Numerous population studies have reported positive correlations between plant rich diets and improved bone strength as well as reduced fracture risk. Although the mechanisms that link fruit and vegetable consumption with improved bone quality have yet to be fully defined, many food scientists believe that these foods provide significant amounts of certain nutrients that are beneficial to bone and/or help to maintain optimal pH levels in the body.
Nutrients found in plants that are strongly correlated with bone quality include calcium, potassium, magnesium, vitamin C, and vitamin K.
Calcium rich foods: greens (turnip, collard, dandelion), kale, Chinese cabbage, broccoli.
Potassium rich foods: kale, collards, greens (turnip, mustard), bananas, raisins, cantaloupe, celery, carrots, potatoes, tomatoes.
Magnesium rich foods: Spinach, potatoes, nuts, seeds, wheat, oats, bananas, broccoli, raisins.
Vitamin C rich foods: Citrus fruits, tomatoes, potatoes, peaches, Brussels sprouts, cauliflower, broccoli, strawberries, cabbage, spinach, sweet red peppers.
Vitamin K rich foods: Green vegetables, spinach, broccoli, Brussels sprouts, cabbage.
Source: USDA Nutrient database
Fruits and vegetables have also been proposed to reduce bone loss by modulation of body pH levels through what has been described as the acid-ash theory. This paradigm suggests that certain foods are digested and metabolized in a manner that induces either an acidic or basic alteration in body pH. Animal based proteins (meat and fish), grains, and certain dairy products are considered dietary acids whereas fruits and vegetables are bases.
When a diet rich in acid producing foods is consumed, a linear relationship exists between urinary acid and urinary calcium loss. It has been postulated that this calcium loss comes directly from bone and the accumulation of these losses over a lifetime could explain the progression of osteoporosis. Conversely, diets composed of plant based foods are reported to have a skeletal protective effect as the alkaline nature of their digestion and metabolism neutralize pH and preserve bone mineral.
Although food scientists continue to debate the validity of the acid-ash hypothesis on the grounds that urinary calcium losses are only surrogate measurements of bone turnover (or osteoporosis) and may not reflect actual skeletal calcium balance.
In summary, a multitude of scientific studies have demonstrated that a plant based diet, rich in fruits and vegetables, is positively correlated with better bone quality and reduced fracture risk. The mechanisms that lead to these outcomes requires further scientific clarification but may be related to the presence of certain nutritional factors or modulation of body pH.
Suggested Reading List:
Buclin T, Cosma M, Appenzeller M, Jacquet A, Decosterd L, Biollaz J, Burckhardt P 2001 Diet acids and alkalis influence calcium retention in bone. Osteoporos Int 12:493-499.
Fenton T, Eliasziw M, Lyon A, Tough S, Hanley D 2008 Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash hypothesis. Am J Clin Nutr 88:1159-1166.
Jenkins D, Kendall C, Vidgen E, Augustin L, Parker T, Faulkner D, Vieth R, Vandenbroucke A, Josse R 2003 Effects of high vegetable protein diets on urinary calcium loss in middle aged men and women. Eur J Clin Nutr 57:376-382.
Macdonald H, Black A, Aucott L, Duthie G Duthie S, Sandison R, Hardcastle A, Lanham New S, Fraser W, Reid D 2008 Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: A randomized controlled trial. Am J Clin Nutr 88:465-474.
New S, 2003 Intake of fruit and vegetables: Implications for bone health. Proc Nutr Soc 62:889-899.
Remer T, Manz F 1995 Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc 95:791-797.
Sebastian A, Frassetto L, Sellmeyer D, Merriam R, Morris R Jr 2002 Estimation of the net acid load of the diet of ancestral preagricultural Homo sapiens and their hominid ancestors. Am J Clin Nutr 76:1308-1316.