There is a simple equation that needs to be solved to gain or loose weight. (Calories In) – (Calories Out) = (Eventual Weight Difference). This is sometimes referred to by the acronym CICO. The outcome is noted as “eventual” since there are many day to day changes that can alter this, which is sometimes just referred to as water weight. It’s true that you can gain weight by just drinking water or eating a heavy amount of a low or no calorie food, but in two to three days your body will sweat or otherwise dispose of this with minimal effort.
The calories out portion of the equation is controlled by two things, exercise and time. Sure you can burn some calories moving or working out, but a huge amount of the weight or calorie you burn is just living. Even lying in bed all day will burn calories, and the amount is called your basal metabolic rate (sometimes “base” metabolic rate). This can vary from 500-2000+ calories depending on your size. A 220lb person with a lot of muscle (muscles burn more calorie even just resting) can burn 2200 calorie sleeping all day, while someone who is 120lbs might only burn 1300. There are calculators available to determine your BMR.
Another option to determine your BMR is to take a lab test. This is helpful since online calculations are averages. If you have a condition that changes your metabolism (like hypothyroidism, which can drop your BMR by 10-20%, enough to elongate any weight loss from a small 200 calorie estimated deficit), then finding your actual BMR can help with maintaining a proper diet. Similarly if you have significant muscle or a general build that is not average for the calculations the. A test will help.
Once you know how many calories you burn as a baseline just sitting around, you need to add in how many calorie you burn. Just walking to the bathroom, getting dressed, or picking up your phone can burn energy with a strenuous job that has you on your feet this can be 500-800 calories a day. A step tracker, like the Apple Watch or Fitbit, can help estimate how much energy this is. Going to the gym, hiking, swimming, or jumping rope (especially with a fun jump rope tracker this can be one of the best calorie burning activities) will amp this calories burned number up.
Once you have both numbers, add them up for your calories out. Now if you eat less than this by 3500 calories you will loose a pound! Most people suggest spreading this average over a week so you have a 500 calorie average daily deficit (7 days x 500 calories a day = 3500 calories). If this zaps energy levels then eating a little more and having a 100 calorie daily deficit in your CICO calculation will have you losing a pound a month (or 35 days).