Kidney stones affect approximately 1 in 11 people in the United States, although only 1 in 20 were affected 20 years ago. The incidence of kidney stones has been rising steadily after World War II and affects more men than women. Anyone who has passed a stone knows how painful it can be. Typically, those that have had one stone will continue to produce subsequent stones, many times requiring medication or a surgical procedure. The recurrence rate in these individuals is 50-80%. There is good news for those afflicted with kidney stones however! A whole-food, plant-based diet has shown to help prevent, treat and significantly reduce or eliminate the recurrence of future stones. Dr. Michael Greger's video How to Prevent Kidney Stones With Diet points out that the "Average American intake of meat markedly increases risk of kidney stones. By the late 1970’s we knew that the only dietary factor consistently associated with kidney stones was animal protein. The higher the intake of animal protein, the more likely the individual is to have multiple stones rather than just have a single stone episode. Not protein in general, but specifically high in animal protein. Conversely, a diet low in animal protein reduces the overall probability of forming stones which may explain the apparently low incidence of stones in vegetarian societies." Dr. Greger also cites the results of a study conducted in 2014 where hospital admissions data was used to compare in detail the prevalence of kidney stones in vegetarians and non-vegetarians. Their findings indicated that "Vegetarians were indeed at a lower risk of being hospitalized for kidney stones compared to those that ate meat. Among meat-eaters, increased meat intake is associated with a higher risk of developing kidney stones, whereas, a high intake of fresh fruit, fiber and magnesium may reduce the risk."
Doctor John McDougall explains further in his May 1999 Newsletter, "Diet has been recognized as the cause of kidney stones for many years. Industrialized countries have a higher incidence of stones compared to underdeveloped countries; and high dietary protein intake is believed to be the cause. Vegetarians have a low incidence of kidney stones. High protein intake is known to cause increased calcium excretion. Calcium-based stones make up 80 to 95% of the total number of stones people develop. An elevated concentration of calcium in the urine (hypercalcuria) is the most frequently found abnormality of people who form stones and is present in up to 60% of patients with kidney stones. High protein, high meat diets also increase other substances in the urine that lead to the formation of kidney stones, such as uric acid and oxalic acid. Super-saturation of the urine with calcium, oxalic acid, and uric acid leads to the precipitation of a stone. The average American diet, which is high in protein and low in fruits and vegetables, generates a large amount of acid from the sulfate and phosphate containing amino acids. The highest acid loads are provided by red meat, poultry, fish, and eggs. Some cheeses and grains provide acid. Phosphoric acid from colas is another source of strong acid. Fruits and vegetables actually provide alkaline materials to neutralize the acids from other sources, thus preventing kidney stones. The elderly may be even more sensitive to the effects of an acid-laden diet."
Why are animal products acid-forming? Doctor McDougall answers this question by stating, "Proteins are made from chains of 20 different amino acids that connect together in varying sequences. The most important distinction between animal and plant-derived protein is that animal proteins contain very large amounts of the basic element sulfur. This sulfur is found as two of the twenty primary amino acids, methionine and cysteine. Derived from these two primary sulfur-containing amino acids are several other sulfur-containing amino acids. Amino acids, as the name implies are acids; the sulfur-containing amino acids are the strongest acids of all, they breakdown into powerful sulfuric acid." Although these sulfur-containing amino acids are necessary for survival, once our needs have been met, excess protein is eliminated through the kidneys which places a tremendous burden on our bodies, especially the kidneys. An excess of these powerful acids (like methionine) are the primary cause of kidney stone formation. Read the article The Art of Selling Slow Poisons for more information.
Dr. McDougall continues in greater detail, "The kidneys attempt to return much of this filtered calcium back to the body, but the acid and sulfur-containing amino acids from the animal foods prevents the body’s attempts to conserve calcium. The final result is each 10 grams of dietary protein in excess of our needs (30 grams daily) increases daily urinary calcium loss by 16 mg. Another way of looking at the effects is: doubling protein intake from our diet increases the loss of calcium in our urine by 50%. Plant proteins do not have these calcium losing effects under normal living conditions."
Dustin Rudolph PharmD points out in his article, Acid/Base Balance - How do Your Favorite Foods Stack Up? that our bodies function their best and avoid disease in an alkaline environment. When the diet consists of higher sulfur-containing amino acids foods (meat, dairy, eggs) the body responds by pulling calcium citrate and calcium carbonate from the body to neutralize the acid load. Knowing if a food overburdens the kidneys can be helpful in modifying the diet. The PRAL scoring system refers to the potential impact that foods have on the kidneys and uric acid levels. Foods are assigned an acid/alkaline value according to their potential renal acid load (PRAL). The higher the score, the more acidic the food. Beef, poultry, fish, cheese and seafood are acid-forming while hard cheese, especially parmesan is the most acidic.
Rudolph notes in his article that the recommended daily requirement for methionine (powerful sulfur-containing amino acid which breaks down to sulfuric acid) is 10.4 mg/kg per day which would be approximately 700 mg for a 150 pound person. "It is not uncommon for many people to get 3-5 times this amount in their daily diet. Nutritiondata.com has a list of foods ranked from highest to lowest levels of methionine content. Fish, meat, and eggs are all at the top of the list. One can of tuna provides 1246 mg of methionine so you can see how easy it is to get too much." For information regarding methionine restriction and cancer, see the links below.
Dr. Michael Greger provides another scoring system in his video How to Treat Kidney Stones With Diet which is called the "LAKE" score, or Load of Acid to Kidney score. This system "takes into account both the acid load of foods and their typical serving sizes which can be used to help prevent both uric acid and calcium kidney stones." The video demonstrates how fish, especially tuna, was the single most acid-producing food. In fact, an interventional study conducted by British researchers studied the effects of added animal protein in their subject's diet. After an extra can of tuna fish was added, they measured stone-forming risk factors in their urine. Factors such as how much calcium, oxalate and uric acid was present before and after the consumption of tuna was recorded. The study concluded that the "overall probability of forming stones increased 250% during those days they were eating extra fish." Individuals that suffer from kidney stones are typically advised to reduce their intake of red meat to decrease their stone recurrence risk. Yet when fish samples including salmon and cod were compared to chicken and steak in a study conducted in 2014, "They found that gram for gram fish may actually be worse, in terms of uric acid production." The LAKE scoring system ranks pork as the second most acid-forming, followed by poultry, cheese, then beef. Eggs are more acidic than beef, but since the serving size had been adjusted due to people eating smaller portions of eggs during a meal, they scored lower than beef. Beans, fruits, and particularly vegetables are the most alkaline-forming of all foods.
Uric acid-based stones are the second most common type of kidney stone (after calcium based) that can be treated using a whole-food, plant-based diet. Dr. Greger states in his video that the "reason a reduction in animal protein helps is not only because it reduces the production of acids within the body, a reduction of animal protein also limits the excretion uric acid crystals that can act as a seed to form calcium stones, or can create entire stones themselves. Removing meat from the diet and switching to a plant-based diet can remove 93% of uric acid crystallization risk within days. To minimize uric acid crystallization, the goal is to get the urine pH up to ideally as high as 6.8. A number of alkalinizing chemicals have been developed, but we can naturally alkalize our urine up to the recommended 6.8 using purely dietary means." Those eating the standard Western diet typically have an acidic urine pH of 5.95. After switching to a plant-centered diet, the pH reaches the target of 6.8. "Through dietary changes alone we may be able to dissolve uric acid stones away completely without the use of drugs or surgery." This can be accomplished by drinking plenty of water a day, restricting or eliminating animal protein, reducing salt and centering the diet around whole, natural plant foods. "Only those who markedly decrease their animal protein intake may expect to benefit from dietary recommendations."
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