Nutritional Regulation of Bone

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In the USA, minority populations are growing rapidly. The expected population increase from 2010 to 2015 is 37% for Asians and 20% for Black/African Americans (AA) compared to only 13% for White/Caucasians (C). It is well known that endocrine profiles may vary in these ethnic groups, and this may be associated with adipose depots that differ from Cs. For example, AA’s have higher rates of obesity than Cs, and metabolic syndrome is more prevalent in South Asians (SAs) as compared to other ethnic groups. While bone mineral density (BMD) in SAs is similar to Cs, fracture risk begins at an earlier age, and it is unclear if this is related to their lower muscle mass, higher visceral adipose tissue or altered an endocrine profile. AAs have higher muscle mass, BMD and lower fracture risk, compared to C. There are a rising number of fragility fractures in all ethnicities, and more recently, it has been shown that higher BMD in the obese is not protective. Weight loss is recommended to reduce risks associated with obesity and metabolic syndrome, but there are also changes in BMD and geometry and increased fracture risk. Previous weight loss studies have shown that postmenopausal women are particularly vulnerable to BMD loss, yet these studies reflect the response in C women. Weight loss also differentially attenuates BMD and skeletal muscle mass at different anatomical sites and these same sites show variation in fracture risk by ethnicity. Since visceral adiposity is associated with compromised BMD, this too may affect bone differently across ethnic groups. Moreover, the variations in hormones and cytokines among ethnic groups may explain a differential bone response to wt change in these populations. In addition, Ca absorption is compromised during caloric restriction, and therefore it is important to determine if it is a risk factor for weight loss induced bone loss across ethnicities. The central hypothesis is that there will be BMD loss in all ethnic groups due to wt loss that will be partially explained by a reduction in Ca absorption, whereas site specific BMD loss will differ between ethnic groups and be related to the regional changes in muscle mass. In the proposed studies, we will study 3 ethnic groups (SA, AA and C) of postmenopausal overweight/obese women before and after weight loss to: 1) determine the effect on BMD, bone geometry and strength; 2) determine how BMD changes relate to changes in total and regional muscle mass and fat depots; and 3) examine if Ca absorption contributes to BMD changes with weight loss. Understanding ethnic-specific responses of bone and soft tissue to weight loss is novel and important due the unique metabolic profiles and disease risks in these ethnic groups. The ultimate goal is to develop and encourage healthy weight control strategies that are tailored to address ethnic diversity in the prevention of obesity and osteoporosis.