Considerable debate surrounds what proportion of the energetic macronutrients might represent the ‘ideal’, but let us assume that you are observing a high-protein diet, providing 2.0 grams of protein per kilogram of body mass per day, and let us assume, also, that you would like to maintain a slight energy deficit in order to metabolise fat quickly whilst facilitating hypertrophy.
First, you must approximate your Total Daily Energy Expenditure (TDEE), which is calculated by estimating your Basal Metabolic Rate (BMR), then multiplying that figure by a factor known as the Physical Activity Level (PAL). Various formulae have been proposed, perhaps the most well-known of which is the Harris-Benedict equation, which has undergone a number of revisions since its original publication in 1918. The 1990 revision by Mifflin and St. Jeor is as follows:
Men: BMR = 10 × mass (kg) + 6.25 × height (cm) - 5 × age (years) + 5
Women: BMR = 10 × mass (kg) + 6.25 × height (cm) - 5 × age (years) - 161
These equations do not account for differences in body composition, however, and are therefore best used only when body fat is not known. When body fat is known, it is preferable to use the Katch-McArdle equation, which accounts for the fact that BMR is primarily a function of fat-free mass, and is largely independent of height, age, and sex once fat mass is discounted. The equation is as follows:
BMR = 370 + 21.6 × mass (kg) × ( 1 - fat% ÷ 100 )
Thus, your BMR would be estimated by the Katch-McArdle formula to be 1,414 Cal (5,918 kJ). And this must then be multiplied by a factor which represents your physical activity level, as follows:
Activity level Description PAL
Sedentary Clerical worker/person doing little or no exercise 1.40-1.69
Moderately active Construction worker/person running 1 hour per day 1.70-1.99
Vigorously active Agricultural worker/person swimming 2 hours per day 2.00-2.40
Extremely active Competitive cyclist/multi-sport athlete > 2.40
Let us assume that you are most aptly described as ‘moderately active’, and that your PAL is 1.7. TDEE is thereby calculated as follows:
TDEE = BMR × PAL
Thus, your Total Daily Energy Expenditure is approximately 2,400 Cal (~10,000 kJ), and applying a deficit of 20%, for example, your Daily Energy Intake (DEI) should be 1,920 Cal (8,000 kJ). The relative proportions of the energetic macronutrients—protein, carbohydrate, and fat—that should be contained in your diet can hereby be calculated from this figure. Their energy content is summarised as follows:
Nutrient Energy density (Cal/g)
At a body mass of 130 lbs (59 kilograms), your protein intake should be around 118 grams per day, which therefore equates to around 25% of your DEI. That is:
118 (g) × 4 (Cal/g) ÷ 1,920 (Cal) = 0.2458 ≃ 25%
It is generally recommended that fat not exceed 30% of DEI. So you can calculate the final quantities based upon proportions of protein, carbohydrate, and fat as 25 : 45 : 30, respectively.
Nutrient Proportion (%TDEE) Energy (Cal) Amount (g/day)
Protein 25 0.25 × 1,920 = 472 118
Carbohydrate 45 0.45 × 1,920 = 864 864 ÷ 4 (Cal/g) = 216
Fat 30 0.30 × 1,920 = 576 576 ÷ 9 (Cal/g) = 64
So based upon these proportions, and the assumptions that I have made at the beginning of this post, you would design your diet around a daily intake of 118 grams of protein, 216 grams of carbohydrate, and 64 grams of fat. Of course, you could tweak these variables according to your needs and priorities. It has been found, for example, that greater protein intake tends to result in more rapid fat loss, given the same caloric deficit, and the evidence suggests that for healthy individuals, higher protein intake (of up to 2.4 grams per kilogram of body mass per day) is safe. It should be noted, however, that lowering carbohydrate intake may limit both exercise performance and hypertrophy.
I hope that helps.