Calorie Requirements Explained
The very first step in body weight maintenance is to estimate just how many food calories you need to consume on a daily basis. This starting point is important if your goal is to gain muscle weight or to lose fat. There are many methods to determine what your calorie requirements. The most important thing to be concerned with is getting results. All methods have their limitations and are intended as a starting point only. Once you have a starting point you will need to keep track of your calorie consumption and compare with measurements. From this starting point you will need to adjust your calorie consumption appropriately.
The human body consumes or burns calories each and every day just to sustain life. This maintaining of vital organ function is called your basal metabolic rate (BMR) or basal energy expenditure (BEE).
This value can be directly measured using indirect calorimetry or it can be estimated using various formulas. Additional calories are burned during physical activity and during digestion, which is also referred to as the thermic effect of food (TEF). Your total daily calorie expenditure can be estimated by multiplying BMR by an “activity factor”, which also takes TEF into account.
Estimating Basal Metabolic Rate
If measurement through indirect calorimetry is available to you, this is the best option. You may be able to find a local gym, training studio or university that provides this service. If not, there are several formulas that can be used to estimate BMR. The two we will discuss here are the Katch-McArdle and Harris Benedict forumla. If you know what your body fat percentage is the Katch-McArdle method is preferred. If you don't know your body fat percentage the Harris Benedict formula will suffice.
The more popular Harris-Benedict equation has several problems with it, the biggest being the absence of accounting for body composition. There is a significant difference between the basal metabolic rate of a 200 pound man with 10% bodyfat and 200 pound man with 25% bodyfat due to the difference in lean body mass.
Also, the methods used when the Harris-Benedict equation was developed also failed to account for TEF, so it tends to overstate BMR slightly. Rather than BMR, the result is closer to resting metabolic rate (RMR)/resting energy expenditure (REE). In addition to calories burned sustaining vital organ functions, RMR also includes calories burned due to TEF, which can vary depending on the time between the last meal and testing as well as the macronutrient composition of the meal.
Estimating Calories Burned Due to Activity and Thermal Effect of Food
After estimating your BMR you would need to determine the additional calories burned by activity and digestion. In Exercise Physiology: Energy, Nutrition and Human Performance, the authors provide several “activity factors” to multiply by your BMR to estimate your average daily calorie expenditure. These also account for TEF:
These activity factors do not have enough detail about them to make a good determination where you fit in. Keep in mind that this is intended only as a starting point and there will be some adjustment required based on your individual results. It is better to start at lower levels and gradually increase calories, especially if your goal is the loss of fat. Surprisingly, even if your goal is increased muscle mass, which requires a calorie surplus, it is better to start low at first and gradually adjust upwards than to start high and find you’re gaining more body fat than muscle.
Although the above should provide a reasonably good estimate of your daily calorie expenditure, to be successful you must track daily calorie intake and adjust accordingly.
If your goal is to lose fat and you have properly calculated your daily calorie deficit (the difference between your daily calorie expenditure and intake), your weekly fat loss should equal roughly your weekly calorie deficit (daily calorie deficit x 7) divided by 3,500 (the approximate number of calories stored in a pound of body fat). Remember, there are many factors that can affect weight loss and gain, such as hydration, so don’t worry too much if you’re off a pound one way or the other as long as your measurements are consistently moving in the right direction.
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