Like many confusing nutrition messages, some claim too much protein is bad for bone health. What is the scientific consensus, and what does this mean for people with or wanting to avoid osteoporosis? What other nutrients are important? First, let’s look at osteoporosis.
All living tissues, including bones, are constantly getting rid of old cells and generating new cells. With aging, however, the rate at which bones are replaced slows down.
Osteoporosis, meaning porous bones, happens when too much bone is lost and not enough produced, resulting in reduced bone mineral density and a fragile skeleton easily prone to fractures. It is different to osteoarthritis, which results from degenerated cartilage in the joints.
Sarcopenia – age related muscle loss – is closely related to osteoporosis, and they are impacted by similar factors. Bone health is therefore considered not just a skeletal problem, but a musculoskeletal problem.
Osteoporosis is a significant global concern – one in three women and one in five men over 50 may suffer from a fracture caused by osteoporosis. But there are ways to prevent and even treat it, including physical activity, sunshine and good nutrition.
Calcium is commonly known to be important for bones, and most know vitamin D is important too – it helps bones absorb calcium. Perhaps less well known is that magnesium may also prevent bone turnover and improve bone mineral density.
For good bone health, the National Osteoporosis Foundation recommends dairy products, fish (canned fish like sardines with bones for calcium; oily fish like salmon, mackerel, tuna and sardines for Vitamin D), and a variety of fruit and vegetables for their mineral content (calcium, potassium, magnesium), vitamin C and vitamin K.
Protein is not only a key constituent of muscle, it comprises about 50% of bone volume and around 30% of bone mass. It is also associated with increased production of insulin-like growth factor, which helps make bones, and better intestinal calcium absorption.
Some studies suggest eating too much protein increases calcium excretion in the urine, leading to concerns about high protein intake for bone health. This is thought to occur because protein increases the body’s acidity, so calcium – an alkaline mineral – is released to restore balance.
However numerous studies have refuted this; in fact when calcium intake is adequate, higher protein diets are linked with higher bone mass and less fractures. Any loss may also be offset by increased calcium absorption.
Furthermore, low protein intakes (<0.8g/kg per day) reduce calcium absorption which in turn stimulates the release of parathyroid hormone to tell bones to release calcium and restore its balance in the blood.
What are good protein sources for bone health? Some studies have suggested higher meat consumption increases calcium excretion, but others have refuted that. Soy protein could reduce insulin-like growth factor so may not be a good choice.
Fish, chicken and eggs provide protein. Dairy foods are good protein and calcium sources. Legumes are a good source of protein and other nutrients but should be well soaked then cooked in fresh water to reduce phytates (which could interfere with calcium absorption). Similarly, nuts provide protein along with fibre and other nutrients.
To maintain a healthy acid-alkaline balance, other dietary factors also need consideration. In particular, plant foods like fruit and vegetables abound in potassium and other alkaline minerals, so eating more of these would help prevent bones’ need to release calcium.