One of those "essential" amino acids is methionine.
One needs methionine for many human metabolic functions
including digestion, detoxification of heavy metals, and
muscle metabolism. However, an excess of methionine can be
toxic and create that acid condition in your blood.
The center atom of methionine is sulfur. That's the problem.
Eat foods containing too much methionine, and your blood
will become acidic. The sulfur converts to sulfates and weak
forms of sulfuric acid. In order to neutralize the acid, in
its wisdom, the body leaches calcium from bones.
"Dietary protein increases production of acid in the blood
which can be neutralized by calcium mobilized from the
skeleton." {American Journal of Clinical Nutrition, 1995;
61,4}
Animal proteins contain more methionine than plant proteins.
Let's compare cow's milk to soymilk:
Methionine in 100 grams of soymilk: .040 grams
Methionine in 100 grams of whole milk: .083 grams
Methionine in 100 grams of skim milk: .099 grams
Now, let's compare 100 gram portions of tofu to meat:
(All of the meat products are lean and without skin)
Silken soft tofu: .074 grams of methionine
Hamburger: .282 grams of methionine
Roast ham: .535 grams of methionine
Baked codfish: .679 grams of methionine
Roast chicken: .801 grams of methionine
Why do nations with the highest rates of bone disease also
have the highest milk consumption rates? The highest rates
of osteoporosis are to be found in America, Denmark, Holland, Norway,
and Sweden.
We are told to consume 1000 milligrams per day of calcium.
Inuit Eskimos consume 3500 milligrams of calcium each day,
and by age 40 are crippled.
THE KEY TO OSTEOPOROSIS
It's not how much calcium you eat. It's how much calcium you
prevent from leaving your bones.
WHY DOES CALCIUM LEAVE BONES?
In 1988, N.A. Breslau and colleagues identified the
relationship between protein-rich diets and calcium
metabolism, noting that protein caused calcium loss. His
work was published in the Journal of Clinical Endocrinology
(1988;66:140-6).
A 1994 study published in the American Journal of Clinical
Nutrition (Remer T, Am J Clin Nutr 1994;59:1356-61) found
that animal proteins cause calcium to be leached from the
bones and excreted in the urine.