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The Harris–Benedict equation (also called the Harris-Benedict principle) is a method used to estimate an individual's basal metabolic rate (BMR).. The estimated BMR value may be multiplied by a number that corresponds to the individual's activity level; the resulting number is the approximate daily kilocalorie intake to maintain current body weight.
Based on the work of Atwater, it became common practice to calculate energy content of foods using 4 kcal/g for carbohydrates and proteins and 9 kcal/g for lipids. [2] The system was later improved by Annabel Merrill and Bernice Watt of the USDA, who derived a system whereby specific calorie conversion factors for different foods were proposed. [3]
The respiratory quotient value indicates which macronutrients are being metabolized, as different energy pathways are used for fats, carbohydrates, and proteins. [1] If metabolism consists solely of lipids, the respiratory quotient is approximately 0.7, for proteins it is approximately 0.8, and for carbohydrates it is 1.0.
The distribution of macros will vary based on your personal goals and macro ratio — a bodybuilder or weightlifter might want to increase the amount of protein on their plate.
The Holliday-Segar formula is a formula to help approximate water and caloric loss (and therefore the water requirements) using a patient's body weight. [1] Primarily aimed at pediatric patients, the Holliday-Segar formula is the most commonly used estimate of daily caloric requirements. [ 2 ]
where f is the body fat percentage. According to this formula, if the woman in the example has a body fat percentage of 30%, her resting daily energy expenditure (the authors use the term of basal and resting metabolism interchangeably) would be 1262 kcal per day.
Macronutrients are defined as a class of chemical compounds which humans consume in relatively large quantities compared to vitamins and minerals which provide humans with energy. Fat has a food energy content of 38 kilojoules per gram (9 kilocalories per gram) proteins and carbohydrates 17 kJ/g (4 kcal/g).
For example, the United States government estimates 8,400 and 10,900 kJ (2,000 and 2,600 kcal) needed for women and men, respectively, between ages 26 and 45, whose total physical activity is equivalent to walking around 2.5 to 5 km (1 + 1 ⁄ 2 to 3 mi) per day in addition to the activities of sedentary living.