A research study published in the Journal of the American Medical Association produced a report
by the Board of the Institute of Medicine to determine optimal intake of the
macronutrients protein, carbohydrates, and fats. Regarding protein intake, they determined the
recommended daily allowance (RDA) for those 18 years of age and older was 0.8 g
of protein per kilogram body weight per day. In plain English, this means
.36 grams per pound of body weight.
It was also noted the dietary guidelines published by the U.S.
Department of Agriculture and Governmental programs, such as the school lunch
program for children and Meals on Wheels for elderly persons, use the .36
grams/pound/day as well. Same for dietary guidelines published in the dietetic
literature, the popular press, and various nutritional computer programs - a
recommend protein intake of .36 grams/pound/day.
In example, a 190 pound person would need only 68.4 grams of
protein per day. That requirement could be met
by ingesting a 4 ounce skinless chicken breast, half a cup of low-fat cottage
cheese, and half a cup of crushed walnuts in one day.
The RDA for protein was based on the results of all available
studies that estimated the minimum protein intake required to avoid progressive
loss of lean body mass as reflected by nitrogen balance. The Food and
Nutrition Board admitted that relying solely on results from nitrogen balance
studies to determine the RDA did have limitations, because this method does not
measure any relevant physiological end point. Additionally, the existing data
were gathered almost exclusively in college-aged men and a greater nitrogen
intake was likely required to maintain nitrogen balance in elderly persons.
Regardless of whether .36 grams/pound/day is an appropriate value for the RDA
for elderly persons as well as for individuals 18- to 50-years-old, the point
is the RDA is functionally defined as the amount of protein needed to avoid a
deficiency that would lead to a progressive loss of lean body mass (as
reflected by negative nitrogen balance).
The Acceptable Macronutrient Distribution Range (AMDR) of
protein was noted to be between 10% and 35% of the daily energy intake (DRI). For example, the
daily energy requirement of a sedentary 19-year-old reference man (5’-9” tall
and 167 pounds) is estimated to be 17.2 total calories per pound (2,872 total
calories/day). Ten percent of this caloric intake as protein would equal .43
grams/pound/day (72 grams) and 35% would equal 1.5 grams/pound/day (250
grams!). Thus, the RDA is below the
lowest intake recommended by the AMDR when considered in the context of the
overall dietary intake of macronutrients.
This discussion is relevant to nutrition policy only if there is
evidence the optimal level of protein intake differs from the minimal
requirement. The wide range recommended in the AMDR (10%-35% of energy intake)
implies uncertainty regarding the exact optimal level of protein intake. This
uncertainty reflects in part a relative lack of research addressing this issue.
In addition, the wide range reflects, by deduction, uncertainty regarding the
optimal levels of carbohydrate and fat in the diet.
The problem of widespread misinterpretation and improper
application of the RDA arises from the fact the Food and Nutrition Board
maintained the historically familiar term "recommended dietary
allowance," but functionally defined it in terms misunderstood by most
individuals. The distinction is that
a requirement clearly defines the minimum amount needed, whereas no such
implication is conveyed with the any recommendations.
These points notwithstanding, there is ample evidence the
optimal level of protein intake is greater than the RDA. A variety of studies have
shown levels of protein intake above the RDA benefiting muscle mass, strength,
bone health, maintenance of energy balance, cardiovascular function, and wound
healing. Close examination of these and related research studies should enable
a reasonable estimation of the optimal level of protein intake in a variety of
circumstances.
It was concluded there was no evidence documenting an upper
level of protein intake beyond which adverse effects would ensue. Consequently, the DRI indicated
there is no tolerable upper intake level for protein.
The MINIMUM amount of protein for athletes should be at least
.55 grams/pound/day. Depending upon
your sport or training regimen, the daily requirement can go as high as .9 to 1
grams/pound.
