![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
3 Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, TN 38105; 4 Nutrition Research, National Dairy Council, Rosemont, IL 60018-5616; and 5 Nestle R&D Center, Solon, OH 44139
* To whom correspondence should be addressed. E-mail: lisas{at}rosedmi.com.
The acid ash hypothesis proposed by Wachman and Bernstein (1) in 1968 put forth the paradigm that the net acid produced from the Westernized diet could contribute to the development of osteoporosis. Algorithms designed specifically to quantify the relative acidity of the diet have been developed. These equations are empirically derived relationships between nutrient analysis from food tables and the quantity of acid excreted in the urine (2,3) and estimate net endogenous acid production (4). The underlying premise of these diet-based algorithms is that dietary intake is the modulating factor that protects bone against excess metabolic acid production. In healthy individuals, the buffering of metabolic acid is under control of the kidneys, lungs, and skeleton. In theory, when the diet is unable to provide sufficient buffering, the skeleton is utilized to maintain blood hydrogen ion concentrations, keeping pH between 7.35 and 7.45 (5).
Research documenting the detrimental effects of a relatively acid-producing diet on bone mineral density in free-living individuals has yielded small but not always statistically significant effects (6–11), causing some to speculate about the effects of an acid-producing diet per se. The long latency period required before current technology can assess detrimental effects on bone mineral density has been a limitation of many studies. The long-term studies of MacDonald and New and their colleagues (12,13) support Wachman and Bernstein's assertion that 15% of skeletal calcium can be lost over a decade to buffer a mild metabolic acidosis as a result of dietary practices (1). Researchers investigating metabolic acidosis have shown that small downward deflections of pH lead to increased osteoclastic activity, an indicator of bone resorption (14–17). Metabolic studies support the concept that a higher alkaline state manipulated by diet or pharmacological agents yields positive effects on calcium balance and increased blood pH levels (17). It is through these clinical studies that potassium has emerged as a pivotal factor in determining whether a person's diet is a net acid- or alkaline-producing entity.
Rafferty et al. (18) assert that increases in dietary potassium result in decreased urinary calcium but are balanced by a compensatory decline in calcium absorption, thus resulting in no net change in calcium balance. Others (19) have challenged their findings by stating that these results are applicable only when the increasing source of potassium is from dairy products. Although fruits and vegetables are important sources of potassium, they also provide buffering through the generation of bicarbonate (19). Regardless of source, higher potassium intake has been positively associated with bone metabolism (5,12).
The role of dietary potassium in modulating bone mass resides in the complex interaction between the interstitial fluid that surrounds the crystalline bone and the systemic extracellular fluid. The bone's interstitial fluid has higher concentrations of potassium and sodium and lower concentrations of calcium and phosphorus compared with bone crystals or plasma (20). The potassium content of the bone's interstitial fluid is directly related to the quantity of potassium consumed and is the skeletal compartment's first line of defense in buffering metabolic acid loads (5,20). Thus, if potassium intake is higher regardless of food source, then there will be adaptations that affect not only calcium balance (18) but metabolic indices of bone metabolism such as markers of bone resorption (20). The presence of potassium and bicarbonate in fruits and vegetables may be dually important in providing an increased buffering capacity, although other components such as essential oils and monoterpenes (21–23) may also be responsible for that action.
In concert with the acid-base literature, protein intake is considered to be a net acid-producing substance and thus a net negative risk factor for bone dissolution. However, substantial literature supports the beneficial effects on skeletal metabolism when higher protein levels are consumed in concert with adequate calcium, potassium, and other minerals, regardless of the source of protein (24–26). The Dietary Approaches to Stopping Hypertension (DASH) diet (27) is a calcium-rich diet that emphasizes fruits, vegetables, and low-fat dairy products. This diet underscores the importance of consuming a complement of foods from meats, grains, dairy, fruits, and vegetables as prudent for promoting optimal bone health. In the following articles, Rafferty and Lanham-New carefully review the evidence on the interaction of specific diet components that impact bone health and conclude that a balanced diet with recommended servings of dairy products and a variety of fruits and vegetables is prudent for optimal bone health. Additionally, they comment on future research directions for consideration by the scientific community.
 |
FOOTNOTES |
|---|
2 Author disclosures: F. A. Tylavsky and L. Harkness, no relationships to disclose; L. Spence is employed by the National Dairy Council, a sponsor of the supplement publication.
|
LITERATURE CITED |
|---|
 TOP LITERATURE CITED |
|---|
1. Wachman A, Bernstein DS. Diet and osteoporosis. Lancet. 1968;1:958–9.[Medline]
2. Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr. 1994;59:1356–61.
3. Remer T, Manz F. Potential renal acid load of foods and influence on urine pH. J Am Diet Assoc. 1995;95:791–7.[Medline]
4. Frassetto LA, Lanham-New SA, Macdonald HM, Remer T, Sebastian A, Tucker KL, Tylavsky FA. Standardizing terminology for estimating the diet-dependent net acid load to the metabolic system. J Nutr. 2007;137:1491–2.
5. Green J, Kleeman C. Role of bone in regulation of systemic acid-base balance [editorial review]. Kidney Int. 1991;39:9–26.[Medline]
6. Tucker K, Hannan M, Kiel D. The acid-base hypothesis: diet and bone in the Framingham osteoporosis study. Eur J Nutr. 2001;40:231–7.[Medline]
7. New S, Robbins S, Reid D. Fruit and vegetable consumption and bone health: is there a link? In: Burckhardt P, Dawson-Hughes B, Heaney RP, editors. Nutritional aspects of osteoporosis 97. Rome: Ares-Serono Symposia Publications; 1998.
8. New S, Robins S, Campbell M, Martin J, Garton M, Bolton-Smith C, Grubb D, Lee S, Reid D. Dietary influences on bone mass and bone metabolism: further evidence of a positive link between fruit and vegetable consumption and bone health? Am J Clin Nutr. 2000;71:142–51.
9. New S, Bolton-Smith C, Grubb D, Reid D. Nutritional influences on bone mineral density: a cross-sectional study in premenopausal women. Am J Clin Nutr. 1997;65:1831–9.
10. Michaelsson K, Holmberg L, Mallmin H, Wolk A, Bergstrom R, Ljunghall S. Diet, bone mass, and osteocalcin: a cross-sectional study. Calcif Tissue Int. 1995;57:86–93.[Medline]
11. Eaton-Evans J, McIlrath E, Jackson W, Bradley P, Strain J. Dietary factors and vertebral bone density in perimenopausal women from a general medical practice in Northern Ireland. Proc Nutr Soc. 1993;52:44A.
12. MacDonald HM, New SA, Fraser WD, Campbell MK, Reid DM. Low dietary potassium intakes and high dietary estimates of net endogenous acid production are associated with low bone mineral density in premenopausal women and increased markers of bone resorption in postmenopausal women. Am J Clin Nutr. 2005;81:923–33.
13. New SA, MacDonald HM, Campbell MK, Martin JC, Garton MJ, Robins SP, Reid DM. Lower estimates of net endogenous non-carbonic acid production are positively associated with indexes of bone health in premenopausal and perimenopausal women. Am J Clin Nutr. 2004;79:131–8.
14. Bushinsky DA. Metabolic alkalosis decreases bone calcium efflux by suppressing osteoclasts and stimulating osteoblasts. Am J Physiol. 1996;271:F216–22.[Medline]
15. Bushinsky DA, Gavrilov K, Chabala JM, Featherstone JD, Levi-Setti R. Effect of metabolic acidosis on the potassium content of bone. J Bone Miner Res. 1997;12:1664–71.[Medline]
16. Bushinsky DA, Gavrilov KL, Chabala JM, Levi-Setti R. Contribution of organic material to the ion composition of bone. J Bone Miner Res. 2000;15:2026–32.[Medline]
17. Lemann J, Jr., Bushinsky DA, Hamm LL. Bone buffering of acid and base in humans. Am J Physiol Renal Physiol. 2003;285:F811–32.
18. Rafferty K, Davies KM, Heaney RP. Potassium intake and the calcium economy. J Am Coll Nutr. 2005;24:99–106.
19. Sebastian A, Frassetto L, Morris MC. Letter re: Long-term persistence of the urine calcium-lowering effect of potassium bicarbonate in postmenopausal women. J Clin Endocrinol Metab. 2005;90:4417–8.
20. Krieger NS, Frick KK, Bushinsky DA. Mechanism of acid-induced bone resorption. Curr Opin Nephrol Hypertens. 2004;13:423–36.[Medline]
21. Muhlbauer RC, Lozano A, Reinli A. Onion and a mixture of vegetables, salads, and herbs affect bone resorption in the rat by a mechanism independent of their base excess. J Bone Miner Res. 2002;17:1230–6.[Medline]
22. Muhlbauer RC, Lozano A, Palacio S, Reinli A, Felix R. Common herbs, essential oils, and monoterpenes potently modulate bone metabolism. Bone. 2003;32:372–80.[Medline]
23. Dolder S, Hofstetter W, Wetterwald A, Muhlbauer RC, Felix R. Effect of monoterpenes on the formation and activation of osteoclasts in vitro. J Bone Miner Res. 2006;21:647–55.[Medline]
24. Dawson-Hughes B. Interaction of dietary calcium and protein in bone health in humans. J Nutr. 2003;133:852S–4S.
25. Massey LK. Dietary animal and plant protein and human bone health: a whole foods approach. J Nutr. 2003;133:862S–5S.
26. Bonjour JP. Dietary protein: an essential nutrient for bone health. J Am Coll Nutr. 2005;24:526S–36S.
27. Lin PH, Ginty F, Appel LJ, Aickin M, Bohannon A, Garnero P, Barclay D, Svetkey LP. The DASH diet and sodium reduction improve markers of bone turnover and calcium metabolism in adults. J Nutr. 2003;133:3130–6.
This article has been cited by other articles:
|
|
 |
|
  E. Wynn, S. A. Lanham-New, M.-A. Krieg, D. R. Whittamore, and P. Burckhardt Low Estimates of Dietary Acid Load Are Positively Associated with Bone Ultrasound in Women Older Than 75 Years of Age with a Lifetime Fracture J. Nutr., July 1, 2008; 138(7): 1349 - 1354. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
