When I coach individuals on how to manipulate Calories to lose weight, I often get stolid stares immediately followed by some version of the statement “but, I don’t even know how many Calories I should be consuming”. I am quick to forget that the first step in this whole process is often the most problematic and perplexing part. And rightfully so – there is a myriad of methods that can be utilized to calculate the Calories you need. And there is typically a bit of merit to each of the methods. However, there are a few equations that are consistently used in both research and the most credible professional exercise and nutrition organizations.
One of the most used and accurate equations is the Cunningham Equation. Unfortunately, this equation takes into account fat free mass (everything outside of fat, i.e. muscle, bone), which is difficult to measure unless you have access to tools that assess body composition. If you do, indeed know your lean mass, though, the equation is as follows:
Resting Metabolic Rate = 500 + (22 x fat free mass [kg])
So, let’s say you have 80 kg of fat free mass:
Resting Metabolic Rate = 500 + (22 x 80 kg) = 2,260
This means that at rest (not factoring activity), you require ~2,260 Calories per day.
If you do not have access to measurements for fat free mass, another suitable equation to use is the Harris-Benedict equation:
Resting Metabolic Rate for MEN =
66.47 + (6.23 x weight in pounds) + (12.67 x height in inches) – (6.76 x age in years)
Resting Metabolic Rate for WOMEN =
655.1 + (4.34 x weight in pounds) + (4.69 x height in inches) – (4.68 x age in years)
So, let’s say I’m a 160 pound, 5’6”, 27-year-old woman:
Resting Metabolic Rate for WOMEN =
655.1 + (4.34 x 160 pounds) + (4.69 x 66 inches) – (4.68 x 27 years) =
655.1 + (694.4) + (309.54) – (126.36) = 1,785
Then, we have to factor in activity level. Here is a good rule of thumb for factoring in physical activity to you total daily Caloric need:
Little to no exercise
BMR x 1.2
Light exercise (1-3 days per week)
BMR x 1.375
Moderate exercise (3-5 days per week)
BMR x 1.55
Heavy exercise (6-7 days per week)
BMR x 1.725
Very heavy exercise (two-a-days, extra heavy workouts)
BMR x 1.9
So, above, if this woman works out 4 days per week, and is thus considered moderately active:
Daily Calories needed = BMR x 1.55 = 1,785 x 1.55 = 2,767 Calories
However, this is not factoring in weight loss! For maintainable weight loss, you really should not have more than a 500 Calorie deficit per day – this is where you have a greater potential to see the negative metabolic implications that are often associated with starvation (i.e. a decrease in resting metabolism, significant muscle loss). So, from above:
Daily Calories needed = 2,767 Calories – 500 Calorie daily deficit = 2,267 Calories, daily
Some things to consider with cutting Calories for weight loss:
Keep protein intake high - ≥ 30% of your total Calorie intake from protein (2,267 Calories x 30% = 680 Calories, or 170 grams of protein)
Modestly decrease carbohydrate intake. Try not to cut out carbohydrates too much – this is where we see decrements in the gym. No good!
Time carbohydrates correctly – eating them after a workout is a great time! They will most likely more readily be stored in muscle compared to fat.
Maintain a sound resistance training program to help building highly metabolic muscle! New to weight training? – Try 2-3 days per week of exercises that target all major muscle groups using 3-4 sets of 8-12 repetitions, each.
Find the proper equation to assess your daily Caloric need, and factor in your physical activity level. With weight loss, try not to exceed a 500 Calorie per day deficit, and keep your protein intake and resistance training high!