If you are on a diet, alcohol is bad for you. Plain and simple. For some, this might be more painful to hear than "sugar is bad for you" and "fried foods are bad for you," but you can't argue with science. When you consume alcohol, your body uses that for fuel first, which delays fat burning.

Alcohol also contains almost twice as many calories as carbs and proteins. What's worse, these are "empty" calories, meaning that they provide no nutritional value.

When you down a few beers, your inhibitions are also squashed, making it more likely for you to cheat on your diet. A couple mojitos might be all that's needed to break down your willpower enough to think that eating a couple friend chicken drumsticks is a good idea. Also, despite all those calories you are consuming, alcohol actually increases your appetite.

Every time you booze up, you also decrease your body's total testosterone level. Testosterone is a powerful fat burner and muscle builder. So the less testosterone you have, the slower your muscles build while working out, and the slower your metabolism will be. And the slower your metabolism is, the harder it is to lose weight, no matter how disciplined you are in your fitness training program.

Alcohol also wrecks havoc on your internal organs, including your stomach and liver, which are important to keep in good health if you want to see fat loss progress. If you stomach isn't working at its peak, your foods will be digested less efficiently, which means more will be stored as fat. Your liver needs to be in prime condition because that's the organ that turns fat into energy.

If you must drink some brews with your friends, try to stick to light beer. The diet damaging effects of alcohol are still there, but it won't be as bad because there are fewer calories. Bottom line, listen to your personal trainer…