When discussing whether a food like peanuts is acidic or alkaline, the term refers less to the food’s initial pH and more to the metabolic effect it has inside the body. The standard measure of acidity uses the pH scale, ranging from 0 (acidic) to 14 (alkaline), with 7 being neutral. The momentary pH of a food does not determine its long-term effect on the body’s acid-base balance. The body constantly works to maintain a tightly regulated pH within a narrow range, regardless of diet.
Measuring Dietary Acidity: The PRAL Score
The true classification of a food as acid- or alkaline-forming is determined by the Potential Renal Acid Load (PRAL) score. The PRAL score estimates the amount of acid or base a food generates after metabolism and how much of that load the kidneys must process. This calculation accounts for acid-forming nutrients (protein and phosphorus) and alkaline-forming minerals (potassium, magnesium, and calcium). A positive PRAL value indicates an acid-forming effect, while a negative PRAL value signifies an alkaline-forming effect.
The PRAL method provides a more accurate measure of dietary acid load than older concepts like “ash residue,” which only analyzed mineral content. This explains why some foods acidic outside the body, like citrus fruits, can be alkaline-forming once metabolized. For instance, the organic acids in lemons are metabolized into bicarbonate, an alkali. The final score is measured in milliequivalents (mEq) per 100 grams of food, quantifying the load placed on the kidneys for excretion.
The Classification of Peanuts
Peanuts are classified as an acid-forming food, possessing a positive PRAL score. The typical PRAL value for peanuts is around +8.3 mEq per 100 grams, and processed peanut butter has a similar positive value of approximately +7.35 mEq per 100 grams. This places them firmly in the acid-forming category alongside other protein-rich foods and grains, though at a much lower level than high-protein animal products like cheese or meat.
The reason peanuts are acid-forming is primarily due to their high content of protein and phosphorus. When the body metabolizes proteins, it produces sulfuric acid from sulfur-containing amino acids. The phosphorus found in peanuts is also converted into phosphoric acid. Since peanuts do not contain enough alkalizing minerals like potassium and magnesium to counteract these elements, the net effect on the body is acidifying. This classification holds true for raw peanuts, roasted peanuts, and most types of peanut butter.
What This Means for Acid-Base Balance
For a healthy individual, consuming acid-forming foods like peanuts does not pose a threat to the body’s overall acid-base balance. The body uses highly efficient buffering systems, primarily the lungs and kidneys, to maintain blood pH within a narrow, slightly alkaline range (7.35 to 7.45). The kidneys manage the dietary acid load by excreting excess acid in the urine, making the consumption of positive-PRAL foods a routine task.
The interest in dietary acidity often stems from the popular alkaline diet, which suggests acid-forming foods cause the body to become overly acidic, leading to disease. However, the body’s pH is tightly regulated and cannot be significantly altered by diet alone; only the pH of the urine changes in response to the dietary acid load. Individuals who experience discomfort, such as acid reflux or heartburn, after eating peanuts are likely reacting to the food’s high fat content. High fat can cause the lower esophageal sphincter to relax, allowing stomach acid to back up into the esophagus, which is a mechanical issue unrelated to the PRAL score.