Diet, Aging, and Muscle by Joe Friel
Popeye was right: eating spinach can make you stronger and more muscular, especially if you're over age 50. Let me explain.
It's apparent that as we grow older muscle mass is lost. Although this loss is slowed somewhat by weight lifting and vigorous aerobic exercise, it still happens. Even athletes in their 60s typically demosntrate considerably less muscle than they had in their 40s.
Now there is research that shows why (1). Nitrogen, which is an essential component of muscle protein, is given up by the body at a faster rate than it can be taken in as we get older. This is due to a gradual change in kidney function that comes with aging producing an acidic state in the blood. Essentially, we are peeing off our muscles as we pass the half-century mark in life.
Also, with a net loss of nitrogen, new muscle cannot be formed. This same acidic state of the blood also explains why calcium is lost with aging resulting in osteoporosis for many, especially women, with advanced age (2).
The key to reducing, or even avoiding, this situation is to lower the blood's acid level by increasing its alkalinity. There are studies demonstrating that taking a supplement called potassium bicarbonate daily for as few as 18 days increases the blood's alkaline level by balancing nitrogen in the body (2,3). While it can be purchased relatively inexpensively in laboratory supply shops, potassium bicarbonate is not currently available as an over-the-counter supplement, and there are no long-term studies of its effects on health. There is some evidence that it contributes to irregular ECG readings.
But there is also a natural way of achieving this same result through diet by eating foods that increase the blood's alkalinity - fruits and vegetables. Fats and oils have a neutral effect on blood acid. All other foods, including grains, meats, nuts, beans, dairy, fish, and eggs, increase the blood's acidity (4). If your diet is high in these latter foods but low in fruits and vegetables, you can expect to lose muscle mass and bone calcium as you age.
Remer's study ranks foods in terms of their effect on blood acidity and alkalinity. For example, the food that has the most acidic effect therefore contributing to a loss of nitrogen and ultimately muscle is parmesan cheese. The food Remer found to have the greatest alkaline effect thus reducing nitrogen and muscle loss is raisins. Among vegetables, spinach was the most alkaline food. See what I mean? Popeye was right.
Here is a ranking of common foods and their effect on alkalinity and acidity taken from Remer's study. The higher a food's positive acidic ranking, the more likely it is to contribute to a loss of muscle mass and bone-mineral levels. The more negative the foods alkaline ranking, the more beneficial is the effect on these measures.
Acid Foods (+)
Grains: brown rice +12.5, rolled oats +10.7, whole wheat bread +8.2, spaghetti +7.3, corn flakes +6.0, white rice +4.6.
Dairy: parmesan cheese +34.2, processed cheese +28.7, hard cheese +19.2, cottage cheese +8.7, whole milk +0.7.
Legumes: peanuts +8.3.
Meats, Fish, Eggs: trout +10.8, turkey +9.9, chicken +8.7, eggs +8.1, beef +7.8.
Alkaline Foods (-)
Fruits: raisins -21.0, black currants -6.5, bananas -5.5, apricots -4.8.
Vegetables: spinach -14.0, celery -5.2, carrots -4.9, lettuce -2.5.
Frassetto, L.A., et al. 1996. Effect of age on blood acid-base composition in adult humans: Role of age-related renal function decline. American Journal of Physiology 271 (6-2): F1114-1122.
Sebastian, A., et al. 1994. Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate. New England Journal of Medicine 330 (25): 1776-1781.
Frassetto, L.A., et al. 1997. Potassium bicarbonate reduces urinary nitrogen excretion in postmenopausal women. Journal of Endocrinology and Metabolism 82 (1): 254-259.
Remer, T., and F. Manz. 1995. Potential renal acid load of foods and its influence on urine pH. Journal of the American Dietetic Association 95 (7): 791-797.
Joe Friel is the author of The Cyclist's Training Bible, The Triathlete's Training Bible, and Cycling Past 50. He is a certified coach by USA Cycling and USA Triathlon and has been coaching endurance athletes for two decades. He may be reached by email at firstname.lastname@example.org.