Protein

When it comes to nutrition, we seem to know so little. Of the three major components of our diet, we debate quite a lot in this day and age, whether to eat low carb or low fat, mainly because we are preoccupied with obesity.

What about protein?

The US guidelines recommend a daily protein dietary allowance, measured as intake per body weight, is 0.8 g/kg. However, this recommendation is based on structural requirements, but disregards use of protein for energy metabolism. Too much protein puts strains on kidney. Proteolytic fermentation in our gut, breaks down proteins in food, and can produce toxins and carcinogens. Thus, a diet lower in protein reduces exposure to toxins.

Proteins are made of amino acids, out of which 8 (or 9 if we count histidine) are essential for humans and must obtain from food sources.

I do not know how much research has been done, but the optimal levels for essential amino acids as recommended by the Institute of Medicine's Food and Nutrition Board are as follows:

Essential Amino Acid/ mg/g of Protein
Tryptophan/ 7
Threonine/ 27
Isoleucine/ 25
Leucine/ 55
Lysine/ 51
Methionine+Cystine/ 25
Phenylalanine+Tyrosine/ 47
Valine/ 32
Histidine/ 18

Unfortunately, unless you are doing research, nobody can follow the above profile.

Most animal sources have the complete complement of all the essential amino acids in adequate proportions. Apart from soybeans, vegetable sources of protein are more often lacking in one or more essential amino acids than animal sources, typically being deficient in lysine and methionine. Therefore, it is more complicated to be a vegetarian. I am a non strict vegetarian, as I eat fish, seafood and eggs. My grandmother was a strict vegetarian (vegan) since the age of 60 and lived till 91. So I do believe that one can be healthy and vegetarian. Tofu was her source of essential amino acids.

It is generally accepted that caloric restriction extend life span. Methionine restriction imparts at least some of the effects of CR without the CR.

One interesting aspect of all those long lived Chinese people (over the age of 90), is that they all eat very little in general and even less in meats. Practically people who could remember the years of great famine (1958-61), were forever affected and even if they could have a lot of foods available to them today, they still would not eat a lot. Therefore, it seems to me that they are not only doing CR, but also methionine restriction.