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Body protein - Daily requirement - Indispensable amino acids - Protein quality - PDCAAS - Optimum intake

Protein excess

Any dietary excess has adverse health consequences, and proteins are no exception. Since the body cannot store proteins, any excess is broken down in the liver and eliminated through the kidneys. Thus, excess protein elimination puts

additional burden on the kidneys,

possibly causing organ damage in the long run. The kidneys being miraculously efficient, even significant reduction in their capacity wouldn't cause noticeable health effect in most people. However, for those less fortunate, with less than healthy kidneys, it can make a difference between getting by fine, and having serious health problems.

The increased rate of fluid output reduces the time that the kidneys have to reabsorb the minerals, which are consequently lost with the fluid at a higher rate. More so, if calcium plasma levels are elevated to buffer acidifying effect of high-protein diet. It was long though that loss of calcium due to high-protein intake promotes bone loss (osteoporosis).

According to the long-term study of The American Journal of Clinical Nutrition, even moderately elevated protein intake of 75g per day, with daily calcium intake as high as 1400mg, already results in

more calcium lost than absorbed.

 Some recent studies, however, indicate that urinary loss of calcium due to higher protein intake is offset by better absorption rate. But these studies do not address long term effects, nor how this may vary individually in the population at large.

In addition to possible negative effect on body calcium level, there is a number of undesirable metabolic consequences of high-protein diet.

Excess amino acids, as most other nutrients, can also have toxic effect, but only if taken in supplemental form in very large doses, or in large quantities for prolonged periods of time. Some amino acids can cause complications in pregnancy; some can negatively interfere with MAO drugs.

Excessive dietary intake of proteins can negatively affect body's ability to use other nutrients, and cause deficiencies (for instance, calcium, iron - from excessive soy or dairy protein18 - or vitamin B67).

The level of protein intake at which it becomes excessive is somewhat arbitrary, and varies individually. In general, excessive intake probably begins at about 20% of total calories from proteins, somewhat less toward the higher end of caloric intake range, and somewhat more toward the lower end.
 

Amino acid deficiency

Individual cases of protein deficiency in adults are very rare in developed countries (read: in the absence of starvation) except for those at highly restricted caloric intake and, probably, for older folks. Some studies indicate that 0.8g/kg/day protein intake may not be generally sufficient to satisfy protein needs of the elderly, most likely due to proteins being utilized less efficiently.

Along these lines, safe protein intake does not necessarily guarantee your body is getting all the protein it needs. While unlikely, deficiency is still possible and, in its origin, not likely to be protein-intake-related. It can be caused by faulty digestion, absorption and/or assimilation (low stomach acid and/or pancreatic enzymes, malabsorption, deficiency in nutrients needed to metabolize amino-acids, etc).

Thus correcting these problems also corrects amino acid deficiency. Otherwise, you may get into unhealthy vicious circle of craving (even more) protein-rich foods, resulting in unbalanced, poor diet, while what your body really needs are nutrients needed to efficiently digest and metabolize already available proteins.

Much of publicly circulating information related to dietary protein and its health significance results from lobbying of the powerful meat and dairy industries. It perpetuates the hype that one needs to consume significant proportion of high-protein foods in order to maintain optimum health.

The fact is that, around the world, native groups of people with the highest life expectancy and lowest disease rates all have diets with moderate to low - down to ~50g a day - protein intake, mostly from plant sources (which may have generally better rate of utilization by the body). This intake level is also close to the estimated minimum safe level of protein consumption of 0.75g/kg/day.

On the other hand, Eskimos, who consume as much as 250g-400g of animal proteins a day, have low life expectancy and often very high rates of osteoporosis.

This is a strong real-life indication that

moderation in protein consumption supports optimum health,

as opposed to protein excess. Not surprising, mind you, since this is rather a general rule.

But we can't directly compare humans leaving in different conditions. Protein needs - as well as those for most other nutrients - are likely to be higher for us, living in much more polluted and stressful environment of the modern world, than for native people in near-pristine environments.

Specific figure is necessarily speculative to some degree and, as always, reflecting broad average - but the overall set of known factors seems to be indicating that the optimum average protein intake in developed countries shouldn't be lower than ~1g/kg/day.

However, there is always the level after which protein intake becomes excessive and unhealthy. That level, for adults - with the possible exception of the elderly, or individuals with impaired protein absorption/utilization - seems to be placed above ~1.5g per kg of body weight a day.

In other words, optimum daily protein intake in urban environments is probably in the the range between 1-1.5g per kg (0.45-0.68g/lb) of body weight.
 

Years and decades of promoting "quality" proteins and high-protein foods have created a myth of their nutritional superiority. The facts, however, seem to be pointing to the opposite.

 Our protein and essential amino acids needs can be satisfied with most any natural food alone - brown rice, wheat flour, corn, potatoes, asparagus, broccoli, pumpkin, beef, egg, milk, etc. - providing it is ingested in the quantity needed to fulfill daily caloric requirement. Thus, any actual diet combining various foods

will also satisfy body's protein and essential amino acid requirements.

There is no danger of protein deficiency for vegetarians, or even vegans, unless they starve themselves. The concept of protein "value", or "quality" - with animal proteins rating generally higher than plant proteins - beside being flawed, is of secondary importance at best. Nevertheless, it is not only given the center spot but is, evidently, also mishandled.

Labeling proteins as being of different "value", or "quality" when coming from different foods is directly misleading. The difference is purely quantitative - including several percentage points lower average absorption of plant proteins - and should be clearly presented as such. In fact,

diets based on moderate-protein foods are inherently
better balanced nutrients-wise, hence also healthier.
 

Bioavailability of heat denatured proteins

An important consideration not taken into account with the PDCAAS is the form of protein intake. Heated (cooked) proteins are denatured by higher temperatures, quickly and completely as the temperature reaches as little as 60°C.

Denaturing is another word for re-structuring of the protein's natural molecular form. It is also done by the stomach acid in the process of digestion. However, if we assume that the way the stomach acid does it enables the enzymes to optimally break down protein molecules into amino acids, denaturing of proteins by cooking - unless identical to that caused by the stomach acid (highly unlikely) - will result in less than optimal enzymatic action (which works on a lock-and-key principle), and

lower amino acid bio-availability.

If so, at the two extreme ends, row-food diet needs to supply less protein than all-cooked diet. In effect, cooked foods would have lower effective protein content than what their nominal raw "label" implies. 

Processed foods are also often exposed to heat, acids and/or alkali, which means that their usable protein content is probably lower than what their labels indicate.

There is neither consensus nor reliable studies on the subject of how much cooking and processing lower protein bio-availability (it probably varies both, individually and with the protein type). It is surprising, considering how important it could be in determining our actual protein needs. The two least likely scenarios are: (1) no appreciable reduction in absorption/assimilation on one, and (2)near complete bio-degradation on the other end. The truth is, most likely, somewhere in between, and yet to be determined.

Raw vs. cooked differentiation is important not only protein-wise, but for our nutritional needs in general. By preserving enzymes, vitamins and other nutrients, as well as by avoiding possibly harmful alteration of food molecules caused by cooking, raw food diets are all but certain to allow for

lower caloric and nutritional requirements

than cooked food diets. Unfortunately, there is very little research done on this subject. Let's just recall that lower caloric intake alone has been proven in laboratories over and over again to be the only known factor to significantly prolong the life span.

Conclusion

All the facts in this lengthy consideration seem to be convincingly turning the table against the common notion of the superiority of animal-origin foods as a source of "quality protein". Plant foods are as efficient protein source, and they are certainly the healthier one from the standpoint of body's overall nutritional needs.