatment” (King, et al., 2018). The gastric band did not have an increased association with alcohol misuse. The rate of misuse increased in both men and women after surgery, but especially in women. “In sum, the weight loss associated with bariatric surgery may explain the short-term decreased cirrhosis risk, but the longer-term increased risk of alcohol misuse may predispose to increased risk of [alcoholic cirrhosis]” (Mellinger, et al., 2022).
Alcohol use disorder is more prevalent in men, but women are more likely to have bariatric surgery. “As such, a greater number of women than men may be struggling with post-bariatric [alcohol use disorder]. For example, among bariatric patients seeking substance abuse treatment in an inpatient treatment facility, 70.4% (n=38) were women” (Ivezaj, et al., 2020). Alcohol dehydrogenase that comes from the liver metabolizes most ethanol, but some alcohol metabolism occurs in the digestive mucosa; therefore, bypassing the stomach may result in increased hepatic delivery of alcohol. Women have less gastric alcohol dehydrogenase and smaller volume of distribution of alcohol than men. In addition, “Women in the general population as well as those undergoing bariatric procedures are more affected by anxiety and depressive disorders than men which may predispose them to alcohol misuse. Alcohol problems more commonly go undetected in women, and women are less likely to access alcohol treatment.” All these factors could contribute to the reason that women develop “[alcoholic cirrhosis] and alcoholic hepatitis with less total alcohol consumption as well as a shorter duration of alcohol consumption compared to men” (Mellinger, et al., 2022).
Some studies have evaluated potential measures that can be taken to try to reduce public consumption of alcohol and obesity prevalence. A group in Australia found that introducing a volumetric tax reduced mean alcohol intake by 20.7% and introducing a minimum floor price reduced alcohol consumption by 9.2%. The volumetric tax led to a −0.90 kg weighted average change in weight and a 0.34 kg/m2 decrease in BMI (Robinson, et al., 2020).
Another group of researchers aimed to identify unique higher risk groups based on reported alcohol, food addiction, and BMI and to see if these unique groups differed in their risks of alcohol use disorder based on “behavioral reinforcer pathology”. They found that those with higher weight and alcohol use severity also had higher environmental reward deprivation. In other words, their environments were “devoid of other sources of reward such as healthy recreational or leisure activities.” The authors concluded that “environmental reward deprivation is a risk factor for both alcohol use disorder and obesity” (Buscemi, Acuff, Minhas, MacKillop, & Murphy, 2022). Another intervention by another group aimed to see if a community-based intervention could decrease alcohol consumption and obesity in men. In the intervention group, men received 95 text messages with questions asking for a response. Higher responses to texts related to those that delt with “awareness that drinking encourages unhealthy eating, perceive benefits of drinking less, and awareness of the harmful effects of obesity” with example responses such as “I eat a lot of junk food while having a can of beer in the house,” “To stave off periods of gout, lose weight, feel generally healthier,” and “I struggle on the golf course after 1st 9 when I drink more.” Unfortunately, the average body weight of participants did not change between baseline and follow-up. Over this period some men lost weight, some remained unchanged and some gained weight (Irvine, et al., 2017).
In the look ahead study, those in the intensive lifestyle intervention group lost the most weight regardless of alcohol consumption as compared to those without intensive lifestyle intervention. However, when evaluating alcohol consumption at year 4, those that met “a categorical weight loss of ≥10% differed by alcohol trajectory group (p=0.002;).” The percent of participants who achieved ≥10% weight loss was 27.5% in the alcohol abstaining group vs 4.8% in the consistent heavy drinker group. The alcohol abstainer group had 52.4% of participants who met a 5% weight loss, compared to 33.3% of consistent-heavy drinkers. Also interesting was the study found that “Contrary to previous reports of declines in alcohol consumption during behavioral obesity treatment, we found that individuals in the [intensive lifestyle intervention group] did not decrease their alcohol intake more than those in the [diabetes support and education control]” (Chao, Wadden, Tronieri, & Berkowitz, 2019).
Chao and colleagues stated in their study, “Alcohol is energy dense, containing 7.1 kcals/gram and may be an important factor related to weight. Alcohol is inefficient in facilitating satiety, and calories from alcohol usually add, rather than substitute, for energy ingested through other dietary sources. Consumption of alcohol is linked to disinhibited eating and increased food intake, possibly through neural mechanisms related to energy regulation” (Chao, Wadden, Tronieri, & Berkowitz, 2019). Thus, the authors bring up a good point. Alcohol contributes to a high number of kcal/gram, but also disinhibits individuals from dietary restraint, leading to excess intake of calories.
The evidence overall regarding alcohol contributing to weight gain is mixed. It is established men consume approximately three times more alcohol than women and report drinking more beer. Beer is higher in energy density per standard drink than wine, which women are more likely to drink. If studies do not consider the energy density of alcohol beverages, this could explain for some of the discrepancy. In addition, many studies also fail to consider physical activity when evaluating alcohol consumption and weight gain (Traversy & Chaput, 2015). These, as well as the aforementioned factors by Traversy & Chaput, could explain why there is discrepancy in relation to alcohol use and weight.
In summary, firstly, ethanol is toxic to the liver and the cells that line the gut and may affect gut and brain hormones. Secondly, men are more likely than women to have alcohol use disorder, but women are more likely to have a higher relative risk of alcohol use disorder after bariatric surgery than men. Thirdly, more research needs to be conducted on how alcohol can affect body weight. Alcohol also has hormonal influences on the body. Specifically, alcohol will lower Leptin, GLP1, and Serotonin—hormones associated with improved satiety signals and improved mood. Alcohol also inhibits fat oxidation (breakdown of fat), suggesting that frequent alcohol consumption could lead to fat sparing, and thus higher body fat in the long term. Despite these known physiological changes, “The mixed evidence with respect to alcohol’s role in promoting obesity is a product of many factors [e.g., gender, type, frequency, and amount of alcohol consumed, drinking pattern (e.g., binge drinking), physical activity level, sleeping habits, depression symptoms, psychosocial problems, chronic illness, medication use, disinhibition eating behavior trait, history of alcohol use, predisposition to gain weight, etc.]” (Traversy & Chaput, 2015).