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Moderate weight loss in obese and overweight men preserves bone quality

Background: Weight loss (WL) negatively affects bone mineral density (BMD) in older populations and has specifically been shown in women.

Objective: In this prospective controlled trial, we examined variables of bone quality and endocrine changes after intentional WL in men.

Design: Thirty-eight overweight and obese [mean ± SD body mass index (in kg/m2): 31.9 ± 4.4; age: 58 ± 6 y] men were recruited to either WL through caloric restriction or weight maintenance (WM) for 6 mo.

Results: There was a −7.9 ± 4.4% and +0.2 ± 1.6% change in body weight in WL and WM groups, respectively. There was a greater increase in femoral neck and total body BMD and bone mineral content (BMC) in the WM group than WL group (P-interaction effect < 0.05). In contrast, there was a trend for the tibia cortical thickness and area to decrease more in the WM group than WL group (P ≤ 0.08). There was a decrease in the periosteal circumference in both groups over time (P < 0.01) and no statistically significant changes in trabecular bone. The circulating total, free and bioavailable estradiol decreased in the WL group compared with WM group, and changes were different between groups (P < 0.05). Serum total and bioavailable testosterone increased in both groups (P < 0.01). Serum 25-hydroxyvitamin D increased to a similar extent in both groups (P < 0.05).

Conclusions: Moderate WL in overweight and obese men did not decrease BMD at any anatomical site or alter cortical and trabecular bone and geometry. Also, despite increased BMD at some sites when maintaining excess body weight, cortical bone showed a trend in the opposite direction.

Full-text

Alex’s Notes: Wolff’s law states that bone will adapt to the load placed upon it. Outside of exercise, the most common load we carry is our bodies. It follows then, that weight loss can also promote bone and muscle loss with older age. Indeed, postmenopausal women undergoing voluntary dieting experience a significantly greater loss of bone mineral content (BMC) and density (BMD) than there weight-stable peers. In men, a one-year weight loss intervention resulting in a 6.4% reduction of body weight also resulted in a 1.5% total body BMD loss. At the same time, however, there is evidence that obesity is associated with compromised bone quality.

Given the above, the lack of quality bone measurements within the referenced studies, and the fact that bone homeostatic mechanisms are complex, the current study examined the effects of caloric restriction on BMD, geometry, and strength to determine the risk-benefit ratio of weight loss in middle-aged and older obese and overweight men. Additionally, because weight loss alters sex steroids, 25-hydroxyvitamin D [25(OH)D], and parathyroid hormone (PTH), these hormones were investigated to determine whether they can explain changes in bone parameters.

Who?

Forty-four older (50-72 years) men with BMIs ranging from 25-39 that were not undergoing treatment or diagnosed with diseases that influences calcium or bone metabolism participated in the study.

What?

The participants were divided into two groups for the 6-month study period: weight loss (WL) and weight maintenance (WM). Unfortunately, there was no randomization, which may increase the risk of a type-1 error and reduce the reliability of the p-value, but nonetheless, those men who volunteered to lose weight were placed in the WL group. The WL group was counseled and offered weekly classes for the first eight weeks, followed with bi-weekly classes for the remainder of the six months where they followed a standard behavior modification nutrition education program. Caloric intake was individualized and attempted to be reduced by 500-600 kcal/day for moderate weight loss.

Conversely, the WM group was simply asked to maintain their weight (defined as a <2.5% change in body weight from baseline to the end of the 6-mo study) with no further intervention. All participants were weight stable for the preceding three months, so the request wouldn’t have been difficult for the WM group. Additionally, any participants in the WL group that failed to lose weight in the first seven weeks were eligible to join and complete the study as part of the WM group if they desired.

Everyone was instructed on how to determine portion sizes and complete food diaries, which were assessed at baseline and months 1, 3, and 6 for adherence to diets. Everyone was also provided 400 IU of vitamin D and a variable amount of calcium to standardize dietary intake of these bone-related compounds. A food-frequency questionnaire was used to determine dietary calcium intake, and the supplemented amount was provided to achieve a total daily intake of 1.2g. Finally, participants were instructed to follow their usual exercise regimen and record the amount and type of physical activity performed within their food-diaries.

DXA and pQCT were performed at baseline and six months to determine BMD, BMC, body composition, and geometry and strength indexes of the tibia. Blood and urine was collected at 1, 3, and 6 months.

And?

As expected, during the intervention, there was lower intake of total calories in the WL group (1595 kcal/d) than WM group (2097 kcal/d). Protein intake was also lower in the WL group (81g) compared to the WM group (87g), but as a percentage of energy was slightly higher (20% vs 17%). There were also no differences in intakes of calcium, magnesium phosphorous, vitamin D, or vitamin K, all of which play central roles in bone metabolism.

The lower caloric intake led to a 7.9% average weight loss in the WL group (~8 kg), of which 68% (5.5 kg) was fat mass and 18% (1.5 kg) was lean body mass. However, the WL group also had a significant 6.6% reduction of total body BMC, with the only significant reduction in BMD being in the femoral neck (connects the head of the femur to the shaft). There were no significant differences between groups in trabecular variables, although there was a trend (p=0.06) for cortical thickness to increase in the WL group compared to being reduced in the WM group. Given the sedentary nature of the participants, I would say that the body composition changes were pretty good, and the loss of BMC is to be expected in persons who don’t exercise (Wolff’s law, use it or lose it).

Sadly, 42% of men had serum 25(OH)D concentrations below 20 ng/mL, while only 21% of men had serum 25 (OH)D concentrations greater than 30 ng/mL. Interestingly, both 25(OH)D and testosterone concentrations increased through the intervention, which may be related to the vitamin D supplement that all participants were required to take. Total, free, and bioavailable estradiol also was significantly different between the groups, decreasing in the WL group and increasing in the WM group.

When everything was ran through multivariate analysis to find associations, it was determined that changes in total body MBD were positively related to changes in body weight, fat free mass, and total body fat. Conversely, body fat tended (p=0.06) to inversely correlate with the stress-strain index (measurement of bone strength). For hormones, total body BMD inversely correlated with testosterone, and femoral neck BMD and cortical thickness were positively correlated with serum 25(OH)D levels. Free estradiol inversely correlated with changes in cortical thickness, and the stress-strain index, and tended (p=0.06) to positively correlate with the endosteal circumference (a layer of vascular tissue lining the inside of some bones such as the femur).

Overall, changes in body weight and 25(OH)D concentrations explained 25% of the variance in femoral neck BMD; changes in fat free mass explained 19% of the changes in total body BMD; and changes in free estradiol explained 14% of the changes in cortical thickness at the tibia.

Bottom line

Osteoporosis and bone loss in older men is a burden on the aging society that increases fracture risk and downstream complications. In the current study, weight loss resulted in no significant changes to BMD, geometry, or strength. Yet body composition improved. Additionally, body fat tended to correlate negatively with bone strength, while all components of body weight increased BMD. Thus, it appears that weight loss in older age is not detrimental, and in fact being overweight is.

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