High Protein Diets Threaten Bones and Muscles

"Alkali Load" May Help Conserve Bone and Muscle


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.

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.

Another study produced similar results:

Fruits and vegetables are metabolized to bicarbonate and thus are alkali-producing. But the typical American diet is rich in protein and cereal grains that are metabolized to acid, and thus are acid-producing. With aging, such diets lead to a mild but slowly increasing metabolic "acidosis."

The researchers conducted a placebo-controlled study involving healthy male and female volunteers aged 50 or older. Key measurements were taken at the beginning and end of the intervention, which lasted three months.

A group of 78 volunteers had been provided either of two bicarbonates—potassium or sodium—along with their usual diet and exercise regimes. Key bone mineral nutrients were controlled to reduce variation in study outcomes. The bicarbonate groups consumed an amount of bicarbonate equivalent to about 9 servings of fruits and vegetables daily. This allowed the researchers to look at possible acid-neutralizing effects from an adequate, not high, alkali load.

The results showed that the 78 volunteers in the bicarbonate groups had significant reductions in biomarkers that are associated with bone loss and fracture than the 84 in the no-bicarbonate, or control, group.

The authors concluded that increasing the alkali content of the diet, for example by consuming more fruits and vegetables, merits further study as a safe and low-cost approach to improving skeletal health in older men and women.