Many people in the Health and Fitness space (including myself) preach about 'Finding Balance' when going about your fitness endeavors. And when discussing the topics of Alcohol and Fitness, that Balance is very, very important.
CALORIE INTAKE
Alcohol is sometimes referred to as 'The Fourth Macronutrient'. This is because, similarly to the other macros, pure alcohol has a calorie content of about 7 calories per gram. However, the calorie content your drink of choice has can be a lot higher, and quickly increase, once you add in your heavily sweetened mix or use a stronger (more calorie-dense) liquor. Now add in a long night of trips to the bar for refills, or drunk snacking on whatever around you is edible, you'll easily find yourself consuming over 1,000 calories in a short 2 - 3 hour window. Doing this on a consistent basis (1-2 times per week) can lead to unwanted weight gain as it will add to your total calorie intake for the day/week.
BREAKDOWN / FAT STORAGE
Alcohol will not directly make you gain body fat. When we consume any type of alcohol, the body breaks it down in the Liver. During this process, the body stops the breakdown of Carbohydrates and Dietary Fat until it processes the alcohol. Your body also begins to slow down Fat Oxidation (fat burning) to prioritize the removal of the toxins brought in by the drink. This means that fatty foods consumed before/during the time you drink will be stored as body fat at a much faster and easier rate. That being said, Fat storage will only occur when you're in a calorie surplus (calories consumed > calories burned) but unfortunately, as mentioned above, a night out drinking can easily put you into a Caloric Surplus which over time will cause fat gain.
MUSCLE GROWTH / SLEEP
The gym is the last place you'll want to go when fighting a hangover. A long night out can cause motivation to be forgotten about and your energy levels next to nothing from lack of sleep. When you're sleeping with alcohol in your system, the brain does not fully 'shut down' and rest. The REM stage (which is the most restorative stage of sleep) is disrupted and can lead to inhibited muscle recovery from the prior training session.
For the sake of gaining muscle and strength, moderate drinking will not inhibit your goals, however, it can indirectly become an issue if the amount of alcohol being consumed is enough to keep you from hitting your goals/sleeping well. Drinking on a regular basis can put Muscle Protein Synthesis (the building of muscle tissue) on hold and impair recovery from previous training sessions and should be avoided to the best of your ability (the 'balance'). This is especially true for men as it will lower Testosterone levels which can open up another array of issues.
A WAY AROUND IT
Given some of the topics above (and many more that can be discussed), alcohol consumption may seem totally detrimental. However, it will only become an issue once it's abused to the point that it can inhibit your health and keep you from hitting your goals. I incorporate drinking/going out in a few simple and effective ways that keep me from missing out on memorable times.
One thing I like to do is try and find out when any upcoming events are happening to allow me to know the next time I'll be drinking, compared to the most previous time (giving myself some time between). Keeping this in mind, a few days prior, I like to really emphasize nutrition, sleep, and hydration.
On the day that I plan on drinking, I will adjust my total calorie intake for the day to compensate for the calories I'll be consuming from the drinks. For example, say I plan on having 6-8 drinks (at approx 100 cals ea.), I'll drop my total cal intake for the day by 600-800. This calorie reduction from food will look like dropping calories coming from Carbs and Fats and increase total protein intake. Prior to drinking, I will make sure to have a meal higher than normal in protein, and lower in Carbs and Fats. To keep the calories low (and be able to have more drinks) I will opt for straight alcohol or mixed drinks with diet sodas to tonic water.
