High protein diets and bone health
By Anna Edwards – APD
High protein diets have become one of the hottest diet trends over the past few decades, both with the public and researchers alike. Protein foods can be found in abundance in our food supply, and include meat, eggs, chicken, fish, legumes, dairy, soybeans, and nuts. High protein diets are hard to define, but it is generally accepted that if you consume more than the recommended 15-25% of your daily kilojoules from protein, then you are eating a diet high in protein. Most Australians already eat 20-40g more than the RDI regardless, of if they were actively trying to or not. This could be seen as a good thing, as high protein diets have shown numerous benefits for our health, but is there a downside to all of this protein positivity?
It is well known that protein is an important nutrient for bone health, and is essential for bone growth, bone maintenance, and renewal. Consuming a low protein diet has been shown to significantly impair bone strength and integrity, increasing the risk of fractures, osteoporosis development, and sarcopenia in the elderly. Yet despite the high protein hype, there are real concerns that high protein diets may lead to reduced bone mineral density and osteoporosis. Research has consistently shown since the 1920s that high protein diets increase calcium losses through urine (hypercalciuria), potentially having an adverse effect and negatively impacting bone health. So, does this mean if you eat a lot of acid-producing protein each day, you may inadvertently be setting yourself up for poor bone health later in life?
In the past, researchers claimed that hypercalciuria seen with high protein diets was due to the metabolic acidity caused by protein breakdown, in particular, protein that comes from animals. This theory, known as the acid-base theory, points to the sulphur-containing amino acids present predominantly in animal proteins causes bone loss through increasing the acid load in our bodies when digested. As a result, this causes our blood pH to drop and become acidic, leading to what is known as a low-grade metabolic acidosis state. As a result, the body tries to fix this acidity by drawing calcium from our bones to bring the blood pH back to normal. The residual calcium is then lost in our urine. Studies showed that for every 1g of protein eaten, about 1mg of calcium is lost. Naturally, when scientists first saw these findings and realised the connection between increased hypercalciuria and high protein diets, they issued cautions against consuming a high protein diet.
Fortunately, recent studies have shown these early conclusions around high protein diets and bone health to be incorrect, with at least ten recent epidemiological studies concluding that diets high protein are actually associated with better bone health. Scientists have concluded that It is important to remember that protein is only one of many factors that influence bone health, and the effect protein in isolation may have on our bones is modified by other nutrients present in the protein source, particularly calcium. Consuming adequate calcium (at least 600mg) in conjunction with high intakes of protein actually protects bone health, despite the hypercalciuria still occurring. This is because protein has been shown to actually enhance calcium absorption, offsetting hypercalciuria. Other bone healthy nutrients are also found in protein foods, such as potassium in legumes, Vitamin D in dairy, and phosphorus in red meat, that all work together to improve bone health. In addition, there has been no evidence to suggest animal protein is more or less detrimental to bone health, when compared to vegetable protein.
So, what is the take-away message for you If you already eat a diet high in protein, or you are looking to eat more protein-rich foods each day? Well, evidence suggests that you don’t need to worry; your bone health won’t suffer and may actually improve, as long as you balance your protein intake with plenty of calcium-rich foods, vegetables, fruits and wholegrains, to help counteract the increased acid load from eating high protein foods. Calcium, in particular, is important to make sure you consume enough of, so by following the RDI for calcium each day would be a great place to start. To help you get started, here are some top foods to include for both a protein AND calcium hit:
- One cup (250mls) of low fat or skim milk (300mg calcium and 8g protein)
- One cup (250mls) of calcium-fortified soymilk (300mg calcium and 10g protein)
- 100g firm tofu (make sure it includes calcium-sulphate, e516, in the label for 300mg calcium and 12g protein)
- 100g of canned sardines or salmon with the bones (540mg calcium and 21.5g protein)
- 100g almonds (250mg calcium and 19.5g protein)
If you follow these calcium guidelines, protein really will be your best bone friend!