Questions in Protein Land

How much and what kind of protein do we need?

In the USA, the National Academy of Sciences RDA for total protein is currently 0.80 g/kg/day. For my 75 kg, that's 60 g/day. This is based on nitrogen loss by healthy adults, and doubled for safety to ensure that it covers 98% of the American population. It assumes that you are not under any unusual stress such as body building, endurance training, or metabolic disorder.

Typical European recommendations are a lot higher: 80-120 g/day for a moderately active male of my weight and age.

Then, if that isn't disagreement enough, there are the RDA's for the essential amino acids individually, from the World Health Organization (1985) and the USA National Academy of Sciences:

amino acidWHONAS
Isoleucine1019 mg/kg/day
Theronine 720
Tryptophan3.5 5
total protein750800

The WHO RDA's for these 'essential 8' dietary amino acids (growing children need a 9th) total only 11% of their total protein RDA, while the NAS RDA's total 25% of their protein RDA. And, the 8 total 39% of the total protein in our bodies. Clearly, the criteria for the total protein and individual amino acid requirements are incompatible, even though each is widely used as the basis for government regulations.

What about an upper protein limit? North American dieticians generally recommend a maximum of 20% protein by calories for average adults. They differ on how much, if any, more are a maximum for training athletes or bodybuilders.

The aboriginal Ihalmuit of the Barren Lands of northern Canada required one handful of fat for each three of lean meat to avoid protein toxicity, which works out to about 30% protein by calories. But, their diet had virtually no carbohydrates, they were selected ruthlessly by their climate over thousands of years for survival on their diet, and had unusually large livers.

I note concerns that a high protein diet is linked by some to osteoporosis in later life. 20% seems an upper limit for a sensible person without a health problem related to protein metabolism.

What about protein 'quality' measures such as the TPD or PDCAAS? There are many valid criticisms of this approach, but the sufficient one here is that they all assume that solely one food is being eaten. This site is about balanced diets - many foods.

A few comments

When I put numbers on the foods I eat, using data from the USDA), I get that a 3000 calorie/day diet, as is recommended for a person of my weight and activity, supplies some three times the NAS RDA's for amino acids and twice their total protein RDA, even with a mostly-vegetarian natural diet, when balanced for other nutrients. This is supported by most dieticians, who note that the average North American eats three times the protein they need, and that amino deficiencies are non-existent here with any diet that is even remotely balanced.

I tried to optimize a 3000 calorie/day diet to provide precisely the WHO amino RDA's, and couldn't find one that also supplies an even remotely acceptable balance of other nutrients - any sensible diet supplies far more of the aminos than WHO. When I repeated the attempt with the NAS amino RDA's, the fit was poor, and relied heavily on vegetable oils, refined sugars, and purified starches such as tapioca to keep the amino content down. For now, I normalise the NAS amino RDA's to the contents of total mammal protein and the NAS total protein RDA. I note that this approach leads to the average of the individual amino acid %RDAs being equal to the total protein %RDA supplied by my diet of mostly natural foods.

Regulations based on the current NAS RDA's for amino acids are probably inappropriate given the state of flux of the relevant science, but the 1985 WHO RDA's are unacceptable except as dietary minima requiring urgent action.

John Sankey
other notes on nutrition