The 6 Factors influencing your daily calorie needs

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The 6 Factors influencing your daily calorie needs

Your daily calorie requirements depend on six major factors. The formulas for calorie calculations you are about to learn take into account all six of these factors to get the most accurate estimate possible.

1) Basal Metabolic Rate (BMR)
BMR is the total number of calories your body burns for normal bodily functions, including digestion, circulation, respiration, temperature regulation, cell construction, and every other metabolic process in your body. In other words, your BMR is the sum total of all the energy used for basic bodily functions, not including physical activity. BMR usually accounts for the largest amount of your daily calorie expenditure – about twothirds. BMR is at its lowest when you’re sleeping and you’re not digesting anything. BMR can vary dramatically from person to person depending on genetic factors. You probably know someone who can eat anything they want yet they never gain an ounce of fat. This type of “fast metabolism” person has inherited a naturally high BMR.

2) Activity Level
Next to BMR, your activity level is the second most important factor in how many calories you need every day. The more active you are, the more calories you burn; it’s that simple. Become more active and you burn more calories. Sit on the couch all day long and you hardly burn any.

3) Weight
Your total body weight and total body size are also major factors in the number of calories you require. The bigger you are, the more calories you’ll require to move your body.

4) Lean Body Mass (LBM)
Total body weight correlates with the number of calories you require, but separating your total weight into its lean and fat components allows you to calculate your calorie needs even more accurately. The higher your LBM, the higher your BMR will be. This is very significant when you want to lose body fat because it means the more muscle you have, the more calories you will burn at rest. Muscle is metabolically active tissue, and it requires a great deal of energy to sustain it. The best way to increase your BMR is to increase your LBM. This is why you could say that weight training helps you lose body fat, albeit indirectly.

5) Age
Metabolic rate tends to slow down with age. Therefore, the number of calories the average person requires also goes down with age. Fortunately, you can prevent and even reverse the age-related slowdown in metabolism by developing more muscle through weight training and nutrition.

6) Gender
Men usually require more calories than women. The average male has a maintenance level of 2800 calories per day. The average female requires only 2000 calories per day to maintain. The reason for this difference is not so much a sex-related issue as a body weight and muscle mass issue; the average man carries much more muscle mass than the average female and this explains the spread in calorie requirements between men and women. Except for individual genetically-related differences in BMR, a 140 pound man and a 140 pound woman would have the same calorie requirements if their activity levels were identical.

Methods of determining caloric needs

There are many formulas you can use to determine your daily calorie needs using these six factors. Any formula using LBM in the calculations will always be more accurate than one based only on bodyweight. However, you can still get a very accurate estimate of your calorie expenditure just from body weight alone.

The “quick” method (based on total bodyweight)
A fast and easy method to determine how many calories you need is to use your total current weight times a multiplier for TDEE.

Fat loss = 12 – 13 calories per lb. of bodyweight
Maintenance (TDEE) = 15-16 calories per lb. of bodyweight
Weight gain = 18 to 20+ calories per lb. of bodyweight

This is a very easy method to estimate caloric needs, but its most obvious drawbacks are not taking into account activity levels or body composition. If you’re extremely active, this formula will underestimate your calorie requirements. Using this formula, a lightly active 50-year-old woman who weighs 235 lbs. would have a TDEE of 3055 calories per day (235 X 13). Since almost all women will rapidly gain weight on 3000 calories per day, this illustrates another flaw in the quick formula – it will overestimate your calories if your fat is significantly higher than average. Despite these drawbacks, the quick formula is a good way to get a quick ballpark estimate, as long as your body fat is average or less.

Equations based on BMR.

A more accurate method for calculating TDEE is to determine basal metabolic rate (BMR) first, then multiply the BMR by an activity factor to determine TDEE. There are two formulas you can use to calculate your BMR. The Harris-Benedict formula is the one you will use if you don’t know your LBM (you don’t need body composition information to use this formula). If you know your LBM, you should use the Katch Mcardle formula for the most accurate calorie estimate of all.

The Harris-Benedict formula (BMR based on total body weight)

The Harris-Benedict formula uses the factors of height, weight, age, and sex to determine basal metabolic rate (BMR). This makes it more accurate than determining calorie needs based on total bodyweight alone. The only variable it doesn’t take into consideration is lean body mass. This equation will be very accurate in all but the extremely muscular (will underestimate caloric needs) and the extremely overfat (will overestimate caloric needs).

Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) – (6.8 X age in years)
Women: BMR = 655 + (9.6 X wt in kg) + (1.8 X ht in cm) – (4.7 X age in years)
Note: 1 inch = 2.54 centimeters
1 kilogram = 2.2 lbs.
Example:
You are male
You are 30 yrs old
You are 5′ 8 ” tall (172.7 cm)
You weigh 172 lbs. (78 kilos)
Your BMR = 66 + 1068 + 863.6 – 204 = 1793 calories/day

Once you know your BMR, you can calculate TDEE by multiplying your BMR by the following activity factor.

Activity factor
Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or
2 X day training, marathon, football camp,
contest, etc.)
Continuing with the previous example:
Your BMR is 1793 calories per day
Your activity level is moderately active (work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1793 = 2779 calories/day

Katch-McArdle formula (BMR based on lean body weight)

The Harris-Benedict equation has separate formulas for men and women because men usually have a higher lean body mass and a larger bodies.
Since the Katch-McArdle formula accounts for LBM, this single formula applies equally to both men and women and it is the most accurate method of determining your daily calorie needs.

BMR (men and women) = 370 + (21.6 X lean mass in kg)
Example:
You are male
You weigh 172 lbs (78 kilos)
Your body fat percentage is 14% (24.1 lbs fat, 147.9 lbs lean)
Your lean mass is 147.9 lbs (67.2 kilos)
Your BMR = 370 + (21.6 X 67.2) = 1821 calories
To determine TDEE from BMR, you simply multiply BMR by the activity factor:
Continuing with the previous example:
Your BMR is 1821
Your activity level is moderately active (you work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1821 = 2822 calories

As you can see, the difference in the TDEE as determined by both formulas is statistically insignificant (2779 vs. 2822 calories) because the man we used as an example is average in body size and body composition. The primary benefit of factoring LBM into the equation is increased accuracy when your body composition leans to either end of the spectrum (very muscular or very obese). This is yet another reason to monitor your body fat percentage and not just your body weight.

Adjust your caloric intake according to your goal

Once you know your TDEE (maintenance level), the next step is to adjust your calories according to your primary goal. The mathematics of weight control are simple:

1) To keep your weight at its current level, you should remain at your daily caloric maintenance level.
2) To lose weight, you need to create a calorie deficit by reducing your calories slightly below your maintenance level (or keeping your calories the same and increasing your activity above your current level).
3) To gain lean body weight, you must increase your calories above your maintenance level (and engage in a program of progressive resistance training).

How to adjust your calories for fat loss

Now let’s talk about how many calories you should eat to lose body fat. A calorie deficit that’s too large or maintained for too long, will eventually invoke the starvation response and slow your metabolism. Nevertheless, you must have a calorie deficit if you want to lose fat. The secret is to use a small calorie reduction and to avoid any diet that calls for extremely large calorie reductions.

Body fat is nothing more than stored energy. To release stored energy, you must be in a calorie deficient state. Calories not only count, they are the most important factor in a fat loss program. If you are eating more calories than you burn, you will not lose fat, no matter what you’re eating or what kind of training you’re doing. Some foods may get stored as fat more easily than others because of the way they affect your hormones and blood sugar, but always bear in mind that too much of anything will get stored as fat. You can never override the laws of energy balance.

There are 3500 calories in a pound of stored body fat. In theory, if you create a 3500-calorie deficit per week through diet, exercise or a combination of both, you will lose one pound. If you create a 7000 calorie deficit in a week you will lose two pounds. The calorie deficit can be created through diet, exercise or preferably with a combination of both. Because we already factored in the exercise deficit by using an activity multiplier, the deficit we are concerned with here is the dietary deficit.

The strictly mathematical model of calories in versus calories out doesn’t always work because of the body’s weight regulating mechanism – also known as the starvation response. Nevertheless, the mathematical model gives you a starting point, and as long as you follow the 8 strategies you learned in chapter two for avoiding the starvation mode, you will continue to get steady, predictable fat loss by using a small, temporary calorie deficit in conjunction with aerobic exercise and weight training.

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The 6 Factors influencing your daily calorie needs