Losing fat only works by creating a calorie deficit. That means you need to eat fewer calories than you burn. There are things that help with that, and things that hurt.
By creating a deficit your body needs to come up with the energy to keep you moving and living and it turns out that fat stores are a great deposit of energy. So using theoretical numbers, say you eat 1500 calories each day and burn a total of 2000 a day. That 500 calorie difference will come from fat stores. And over the course of a week, that 500kcal/day deficit will result in a pound of fat lost.
Now, we have a few different ways of burning calories. First we have our BMR, or Basal Metabolic Rate. This is the amount of calories we burn simply by being alive. This is the energy that our internal organs run on. It powers our immune system and healing processes and all the little things we don’t have to think about. You would burn this amount by just sitting on the couch all day long.
Next we have NEAT. Non-Exercise Activity Thermogenesis. This is just the number of calories burned through activity. Cleaning the house, taking a walk, shopping, fidgeting, etc., etc. This might be the most important number to consider in long term weight loss success. This is why you seen so many experts advocating for increased overall activity levels each day. The number of calories used by being highly active can be rather high.
Then we have workouts. Usually calorie burn from workouts is drastically over-estimated. I just did an absolutely killer workout, I weigh over 200 pounds, and I was working hard for about 70 minutes…and I burned 500 calories according to my Apple Watch. For a lot of people, that amount of effort would seemingly burn way more than 500 calories. And increasing the time and difficulty of your workouts will eventually bite you. There’s only so much you can truly recover from. So relying on workouts as the primary way of creating a deficit will almost always let you down. This is why you hear the phrase “You can’t out train a bad diet.”
The benefit of training lies in increasing your abilities, rather than simply burning calories. Getting stronger. Increasing health of everything from your joints to your heart and brain. Increasing your fitness, which is becoming better a specific exercise tasks like running or biking or moving some kind of weight more efficiently.
Now, let’s take those hypothetical numbers from before. Say you have maxed out your day and burned through 2000kcal. Your BMR is pretty constant, you’re being highly active and you’re getting your workout in. That totals 2000kcal and doing more exercise/activity will negatively impact your recovery, so that’s not really an option. Do you know how easy it is to eat 2000kcal? Go measure out a proper tablespoon of peanut butter, like with a real measuring spoon. That’s nearly 100 calories by itself. And who in the world actually eats that amount of peanut butter?? Calories can add up QUICKLY.
This is why controlling your diet is so important for fat loss. You can have a MUCH greater impact on how many calories you bring in than you can on the calories you burn.
And you don’t have to live forever in a calorie deficit. I hope you can see from all this writing that a calorie deficit is used for a specific purpose. Once you reach your goal you can then transition to eating at a maintenance level where you neither lose nor gain weight.
There is a ton of nuance to all this, of course. And figuring out what works FOR YOU will determine the amount of success you see. But essentially fat loss success is going to come down to the things listed here.