Podcast Summary: Endocrine Feedback Loop

Episode: EFL067 – Bariatric Surgery and Changes in Body Composition and Musculoskeletal Health
Host: Dr. Chase Hendrickson (Vanderbilt University)
Guests: Dr. Andrew Craftson (University of Michigan), Dr. Ann Schaefer (University of California, San Francisco)
Date: November 20, 2025

Overview

This episode explores the findings from a recent study published in the Journal of Clinical Endocrinology and Metabolism (May 2025) on one-year changes in body composition, muscle strength, and bone density following three types of metabolic bariatric surgery: one anastomosis gastric bypass (OAGB), Roux-en-Y gastric bypass (RYGB), and sleeve gastrectomy (SG). The discussion centers around surgical impact on musculoskeletal health, highlighting important clinical considerations and implications for patient management.

Key Discussion Points & Insights

1. Background and Rationale

(00:00–06:39)

• GLP-1-based pharmacotherapies have shifted focus away from bariatric surgery, even though surgery is the most effective obesity treatment with the best long-term outcomes.
• Bariatric surgery rates are declining (25% reduction attributed to increased use of weight loss medications), but many patients are still eligible and may need surgery, especially as medication coverage is limited.
• Misconceptions, cost, and concerns regarding surgical risks (including impact on nutrient absorption and body composition) limit both referrals and patient uptake.
• Dr. Ann Schaefer highlights that bariatric surgery leads to:
  • Increases in bone turnover markers.
  • Declines in bone mass, bone mineral density (BMD), and bone microarchitecture, sometimes exceeding physiologic adaptation and resulting in increased fracture risk.

“Metabolic and bariatric surgery does result in early and pretty dramatic increases in bone turnover... The changes exceed [physiologic adaptation] and actually do become pathologic.”
— Dr. Ann Schaefer [05:41]

2. Surgical Procedures & Expected Changes

(06:39–12:49)

• Sleeve Gastrectomy (SG): Most common, shorter/safer surgery, less malabsorption, but potentially less potent for weight and comorbidity management than RYGB.
• Roux-en-Y Gastric Bypass (RYGB): Gold standard for type 2 diabetes and severe obesity; more potent but increased risk of nutrient and bone complications.
• One Anastomosis Gastric Bypass (OAGB): Gaining worldwide popularity, though limited long-term data exists on nutrient and musculoskeletal outcomes. Not FDA-approved as a primary procedure in the US.

“There is limited long term data and limited information about the long term impact on vitamin and mineral deficiencies, the impact on bone health... [These surgeries] can impact the bones and ... increase bone fracture risk due to nutritional factors, mechanical unloading, hormonal factors and these changes in body composition and bone marrow fat.”
— Dr. Andrew Craftson [09:16]

3. Study Design & Methodology

(13:54–20:44)

• The study is a secondary analysis of an RCT (the "Berry Lifestyle" trial), primarily intended to assess lifestyle program adjuncts to surgery (no effect found).
• This analysis is best characterized as a retrospective cohort study among adults aged 18-65 meeting standard bariatric criteria, with available baseline and one-year DEXA scans.
• Final analyzable cohort: 119 patients (16% OAGB, 33% RYGB, 51% SG).
• Choice of surgery: Based on informed patient/provider preference, but heavily influenced by center practices (potential confounder).
• Key outcomes measured: Total body weight, body composition (fat mass, visceral adipose tissue, lean mass), BMD at hip/neck/spine, six-minute walk test, sit-to-stand test, and handgrip strength.
• Statistical analysis adjusted for confounders: age, sex, menopausal status, ethnicity, surgical center, baseline BMD, etc.

“This is a secondary analysis of an RCT... but I would characterize it as a retrospective cohort study ... the exposure had to predate putting people into those groups.”
— Dr. Chase Hendrickson [13:54]

4. Results: Demographics and Baseline Characteristics

(20:44–22:25)

• Majority women (77%) and premenopausal (72%), average age 46, BMI ~43.
• Similar baseline body composition and physical function across groups.
• High rate of smokers (55%) compared to US norms.

5. Results: Body Composition, BMD, and Function

(22:25–29:37)

Weight Loss:

• All groups: ~25–27% total body weight loss at 1 year, no significant difference between surgical types.

Body Composition:

• No significant differences across surgery types.
• Fat mass ↓ 35–38%, lean body mass ↓ 18–20%, visceral adipose tissue ↓ 27–34%, appendicular lean mass ↓ 17–22%.

Bone Mineral Density:

• More pronounced BMD declines with RYGB and OAGB vs. SG:
  • Total hip: -6.5% (SG) vs. -9 to -10% (RYGB/OAGB)
  • Femoral neck: -3% (SG) vs. -7 to -8% (RYGB/OAGB)
  • Lumbar spine: -2% (SG) vs. -4.5% (RYGB/OAGB)
• Use of T scores to define osteopenia/osteoporosis in premenopausal women may not be clinically relevant.

“I also wished that the authors had done that a little bit differently in order to be consistent with how we do things in clinical practice... how many people had low bone mass for age ... would have been a nice thing.”
— Dr. Ann Schaefer [25:37]

Physical Function and Muscle Strength:

• Absolute grip strength fell by 6.5–9.5%.
• Relative grip strength (adjusted for weight) increased by 16–27%.
• Sit-to-stand time improved by 25–27%.
• Six-minute walk test performance improved by 34–38%.

“After metabolic and bariatric surgery... if you calculate... strength divided by total mass or BMI... that ratio, that relative strength actually increases... we shouldn’t be too quick to say that a person loses strength... people seem to be better off when it comes to physical function, physical performance postoperatively.”
— Dr. Ann Schaefer [29:37]

6. Interpretation & Clinical Implications

(31:59–40:37)

• All surgical types resulted in significant lean mass decline, without differences between procedures.
• Relative strength and function improved across the board.
• OAGB and RYGB led to greater declines in BMD, especially at clinically relevant sites.

Mechanistic Discussion:

• Causes of BMD decline are multifactorial—mechanical unloading, nutritional deficits (calcium, vitamin D, protein), changes in adipokines, sex hormones, gut hormones, microbiota.
• It's difficult to separate the effects of weight loss from those of surgical physiology.

Limitations Acknowledged:

• Unequal group sizes, secondary analysis not powered for certain endpoints, mostly women, lack of bone turnover marker data, measurements by DEXA (potential artifact).

Notable Quotes & Memorable Moments

• On Bone Health:

  “We need to make sure that primary providers and endocrinologists and surgeons are all on the same page giving evidence based advice about nutrition, about evaluation of bone health and following a person along so that we can make sure that we're doing everything we can to maintain bone health as much as possible during the weight loss process.”
  — Dr. Ann Schaefer [40:37]

• On Clinical Management:

  “Just because the calcium level is fine doesn't mean you don't need the calcium... and that there are real reasons why we're doing that, but also that encouragement of the function aspect of things... you will potentially have better quality of life and better function, functional life.”
  — Dr. Andrew Craftson [39:01]

• On Research Gaps:

  “It contributes pretty meaningfully to the scant literature that exists right now about the 1anastomosis gastric bypass... I hope that we'll have data in advance of that so that we're not going into things blind.”
  — Dr. Ann Schaefer [40:37]

Timestamps for Important Segments

• Intro & Background: 00:00–06:39
• Surgical Types & Mechanisms: 06:39–12:49
• Study Design: 13:54–17:47
• Surgical Choice Rationale: 17:47–20:44
• Population & Baseline Data: 20:44–22:25
• Results: Weight & Composition: 22:25–25:37
• Bone Density Results & Interpretation: 25:37–29:37
• Physical Function Outcomes: 29:37–31:59
• Discussion on Mechanisms & Limitations: 31:59–35:47
• Practice Implications: 39:01–42:02

Clinical Takeaways

• Bariatric surgery yields dramatic improvements in weight loss and relative functional status, but comes with a consistent, significant loss of BMD, predominantly with RYGB and OAGB.
• Bone health surveillance and proactive nutrient management is crucial—calcium, vitamin D, protein should be emphasized, and physical function should be assessed, not just BMD scores.
• Team-based, longitudinal follow-up is essential for optimizing musculoskeletal outcomes in bariatric surgery patients.
• Providers should educate patients on the rationale behind supplementation and the need for ongoing monitoring.
• Further research is needed, particularly regarding newer surgical techniques like OAGB and alternative imaging beyond DEXA for more accurate BMD measurement.