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Visitor Questions
Q What do you think about an acid/alkaline balance?

The issue of acid and alkaline foods is a confusing one, because there are several different ways of using these words with respect to food.

The pH of foods

In food chemistry textbooks that take a Western science approach to foods, every food has a value that is called its "pH value." pH is a special scale created to measure how acidic or alkaline a fluid or substance is. It ranges from 0 (most acidic) to 14 (most alkaline) with 7.0 being neutral. One way of thinking about it is that as you get closer to 7.0 from either end, the food becomes less acidic (6.0 vs 5.0, for example) or less alkaline (8.0 vs 9.0, for example).

Limes, for example, have a very low pH of 2.0 and are highly acidic according to the pH scale. Lemons are slightly less acidic at a pH of 2.2. Egg whites are not acidic at all, and have a pH of 8.0. Meats are also non-acidic, with a pH of about 7.0.

Many vegetables lie somewhere in the middle of the pH range. The pH of asparagus, for example, is 5.6; of sweet potatoes, 5.4; of cucumbers, 5.1; of carrots, 5.0; of green peas, 6.2; of corn, 6.3. Tomatoes fit on the pH scale toward the more acidic end in comparison to other vegetables. Their pH ranges from 4.0 to 4.6. However, this range is still higher (less acidic) than fruits like pears (with a pH of 3.9) or peaches (with a pH of 3.5) or strawberries (3.4) or plums (2.9).

Acid-forming foods

Another way to talk about food acidity is not to measure the acidity of the food itself, but the to measure changes in the acidity of body fluids once the food has been eaten. In other words, from this second perspective, a food is not labeled as "acidic," but instead as "acid-forming."

Although the idea of acid-forming foods goes back almost 100 years in the research, there's been very little research published in this area until fairly recently. In earlier publications, acid-forming foods were often talked about as key components of an "acid-ash diet." The term "ash" was used much more commonly in those days to refer to the inorganic components of a diet (mineral elements or molecules not containing carbon) that remained after the digestion and metabolism of food had occurred. This ash was also commonly referred to as a "residue" of the diet. Diets largely devoid of meat, fish, eggs, cheese, and grains were described as "alkaline-ash diets." These diets focused on consumption of fruits and vegetables and also included cow's milk. By contrast, diets containing large amounts of meat, fish, eggs, cheese and grains were described as "acid-ash diets."

Although the term "ash" is seldom used in current research studies on diet, the idea of acid-forming foods has remained a topic of research interest. A new term has been created in the research world to refer to the potential impact of certain foods on the kidneys and urine acid levels. This term is "potential renal acid load" or PRAL. For meats, a PRAL value of 9.5 has been reported by researchers. Alongside of meats in terms of high PRAL value are cheeses (8.0), fish (7.9), flour (7.0), and noodles (6.7). In contrast with these high PRAL values are the values for fruits (-3.1), vegetables (-2.8), fruits, and cow's milk (1.0).

Researchers have been concerned about one particular aspect of high-PRAL food intake, and that concern involves bone health. It's always important for our bloodstream to keep acidity under control. Our kidneys, lungs, and other organ systems work hard to keep our blood pH very close to 7.4. However, if presented with too many acids from the digestion and metabolism of food, our body will try to neutralize those acids using a process called buffering. To buffer an acid, our body needs to link the acid with another chemical called a "base." Sodium, potassium, calcium, and magnesium are minerals that readily form bases for our body to use as acid buffers. One readily available source for calcium is bone, and researchers have wondered whether a diet that is overly acid-forming will place too heavy demands on our bone for calcium buffers. There's some research that suggests this process may take place over the short run (60 days or less), but the long-term impact of excess acid-forming foods in the diet on bone calcium is not clear from studies to date.

One of the factors that high-PRAL foods have in common (with the exception of grains) is their high protein content. Meat, fish, and cheese are all high-protein foods. Because protein is composed of amino acids, and because amino acids can be easily converted in the body to organic acids, it makes sense for high-protein foods to be treated as foods that can increase potential renal acid load. When present-day researchers try to model the potential acid-forming nature of a diet (meaning the potential for a diet to increase the acidity of our urine and acid load upon our kidneys), they always factor in the protein density of the diet. Potassium content, calcium content, and magnesium content are also typically factored in because these minerals readily form bases that can be used to help buffer acids. Sometimes researchers also look at the ratio of a potentially acid-forming component like protein to an available buffering mineral like potassium.

The table below summaries primary higher PRAL and lower PRAL food groups

Food Group PRAL Higher or Lower PRAL
Meats 9.5 Higher
Cheeses 8.0 Higher
Fish 7.9 Higher
Flour 7.0 Higher
Noodles 6.7 Higher
Fruits -3.1 Lower
Vegetables - 2.8 Lower
Cow's Milk 1.0 Lower

Source: Barzel US and Massey LK. (1998). Excess dietary protein can adversely affect bone. J Nutr 128: 1051-1053.

Acid-alkaline and the World's Healthiest Foods

Although the impact of foods on our kidneys and urine acidity is definitely an important topic from the standpoint of diet and health, it is still one very narrow component of our body's acid-base balance. All of our bodily fluids have their own characteristic degree of acidity, and our metabolism works in thousands of ways to protect acid-base levels in all of our tissue. So we would not want to draw any hard and fast conclusions about how to eat from studies on urine acidity and the PRAL value of foods. However, we do believe that research in this area supports our basic approach to healthy eating at the World's Healthiest Foods. We place our greatest emphasis on daily intake of vegetables and fruits, and in this urine acidity research, we discover that vegetables and fruits have lower PRAL values than any other food groups. We also encourage moderation throughout our website with respect to consumption of meats and believe this recommendation is in keeping with urine acidity research that places meats at the top of the PRAL list with a value of 9.5. While the PRAL research was not a factor in our initial construction of the World's Healthiest Foods list, we are reassured to see that our Healthiest Way of Eating is one that should result in little risk with respect to potential renal acid load.

Other approaches to acid-alkaline and diet

On other websites, especially websites interested in macrobiotic eating, Asian medicine, and energy medicine, you'll find detailed discussion of acid-forming and alkaline-forming foods that do not follow this Western science research involving urine acidity and PRAL values. Instead, these approaches typically look at whole body acid-base balance (rather than acidity of one body fluid like the urine) and they talk about "toxic acidic conditions" or the need for a slightly alkaline condition in the body as whole. To find out more about these alternative ways of approach acid-base balance in the body and dietary choices, you may want to visit one or more of the following websites:

http://www.gomf.macrobiotic.net/Info_Macrobiotics.htm (The George Osawa Macrobiotic Foundation)

http://www.kushiinstitute.org/html/articles.html#Food%20&%20Healing (The Kushi Institute)

http://www.ppnf.org/catalog/ppnf/Articles/articles_list.htm (Price-Pottenger Nutrition Foundation)

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