The proponents of the Alkaline Diet are urging you to eat the right foods, but for the wrong reasons. The Alkaline Diet is based on the idea that you should eat foods that have an alkalinizing (pH-raising) effect on the body, while avoiding foods that have an acidifying (pH-lowering) effect on the body. The proponents of the Alkaline Diet often make claims that are clearly nonsense. For example, some of them claim that the diet will cause your blood pH to rise to 8.5, thus killing cancer cells while allowing ordinary cells to survive. That is clearly false. On the other hand, some detractors of the Alkaline Diet also say some things that are false. Some of them are simply against vegan diets, for ideological reasons. Others fail to grasp how an acidic food, such as lemon juice, could end up having a net alkalinizing effect on the body, as I’ll explain below.
If you eat the kind of diet that the promoters of the Alkaline Diet recommend, your health will almost certainly improve. The foods that have the strongest acidifying effect on the body come from animals: dairy foods, meats, fish, and eggs. Grains and beans have only a small acidifying effect. In contrast, nearly all fruits and vegetables have a net alkalinizing effect. For this reason, people who avoid the most acidifying foods will end up eating a vegan diet, including lots of fruit and vegetables.
A vegan diet is great for your health, as long as you don’t eat too much fat (from oils, nuts, or avocadoes) or too much refined sugar (empty calories) and as long as you take a vitamin B12 supplement. A low-fat vegan diet provides plenty of fiber and carbohydrate. It provides no cholesterol or animal protein. As a result, a low-fat vegan diet will stabilize your blood sugar, help you lose weight, and reduce your risk of heart attack, stroke, and many cancers and autoimmune diseases. Yet even if you are eating a lot of alkalinizing fruits and vegetables, your blood pH will not change. It will stay at almost exactly 7.4, unless you get really sick. Nevertheless, the alkalinizing effect of a vegan diet does provide a few benefits: a decrease in the risk of gout, kidney stones, and osteoporosis.
The Alkaline Diet has come under fire from skeptics who point out (correctly) that this diet does not really alter the pH of your blood. Unfortunately, many of these skeptics are unaware of (or in denial about) the health benefits of a low-fat vegan diet. Some of them even fail to understand how an acidic food like lemon juice (pH of 2.0 to 3.0) could have a net alkalinizing effect on the body.
All foods are mixtures of organic and inorganic compounds. If you burn a piece of food in a laboratory, most of the organic compounds will be oxidized to form carbon dioxide and water. After the food is completely burned, you will be left with an ash that contains inorganic compounds. The ash will contain some important cations (pronounced cat-eye-ons), including the alkaline metals (sodium and potassium) and alkaline earth metals (calcium and magnesium), and some important anions, including sulfates and phosphates. If you dissolve that ash in water, the pH of the water could go up or down. If the ash is richer in the alkaline metals and alkaline earth metals than in sulfates and phosphates, the pH of the water will go up (alkalinizing effect). If the ash is richer in sulfates and phosphates than in the alkaline and alkaline earth metals, the pH of the water will go down (acidifying effect).
When you metabolize your food, you burn up most of the organic compounds, including many (but not all) of the organic acids. You will be left with an alkaline or acidic ash, plus the organic acids that your body cannot metabolize. These acidic and alkaline byproducts of metabolism will circulate in your bloodstream until they are lost in your urine. In the meantime, they will seem to have little or no effect on the pH of your blood. Instead, they will mainly affect the pH of your urine. You can make a reasonably accurate prediction of how much of an effect a serving of any food will have on the pH of urine by measuring the amounts of protein (a source of sulfur), phosphorus, calcium, potassium, and magnesium that are in the food and plugging the results into an equation.
The pH of your blood must stay at almost exactly 7.4 (slightly alkaline) all the time, or you will die. To keep the blood pH at 7.4, the body has an elaborate system of buffers. The main buffer is derived from carbon dioxide. The body uses an enzyme called carbonic anhydrase to speed up the conversion of carbon dioxide and water to carbonic acid (H2CO3) and vice versa. Carbonic acid is a weak acid, which means that when it is dissolved in water, only a small percentage of its molecules get pulled apart into hydrogen ions (H+) and the acid’s conjugate base (bicarbonate, HCO3–). An even smaller percentage of the bicarbonate ions get pulled apart into H+ and carbonate ions (CO3–2).
The pH of an aqueous solution is a measure of the concentration of H+ ions. In pure water, the H+ concentration is about 1 ten millionth of a mole per liter, or 1 × 10–7 M, which is a pH of 7 (the negative of the base-10 logarithm of the H+ concentration). If you added enough acid to make the H+ concentration go up to one millionth of a mole per liter (1 × 10–6 M), the pH would go down to 6. In other words, more H+ means lower pH. (That explains why sea water is becoming more acidic as the amount of carbon dioxide in the atmosphere rises!) In contrast, when the concentration of H+ in an aqueous solution goes down, the pH of the solution goes up.
The conjugate bases of a weak acid (e.g., bicarbonate and carbonate ions) are unstable. When they meet up with a hydrogen ion in solution, they are likely to react with it. Thus, a carbonate ion is likely to bond with an H+, to become a bicarbonate ion. A bicarbonate ion is likely to bond with an H+, to become carbonic acid. If the carbonic acid content of the solution rises, more of the carbonic acid gets converted back to carbon dioxide and water. The carbon dioxide can then be lost to the atmosphere.
When you mix a weak acid with its conjugate base, such as mixing carbonic acid with sodium bicarbonate, you get a pH buffer. If you add a little bit of acid to blood, the bicarbonate and carbonate ions will immediately bind most of the incoming hydrogen ions. Thus, the number of hydrogen ions in the solution will go up very little (i.e., the pH will not drop by much). The ability of a solution to take in acids or alkalis without changing its pH is called the buffer capacity.
The carbonic acid/bicarbonate buffer system plays an important role in stabilizing the pH of your blood. If you hold your breath, carbon dioxide will start to build up in your blood. As a result, the pH of your blood will drop (respiratory acidosis). Your brain will notice this drop in pH and tell your respiratory system to breathe faster. As you blow off that extra carbon dioxide, your blood pH will rise back to a normal level. If you hyperventilate, you will cause the carbon dioxide levels in your blood to drop to abnormally low levels. As a result, your blood pH will go up. This effect is called respiratory alkalosis. If some process in your body is generating excess acid or alkali, your respiratory system will try to compensate by adjusting your respiratory rate, to adjust the amount of carbon dioxide in your blood. As a result, your blood pH may still stay close to 7.4, even if you have a serious problem with acid-base balance.
The kidneys also play a role in controlling the pH of the blood. If your blood pH drops too low, you will pass more H+ and less bicarbonate in your urine. As a result, your urine will become more acidic. If the pH of the blood rises too high, you will pass less H+ and more bicarbonate in your urine. As a result, your urine will become more alkaline. Because of these and other regulatory systems, the pH of your blood will stay remarkably steady at about 7.4 (slightly alkaline), as long as you are in reasonably good health. Meanwhile, the pH of your urine will change dramatically, depending on what you have been eating.
If you start eating the Alkaline Diet, your blood pH will not change much. However, your body’s ability to buffer an acid load will increase. This increase in buffering capacity explains why vegan diets are useful in the management of gout. Gout results when the blood becomes oversaturated with uric acid. Uric acid is produced when your body breaks down purines, which come from the breakdown of DNA and RNA. Tissue that is highly active metabolically (e.g., organ meats) is rich in purines. So is beer, because yeast is highly active metabolically. When the blood becomes oversaturated with uric acid from the digestion of purines, the uric acid starts to precipitate out as crystals in the joints (especially of the big toe) and the kidneys. The result is gouty arthritis and kidney stones.
Although many vegetables are also fairly rich sources of purines, vegetable foods do not seem to increase the risk of gout, probably because they raise the blood’s acid-buffering capacity. When the blood’s acid-buffering capacity is high, more of the uric acid can remain dissolved in the blood and urine. As a result, fewer urate crystals will form in the joints or in the urinary tract.
Not all kidney stones are made of urate crystals. Many kidney stones are made of calcium oxalate. Calcium oxalate kidney stones are also a common result of an acid-forming diet. When the ordinary buffering systems are not enough to keep the blood pH at 7.4, the body may borrow some calcium from the bones, to use as an antacid. However, the body must also keep the calcium levels in the blood within a narrow range, or the heart will stop. For this reason, the excess calcium is quickly lost in the urine. In the short run, this problem can lead to the formation of calcium oxalate kidney stones. In the long run, it can contribute to osteoporosis.
Osteoporosis is common only where people eat a highly acidifying high-protein diet. Taking calcium supplements may help to correct the metabolic acidosis in the short run, because of the calcium’s alkalinizing effect. But in the long run, the combination of an acid overload and a calcium overload (either from dairy foods or fish bones or from supplements) can undermine the body’s ability to regulate its calcium content. If the blood calcium levels are chronically high, the body may eventually lose the ability to conserve calcium. As a result, the calcium that has been borrowed from the bones is not effectively replaced. So instead of recommending calcium supplements, doctors should be urging patients to avoid eating animal foods and to eat more vegetables and fruit. Doctors should also urge patients to go outside and play: to get exercise and reasonable exposure to sunshine.
You can measure the effects of diet on urine pH within a matter of hours. But to see the effects of diet on health, you often must study a large number of people over a long period of time. For this reason, much of what we know about the effects of diet has been learned from epidemiologic studies. Some of these studies compare different populations at one point in time. Others focus on people who have migrated from one country to another. Still others track the same population over time. Each of these kinds of studies has its own strengths and weaknesses. For example, differences between countries could be due to confounding variables, such as genetic differences. Unfortunately, many “skeptics” dismiss all of these studies as “pseudoscience” because these epidemiologic studies do not follow the same methods as pharmaceutical research. Up until recently, “skeptics” who worked for the tobacco industry used the same kind of arguments to make people doubt that cigarette smoking causes lung cancer.
In other words, the proponents of the Alkaline Diet are urging you to eat a good diet, but for bad reasons. Meanwhile, the skeptics who debunk the Alkaline Diet are often trying to scare you away from eating a good diet, for equally bad reasons.
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