Doesn't weight training build muscle and increase your metabolic rate and therefore the increase in your metabolic rate reduces fat? And if so, then doesn't this mean that you have gained muscle and lost fat at the same time?

I can understand how you might be confused because it's true that the more muscle you have, the higher your metabolic rate will be and the more fat you will burn as a result of having more muscle.

My point was not that building muscle and losing fat at the same time is impossible, but that attempting to build muscle and lose fat at the same time is not as efficient because you are chasing after two conflicting goals.

Let me explain...

If you want to put on the most muscle possible, you would engage in what's called a 'bulking' diet. That is where you eat 10-15% over your maintenance level calories. The rate of muscle growth can be quite rapid at this level of caloric intake, but the rate of fat gain can often be as high as the rate of muscle gain (a 1:1 ratio).

So why would you ever want to gain fat along with the muscle? Simply because you will gain the maximum amount of muscle possible only if you stay in a caloric surplus. People who want to gain muscle and lose fat at the same time have to alternate periods of caloric surplus with periods of caloric deficit and therefore will gain muscle much more slowly.

Let's talk about cutting diets.

The goal on a cutting diet is to eat 10-20% below your maintenance calories in order to burn as much fat as possible without sacrificing muscle. On any cutting diet, some muscle loss is almost inevitable, but your goal is to maintain as much lean body mass as possible.

A beginner is much more likely to build muscle and burn fat at the same time. (That's why being a beginner is pretty cool). For a beginner, almost anything works because your body isn't used to the stress of training, so great "beginner gains"can be made with virtually any training program.

But after about 6 months, the gains slow down, then nearly stops as you become more advanced and get closer to the limits of your genetic potential.

At this point, You have to work harder and smarter in order to keep your body progressing and changing. Not counting the initial "beginners gains" growth spurt, the only ways I know of to date that you can do both (build muscle and lose fat quickly) is thru anabolic steroids or to be extremely genetically gifted.

You see, testosterone promotes leanness and it builds muscle. Having super high levels will allow you to chase both goals and do it well. Of course, that isn't a risk free path and in the U.S. it is illegal. And there are a slew of other problems with that. I just wanted to insert that point.

Is it impossible to build muscle and lose fat at the same time? Nope. It's possible. It's simply more difficult and not the most efficient approach.

There's an old proverb that says, "If you chase two rabbits, you will catch neither." Gaining muscle and losing fat require different eating methods to achieve. If you attempt to do both, you may end up in limbo going nowhere.

If you don't mind making much slower progress in muscle gains, you can put on muscle and trim down body fat. But many people want faster results, so they focus on a single goal and put all their effort and energy into that one goal.

Then when they reach a certain body fat percentage, they go the other way. Keep all the muscle they just built and lose the fat. In essence, you might start off at 200 lbs, 15% body fat but at the end, you might be 195 lbs, 9% body fat and have more muscle then you did at 200 lbs. Because you gained as much as possible, then cut away the fat. Now you are bigger but leaner.

My recommendation: Pick one goal and stick with it until you are satisfied. It's faster, easier and works better then trying to do both.