RDA is defined as the nutrients present in the diet which satisfy the daily requirement of nearly all individuals in a population. This implies addition of safety factor to the estimated requirement.
Recommended Dietary Allowances of an individual depends on many factors like:
Age
Sex
Physical work
Sedentary
Moderate
Hard (Heavy)
Physiological stress
Pregnancy
Lactation
For all the nutrients (except energy) estimates of allowances are arrived at by determining the average. Taking mean requirement of nutrients and adding twice the standard deviation of the mean.
Requirement = Mean ± 2SD
The value obtained will cover more than 97.5% of the population which is composed of individuals with a satisfactory normal distribution of requirements.
ICMR has defined well nourished Indian adults who had satisfactory growth during childhood as
Reference Man who is between 20 – 39 years of age and weighs 60 kg. He is free from disease and physically fit for active work. On each working day he is employed for 8 hours, spends 4-6 hours sitting and moving about, and 2 hours in walking or in active recreation or household duties and 8 hours in bed.
Reference Woman who is between 20-39 years of age and healthy, and weighs 50kg. She may be engaged 8 hours in general household work or in light industry or in any other moderately active work. Apart from 8 hours in bed, she spends 4-6 hours sitting or moving around in light activity, and 2 hours walking or active recreation or household chores.
Scientists have prescribed RDA for adults, depending on the level of activity of an individual.
Sedentary workers: Those who sit and do work using brain and hands. Ex: teachers, clerks, typists, officers
Moderate workers: Work vigorously for a few hours using many parts of the body like hands, feet and muscles. Ex: postman, mali, maid servant, housewife doing all household work.
Heavy workers: Use different parts of body for several hours. Ex: rickshaw pullers, coolies, workers in mines, sports persons, masons etc.
Participants