Studies suggest that increased intakes of plant-based foods and decreased consumption of animal-based foods may reduce the risk of chronic diseases such as cardiovascular disease, type 2 diabetes, and certain types of cancers. However, plant-based diets can lead to low intakes of such nutrients as calcium and vitamin D, which are important for bone health. In addition to these micronutrients, adequate intake of protein is also necessary for maintaining bone health throughout the life cycle. Studies have also demonstrated that certain amino acids influence bone metabolism differently.
Animal- and plant-based protein sources have varying amino acid profiles and therefore may have diverse effects on bone. Yet, no controlled, long-term intervention study regarding the effects of replacing animal protein with plant-based protein on bone and mineral metabolism has been carried out among healthy people.
As adherence to a more plant-based diet may cause a risk for bone health, Suvi Itkonen (University of Helsinki) and colleagues investigated the effects of partial replacement of animal-based protein sources with plant-based protein sources on bone turnover and mineral metabolism. Using a whole-diet approach, 107 women and 29 men participated in a 12-wk randomized clinical trial. Subjects were randomly assigned to consume 1 of 3 diets differing in protein composition: 1) 70% animal protein, 30% plant protein, 2) 50% animal protein, 50% plant protein, and 3) 30% animal protein, 70% plant protein. Differences in bone formation, mineral metabolism markers, and nutrient intakes were examined.
Study results published in The Journal of Nutrition found that partial replacement of animal proteins with plant-based proteins increased markers associated with bone turnover, indicating a possible risk for bone health. Moving from mostly animal-based protein sources towards plant-based protein sources indicated that the dietary change was associated with accelerated bone turnover. However, dietary intakes of calcium and vitamin D were below the recommended levels in the plant group, which may have also impacted bone turnover. Thus, it remains unclear whether differences in protein intake or quality played a major role.
Nonetheless, one could speculate that different amino acid compositions of the diets may have an effect on bone turnover. A corresponding editorial by Connie Weaver (Purdue University) provides further insights regarding unanswered questions about whether dietary protein, and animal protein in particular, compromises bone health.
Itkonen ST, Päivärinta E, Pellinen T, Viitakangas H, Risteli J, Erkkola M, Lamberg-Allardt C, Pajari AM. Partial Replacement of Animal Proteins with Plant Proteins for 12 Weeks Accelerates Bone Turnover Among Healthy Adults: A Randomized Clinical Trial. The Journal of Nutrition, Volume 151, Issue 1, January 2021, Pages 11–19, https://doi.org/10.1093/jn/nxaa264.
Weaver CM. Plant Protein Meal Patterns May Compromise Bone Health. The Journal of Nutrition, Volume 151, Issue 1, January 2021, Pages 7–8, https://doi.org/10.1093/jn/nxaa346.
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