We all know the drill. Researchers propose hypotheses, then test them scientifically to determine their validity. If the hypothesis does not stand up to rigorous scientific scrutiny, we expect the original hypothesis to die and never to be mentioned again. Right? Unfortunately, this rarely happens. Often belief trumps science and the hypothesis becomes accepted as fact by the public and many in the scientific community, even when it’s not true. This appears to be the case for the acid load hypothesis of osteoporosis or that animal proteins are bad for bones. However, a review of the evidence by a respected bone expert dispels this hypothesis as a myth.
Hypothesis: The nutritional acid load impact on osteoporosis
This hypothesis suggests that foods associated with an increased urinary acid excretion, such as animal proteins from meat and dairy foods (milk, cheese, and yogurt), are harmful to the skeleton, leading to osteoporosis and an increased risk of fragility fracture. Conversely, foods producing neutral or alkaline urine would favor bone growth and calcium balance, helping to slow bone loss and reduce fracture risk.
As pointed out in a recent review available in full text, this theory currently influences nutrition research, dietary recommendations and the marketing of alkaline salt products or medications aimed at optimizing bone health and preventing osteoporosis. It originally stemmed from classic investigations in patients suffering from chronic kidney diseases (CKD) conducted in the 1960s.
Hypothesis not proven: Review dispels theoretical link
Using a historical perspective, Jean-Philippe Bonjour, a respected bone expert from Switzerland, dissects out speculation from experimental facts and deftly dispels the acid load hypothesis of osteoporosis by explaining the natural role of the kidney in healthy individuals.
The author emphasizes the essential role of the renal tubule in systemic acid–base and calcium balance. Here are a few highlights:
- Both the amount and type of protein has been shown to alter the acidity in urine, but has not shown effect on altering the acidity or alkalinity of blood.
- Regulating such acid-base balance throughout the body is a role of the kidneys and lungs, not bone minerals.
- Food intake, except in cases of severe renal insufficiency, does not have an effect on whole-body acid-base balance.
- Clinical and observational evidence does not support advocating alkaline-rich diets or eliminating animal protein from the diet to favorably influence bone-health.
This review indicates that research does not support the belief that animal proteins and their acid-load can contribute to the development of osteoporosis. But don’t take my word for it. The paper is available free and is a great resource to help you answer questions about protein and bone health. I hope reading it will renew your confidence in advocating the bone health benefits of dairy products throughout life.
After all, dairy foods, such as milk, yogurt, and cheese are a source of high-quality protein as well as other nutrients, like calcium and vitamin D (when fortified) that have been shown to contribute to bone health. For more information on the supporting science on protein and bone, see this science summary posted on NationalDairyCouncil.org.
Don’t hesitate to send me your comments and questions.