Oxalates are chemicals found in plant foods but not in most animal foods. Some people are more likely to form  kidney stones if they eat foods high in oxalates.

Measurement of oxalate content in vegetables commonly consumed in New Zealand shows that cooking reduces the oxalate content of the food by leaching losses into the cooking water.

There was a high proportion of water-soluble oxalate in most of the tested raw vegetables. Boiling markedly reduced soluble oxalate content by 30-87% and was more effective than steaming (5-53%) and baking (used only for potatoes, no oxalate loss). An assessment of the oxalate content of cooking water used for boiling and steaming revealed an approximately 100% recovery of oxalate losses. The losses of insoluble oxalate during cooking varied greatly, ranging from 0 to 74%. Because soluble sources of oxalate appear to be better absorbed than insoluble sources, employing cooking methods that significantly reduce soluble oxalate may be an effective strategy for decreasing oxaluria in individuals predisposed to the development of kidney stones.

Recker et al. (1988), using 45Ca as an extrinsic label, found that Ca
absorption in post-menopausal women from milk products (whole milk, chocolate milk,
yoghurt, imitation milk, cheese) was similar to calcium carbonate, with means ranging from
22 to 27 YO from a 25 mg dose. The present experiment re-affirms the results of the original
balance studies on dairy and plant foods in that the Ca in skimmed milk was better
absorbed than that in watercress soup. The reason for this is unclear but may be
attributable to substances present in the watercress soup that bind Ca thereby rendering it
less absorbable, e.g. oxalate (Pingle & Ramasastri, 1978) and fibre (Kelsay et al. 1979), plus
the fact that certain components of milk have been implicated as enhancers of Ca
absorption, e.g. lactose (Charley & Saltman, 1963) and casein (Lee et al. 1979).

But two findings were unexpected. First, bone resorption—in which calcium is taken away from bones via the bloodstream—was the same for omnivore women as for vegan women.

"The current model predicts increased bone resorption for people who consume large amounts of animal protein, so it was somewhat surprising that bone resorption was the same for both groups of our volunteers," Van Loan notes.

Second, bone formation was significantly less in omnivore women than in vegan women. This happened even though the omnivore women had a higher calcium intake than did the vegan volunteers. (The volunteers did not differ in their intake of other nutrients that affect bone health, such as magnesium.)

Using the model as a basis, "one would not have predicted a significantly greater amount of bone formation for vegan volunteers than for omnivore volunteers," Van Loan adds.

The implication for people who eat high amounts of animal protein may be important: Specifically, over time, the net effect of a lower amount of bone formation would likely be a decrease in bone density.

...there is now evidence that due to the effects of a high intake of protein on the calcium
excretion and acid-base balance, the bone stability is detrimentally affected. Sulfur-containing
amino acids from protein are metabolized to sulfuric acid. An imbalance between acid and base-forming
constituents in food leads to a chronic net acidification, and without compensation a chronic metabolic
overacidification (latent acidosis) develops. Above all animal protein increases the renal net acid excretion
in contrast with vegetable protein...

Although latent acidosis leads on the one hand to a release of bases from
the bones to maintain the acid-base balance, the released minerals, above all calcium, are lost via the
urine, and in the long run this results in a decrease of the bone mineral content and bone mass. Additionally,
latent acidosis stimulates the activity of bone-resorbing osteoclasts and inhibits the activity of
bone-forming osteoblasts.....

Conclusion: Throughout the world, the per capita consumption of animal protein is associated with a
higher hip fracture risk in women over 50, and the consumption of vegetable foods with a lower risk.
However, the analysis of the bone density measurements showed no correlation with the intake ratio
from animal and vegetable protein, particularly not when the body weight and age were taken into account.
It can therefore be concluded that an adequate diet corresponding to a high total protein intake
and resulting higher body weight plays an important role with regard to an adequate bone density.
On the other hand, elderly women with a high proportion of animal protein showed a clearly more rapid
loss in bone density and a higher risk of hip fracture than women with a lower proportion. With advancing
age, the excess acidity caused by the high protein consumption has a particularly disadvantageous
effect on the bone stability because due to the declining kidney function, the capacity to excrete acids
steadily decreases. In addition, latent acidosis leads to an increased breakdown of muscle protein. Nitrogenous degradative products like, for example, glutamine serve as initial compounds for the synthesis of basic ammonia in the kidney cells. Like the bones, the muscular system becomes involved
as a base reserve for maintaining the acid-base balance with the consequence that with declining muscular strength in old age, the risk of hip fractures resulting from falls increases.

Taken together, the results confirm the hypothesis that an increased intake of protein of vegetable origin
and concomitant reduction of the consumption of animal protein reduces the nutrition-induced acidification; as a result of the protection of the body’s endogenous reserves this provides, both the bone loss as well as the risk of hip fracture in old age can be reduced. The basic minerals occurring mainly in vegetable foods which reduce protein-induced acidification are assumed to be responsible for this effect.

Advocates claim that consuming a diet high in acidic foods, such as animal protein, sugar, caffeine, and processed foods, may disrupt the pH of the bloodstream, and increase a person's likelihood of developing chronic or degenerative diseases. Foods that are acidic include sugar, caffeine, wheat, saturated fats, processed foods, carbonated beverages, peanuts, pasta and white rice.

ACIDIFYING
BEANS & LEGUMES
Black Beans
Chick Peas
Green Peas
Kidney Beans
Lentils
Pinto Beans
Red Beans
Soy Beans
Soy Milk
White Beans
Rice Milk
Almond Milk

ALKALIZING
PROTEIN
Almonds
Chestnuts
Millet
Tempeh (fermented)
Tofu (fermented)
Whey Protein Powder