For one thing, most of us vastly overestimate how many calories we burn during a workout. The truth is, it takes a lot to burn just one calorie. 30 minutes of vigorous exercise might buy you 300 calories. Think about how little that is, in the scheme of things. Exercise is not going to compensate for your three glasses of wine a night, or your morning bagel. It’s a numbers game. You simply can’t do enough exercise to compensate for regular bad food choices.
The other thing about exercise is that it makes you much hungrier. It’s ridiculously easy to eat back what you’ve worked off. Three hundred calories spread out over the course of the day is a nibble here, and a nibble there. It’s not a ton of food. Add to that the sense of entitlement we get after having worked out, and you have a recipe for disaster. You might allow yourself dessert one night, or an extra cocktail with dinner because you went to the gym that morning. Well, there goes your 300-calorie deficit. Now you’re working your butt off just to maintain your weight. And that’s assuming you’ve accurately gauged how many calories you’ve burned. If you’re overestimating how much you’re burning, then you might end up gaining weight. Like I said, it’s a numbers game.

Here’s the great thing about figuring out the food first. For one thing, when you focus on the food alone, you can focus on the food alone. Completely revamping your lifestyle all at once is really, really hard. In fact, it can be downright impossible. Yet that’s what most of us attempt. From one day to the next, we expect to overhaul our diet, eat less, tolerate more hunger, drink a gallon of water, take all of our vitamins, start working out an hour each day, and oh yeah, only drink alcohol in moderation and be in bed by 9 pm. Ha! No wonder so many of us fail. But if you only pay attention to the food for a period of time, you won’t end up so overwhelmed. Trust me, it’s enough work to plan your meals and resist your biggest temptations. That’s a full time job in and of itself. Giving yourself time to do that allows you to get comfortable with the single most important part of your new lifestyle. Once you’re in a groove, you can add more.
The other great thing about dealing with nutrition alone is that you’ll get a really good sense of your resting metabolic rate, or how many calories your body burns on its own, day-to‐day. You don’t need to worry about figuring out a number. It’s actually much easier than that. Eat less. Did you lose weight that week? Great. Your body burns more than that amount of food. Not lose any weight? You need to eat even less. You will very quickly figure out roughly how much food you need to eat to lose weight. Once you add exercise, do your best to eat roughly the same amount, and you’ll lose even more. You may need to add a snack here or there, because pre- and post-workout nutrition is super‐important. But you’ll already have a realistic idea of how much you should be eating day-to-day, and can adjust from there.
It really is that simple. Not easy, simple. I hear people all the time saying things like, “I don’t know why I’m not losing any weight.” I do. You’re eating too much. I used to say that all the time. It wasn’t an excuse. I truly didn’t know why I wasn’t losing, because I thought I was doing everything right. But now, knowing exactly what I need to eat to lose, gain, or maintain, I can tell you that I was eating way too much.
SOURCE: Tips on Life and Love