The Effect of a High-Protein Diet on Bone Health

In the U.S., more than 53 million adults age 50 years and older are at increased risk of bone fracture due to the estimated prevalence of low bone density and osteoporosis. Having strong bones is an important consideration in terms of overall health and quality of life. There are a number of risk factors that influence the development of osteoporosis, some of which are modifiable including smoking or drinking alcohol and a lack of physical activity and others which cannot be changed, such as a person's age and race. As we age, preserving bone mass is critical to help minimize the risk of developing osteopenia or osteoporosis and preventing fractures.

In addition to adopting a healthy lifestyle, there also are ways to promote bone health during each stage of life. It is well known that sources of calcium and vitamin D are important, but there are other nutrients that can also influence bone health.

Protein is known to be essential to bones, since it makes up about half of its volume, but research in the past has suggested that too much dietary protein could affect bone health. In contrast, other researchers have observed that older adults who had lower protein intakes had a higher incidence of hip fractures, so a higher protein diet was thought to have a protective effect. However, the findings of this research could not be generalized to other demographics.

A theory called the "acid-ash hypothesis" has been used to explain the physiological responses that occur when higher protein diets are consumed. Eating a larger amount of higher acid-producing foods, which is typical of a Western diet, has shown to result in the excretion of higher levels of urinary acid and calcium, suspected indicators of bone loss; however, the use of these markers has been questioned due to the increased intestinal absorption of calcium that occurs in response to a higher protein diet.

Other observational studies have shown that diets which included adequate sources of potassium and magnesium due to the inclusion of fruits and vegetables were "associated with greater bone mineral density (BMD)" due to their alkaline nature.

A recent systematic review and meta-analysis from the National Osteoporosis Foundation found no adverse effects with high protein intake (quantified as more than 90 grams per day or 25 to 30 percent of total energy intake) on bone health in the general population. The evidence they found supporting a high protein diet to promote bone health, however, was also limited, with only moderate evidence showing a protective effect when looking at the lumbar spine. The review also noted inconsistent findings in the relationship between fracture risks and intake of dietary calcium and protein. Studies exploring the relationship between these nutrients are limited and generally have sample sizes too small to generate significant power.

Due to the complexity of bone turnover, many researchers agree that more studies need to be conducted, especially on a longer-term basis to assess changes in bone mineral density and risk of fracture. In the meantime, eating plans that include adequate protein and are consistent with the Dietary Reference Intakes (DRIs) continue to be recommended for bone health.

References:

• National Institute of Health. Osteoporosis and Related Bone Diseases National Resource Center. Accessed July 26, 2021.
• Nicoll R, Howard JM. The acid-ash hypothesis revisited: a reassessment of the impact of dietary acidity on bone. J Bone Miner Metab. 2014 Feb 21.
• Misra D, Berry SD, Broe KE, McLean RR, Cupples LA, Tucker KL, Kiel DP, Hannan MT. Does Dietary Protein Reduce Hip Fracture Risk in Elders? The Framingham Osteoporosis Study. Osteoporos Int. 2011;22(1):245-9.
• Hanley DA, Whiting SJ. Does a Dietary Acid Content Cause Bone Loss, and Can Bone Loss Be Prevented With an Alkaline Diet? J Clin Densitom. 2013 Oct-Dec;16(4):420-5.
• Shams-White MM, Chung M, Du M, et al. Dietary protein and bone health: a systematic review and meta-analysis from the National Osteoporosis Foundation. Am J Clin Nutr. 2017;105:1528-43.