A bone to pick: Researchers dispute both 'benefits' and 'dangers' of protein for bones

Researchers from the Department of Nutritional Sciences at the University of Surrey undertook a systematic review and meta-analysis of how protein intake can impact bone health of adults and children.

The PubMed database was searched for all relevant human studies from the 1st January 1976 to 22nd January 2016, including all bone outcomes except calcium metabolism with searches identifying 127 previous studies published over a 40 year period.

The findings, published in the journal Osteoporosis International​, concluded that increasing protein intake beyond official recommendations had minimal benefit for bone health in healthy adults but also no detrimental effect. The populations studied who consumed higher than the recommended 0.75g/Kg/day had an intake varying from 0.8 to 1.3 g/Kg/day.

Researchers found that only 4 per cent of bone density and bone mineral content in adults is dependent on protein intake with the remaining 96 per cent due to other factors.

These were not examined in the research but could include other nutritional factors including, age, body weight and genetics.  In adults protein supplementation via protein shakes or tablets was also not found to reduce the risk of fractures nor improve bone health.  

Equally, there was no detrimental effect of increased protein intake.

For children, however, a strong relationship between protein intake and bone health was identified, accounting for up to 14 per cent of bone mineral content. 

Background​

Confusion currently exists about the role of protein in the skeletal system and if it has a positive or negative impact. Protein is a chain of amino acid molecules and is a necessary part of our diet to help cell growth and repair.

Promoters of a positive link highlight dietary protein’s known ability to increase secretion of an insulin-like growth hormone which stimulates development. They point to its role in increasing calcium absorption from the gut which is likely to be beneficial for bone mineralisation.

Opponents argue that a high intake of protein, which is rich in sulphur amino acids, may be bad for bone health as it increases body acidity resulting in a rise in osteoclast activity which absorbs bone tissue during growth and healing.

Lead author Dr Andrea Darling, research fellow at the University of Surrey, said: “Protein is an essential part of our diet and is required for a number of bodily functions including cell growth and repair. ​

"What we have found is that in healthy adults, who are meeting the nutritional requirement for protein, increased levels of protein has no extra benefit for bone health, but equally is not detrimental. ​

"This may differ in the older population who tend to have lower protein intakes and whose bones have become weaker with age. Moreover, more research is needed to examine the impact extra protein can have on this particular group.”​

In the UK, adults are advised to eat 0.75g of protein for each kilogram they weigh, based on the Reference Nutrient Intake (RNI). On average, men should eat 55g and women 45g of protein daily.

Source: Osteoporosis International​
https://doi.org/10.1007/s00198-019-04933-8​
"Dietary protein and bone health across the life-course: an updated systematic review and meta-analysis over 40 years"​
Darling. A.L., et al​