Dr. Mary (Clifton) Wendt,
Why do vegetarians have half the risk of kidney stones over omnivores? There are two good reasons for this finding....Decreasing meats and processed dairy cuts the risk of kidney stone by 40%.
Have you ever had a kidney stone?
I developed kidney stones in college. Childbirth and kidney stone pain is very similar in intensity, but passing a kidney stone is continuously miserable, instead of the coming-and-going pain experienced with labor. Regardless, I don't want to get another one.
I've been reading with interest the recent concerns surfacing about high oxalate concentrations in smoothies. Oxalates are naturally present in our bodies. They are also present in varying levels in certain plant foods. 80% of kidney stones are made up of calcium oxalate. Some other symptoms, such as fatigue and vaginal pain, are associated with dietary oxalates, but these associations are unproven. Low oxalate diets are sometimes recommended to decrease the kidney stone development.
I've gained weight during my recent move to Minnesota from Michigan, and I've been shrinking with the help of the Green Mango Smoothie I make one each morning before work. I mix one up and split it with my daughter, Anna, and we both feel better than ever. With a personal history of kidney stones, however, I started to get concerned that my smoothies might be putting me at risk for another stone.
There are only nine foods that are shown to significantly increase urinary concentrations of oxalates: parsley, spinach, rhubarb, beets, nuts, chocolate, tea, wheat bran, and strawberries. Which is a big surprise, since a lot of other vegetables are high in oxalates (check out the content of your fave veggie here):
Why do some foods that are high in oxalates not increase the amount of oxalate in the urine? It's probably because greens, fruits, and vegetables are very high in calcium too. Calcium binds the oxalates in the food while it is still in the intestine, limiting the absorption and allowing the potentially harmful oxalates to be excreted from your precious, beautiful body.
Why do vegetarians have half the risk of kidney stones over omnivores? There are two good reasons for this finding.
ONE: Meat consumption results in increased acidity in the urine. The body responds to the increased acidity by adding calcium to the urine, much in the same way my mom takes a Tums when her stomach hurts. The increased calcium in the acidic urine binds the oxalate and whammy! A stone is formed. Keeping the urine alkaline with proteins from grains and beans reduces the calcium in the urine and minimizes the risk of calcium-oxalate stones.
TWO: Collagen in meat supplies the amino acid hydroxyproline, which is metabolized to oxalate. The daily turnover of collagen from your own body is a major source of hyroxyproline. Just turning over your own collagen accounts for 5-20% of the urinary oxalate daily. Dr. John Knight of Wake Forest University School of Medicine in Winston-Salem, N.C. compared oxalate levels in the urine after feeding people diets loaded with gelatin (which is made from the cow skeleton and loaded with collagen) vs whey, which is a protein by-product of the cheese industry. Urinary oxalate increased dramatically for the entire 24 hour collection period for those consuming the gelatin. Just eating 5-10 grams of gelatin significantly increased oxalates in the urine for six hours.
How much collagen is in meat? Samples of lean meats contain from 2.5-4.9% collagen by weight (Food Chemistry -1995;53:209-210) and hamburgers are up to 7.1% Journal of Food Science (1999;64:377-383). Hot dogs and sausages, made from scraps and pieces, are up to 19% collagen by weight (J Agric Food Chem. 1992;40:790-800). Meat that contains 7% collagen will have 7 grams per 3 1/2 ounce serving and 10 grams per about one third of a pound. Meat servings in the range of a hot dog or quarter pounder will increase urinary oxalates for an entire day after consumption.
Several dietary supplements promoted for skin, bone, and joint health also contain gelatin at 10 grams per recommended dose.
What should a person who wants to limit their dietary oxalates do?? Urinary oxalate is predominantly caused by the oxalate created in your own body from collagen breakdown, but it may also be affected by dietary intake of oxalate and calcium.
Although oxalate-rich foods enhanced excretion of urinary oxalate in normal volunteers, the increase was not proportional to the oxalate content of the food. Fruits and veggies that are high in oxalates are often high in calcium too, which prevents the absorption of the oxalate by binding it up in the intestine.
Increased dietary calcium intake may reduce urinary oxalate excretion by binding more oxalate in the gut.
Collagen in meats break down into hydroxyproline, which then breaks down into oxalates. Meat represents a significant source for oxalates in omnivores. One serving of meat increases urinary oxalate levels for 24 hours.
Decreasing meats and processed dairy cuts the risk of kidney stone by 40%. Check out your supplements and reconsider gelatin-containing products. Avoid gelatin-containing foods and desserts.
We began this archive as a means of assisting our visitors in answering many of their health and diet questions, and in encouraging them to take a pro-active part in their own health. We believe the articles and information contained herein are true, but are not presenting them as advice. We, personally, have found that a whole food vegan diet has helped our own health, and simply wish to share with others the things we have found. Each of us must make our own decisions, for it's our own body. If you have a health problem, see your own physician.