Use of Recommended Dietary Intakes in Planning Balanced Diets

The Recommended Dietary intake (RDI) is the amount of a nutrient to be actually consumed in order to meet the requirements of the body. Recommended dietary  intakes are hence based on requirements. Now what do we mean by the term "requirement"?  The requirement for a particular nutrient is the minimum amount that needs to be consumed to prevent symptoms of deficiency  and to maintain satisfactory levels of the nutrient in  the body. As mentioned  earlier,  recommended dietary intakes are based on requirements. How do we convert a requirement  figure into recommended  dietary  intakes or RDIs? The RDIs are basically the requirement plus a safety margin. 

Relationship between  requirement  and  recommended dietary Intake 

The safety  margin is added on to cover factors like: 

• variation in  requirement from individual to individual 
• periods of low intake  (periods of leanness) 
• nature of diet 
• cooking losses 

Some of these points can be well illustrated with the following example. In experiments conducted with adults it was found that when the intake of vitamin C was 20 mg/day, vitamin C deficiency or scurvy could be prevented and satisfactory levels of vitamin C could be maintained in the body. Since  all the persons studied were able to satisfactorily maintain body vitamin C levels at an intake of 20 mg/day, there was no need to make allowances for individual variation. Now, how is this figure for requirement converted into an intake figure for adults? Vitamin C is easily destroyed on cooking. On the average, a figure of 50 percent cooking losses was considered  reasonable. The recommended  intake was therefore fixed at double the requrrement i.e. 40 mg per day. 

In addition to the factors already discussed, the nature of the diet has a significant influence on the RDIs fixed for certain specific nutrients. Take protein for example. Many Indians cannot afford animal protein and hence they consume a diet which supplies vegetable protein. Since vegetable protein is utilized to a relatively lower extent,  more  protein needs to be consumed and therefore RDIs increase.Similarly, in the case of iron, the availability of iron to the body depends on the type of food consumed. Absorption of iron from typical Indian diets is low as you learnt in the previous unit. Therefore more iron needs to be consumed to meet the requirement i.e. the RDI is fixed at a higher level. 

You have now gained an idea about the concepts of requirement and recommended dietary intakes. There are three important points that you need to remember.

• RDls are set high enough to meet the  needs of almost all healthy people: In other words, a generous margin is usually given for individual variation in a population of normal healthy individuals. 
• RDls do not apply to people who are suffering from a disease which  influences the nutrient  needs: A disease can cause an increase or decrease in the requirement of one or more specific nutrients. Sometimes medicines  prescribed during illness influence nutrient need. For instance,  when one takes antibiotics one also has to consume more of the B-complex vitamins. The RDIs only apply to individuals who are normal and not suffering from a disease likely to influence nutrient  requirements. 
• Recommended dietary intakes for adults are based on sex, age, body size and activity level: In the case of adults, there are substantial variations in RDIs particularly for energy and protein  depending on the age, body weight and activity pattern. This is why working out RDIs on the basis or  "reference individual" is useful. RDIs have, in fact, been  fixed using this principle. The Reference man is an Indian  man in the age group of 20-39 years doing moderate work and weighing 60 kg. Similarly, an Indian woman 20-39 years old do moderate work and weighing 50 kg is referred to as the Reference woman. You would notice that the age range. weight and activity level have been specified in  both cases. 

Some of the salient  features of recommended dietary intake and how  they are expressed are summarized in the following points. You will  also come across explanations  for various terms used.

i)  RDIs are expressed in kilo calories (K cal), grams (g), milligrams (mg) or micro grams  (ug): RDIs  for energy are expressed in  K cal. One kilo calorie is the amount of heat required to  raise the temperature of one kilogram of water 1000 milligrams (mg) make one  gram  and 1000  micro grams (ug) make one milligram. The RDIs for  protein are given  in grams while RDIs for  vitamins are expressed in  milligrams or  micro grams.

The reference man and woman

ii) RDIs for energy for adult men and women are based  on activity levels: Activity levels can  be described as sedentary (light), moderate or heavy. The more the activity, the higher  would be  RDIs for energy.

iii)RDIs for  thiamine, riboflavin and niacin are  dependent on RDIs for energy: The relationship between the RDIs for these vitamins and energy is as follows: 

RDI for thiamine = 0.5 mg/ 1000 K cal; RDl for riboflavin = 0.6 mg/ 1000 K cal: RDI for  niacin  = 6.6 mg/1000 K cal. Can you explain why such a relationship exists? We discussed this aspect. You would remember that these three vitamins play a vital role in the release of energy from  carbohydrates, fats  and  proteins.

iv)RDIs for protein are based on body weight: The  relationship can be expressed as 1g protein  per kg body  weight in the case of the adult. It varies for other age  categories.

v)RDIs for energy and protein are given as additional  intakes in  pregnancy and lactation:  Pregnancy and  lactation are periods of "physiological stress" because    nutrient needs  increase  considerably to meet the needs of the growing foetus (in the case of pregnancy) and production  of milk (in the case of lactation when the  mother breastfeeds the baby). RDIs are given  in terms  of additional intakes  (indicated by a "+"  sign) for  some  nutrients like energy and protein. RDIs  for the other nutrients are given as total intake figures.

vi)In  infancy RDIs for energy, protein, iron, thiamine,  riboflavin and niacin are expressed  per kg body weight:  Here the expression "body  weight"  refers to the body  weight expected  for a  healthy,  normally  growing infant of a particular age. Infancy is also a period of    physiological stress just  like any period  characterized by rapid  growth.

vii) RDIs for vitamin A have been given in  terms of retinal or alternatively in terms of  beta carotene: Carotene is a  precursor of vitamin A, as you  know. The body cannot utilize all the carotene consumed to make retinal, About half of the beta carotene consumed is absorbed.  further, only about 50 per cent of the amount absorbed  can be converted' to retinal. In other words, only 25 percent of the  consumed  beta carotene is actually  converted into retinal. Hence  for every 100 units of beta carotene taken in. only 25 is available to the body as retinal. This is why the carotene-retinal ratio is 4: 1.

 Four  units of carotene make one unit of retinol in the body

Most diets  provide  both retinal and carotene. However. RDIs are given  in terms of either retinal or beta  carotene.  It would therefore help if  we express the total vitamin A content of the diet either  as retinal or beta carotene. To express the total vitamin A content of the diet in terms of retinal, the following relationship can be used: 

Total Vitamin A as retinal(in micro grams) =  Retinal (micro grams) +  Beta Carotene in micro grams/4 

Example: Assume a diet supplies 50 micro grams retinal and 2800 micro grams beta carotene. The total vitamin A supplied by the diet  would be 

50+(2800/4) = 50+700 = 750 micro grams

we have so far studied the concepts of requirement and recommended dietary intake. We  have also examined the RDIs for Indians  Now we  can move on to the study of how these are used in planning  balanced diets. 

The amounts of different foods to be consumed  would  depend on the RDIs. The higher the RDI for a  particular nutrient, the more should  be the consumption  of foods rich in that  nutrient. The amount of cereal consumed by a heavy worker. for example, should  be more than that consumed by a  light worker. Why is  this so? This is  because  of the  fact that energy requirements are far more for heavy workers and because cereals are a source of carbohydrates and, therefore, energy. Detailed information on planning  balanced diets for infants.  preschoolers, school children,  adolescents,  pregnant and lactating  women is given in  Block3. In all these cases, the amount of food to be consumed would be dependent primarily on the RDls.