I am often asked about the impact of dietary nutrients on bone health, particularly as many patients with low bone density, many with a history of multiple fractures, are referred to me. Many factors affect bone density, an important predictor of fracture risk, including genetics, body weight and muscle mass, bone loading exercise, menstrual status, other hormonal factors, nutritional status, optimal absorption of dietary nutrients, and medication use.
Dietary nutrients include macronutrients (carbohydrates, proteins, fat, and fiber) and micronutrients (such as dietary minerals and vitamins). The importance of micronutrients such as calcium, phosphorus, magnesium, and vitamins C, D, and K in optimizing bone mineralization and bone formation has been well documented.
The impact of protein intake on bone health is slightly more controversial, with some studies suggesting that increased protein intake may be deleterious to bone by increasing acid load, which in turn, increases calcium loss in urine. Overall data analysis from multiple studies support the finding that a higher protein intake is modestly beneficial for bone at certain sites, such as the spine.
Though data regarding the impact of dietary carbohydrates on bone are not as robust, it’s important to understand these effects given the increasing knowledge of the deleterious impact of processed carbohydrates on weight and cardiometabolic outcomes. This leads to the growing recommendations to limit carbohydrates in diet.
Quality and quantity of carbs affect bone health
Available studies suggest that both the quality and quantity of carbohydrates that are in a diet as well as the glycemic index of food may affect bone outcomes. Glycemic index refers to the extent of blood glucose elevation that occurs after the intake of any specific food. Foods with a higher glycemic index cause a rapid increase in blood glucose, whereas those with a low glycemic index result in a slower and more gradual increase. Examples of high–glycemic index food include processed and baked foods (such as breakfast cereals [unless whole grain], pretzels, cookies, doughnuts, pastries, cake, white bread, bagels, croissants, and corn chips), sugar-sweetened beverages, white rice, fast food (such as pizza and burgers), and potatoes. Examples of low glycemic index foods include vegetables, fruits, legumes, dairy and dairy products (without added sugar), whole-grain foods (such as oat porridge), and nuts.
A high–glycemic index diet has been associated with a greater risk for obesity and cardiovascular disease, and with lower bone density, an increased risk for fracture. This has been attributed to acute increases in glucose and insulin levels after consumption of high–glycemic index food, which causes increased oxidative stress and secretion of inflammatory cytokines, such as interleukin 6 and tumor necrosis factor alpha, that activate cells in bone that increase bone loss.
Higher blood glucose concentrations induced by a higher dietary glycemic index can have deleterious effects on osteoblasts, the cells important for bone formation, and increase bone loss through production of advanced glycation end products that affect the cross linking of collagen in bone (important for bone strength), as well as calcium loss in urine. This was recently reported in a study by Garcia-Gavilan and others, in which the authors showed that high dietary glycemic index and dietary glucose load are associated with a higher risk for osteoporosis-related fractures in an older Mediterranean population who are at high risk for cardiovascular events. Similar data were reported by Nouri and coauthors in a study from Iran.
The quantity and quality of dietary carbohydrates may also have an impact on bone. The quality of carbohydrates has been assessed using the carbohydrate quality index (CQI) and the low carbohydrate diet score (LCDS). The CQI takes into account dietary fiber intake, glycemic index, intake of processed vs. whole grain, and solid vs. total carbohydrates in diet. A higher CQI diet is associated with reduced cardiovascular risk. Higher LCDS reflects lower carbohydrate and higher fat and protein intake.
Diets that are rich in refined or processed carbohydrates with added sugar are proinflammatory and increase oxidative stress, which may lead to increased bone loss, low bone density, and increased fracture risk. These foods also have a high glycemic index.
In contrast, diets that are rich in whole grains, legumes, fruits, vegetables, nuts, and olive oil have a lower glycemic index and are beneficial to bone. These diets have a higher CQI and LCDS (as reported by Nouri and coauthors) and provide a rich source of antioxidants, vitamins, minerals, and other nutrients (such as calcium, magnesium, and vitamins B, C, and K), which are all beneficial to bone. Gao and others have reported that implementing a low glycemic index pulse-based diet (lentils, peas, beans) is superior to a regular hospital diet in preventing the increase in bone loss that typically occurs during hospitalization with enforced bed rest.
Most reports of the impact of carbohydrates on bone health are from observational studies. In an interventional study, Dalskov and coauthors randomly assigned children aged 5-18 years who had parents with overweight to one of five diets (high protein/low glycemic index, high protein/high glycemic index, low protein/low glycemic index, low protein/high glycemic index, or regular) for 6 months.
Contrasting with our understanding that protein intake is overall good for bone, this study found that among patients receiving a high–glycemic index diet, those who were on a high-protein diet had greater reductions in a bone formation marker than did those on a low-protein diet, with no major changes observed with the other diets. This suggests the influence of associated dietary nutrients on bone outcomes and that protein intake may modify the effects of dietary carbohydrates on bone formation. Similarly, the fat content of food can alter the glycemic index and thus may modify the impact of dietary carbohydrates on bone.
In summary, available data suggest that the quantity and quality of carbohydrates, including the glycemic index of food, may affect bone health and that it is important to exercise moderation in the consumption of such foods. However, there are only a few studies that have examined these associations, and more studies are necessary to further clarify the impact of dietary carbohydrates on bone as well as any modifications of these effects by other associated food groups. These studies will allow us to refine our recommendations to our patients as we advance our understanding of the impact of the combined effects of various dietary nutrients on bone.
Madhusmita Misra, MD, MPH, is chief of the division of pediatric endocrinology, Mass General for Children, Boston, and serves or has served as a director, officer, partner, employee, advisor, consultant, or trustee for AbbVie, Sanofi, and Ipsen.
A version of this article first appeared on Medscape.com.