Last month, we reviewed research related to acid-base balance and diet. To summarize: meats, dairy products, and grains are acid-forming, meaning that after these foods are digested and metabolized, they influence body fluids to be acidic. This is due to the particular mix of amino acids and minerals such as sulphur and phosphate. In contrast, vegetables and fruits influence toward the slightly alkaline direction that our body needs due to the somewhat different mix of amino acid plus potassium, magnesium, and other minerals. (The sour, acidic tastes of many fruits is due to compounds that are broken down during digestion and don’t play a role here.)
Our lungs and kidneys play key roles in keeping our arterial blood within the narrow pH range (7.35-7.45) that is required for life and good health. This is done mainly through exhaled CO2 and by variable amounts of certain compounds excreted in our urine. If we consume excessive amounts of acid-forming foods, the body must tap its alkaline reserves in order to maintain the proper pH. North American diets are so heavily weighted in the acid-forming direction that there is an impact on our kidneys, and subsequently on our muscles and bones. Consequences of our acid-forming diets can include kidney damage, kidney stones, the muscle wasting, and possibly the dissolution of bone.
After any food is eaten, digested and absorbed, compounds that are acidic or alkaline end up in our kidneys. The kidney can excrete or retain various substances in the urine to bring our pH back within the ideal range and in the process draw on calcium (an alkali) from bones and the amino acid glutamine from muscle to help neutralize an acid load. Calcium salts are lost in the urine and in some cases when the urine is acidic and concentrated, these settle out in the form of kidney stones.
High intakes of protein from meat, cheese, other animal proteins, and grains increase urinary calcium. One key to preventing so much calcium from flowing out is to consume a less acidic diet. Of course we definitely need adequate protein intakes to maintain our bones; very low protein diets are not the answer. The alkaline effects of a diet centered on vegetables, fruits, and legumes appear to protect against hip fractures. Many bone building vitamins and minerals in these plant foods help too.
Glutamine is an amino acid in muscle protein that can help neutralize an acidic environment. The body can counteract acidosis by breaking down muscle, thereby liberating glutamine plus other amino acids that can be converted to glutamine. Amino acids are then excreted, causing an overall loss of muscle protein. A shift in diet towards fruits and veggies may minimize or slow these losses.
As we age, mild acidosis can worsen, possibly due to a decline in kidney function or to dietary changes. This may explain some loss of muscle and bone that can occur.
Learn more from our award-winning instructors, Vesanto Melina, MS, Registered Dietitian and Brenda Davs, Registered Dietitian in the Advanced Vegan and Raw Nutrition Training in April.