One of the most interesting nutrition books I have read over the years is Sapty Brook's Eco-Eating.
Sapoty Brook is a long-time raw-foodist who developed a remarkable chart based on the concept of balancing the dominant minerals in foods: Ca = calcium, P = phosphorus, Na = sodium, K = potassium for optimal performance.
The CaPNaK chart is one of the best nutritional tools to master. It objectively replaces some of the subjective classifications of foods coming from macrobiotics. Its value for us consists in the knowledge of which foods are acid-forming (phosphorus dominant) and alkaline-forming (calcium dominant) and which foods are yin (potassium dominant) and yang (sodium dominant), based on their minerals.
Sapoty Brook's deductions are summarized as follows:
We should eat a healthy balance of foods so that the dominant four minerals (Ca, P, Na, or K) all balance against each other.
if you eat foods high sodium and phosphorus (cooked animal foods), you need to balance that stimulation out with foods high in calcium and potassium (fruits and green vegetables) – this is right in line with the food combining principles that have been taught for decades. If you eat foods high in potassium and phosphorus (nuts and bananas), you tend to crave foods high in calcium and sodium (spinach and kale).
The chart exposes some nutritional myths. In general, most fruits are slightly acid forming, not alkaline-forming. Almonds, we see, are phosphorus-dominant foods, and are not an excellent source of alkalinity. Carrot juice, long recommended for its alkalinity, is also found to be phosphorus dominant and thus acid-forming to a certain degree.
Calcium, phosphorus, sodium and potassium are not the only minerals in foods. Other alkalizing minerals include chlorine and sulfur. These are usually secondary and an tertiary minerals in foods. Sapoty Brook's chart is still very accurate, because foods high in magnesium (such as olives) are usually high in calcium; foods high in chlorine (such as avocados) are also usually high in phosphorus.
To clear any confusion: Many alkaline fruits contain citric and other acids; they will have an acid pH reaction in digestion, but because of their high content of alkaline-forming minerals (calcium, magnesium), their reactions can alkaline in the body tissues. Thus, they usually alkalize the body and neutralize the acid-forming mineral residues. However, if one is already deficient alkaline minerals, citric acid will not be broken down properly and thus citrus fruits will be acidic because the alkaline minerals within the food cannot be accessed properly.