Your metabolism is simply the rate at which your body burns energy.

Just like a car needs gas to run, your body needs calories to fuel its systems—like digestion and circulation—as well as movement.

When you eat too many calories, your body stores the excess as fat. The tricky part is that calories from sugar are more likely to be stored as fat because sugar sends a signal to your body that large amounts of calories are coming in. And that’s often true, as sugary foods can pack in a lot of calories. But I’ll keep things simple for now.

Having a FAST metabolism means your body burns more calories. If you’re looking to lose weight, you need to burn more calories than you consume. This means you should eat less, but you also need to know how calories are burned. There are three main ways your body burns calories:

1. Basal metabolic processes: This is the number of calories your body burns just to stay alive while at rest. This is referred to as your Basal Metabolic Rate (BMR). The more muscle you have, the higher your BMR will be, and the less muscle you have, the lower it will be. Muscle burns calories even when you’re not moving.
2. Thermic effect of food: Digestion requires some energy. It’s not a huge amount, but your body burns a bit more energy to break down proteins and fats than it does to break down carbohydrates. This accounts for roughly 10% of your daily calorie intake.
3. Physical activity energy expenditure: These are the calories burned through movement. The more you move, the more you burn. Simple activities like walking or shopping won’t burn significant calories, despite what health organizations suggest. Even an hour of intense exercise may only increase your daily calorie burn by around 20%.

So, what’s the best way to burn more calories? The key is building muscle. This means lifting weights.

Let’s break it down: imagine your Basal Metabolic Rate (BMR) is 1,000 calories per day. You eat 1,500 calories a day (which is a bit low for most people), and you do an hour of spin class. Let’s also assume you’re eating mostly healthy food, with protein or fat at every meal.

Your total calorie burn—BMR + thermic effect from food + exercise—comes out to 1,300 calories. But you’re still gaining weight. If you keep this routine up every day, you’d gain about a pound every 18 days.

Now, let’s boost your BMR by building muscle. This is the only way to increase your BMR. No amount of superfoods, apple cider vinegar, or any other trendy remedies will do it.

If you increase your BMR to 1,200 by building more muscle, while still eating 1,500 calories, your thermic effect from food remains the same. However, your calories burned through exercise and your body’s basic functions will increase.

With a BMR of 1,200, your total calories burned—BMR + thermic effect + exercise—could now add up to 1,530. This means you’ll start losing weight, even with the same caloric intake.

While your body burns calories during and after exercise (especially as muscles recover), the real long-term benefit comes from having more muscle. The more muscle you have, the more calories you’ll burn, even when you’re just walking around.

The first step to losing fat is creating a caloric deficit, and one of the best ways to do that is by lifting weights.