Lauren M. Beckman

The link between obesity and low circulating 25-hydroxyvitamin D concentrations: considerations and implications

Obesity and vitamin D deficiency have both been recognized as major public health issues worldwide, and there is growing evidence that they are related, although the cause–effect relationship remains unclear. Could obesity be contributing to low circulating 25-hydroxyvitamin D concentrations? Alternatively, could low vitamin D status predispose to obesity? In this review, the relationship between low circulating 25-hydroxyvitamin D and obesity, and possible underlying reasons from both perspectives, is presented. One potential mechanism by which obesity could contribute to low serum 25-hydroxyvitamin D is adipose sequestration of vitamin D. On the other hand, adipose tissue has both the vitamin D receptor and the ability to synthesize 1,25-dihydroxyvitamin D, and there is evidence that vitamin D may regulate adipose tissue mass, differentiation and metabolism in ways that might contribute to obesity. Of particular interest, vitamin D deficiency is common both before and after bariatric surgery, and is often difficult to treat, particularly with the more malabsorptive procedures. Additional research is needed to elucidate the complex and multifaceted factors underlying the association between low circulating 25-hydroxyvitamin D and obesity, and to identify optimal treatment approaches in obese individuals and in bariatric surgical patients both before and after surgery.

Changes in Gastrointestinal Hormones and Leptin after Roux-en-Y Gastric Bypass Procedure: A Review

Roux-en-Y gastric bypass is a well-accepted tool for the treatment of obesity and, compared to conventional weight loss methods (eg, diet and exercise) and other weight loss surgeries (eg, gastric banding), it results in considerable weight loss that is maintained long term. Although successful, the mechanisms for weight loss are not completely understood and it is thought that gastrointestinal hormones play a role. Several gastrointestinal hormones have been identified for their effects on appetite, including glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY), leptin, and ghrelin. This review encompasses a literature search that included 45 primary articles and shows that there are alterations in GLP-1, PYY, leptin, and ghrelin postoperatively. GLP-1 and PYY concentrations were usually found to be higher, whereas ghrelin levels were typically lower post- Roux-en-Y gastric bypass than in individuals with obesity, those who were overweight or of normal weight, and in those who underwent procedures other than Roux-en-Y gastric bypass or who achieved weight loss by lifestyle modification. An understanding of how gastrointestinal hormones change after Roux-en-Y gastric bypass may help dietetics practitioners optimize nutrition care for this patient population. A review of the literature also highlighted some research gaps that should be taken into consideration when designing future studies.

Changes in gastrointestinal hormones and leptin after Roux-en-Y gastric bypass surgery.

BACKGROUND Roux-en-Y gastric bypass (RYGB) imparts long-term weight loss, the mechanisms for which are not well understood. Changes in leptin and gastrointestinal (GI) hormones, including glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and ghrelin, may contribute to the relative success of RYGB compared with conventional weight loss methods. This study evaluated changes in GI hormones and leptin post-RYGB. The study also evaluated whether GI hormones differed after a short-term dose of protein or fat. METHODS GLP-1, PYY, ghrelin, and leptin were assessed in 16 women before RYGB and up to 1 year after RYGB. Plasma was collected before and at several times after a short-term equicaloric dose of protein or fat. RESULTS GLP-1 area under the curve (AUC) increased at week 6 and 1 year in the fat beverage (FAT-BEV) group compared with baseline. PYY AUC remained elevated at 1 year in the FAT-BEV group. Ghrelin AUC decreased at week 2, week 6, and 1 year in the protein beverage (PRO-BEV) group compared with baseline. Ghrelin AUC was lower in the PRO-BEV group compared with the FAT-BEV group at week 6. Fasted leptin decreased at all visits in both groups and was lower in the FAT-BEV group compared with the PRO-BEV group at 1 year. CONCLUSIONS Changes from baseline were evident for all GI hormones and leptin; some differences were evident soon after surgery (ghrelin, leptin), whereas others were maintained long term (GLP-1, PYY, ghrelin, leptin). In response to a short-term stimulus, protein suppressed ghrelin and fat potently stimulated GLP-1 and PYY. Future work in this area is warranted.

Serum 25(OH) Vitamin D Concentration Changes After Roux‐en‐Y Gastric Bypass Surgery

To describe serum 25(OH)D changes after Roux‐en‐Y gastric bypass (RYGB) and to determine if fat mass (FM) loss and vitamin D intake are associated with changes in serum levels.

Comparison of DXA and water measurements of body fat following gastric bypass surgery and a physiological model of body water, fat, and muscle composition

Measurement of body composition changes following bariatric surgery is complicated because of the difficulty of measuring body fat in highly obese individuals that have increased photon absorption and are too large for the standard dual-energy X-ray absorptiometry (DXA) table. We reproducibly measured body composition from half-body DXA scans and compared the values of total body fat estimated from total body water (TBW) and DXA measurements before and after Roux-en-Y gastric bypass surgery (RYGB). DXA, TBW (deuterium dilution), extracellular water (ECW; bromide dilution), and intracellular water (ICW) measurement (by subtraction) were made before surgery and at 2 wk, 6 wk, 6 mo, and 12 mo after surgery. Twenty individuals completed baseline and at least four follow-up visits. DXA appeared to underestimate the fat and bone mass in extreme obesity (before surgery), whereas at 6 and 12 mo after surgery, the DXA and TBW fat measurements were similar. The ECW-to-ICW ratio was increased in obese individuals and increased slightly more after surgery. We describe a new model that explains this abnormal water composition in terms of the normal physiological changes that occur in body composition in obesity and weight loss. This model is also used to predict the muscle mass loss following RYGB.

Vitamin D status following bariatric surgery: Implications and recommendations

Individuals with extreme obesity who qualify for bariatric surgery are frequently vitamin D deficient before and after surgery. The anatomical changes that occur during some bariatric procedures may lead to decreased absorption of vitamin D, although vitamin D absorption and metabolism has not been quantified or compared across surgeries, and multiple other factors could influence vitamin D status in these individuals. Vitamin D treatment and dosing studies show that there is variability in how individuals respond to supplementation regimens regardless of the bariatric procedure. It is unknown if improving vitamin D status before and/or after bariatric surgery can affect health-related outcomes in this population beyond the traditional roles of vitamin D. Vitamin D has been purported to positively influence a variety of obesity-related comorbidities. Furthermore, in light of the potential role of vitamin D in immunity and inflammation, it seems important to consider the ramifications of vitamin D deficiency in the postbariatric individual in the critical care setting and particularly in the context of aging. Additional research is needed to develop evidence-based guidelines for optimal treatment of vitamin D deficiency in individuals before and after bariatric surgery and to determine the impact of vitamin D repletion on non-bone health-related outcomes in these individuals.

Nutritional Implications of Bariatric Surgery and the Role of Registered Dietitians

A S THE NUMBER OF INDIVIDUALS WITH OBESITY continues to increase, so has the prevalence of bariatric surgery in the United States and worldwide. Bariatric surgery is currently the only knownmethod that offers both considerable and long-termweight loss. Depending on the surgical procedure, patients can expect to lose between 29% and 87% of excess bodyweight 1 to 2 years postsurgery. Despite the substantial weight loss and improvements in comorbid conditions observed after bariatric surgery, these procedures are notwithout nutritional risk, which underscores the importance of registered dietitians (RDs) to the bariatric surgical care team. Nutritional deficiencies after bariatric surgery can arise from a variety of factors, including surgical modifications of the gastrointestinal tract that reduce dietary intake and/or promote malabsorption, or because of poor patient compliance with treatment recommendations (eg, diet and multivitamin supplementation). In this issue, MoizE and colleagues prospectively evaluated long-term nutritional deficiencies and dietary patterns after both sleeve gastrectomy and Rouxen-Y gastric bypass (RYGB). They demonstrated that nutritional deficiencies anddietary intake patternswere similar up to 5 years after sleeve gastrectomy and RYGB. Insufficient or deficient 25-hydroxyvitamin D appeared to be the most common problem before and up to 5 years after both surgeries, despite implementing a vitamin D supplementation protocol and living in aMediterranean climate (insufficiency defined by MoizE and colleges as 10 to 29 ng/mL [25 to 72 nmol/L] and deficiency defined as 10 ng/mL [ 25 mmol/L]). Considering that amajority of patients in theMoizE and colleagues studywere either insufficient or deficient before surgery suggests that routine supplementation of vitamin D should occur preoperatively. Moreover, the results from MoizE and colleagues and others highlight the importance of vitamin D supplementation in the bariatric surgery patient population and suggest that the frequently recARTICLE INFORMATION

Long-Term Body Composition Changes in Women Following Roux-en-Y Gastric Bypass Surgery.

Background: Although most individuals experience successful weight loss following Roux-en-Y gastric bypass (RYGB), weight regain is a concern, the composition of which is not well documented. Our aim was to evaluate changes in body composition and handgrip strength as a measure of functional status in participants from a previous 1-year post-RYGB longitudinal study who had undergone RYGB approximately 9 years prior. Methods: Five women from an original larger cohort were monitored pre-RYGB and 1.5 months, 6 months, 1 year, and 9 years post-RYGB. Body composition was assessed at all time points using dual energy x-ray absorptiometry and multiple dilution. Handgrip strength was measured using a digital isokinetic hand dynamometer (Takei Scientific Instruments, Ltd, Tokyo, Japan). Results: Mean time to final follow-up was 8.7 years. Lean soft tissue (LST) loss over the ~9-year period was on average 11.9 ± 5.6 kg. Compared with 1-year post-RYGB, 9-year LST was 4.4 ± 3.0 kg lower (P = .03). Fat-free mass decreased over the 9-year period by 12.6 ± 5.8 kg. Mean fat mass (FM) decreased from 75.4 ± 22.6 kg pre-RYGB to 35.5 ± 21.5 kg 1 year post-RYGB but then trended toward an increase of 8.6 ± 7.0 kg between 1 year and 9 years post-RYGB (P = .053). Loss of LST was correlated with loss of handgrip strength (r = 0.64, P = .0005). Conclusion: The continued loss of lean mass associated with decreased handgrip strength occurring with long-term trend toward FM regain post-RYGB is concerning. The loss of LST and functional strength carries particular implications for the aging bariatric population and should be investigated further.

Evaluation of Lean Body Weight Equation by Dual-Energy X-Ray Absorptiometry Measures

Background: When managing patients with disorders that require clinical intervention, a practical assessment of body habitus is valued. The Duffull-Green lean body weight (LBW) equation was derived and validated in adults across a wide body mass index (BMI) range. Whether this predictive equation will perform well in patients at BMI extremes or perform better than a widely used empiric “ideal” body weight (IBW) equation is unknown. Materials and Methods: Calculated LBW and calculated IBW were each compared with the dual-energy x-ray absorptiometry (DXA)–derived lean body mass (LBM) by simple linear regression. A mixed model was used to determine how well the LBW equation performed over time in patients with more than 1 DXA measurement. Results: At time 0, 32 patients were 18–67 years old, and all were obese (BMI: 36–65 kg/m2), while the remaining 7 had parenteral nutrition–dependent intestinal failure (BMI: 17–25 kg/m2). A subset of patients underwent bariatric surgery after time 0 (BMI at follow-up: 22–49 kg/m2). The LBW equation was a predictor of LBM (R2 = 0.67, P < .0001), while the IBW equation was not (R2 = 0.04, P = .25). The LBW equation remained a predictor of LBM over time (P < .0001) without significant interaction by number of months since time 0. Conclusion: The Duffull-Green LBW equation successfully predicted lean body mass in a patient population with a wide range of BMIs at both a single point in time and after considerable weight loss. In the clinical setting, an equation that performs well in various disease states and body sizes is advantageous.