Is eating protein bad for your bones?
Wednesday, May 23, 2018. Author Dr Haran Sivapalan
Wednesday, May 23, 2018. Author Dr Haran Sivapalan
When it comes to building strong, healthy bones, common sense tells us that the more protein we eat, the better, right? In reality, this question has proved to be, if you'll excuse the pun, a bone of contention among some health experts.
It all stems from something called the ‘acid-ash hypothesis'. This theory suggests that, rather than building bone strength, a high protein diet can actually lead to the weakening of bones and, subsequently, an increased risk of fracture. How so?
Proteins are composed of lots of small building blocks: amino acids. The key word here is ‘acids'. When we break down proteins from our diet, the resulting amino acids, particularly sulfur-containing amino acids found in meat and grains, are thought to make the blood more acidic. But, how does this lead to weaker bones?
Like body temperature, the acidity/alkalinity (or ‘pH') of your blood is regulated to a constant level. It's a prime example of homeostasis - the process by which living things maintain a stable internal environment. Accordingly, if your blood becomes too acidic (ostensibly through a high intake of protein), your body responds by trying to buffer the acid and restore the blood to its normal pH (which is between 7.35-7.45).
This is where your bones play a role. Like chalk cliffs and snail shells, your bone mineral is rich in calcium carbonate, an alkali substance that can neutralize acid. When your blood becomes more acidic, your bone tissue is thought to compensate by breaking down (a process called bone resorption), releasing calcium carbonate into the bloodstream.
While successfully counteracting changes in blood acidity, the leeching of calcium (carbonate) from bones could weaken them over time, making them fragile and more prone to fracture. These are features of osteoporosis, a bone condition characterized by a loss of bone mass and bone mineral density (a measure of how much calcium is in your bones).
This alleged association between diet, blood acidity and poor bone health is also a premise for the ‘Alkaline Diet,' which purports to preserve bone density and confer other health benefits by minimizing high-protein, ‘acidic' foods (e.g. meat and dairy) in favour of ‘alkali' foods such as fruits and legumes.
Although a lot of the above makes sense in theory, the empirical evidence simply doesn't stack up.
Firstly, there isn't any evidence to suggest that dietary protein can alter the pH of blood or other tissue fluids. Given this lack of evidence, criticism of the Alkaline Diet as a fad diet predicated on somewhat shaky science seems to be wholly warranted.
Secondly, with regards to bone health, a meta-analytic review of studies found no convincing evidence that a high protein or high ‘acid-load' diet contributes to bone mineral loss or osteoporosis. While some studies suggest that a high protein diet leads to increased excretion of calcium in your urine, this does not reflect changes in bone metabolism and bone density.
Corroborating this, a recent consensus paper from the International Osteoporosis Foundation and the catchily-titled European Society for Clinical and Economical Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases concluded that: "there appears to be no direct evidence of osteoporosis progression, fragility fractures or altered bone strength, with the acid load from a balanced diet origin."
Put simply: a high protein intake, whether from animal or plant sources, won't damage your bones.
In fact, the opposite is true - the same consensus paper established that a high protein diet has numerous benefits for your bones.
Drawing upon all published studies up to 2017, the authors found that eating more protein is linked to:
Arriving at an exact figure is difficult. The studies reviewed in the consensus paper all experimented with various quantities of protein and measured different bone-related outcomes. Nevertheless, the benefits for bone health all seemed to occur above the RDA (Recommended Daily Allowance) of 0.8 grams of protein per kg bodyweight. For example, one study found that a protein intake of 1.3 grams per kg led to significant improvements in bone mineral density of the lumbar spine.
Furthermore, as my colleague Dr. Nathan West has written, we each have different protein requirements. Our genes, our body type, and our fitness goals all influence how much protein we should be eating.
Typically, FitnessGenes recommend a daily protein intake somewhere between 0.8 and 2.4 grams per kg bodyweight. Your genetically optimized protein recommendation appears in your Nutrition Calculator, which is one of the many personalized nutrition insights you get by taking a FitnessGenes test.
Healthy bones need more than just protein. An important caveat to add to the above research findings is that the benefits of protein on bone health require an adequate intake of two other crucial nutrients: calcium and Vitamin D.
For example, the Framingham Offspring Study found that higher intakes of protein reduced the risk of hip fracture, but only when calcium intake was above 800mg per day. Similarly, another trial found that increased dietary protein protects against fractures of the femur exclusively in people taking Vitamin D supplements.
Currently, the RDA for calcium is 1000mg for an adult aged under 50. Foods such as milk, cheese, yogurt, fish (e.g., sardines or salmon), tofu and green leafy vegetables (e.g., broccoli, cabbage, kale, and spinach) are all great sources of calcium.
For your body to absorb calcium and build healthy bones, however, you'll also need enough Vitamin D. The RDA for Vitamin D is 600IU but, as you're probably aware, people differ significantly in how well they can meet this requirement. Factors such as your geographical location, skin color, exposure to sunlight and your particular variants of the HERC2 and VDR genes all affect how much Vitamin D you need to develop strong, healthy bones.