Reducing Dietary Acid Load
Another reason animal protein may be so detrimental to kidney function is that it is generally more acid forming. This is because animal protein tends to have higher levels of sulfur-containing amino acids, such as methionine, which produce sulfuric acid when metabolized in the body. Fruits and vegetables, on the other hand, are generally base forming, which helps neutralize acids in our kidneys.32
Dietary acid load is determined by the balance of acid-inducing foods (such as meats, eggs, and cheese) and base-inducing foods (such as fruits and vegetables). A 2014 analysis of the diets and kidney function of more than twelve thousand Americans across the country found that a higher dietary acid load was associated with significantly higher risk of protein leakage into the urine, an indicator of kidney damage.33
Ancient human diets largely consisted of plants, so they likely produced more base than acid in the kidneys of our ancestors. Humans evolved eating these alkaline (base-forming) diets over millions of years. Most contemporary diets, on the other hand, produce acid in excess. This switch from base- to acid-forming diets may help explain our modern epidemic of kidney disease.34 Acid-inducing diets are believed to impact the kidney through “tubular toxicity,” damage to the tiny, delicate, urine-making tubes in the kidneys. To buffer the excess acid formed by your diet, kidneys produce ammonia, which is a base and can neutralize some of that acid. Counteracting the acid is beneficial in the short term, but over the long run, all the extra ammonia in the kidneys may have a toxic effect.35 The decline in kidney function over time may be a consequence of a lifetime of ammonia overproduction.36 Kidneys may start to deteriorate in your twenties,37 and by the time you reach your eighties, you may be down to half capacity.38
The chronic, low-grade, metabolic acidosis attributed to a meat-rich diet39 helps explain why people eating plant-based diets appear to have superior kidney function40 and why various plant-based diets have been so successful in treating chronic kidney failure.41,42 Under normal circumstances, a vegetarian diet alkalinizes the kidneys, whereas a nonvegetarian diet carries an acid load. This proved to be true even among vegetarians who consumed processed meat substitutes, such as veggie burgers.43
If people are unwilling to reduce their meat consumption, they should be encouraged to eat more fruits and vegetables to balance out that acid load.44 “However,” one kidney doctor editorialized, “many patients find it difficult to follow a diet high in fruits and vegetables and might therefore be more adherent to a supplement.”45
So what did researchers try? Giving people bicarbonate of soda (sodium bicarbonate) pills. Instead of treating the primary cause of the excess acid formation (too many animal products and too few fruits and vegetables), they preferred to treat the consequences. Too much acid? Here’s some base to neutralize it. Sodium bicarbonate can effectively buffer the acid load,46 but, rather obviously, sodium bicarbonate contains sodium, which over the long term may itself contribute to kidney damage.47
Unfortunately, this type of sticking-plaster approach is all too typical of today’s medical model. Cholesterol too high from eating a diet unnaturally high in saturated fat and cholesterol? Take a statin drug to cripple your cholesterol-making enzyme. Diet unnaturally high in acid-forming foods? Swallow some bicarbonate of soda pills to balance that right out.
These same researchers also tried giving people fruits and vegetables instead of bicarbonate of soda and found that they offered similar protections, with the additional advantage of lowering the subjects’ blood pressure. The title of the accompanying commentary in the medical journal was telling: “The Key to Halting Progression of CKD Might Be in the Produce Market, Not in the Pharmacy.”48
Kidney Stones
Eating a plant-based diet to alkalinize your urine may also help prevent and treat kidney stones—those hard mineral deposits that can form in your kidneys when the concentration of certain stone-forming substances in your urine becomes so high they start to crystallize. Eventually, these crystals can grow into pebble-sized rocks that block the flow of urine, causing severe pain that tends to radiate from one side of the lower back toward the groin. Kidney stones can pass naturally (and often painfully), but some become so large that they have to be removed surgically.
The incidence of kidney stones has increased dramatically since World War II49 and even just in the last fifteen years. Approximately one in eleven Americans are affected today, compared with one in twenty less than two decades ago.50 What accounts for this rising incidence? The first clue to an answer came in 1979 when scientists reported a striking relationship between the prevalence of kidney stones since the 1950s and increasing consumption of animal protein.51 As in all observational studies, though, the researchers couldn’t prove cause and effect, so they decided to perform an interventional trial: They asked the subjects to add extra animal protein to their daily diets, the equivalent of about an extra tin’s worth of tuna fish. Within two days of eating the extra tuna, the levels of stone-forming compounds—calcium, oxalate, and uric acid—shot up such that the subjects’ kidney-stone risk increased 250 percent.52
Note the experimental “high” animal protein diet was designed to re-create the animal protein intake of the average American,53 suggesting that Americans could considerably lower their risk of kidney stones by lowering their meat intake.
By the 1970s, enough evidence had accumulated that researchers began to ask whether people suffering from recurrent kidney stones should stop eating meat altogether.54 A study on the kidney stone risk of vegetarians wasn’t published until 2014, though. Oxford University researchers found that subjects who didn’t eat meat at all had a significantly lower risk of being hospitalized for kidney stones, and for those who did eat meat, the more they ate, the higher their associated risk.55
Is some meat worse than others? People who form kidney stones are commonly advised to restrict their intake of red meat, but what about chicken or fish? We didn’t know until another 2014 study compared salmon and cod to chicken breasts and burgers. It found that gram for gram, fish might be slightly worse than other meat in terms of the risk of certain kidney stones, but they concluded that overall, “[s]tone formers should be counseled to limit the intake of all animal proteins.”56
Most kidney stones are composed of calcium oxalate, which forms like a stick of rock when urine becomes supersaturated with calcium and oxalates. For many years, doctors assumed that because the stones are made of calcium, they should counsel their patients to simply reduce their calcium intake.57 As with so much in medicine, clinical practice often flies blind without solid experimental support. This changed with a landmark study, published in the New England Journal of Medicine, which pitted the traditional, low-calcium diet against a diet low in animal protein and sodium. After five years, the study found that eating less meat and salt was about twice as effective as the conventionally prescribed low-calcium diet, cutting kidney-stone risk by half.58
What about cutting down on oxalates, which are concentrated in certain vegetables? Reassuringly, a recent study found there was no increased risk of stone formation with higher vegetable intake. In fact, greater intake of fruits and vegetables was associated with a reduced risk independent of other known risk factors, meaning there may be additional benefits to bulking up on plant foods above and beyond restricting animal foods.59
Another reason a reduction in animal protein is helpful is that it lowers uric acid buildup, which can form crystals that seed calcium stones or form stones all by itself. Indeed, uric acid stones are the second most common type of kidney stones. So it makes sense that to reduce your risk, you should try to reduce excess uric acid production. This can be accomplished either of two ways: by adding drugs or by subtracting meat.60 Uric acid-blocking medications like allopurinol may be effective, but they can have serious side effects.61 On the other hand, removing all meat from a standard Western diet appears to reduce the risk of uric acid crystallization by more than 90 percent within as few as five
days.62
Bottom line: When urine is more alkaline, stones are less likely to form. This helps explain why less meat and more fruits and vegetables appear so protective. The standard American diet yields acidic urine. When people are placed on a plant-based diet, however, their urine can be alkalinized up to a near neutral pH in less than a week.63
Not all plant foods are alkalinizing, though, and not all animal foods are equally acidifying. The LAKE (Load of Acid to Kidney Evaluation) score takes into account both the acid load of foods and their typical serving sizes in order to help people modify their diets for the prevention of kidney stones and other acid-related diseases, such as gout. As you can see in figure 4, the single most acid-producing food was fish, including tuna, followed by pork, poultry, cheese, and beef. Eggs are actually more acid producing than beef, but people tend to eat fewer of them at one sitting. Some grains can be a little acid forming, such as bread and rice, but not pasta, interestingly. Beans are significantly acid reducing, but not as much as fruits are, with vegetables crowned the most alkaline forming of foods.64
Figure 4
Dietary changes can be so powerful they can not only help prevent kidney stones but also, in some cases, cure them without drugs or surgery. Uric acid stones can apparently be dissolved away completely with a combination of eating more fruits and vegetables, restricting animal protein and salt intake, and drinking at least ten glasses of fluid a day.65
Testing Your “Pee-H” with Purple Cabbage
We know that the average Western diet is acid producing, while the average plant-based diet is acid reducing.66 Eating an acid-forming diet can not only affect kidney stone risk but may also produce the systemic, chronic, low-grade metabolic acidosis67—excess acid in the bloodstream—that is thought to contribute to muscle breakdown as you age.68 So what’s the best way to determine how acid forming your diet really is? Perhaps the easiest (and most boring) method is to order some pH paper strips to pee on. Alternatively, why not use what you (should) have right now in your refrigerator: purple cabbage. Purple, or red, cabbage provides one of the single best nutritional bangs for your buck, and you can even use it to perform kitchen chemistry experiments, or in this case, bathroom chemistry.
Boil some purple cabbage until the water turns deep purple, or blend raw cabbage with some water and then strain out the solids. Pee into your toilet then take your purple-cabbage cocktail and pour it into the toilet bowl. (Low-flow toilets work best, because there’s less water in the bowl.) If the liquid in the toilet bowl remains purple or, even worse, turns pink, your urine is too acidic. Blue is the target. If your pee and cabbage water turns blue, your urine is not acidic but neutral or even basic.
Preventing Excess Phosphorus Intake
Having too much phosphorus in the blood may increase the risk of kidney failure, heart failure, heart attacks, and premature death. Excess phosphorus also appears to damage our blood vessels and accelerate aging and bone loss.69 As such, elevated levels appear to be an independent risk factor for early death among the general population.70
Phosphorus is found in a variety of plant and animal foods. Most Americans consume about twice as much phosphorus as they need,71 but it’s not just about how much you eat but how much you absorb. By switching to a plant-based diet, you can achieve a significant drop in your blood phosphorus levels even as your intake levels of the mineral remains constant.72 This occurs because the phosphorus in animal foods appears in the form of a compound called phosphate, which is absorbed into the bloodstream more readily than phytate, the predominant form of phosphorus in plant foods.73 As you may remember from chapter 4, this situation is similar to the case of iron, another essential mineral of which you can get too much. Your body can better protect itself from absorbing too much plant-based iron, but it can’t as effectively stop surplus muscle or blood-based (heme) iron from slipping through the intestinal wall.
The worst type of phosphorus, though, is that found in phosphate food additives. These phosphorus compounds are added to cola drinks and meat to enhance their color.74 (Without added phosphate, Coca-Cola would be pitch black.75) Less than half of most plant phosphorus76 and about three-quarters of natural animal product phosphorus gets into your bloodstream,77 but added phosphate can be absorbed at a rate of nearly 100 percent.78
Phosphate additives play an especially important role in the meat industry. Chicken meat is often injected with phosphates to improve its color, to add water weight (and thus to increase profitability since chicken can be sold by the pound), and to reduce “purge,” the term used to describe the liquid that seeps from meat as it ages.79 The problem with this additive is that it can nearly double the phosphorous levels in meat.80 Phosphate additives have been described as “a real and insidious danger” for kidney patients, since they have diminished capacity to excrete it,81 but given what we now know about excess phosphorus, it’s a concern for us all.
In the United States, eleven different types of phosphate salts are allowed to be injected into raw meat and poultry,82 a practice that’s long been banned in Europe.83 This is because phosphates found in meat and processed foods are considered “vascular toxins,”84 capable of impairing our arterial function within hours of consuming a high-phosphate meal.85 In meat, there’s an additional food safety concern, as adding phosphate may increase the growth of leading food poisoning bacteria Campylobacter in poultry purge up to a millionfold.86
It’s easy to avoid added phosphorus in processed foods—just don’t buy anything containing ingredients with the word “phosphate” in their names, including pyrophosphate and sodium triphosphate.87 With meat, it’s more difficult to determine the phosphate content, as producers aren’t required to disclose injected additives. Added phosphate may be labeled as “flavorings” or “broth” or not labeled at all.88 Meat already contains highly absorbable phosphates; adding more may just add insult to kidney injury. Chicken appears to be the worst offender: A supermarket survey found more than 90 percent of chicken products contained phosphate additives.89
Who Determines Whether Food Additives Are Safe?
In 2015, the U.S. Food and Drug Administration finally announced its plans to all but eliminate trans fats from processed foods,90 citing a CDC estimate that as many as twenty thousand heart attacks each year could be prevented by eliminating partially hydrogenated oils.91 Until June 16, 2015, trans fats enjoyed so-called GRAS status: “generally recognized as safe.”
Why were these killer fats deemed safe in the first place?
Guess who makes the “generally recognized as safe” determination? It’s not the government or a scientific body. It’s the manufacturer. You read that right. The food maker gets to determine whether or not its own product is safe for the public, a process the FDA refers to as “GRAS self-determination.” What’s more, these manufacturers can legally add things to our food supply without informing the FDA.92 An estimated one thousand food-additive safety decisions have never even been reported to the FDA or the public.93
But sometimes food manufacturers do notify the FDA when they introduce a new additive. Sounds responsible of them, doesn’t it? Presumably they found some independent, third-party panel to evaluate the safety of their product so as to avoid a financial conflict of interest, right?
Well, not exactly.
Of all the GRAS safety determinations that were voluntarily submitted to the FDA between 1997 and 2012, 22.4 percent were made by someone directly employed by the manufacturer itself, 13.3 percent were made by someone directly employed by a firm handpicked by the manufacturer, and 64.3 percent were made by a panel either handpicked by the manufacturer or chosen by a firm hired by the manufacturer.94 Are you doing the maths? Yes, zero food safety decisions were made independently.
How could regulators let companies decide for themselves whether the food additives they use in their own products are safe? Follow the money. Three of Washington’s largest lobbying firms reportedly now work for the food industry.95 For example, PepsiCo alone
spent more than $9 million (£5 million) in a single year to lobby Congress.96 The deeper you dig, the less surprising it is that such food additives as trans fats have been allowed to kill thousands year after year.
But hey, according to the manufacturer, they’re safe . . .
Can Diet Protect Against Kidney Cancer?
Each year, sixty-four thousand Americans are diagnosed with kidney cancer, and about fourteen thousand die from it.97 Approximately 4 percent of these cases are hereditary,98 but what about the other 96 percent?
Historically, the only accepted risk factor for kidney cancer has been tobacco use.99 A class of carcinogens in cigarette smoke called nitrosamines are considered to be so harmful that even so-called thirdhand smoke is a concern. The risks of tobacco smoke do not end when a cigarette is extinguished, as residual smoke can stick to walls and other surfaces.100 Around 80 percent of nitrosamines from cigarette smoke can remain in a room, even with normal ventilation,101 so always try to choose smoke-free hotel rooms. Nitrosamines are one of the reasons you can’t smoke indoors without endangering others, even if you smoke without anyone present. As one of the leading scholars in the tobacco control movement recently wrote, “Carcinogens of this strength in any other consumer product designed for human consumption would be banned immediately.”102
Except for one: meat.
Did you know that one hot dog has as many nitrosamines (and nitrosamides, which are similar tobacco carcinogens103) as four cigarettes and that these carcinogens are also found in fresh meat, including beef, chicken, and pork?104 This may help explain the rising rates of kidney cancer over the last few decades despite the falling rates of smoking.
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