Impact of Protein and Alkali Supplementation on Skeletal Muscle in Older Adults

With aging, skeletal muscle mass and performance decline leading to an increased risk of falls and physical disability. There is ongoing research on whether increasing dietary protein intake in older adults improves indices of muscle health and thus translates to a reduction in physical disability. A main concern is that high protein results in a large dietary acid load from the breakdown of protein to acidogenic byproducts, which could in turn promote muscle degradation particularly in older adults with age-related declines in renal excretion of acid. The scientific premise of this project is that the balance between the amount of protein in the diet (anabolic component) and the net acid load of the diet (catabolic component) in part determines whether the diet as a whole has a net anabolic or catabolic effect on muscle. Preliminary data have suggested that a daily alkaline salt supplement (potassium bicarbonate, KHCO3) lowered the dietary acid load and improved lower extremity muscle power in postmenopausal women.

The investigator's central hypothesis is that higher protein intake and a neutralizing alkaline salt will improve muscle performance and mass, compared to their respective placebos, in older men and postmenopausal women. To test the hypothesis, the investigators conducted a randomized, double-blind, placebo-controlled, 2x2 factorial study in underactive men and women age 65 and older on baseline lower protein diets. Participants were assigned to one of four groups: either a whey protein supplement (to raise protein intake to 1.5 g/kg/d) with or without KHCO3 81 mmol/d or an isocaloric placebo supplement with or without KHCO3 81 mmol/d for 24 wks.

Inclusion criteria

• ability to sign informed consent form
• ambulatory community-dwelling men and women
• age 65 years and over
• habitual dietary intake of protein of ≤0.8 g/kg/d
• underactive
• estimated glomerular filtration rate ≥ 50 ml/min/1.73 m2

Exclusion criteria

• participation in a diet or intensive exercise program during the study
• vegetarian (no animal protein)
• oral glucocorticoid use for > 10 days in the last 3 months
• anabolic and gonadal hormones in the last 6 months
• Tamoxifen/raloxifene in the last 6 months
• regular use of alkali-producing antacids (> 3 times per week)
• potassium-containing supplements or products
• non-steroidal anti-inflammatory medications >3 times per week
• antacids containing calcium carbonate, aluminum hydroxide, magnesium hydroxide, or calcium acetate
• insulin
• sulfonylureas
• SGLT2 inhibitors
• a lower extremity fracture in the last year
• kidney stones in the past 5 years
• hyperkalemia
• elevated serum bicarbonate
• hypercalcemia
• uncontrolled diabetes mellitus defined as having fasting blood >150 or hemoglobin A1c >8%
• untreated thyroid or parathyroid disease
• significant immune disorder
• current unstable heart disease
• Crohn's disease
• active malignancy or cancer therapy in the last year
• alcohol use exceeding 2 drinks/day
• current peptic ulcers or esophageal stricture
• other condition or abnormality in screening labs, at discretion of the study physician