Objective: The aim of this study was to investigate the effects of excess body fat on bone mass in overweight, obese, and extremely obese adolescents.
Methods: This study included 377 adolescents of both sexes, ages 10 to 19 y. Weight, height, body mass index (BMI), bone age, bone mineral content (BMC), and bone mineral density (BMD) were obtained by dual-energy x-ray absorptiometry. The results were adjusted for chronological age and bone age. Comparisons according to nutritional classification were performed by analysis of variance, followed by Tukey test. Linear regression models were used to explain the variation in BMD and BMC in the L1–L4 lumbar spinal region, proximal femur, and whole body in relation to BMI, lean mass, fat mass (FM), and body fat percentage (BF%), considering P < 0.05.
Results: For all nutritional groups, average bone age was higher than chronological age. In both sexes, weight and BMI values increased from eutrophic to extremely obese groups, except for BMD and BMC, which did not differ among male adolescents, and were smaller in extremely obese than in obese female adolescents (P < 0.01). Significant differences were observed for FM and BF% values among all nutritional groups (P < 0.01). Positive, moderate to strong correlations were detected between BMD and BMC for BMI, lean mass, and FM. A negative and moderate correlation was found between BMC and BF%, and between BMD and BF% at all bone sites analyzed in males and between BF% and spine and femur BMD, in females.
Conclusion: The results reveal a negative effect of BF% on bone mass in males and indicate that the higher the BF% among overweight adolescents, the lower the BMD and BMC values.
Alex’s Notes: I really have a soft-spot in my heart for children these days. What should be a joyful adolescent enjoying the sun outside and playing/socializing with friends in good health has become a metabolic mess over the last decade. This is really surprising when we consider that weight-loss doesn’t require any particular dietary pattern. Moreover, children enjoy high-intensity activities and the benefits of muscular fitness in youth are extraordinary. Childhood is a critical time for us humans for numerous reasons, not the least of which is that our skeletal system is in overdrive for development and is busy modeling and remodeling our future structural support. Several factors including sex, ethnicity, heredity, diet, exercise, and hormones have all shown to influence bone mass gain during this time. And of course, the amounts of lean body mass and fat mass also play a role. Because of crappy eating habits and lack of physical activity during youth, many kids have become fat, and the study at hand aimed to see the effects of excess body fat on bone mass.
The study utilized 377 adolescents between the ages of 10-19 years. Importantly, none had medical conditions or chronic use of medications, and amusingly, the researchers also excluded children that were vegetarian or didn’t consume dairy products daily. The results were straight-forward,
“This study indicates that significant positive correlations exist between BMD, as well as BMC, and LM and FM in females. In males, the correlations of BMD and BMC are observed with LM only. For female and male adolescents, negative correlations were observed between BF% and femur and lumbar spine BMDs in females, and between BF% and BMD, as well as BMC, in all bone sites analyzed in males.”
In other words, the higher the body-fat percentage of males, the lower the bone mineral density (BMD) and bone mineral content (BMC) across the entire skeleton. For females, this trend exists for the lower back and thigh bones. However, lean-body mass (i.e. skeletal muscle and organs) benefited the skeleton in both genders.
The above is likely due to a complex interaction between the fat tissue and bone tissue. Fat is a known endocrine organ that secretes primarily inflammatory molecules, all of which could easily affect energy balance and have adverse metabolic effects that interfere with bone metabolism. Whatever the reason, being a fat kid is not only unhealthy for the wallet and waistline, but it literally weakens the structure that will be supporting you for the rest of your life. Not cool.