Presents the protein content of common foods and the difficulties in creating low-protein meals.
The Protein Myth
One thing you discover when you try to formulate a low protein diet the difficulty of finding suitable foods. When the national Academy of Science established its Recommended Daily Allowances for protein, it started with the amount of protein and its breakdown products lost by the average adult male body per day28. Since nitrogen is found in proteins but not fats or carbohydrates, its measure serves as a close measure of protein. Obligatory urinary nitrogen losses at about 37 mg/kg/day, fecal nitrogen losses at 12 mg/kg/day, perspiration, hair, fingernails, and sloughed skin nitrogen losses at 3 mg/kg/day and other losses at 2 mg/kg/day imply a protein loss of 0.34g/kg/day or 0.15g/lb/day. Any net recovery from the diet beyond that in the absence of growth is converted to carbohydrate (sugar) and burned for energy or then converted to fat. Of course energy is as legitimate a need as any other and there is nothing bad about getting it from protein, unless you have a condition like some kidney diseases for which a low protein diet is indicated.
Generally people eat until their energy needs, as measured in calories * , are fulfilled. Some people do eat for other reasons but that is topic for a later discussion. A 170 lb adult male typically consumes 2700 to 3000 calories a day. His absolute minimum protein requirement then works out to be about 25 grams of protein per day (170 lbs X 0.15gram/lb/day).
Fat provides about 9 calories per gram consumed. Protein and carbohydrate provide 4 calories per gram. The 25 grams of protein consumed by our 170 lb male then represents (4 X 25)= 100 calories. So, if 100 calories out of 2700 calories consumed per day are protein then our 170 lb male has met his minimal protein requirement. 100 is 3.7% of 2700 so we can further say that a young adult male of any weight or caloric consumption gets his minimal protein requirement when the calories he gets from protein exceed 3.7% of his total caloric intake. Note that the elderly seem to have a somewhat higher protein requirement.
If he is less active, 2000 calories a day may be a more accurate number. In that case 100 is 4% of 2000 and we can say that a less active adult male of any weight or caloric consumption gets his minimal protein requirement when the calories he gets from protein exceed 4% of his total caloric intake (a nice round number).
All foods in the US now carry a nutrition label like the following:
The number of calories and the grams of protein per serving are always listed. If you multiply the grams of protein by 4 and divide by the number of calories, you will get the fraction of calories from protein. Multiply that fraction by 100 to get the percentage of calories represented by protein.
Here is a table of the protein calorie percentage from high to low of some common foods along with their calorie density:29
|Food||Calories/ 100g (3.5 oz)||% as Protein|
|Tuna (canned in water)||116||88|
|Crab meat (blue)||87||88|
|Cottage cheese (solid)||90||61|
|Milk (skim cow)||38||39|
|Hamburger (70% Lean)||270||38|
|Eggs (hard boiled)||155||33|
|Milk (whole cow)||62||21|
|Hot dog (pork?)||330||14|
|Whole wheat bread||260||14|
|Vanilla ice cream||279||7|
|Cassava (yucca) (boiled)||89||0|
As becomes apparent, all staple foods have a protein percentage much greater than the 4% actually needed for protein synthesis by the body. Rice, for example, has the lowest protein content of the grains common in the Western diet yet is 8% in protein calories. A diet of just rice would provide over twice one’s minimum protein needs. Even a diet of just cookies and diet cola (not recommended) could provide sufficient protein.
Of course this assumes that all the protein in the food is absorbed in the digestive process. Probably the less calorie-dense a food is the less true is this assumption. If you ate just broccoli, for example, even though the protein calorie percentage is high, the vast bulk you would have to consume to net enough calories would likely prevent a large fraction of the protein from getting through to the bloodstream.
Note that human milk, the ideal complete food for humans for the period of time when they are growing the fastest, has only 6% of its calories represented by protein!
Increasing the 0.34 minimum as a safety margin, the World Health Organization recommends 0.45 grams/kg/day of protein. Doubling this the United States Department of Agriculture recommends 0.8 grams/kg/day for average healthy adults. For adults ranging from 100 to 200 lbs this is around 20 to 40 grams per day using the WHO number, 40 to 80 using the USDA number. By way of quick reference, a serving (6 oz) of meat or cheese is around 40 grams of protein, a similar serving of milk, beans or tofu around 10 grams, and a serving of grain or vegetable around 4 grams.
You can readily see that a typical Western industrial diet far exceeds these recommended minimums. Most protein ends up converted to carbohydrates and the nitrogen removed becomes a potentially toxic waste product that the body must then dispose of, principally as urea in the urine..
Why then does protein get such a positive press? The reasons are mostly historical. First children have elevated needs for protein to support growth and display symptoms of protein insufficiency during times of famine when adults do not. Second the high protein foods, meat and cheese, have been preferred by the rich and powerful (though this is as much for their fat content and energy density as for their protein) and have gained favor thereby. Third a significant portion of the population, especially in the past in Western nations, are or have been alcoholics and actually manage to consume their calories in alcohol to the exclusion of everything else. Finally government food policies have been given to departments of agriculture where meat and dairy interests are paramount rather than to departments of health.
The dangers of too little protein consumption are more severe than the dangers of too much and it is not surprising that advisories would be conservative on the up side.
Regardless, following the protein cycling diet does not reduce your over-all protein consumption, just the timing of when it is consumed and not consumed.
The term Calorie in this food context is the same as the kilo-calorie in a physics context, that is, the amount of energy required to raise the temperature of 1 kg of water 1 degree centigrade.