The short answer, if you're reading this blog post, is probably not.
If you are new to training, like have under a year of experience, then yes, any addition of fitness will affect both your fat stores and lead to building muscle. Remember that show, "The Biggest Loser", those contestants (dare we say... athletes) lost huge amounts of weight each week, while putting on muscle.
Well, you don't have to be obese to see dramatic results within your first "training year." It's pretty common to see the immediate positive impact on your physique by just adding some form of exercise and reigning in your diet even slightly for those that are just starting out on their fitness journey.
This is great, given that it helps newbies achieve "big wins" and keeps them coming back for more if they like the results and want to keep seeing gains (or losses- depending on their goals).
Things get a little murkier as your "training age" increases. Ever heard someone say, "I've done the same thing for years and now I'm eating less, but I'm still putting on weight."
This is your body saying a few things to you.
First, with age our metabolism changes and that is an undeniable and inevitable reality for all humans. As we age we burn fewer calories for daily activity, and this usually coincides with a decrease in daily movement too, so it's a double whammy.
Secondly, your body is craving CHANGE, nothing kills physical transformation more than repetitive behaviors that don't vary in intensity, ever. It's like that saying, the definition of insanity is doing the same things over and over again and expecting a different result. Your body is very smart, and it adapts to your activities and gets better and more efficient at the things you do everyday. You have to trick it to think you are doing something new. A few ways to trick your body to change and adapt are by varying these factors:
Intensity & Velocity: How fast and hard can you move your body or an object/weight?
Volume: How many sets/reps are you doing? With what weight?
Speed: How fast or slow is your tempo?
These are just a few things that can make a HUGE difference in what you do. A squat is just a squat but it can differ dramatically by adding resistance in the form of weight or bands, where you attach the bands or hold the weight, how fast or slow you move in and out of the position and how many reps and sets you do of the squat. If you always goblet hold 20 pounds and do 3 sets of 10 squats, your body will adjust and adapt to that volume quickly (like within a week) and you need to change something to make your body respond. It may still be hard, or make you tired, but you are getting diminishing returns for your effort at this point.
As your coach, we mess around with these variables all the time to "trick" your body into thinking it's doing something novel. It's also important to mess with more than just one variable. For example, if you are a client that has been lifting the same kettlebell for over a year when you do a standard squat, you probably need to add more resistance in the form of adding a band or raising your weight. We can mess around with your tempo (and we do) but it's important to recognize the need to up the ante in the form of resistance as well.
And for the ladies, I will say it again..... lifting heavy weights will not turn you into a female version of Arnold Schwarzenegger. You need a whole lot more testosterone to bulk up. In contrast, lifting heavier will make you stronger, build lean muscle, and help your body burn more calories at rest with that lean muscle. These are all positive side effects from lifting heavier weights- no bulging biceps and gigantic quads to contend with.
Circling back to burning fat and building muscle at the same time question. Basically a good rule of thumb is to work on one and then the other.
If you are someone that is overweight and needs/wants to lose body fat primarily- we would suggest you work on that first mainly by adjusting your nutrition and adding exercise. Then when you have leaned down a bit you can build strength and muscle to help you continue to get lean.
If you are someone who is at a good place with your weight but just wants to change your body composition a bit, we would suggest lifting and building muscle first, and then futz around with your nutrition to lean you out a bit.
The place where people run into problems is when they try to switch things up and don't stay the course. It takes time to achieve these goals, like 6-12 months. If after 6 weeks, you decided to quit lifting and go on a keto diet instead and then 6 weeks later change to Pilates only, you won't ever get to where you want to be. You have to stick with a plan and see it through. Think about it this way, if you were climbing a mountain and switched trails every few miles to start at the bottom and go on a trail you think will get you to the top faster, and then do that again and again, you aren't actually getting anywhere. Whereas if you stuck to the same trail and slogged through the ups and downs, you would eventually get to the top and achieve your goal. It's not magic, and it's definitely not sexy, but consistency is the key to making your goal achievable, otherwise you're just spinning your wheels and most likely getting frustrated.
So the moral of this fitness story is:
You have to keep your body guessing and you have to be consistent to make a change.