USDA study elevates value of alkaline plant foods versus American’s typical overload of acid-producing grains and meats
by Craig Weatherby
When it comes to building muscle, all you hear about is protein.
For folks engaged in weight training or other serious muscle-building exercise, there’s little doubt that high-protein diets help.
And we all need sufficient protein—about 60 grams (2 oz) per day—to maintain muscle. The US RDA is based on body weight, and ranges from 35 grams (100 lb. person) to 90 grams (250 lb. person) per day.
Thus, it came as little surprise when the results of a recent Canadian study suggested that higher intake of animal protein—albeit still not above the RDA—was the most reliable predictor of muscle mass in older, sedentary women (Lord C et al. 2007).
However, the results of a new study by researchers at the USDA’s Agricultural Research Service suggest that plant foods may help preserve muscle mass in older men and women, thanks to these foods’ propensity to create an alkaline state in the body.
Foods are classified as “alkaline” or “acidic” based on the residues they produce in the body, rather than whether they are alkaline or acidic themselves (For example, acidic grapefruits are metabolized to alkaline residues).
And on balance, most fruits and vegetables produce alkaline residues (See our “Alkaline diets: myth and reality” sidebar, below).
Plant-rich alkaline diets found to slow muscle loss in aging
The USDA-funded researchers studied 384 male and female volunteers aged 65 or older (Dawson-Hughes B et al. 2008).
They measured the volunteers' physical activity, height and weight, and percentage of lean body mass at the start of the study and again after three years.
The participants’ urinary potassium levels were also measured at the outset and end, and diet questionnaires were administered halfway through the study.
The results showed that the volunteers whose diets were rich in potassium (from eating plant foods) averaged 3.6 extra pounds of muscle, compared with the volunteers with half the potassium intake.
This gain almost offsets the average 4.4 pounds of lean tissue that healthy men and women aged 65 and over typically shed in a decade.
Loss of muscle mass in the legs can lead to falls, so this study suggests that older people should be sure to eat ample amounts of vegetables and take supplemental potassium, magnesium, and calcium (Vitamin D is also critical, for bone strength).
A prior study at the same lab found that alkaline diets also build bone strength. As the authors wrote, “…alkaline-producing dietary components, specifically, potassium, magnesium, and fruit and vegetables, contribute to maintenance of BMD [bone mineral density]” (Tucker KL et al. 1999).
Let’s take a look at how foods that produce acid or alkaline states might impact muscle mass.
The pH-muscle connection
The typical American diet is rich in protein, cereal grains and other acid-producing foods. In general, such diets generate tiny amounts of acid each day.
With aging, a mild but slowly increasing state of “acidosis” develops, without producing obvious symptoms or problems.
Acidosis is an abnormality that reflects a relatively acid pH in the tissues. Acidosis is defined as an arterial pH below 7.35, while alkalosis defined as an arterial pH over 7.45.
(“Metabolic” acidosis is an extreme form of pH imbalance, caused by a variety of health problems.)
On average, the normal pH of human blood is slightly alkaline, and many medical observers believe that our diets should reflect this balance and favor alkaline foods slightly, if only to spare the body the effort of maintaining the right balance.
But there are other benefits to a slightly alkaline diet, as research has shown in recent years, and as our evolutionary history suggests should be the case.
A team at the University of California noted that humans’ diets were substantially more alkaline over most of our existence, and turned acidic only during the last few hundred years. They say that over time, our species’ pre-historical diets programmed us to function best on slightly alkaline diets. It is worth quoting from their review (Frassetto L 2001):
- “Among the many health problems resulting from this mismatch between our genetically determined nutritional requirements and our current diet, some might be a consequence in part of the deficiency of potassium alkali salts… which are amply present in the plant foods that our ancestors ate in abundance, and the exchange of those salts for sodium chloride (NaCl), which has been incorporated copiously into the contemporary diet…”
- “…chronic metabolic acidosis has deleterious effects on the body, including… decreased muscle and bone mass in adults… are contemporary humans suffering from the consequences of chronic, diet-induced low-grade systemic metabolic acidosis?"
Grains, fish, meat, poultry, shellfish, cheese, and milk, all produce acidic residues in the body, so the dramatic rise in our consumption of many of these foods in recent history makes the typical Western diet more acid-producing.
This does not mean that you should avoid healthful animal protein in the form of fish and grass fed meats or poultry.
Nor does it mean that proponents of the “alkaline diet” are right to suggest that acidic diets cause major diseases, as this hypothesis lacks much evidence.
In fact, as we reported last week, eating a so-called Paleolithic diet—that is, one high in fruits, vegetables, fish and/or lean meat or poultry, with relatively few grains and starches—is clearly healthful (See “Caveman Diet” Reduces Heart and Diabetes Risks”).
The Paleolithic diet, as defined by Professor Loren Cordain, Ph.D., and other researchers, is not acidic. Despite providing substantial proportions of animal protein, it does not include the abundance of grains and other acidic foods associated with modern diets.
But consumption of fresh fruits and vegetables decreased over time: a change that made the modern Western diet acid-producing.
Diets overly rich in protein and too low in fruits and vegetables appear to trigger acidosis and muscle-wasting, while diets relatively high in potassium-rich, alkaline-residue-producing fruits and vegetables reduce acidosis and should protect muscle mass.
Thus, in addition to taking supplemental alkaline minerals—potassium, magnesium and calcium—one way to prevent chronic acidosis is to eat the recommended five servings of fruits and vegetables per day.
- Dawson-Hughes B, Harris SS, Ceglia L. Alkaline diets favor lean tissue mass in older adults. Am J Clin Nutr. 2008 Mar;87(3):662-5.
- Frassetto L, Morris RC Jr, Sellmeyer DE, Todd K, Sebastian A. Diet, evolution and aging--the pathophysiologic effects of the post-agricultural inversion of the potassium-to-sodium and base-to-chloride ratios in the human diet. Eur J Nutr. 2001 Oct;40(5):200-13. Review.
- Lord C, Chaput JP, Aubertin-Leheudre M, Labonté M, Dionne IJ. Dietary animal protein intake: association with muscle mass index in older women. J Nutr Health Aging. 2007 Sep-Oct;11(5):383-7.
- Tucker KL, Hannan MT, Chen H, Cupples LA, Wilson PW, Kiel DP. Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women. Am J Clin Nutr. 1999 Apr;69(4):727-36.