Agricultural Research Service (ARS)-funded scientists have recently reported that compounds in plant foods, which are alkali-producing, may help preserve bone and muscle mass. Now, a new ARS-funded study suggests that reducing the acid load that accompanies the typical high protein diet may also be important.
ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture (USDA). The study was led by Lisa Ceglia and Bess Dawson-Hughes at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, in Boston, Mass.
Diets high in protein and low in fruits and vegetables result in mild "acidosis" with aging. That's because protein metabolism releases acids into the bloodstream in amounts that override the alkalinizing effect of potassium and bicarbonate in plant foods.
The researchers studied results from a group of 19 healthy individuals, older than 50, who were on a controlled diet. To simulate consumption of the equivalent of eating about 14 servings of fruits and vegetables daily, nine of the participants were randomly assigned to receive 3,510 milligrams daily of potassium bicarbonate in capsules. The other 10 participants were assigned to receive matching "placebo" capsules.
Once the volunteers gradually reached the maximal level of daily potassium bicarbonate or placebo capsules, all 19 participants were successively given a 10-day low (or high) protein diet followed by a 10-day high (or low) protein diet, with a five-day “wash out” period in between.
The researchers wanted to look at both an alkali-producing diet (the potassium bicarbonate group) and an acid-producing diet (the placebo group). Blood, urine and calcium absorption analyses were performed after each diet period, and markers of muscle and bone metabolism were measured.
With increased dietary protein intake, the potassium bicarbonate, or alkalinized, group--when compared to the placebo group--had reduced urinary nitrogen excretion, which is an indicator of reduced muscle wasting. The alkalinized group also had higher levels of IGF-1, a marker of both muscle and bone conservation, and of calcium absorption--a marker of bone conservation--on both protein diets, compared to the placebo group.
The study suggests that the net effect of adequate dietary protein on muscle may be enhanced by reducing its accompanying acid load, according to the authors. Though not tested in the study, increasing intake of fruits and vegetables would be another way to increase the alkali potential of the diet, according to Dawson-Hughes.
The analysis was published in the Journal of Clinical Endocrinology and Metabolism.