Protein has been identified as being both detrimental and beneficial to bone health depends on a variety of factors such as: level of protein in the diet, protein sources, calcium intake, weight loss, exercise patterns and the dietary acid load in our diet. But did you know that protein makes up for roughly 50 percent of bone mass? And that one-third of the mass and the bone protein goes through continuous turnover and remodeling? Not only is a daily intake of protein essential for bone maintenance but the interaction between protein and calcium can literally make or break our bones.
Many factors influence bone mass and the peak bone mass achieved when you are in the third decade of life, are followed usually by more losses than gains. Loss of bone mass (osteopenia) and loss of muscle mass (sarcopenia) that occur with age are closely related, so much so that the factors that affect muscle mass ( eg; protein intake and weight-bearing exercises), also affect bone mass.
Protein And Bone Health
Though popularly believed that a high protein diet puts you at a greater risk of developing osteoporosis and bone fractures, is there truth to this theory? One of the key traits of calcium loss is the increase in the amount of urinary calcium/creatinine, developing a sort of negative calcium balance.
However, studies in which diets provided 30 percent of energy, the same as protein sources have found no significant increase in calcium losses. Also, increased creatinine levels do not necessarily mean reduced bone mass. On the contrary, several studies have observed a positive association between dietary protein intake and increased bone mineral content or decreased risk of fracture. One study found that among premenopausal women, there was a significant positive association between protein intake and bone mineral content, suggesting that dietary protein intake may actually be a determinant of the peak bone mass.
In fact, the presence of other components such as calcium, phosphorus, and potassium in protein-rich foods such as dairy foods appears to counterbalance the losses in urine. Another study tracing the source of the calcium in the urine stated that it may not be from the bone. This may be the extra calcium that gets absorbed through the diet because protein may create an environment for better calcium absorption in the intestines. In healthy adults, when protein intake was increased, urinary calcium increased but its absorption increased as well. However, at low protein intakes, intestinal calcium absorption is reduced and levels of parathyroid hormone increase, causing the release of calcium from bone.
Urinary calcium has also been found to be increased with acid-forming foods such as meat, fish, eggs and negatively associated with plant foods. This is determined by the acid-base status of the diet. Bone loss may be due to the mobilization of skeletal salts to balance the acid generated from acid-forming foods. Clinical studies do not support the idea that animal protein has a detrimental effect on bone health or those vegetable-based proteins are better for bone health. Several studies examining the effect of meat have found no effect on either bone mineral density or markers for bone mineral density.
Also, the effect of protein on bone mass may also depend on calcium intake. If protein intake increases urinary calcium loss due to a higher acid load, negative calcium balance will be resultant depending upon the dietary calcium intake and Vitamin D status. However, taking calcium supplements when the intake of protein is low won’t be beneficial. Concerns about the impact of protein on acid production appear to be minor compared with the alkalinizing effects of fruits and vegetables. Perhaps more concern should be focused on increasing fruit/vegetable intake and correcting calcium intake/Vitamin D status versus reducing good quality protein sources.
Another factor influenced by protein is insulin-like growth factor (IGF-1), which plays a key role in bone metabolism. Higher levels of IGF-1 are osteotropic (promote bone building). As individuals age, there is a decline in serum concentrations of IGF-1 (19). Both the levels and type of protein in the diet may have an effect on IGF-1 levels.
Another contributing factor could be drastic weight loss which also causes loss of bone mass. During weight loss, a higher protein diet has been found to preserve bone mineral better than a lower protein diet. Exercise (weight training) may offset the adverse effects of energy restriction on bone. Changes in bone mass, muscle mass and strength are all co-related. Maintenance of adequate bone strength and density with aging is highly dependent on the maintenance of adequate muscle mass and function, which is, in turn, dependent on adequate intake of high-quality protein and performing resistance exercise. Protein and calcium intake are individualized and are dependent upon age, body composition, level and type of activity, fitness goals and existing health conditions.
As we age, we lose muscle mass and that affects our bone health. Together they are responsible for the decline in mobility, increased risk of fracture and loss of independence in old age. For better bone health, we need weight-bearing exercises and adequate intake of good quality protein along with sufficient calcium and vitamin D. The acid load may be balanced by increasing alkalinizing foods mainly vegetables, low-fat dairy and some fruit.