Most people don't exactly associate drinking with the epitome of 'health', but is it keeping you from reaching your fitness goals to a significant degree? How much your alcohol consumption interferes with your fitness goals will of course depend first and foremost on the type of drinker you are. Do you have one or two drinks a week? Or are you going out hitting the bars ordering round after round or getting noticeably intoxicated once, twice or even three+ times per week? There are some ways that alcohol may be interfering with your ability to lose fat, gain muscle and make progress toward your goals both directly AND indirectly (which is often mistakenly dismissed or overlooked). How, exactly?
First, let's talk about the direct effect that alcohol consumption has on your goals. For fat loss, remember that a consistent environment in which calorie intake is less than calorie output (a calorie deficit) is needed. Alcohol is inherently very high calorie yet not very satiating meaning it is easy to over-consume on calories simply by drinking. That's the most important thing to address. Just to give you an idea, here is the average calorie content of many popularly consumed drinks: Wine - 120-160 calories per glass Beer - 100 (light variations)-250 calories per 12oz beer Hard alcohol - 90-150 calories per 1 oz pour (mixed drinks typically contain 1-2 oz most of the time) Now keep in mind that is just the alcohol content alone, not accounting for calories from mixers like soda, juice, syrups, etc. in many mixed drinks and cocktails. These calorie numbers aren't horrible, until you factor in the reality that most of the time these are additional calories on top of an already well-rounded diet which takes care of calorie needs via food. Very rarely do people drink alcohol as a meal replacement to account for the calorie content. 100-300 extra calories of alcohol is enough to knock you right out of a deficit that you might have been achieving from your diet and/or exercise. Additionally, alcohol does actually inhibit the body's ability to burn body-fat because the liver converts alcohol into another form of usable energy for the body known as acetate. The body has no way of storing acetate in either fat or muscle cells, so it will stop all other processes of burning off body-fat or stored fat/carbohydrates until all of the acetate from the alcohol is burned off. How much acetate the body has to burn off before it can resume fat burning is (of course) relative to the total number of calories consumed from alcohol, so if you are still in a deficit but have some alcohol, this may not be a huge issue. If your goals is to GAIN muscle, alcohol may impact you negatively as well. For muscle gain to occur, the rate of muscle protein synthesis has to be higher than the rate of muscle protein breakdown on a daily basis. Muscle protein breakdown and synthesis is a cycle that's always happening everyday, regardless of what you do. The body breaks down proteins for daily functions, and muscle protein synthesis is spiked via things like eating, exercising, etc. Alcohol consumption inhibits MPS and therefor could be limiting hypertrophy. However, various studies show that in order for the inhibition of MPS caused by alcohol to be significant enough to majorly impact muscle/strength gain, the frequency and intensity of alcohol consumption would have to be more than moderate (defined by 2-4 DRINKS per week, not 2-4 bouts of drinking). So, if you are an occasional social or moderate drinker, it may not be an issue for you at all. If you tend to get fairly intoxicated or consume alcohol on a daily basis, then this is definitely something to consider when it comes to your fitness goals.
Although alcohol does have a direct impact on fitness goals, the indirect impact is perhaps much larger and should be more of a consideration for most people. Alcohol inhibits the body's ability to regulate appetite and interferes with satiety receptors in the brain, meaning alcohol consumption is highly correlated with overeating. Even if you're not 'intoxicated', studies have shown that the number of calories consumed at meals where just one drink was served with the meal was 10-25% greater than meals where no alcohol was served (and that's not even accounting for the additional calories in the actual drink itself). These calories add up VERY quickly and likely do have an impact on your weight loss goals. Drinking alcohol can also contribute to a variety of factors that might yield decreased performance in the gym, which would indirectly impact your strength and muscle gains. Alcohol also interferes with natural sleep cycles. During REM sleep, growth hormone is produced which plays a large role in muscle recovery and the rate at which you gain muscle, and it actually increases fat loss as well. Irregular or insufficient sleep = less growth hormone production = less muscle growth/fat loss. In addition, most studies conducted on the effects of alcohol consumption and fat loss or muscle gain have been consistent in finding that the greatest problems are presented when alcohol intake is not moderated or is excessive. It happens to be that those who have a hard time with balancing alcohol consumption also have a hard time achieving moderation/balance in other areas such as nutrition and exercise, which can be another contributing factor to the detriments of alcohol consumption on fitness goals. Does this mean you can't ever drink if you have fitness goals, or that you have to decide to give up your fitness goals in order to do so? Actually, no. As long as you are accounting for total energy intake, many of the negative side effects that come with alcohol consumption can be avoided with moderating your intake, as with so many other things in health and fitness. If you want to have a drink here and there, it's nothing to ban yourself from or fear. It becomes a problem when the habit grows in frequency or intensity (or when total energy content isn't accounted for). Two to four drinks per week (individual drinks, not occurrences of drinking) is not going to directly negatively impact most people on any fitness endeavor if energy content is accounted for.