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Claim
Strong Support
correlational
Analysis v3

In morbidly obese adults who undergo bilio-pancreatic bypass surgery, thyroid-stimulating hormone levels do not change even when free triiodothyronine levels and body weight change significantly, and...

31
Pro
0
Against

Mechanism

Synthesis from 1 study

How it works

After surgery that stops fat digestion, the body makes less active thyroid hormone but doesn't lower the signal to make more. Instead, the brain starts using how much protein is being broken down to decide how much signal to send — more protein breakdown keeps the signal steady.

Most probable mechanism

In Simple Terms

After surgery that blocks fat digestion, the body makes less active thyroid hormone because it lacks the fats needed to convert it. Even though thyroid hormone levels drop, the brain keeps the signal to make more thyroid hormone steady. Instead of responding to thyroid hormone levels, the brain starts responding to how much protein the body is breaking down for energy — more protein breakdown keeps the signal the same.

Causal chain
1

Bilio-pancreatic bypass diverts bile and pancreatic enzymes away from the duodenum, impairing fat emulsification and digestion.

Verified by multiple studies
which leads to
2

Reduced dietary fat absorption limits fatty acids and cholesterol availability, decreasing deiodinase type 1 activity in liver and kidney.

Supported by evidence
which leads to
3

Decreased deiodinase activity reduces conversion of thyroxine (T4) to triiodothyronine (T3), lowering circulating free T3 levels.

Verified by multiple studies
which leads to
4

Persistent low free T3 does not suppress thyroid-stimulating hormone secretion from the pituitary gland.

Verified by multiple studies
which leads to
5

Increased postabsorptive protein oxidation generates metabolic signals that maintain thyroid-stimulating hormone secretion independently of free T3 or free T4 levels.

Supported by evidence

Evidence from Studies

Supporting (1)

31

Community contributions welcome

31

Influences of obesity and weight loss on thyroid hormones. A 3–3.5-year follow-up study on obese subjects with surgical bilio-pancreatic by-pass

Cohort Study
Human
1997 May

Contradicting (0)

0

Community contributions welcome

No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

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Source Study

Influences of obesity and weight loss on thyroid hormones. A 3–3.5-year follow-up study on obese subjects with surgical bilio-pancreatic by-pass

Score: 31
DOI: 10.1007/BF03350300

Similar Assertions

After bariatric surgery, morbidly obese adults maintain normal levels of free thyroxine and thyroid-stimulating hormone over three to three and a half years, even though their free triiodothyronine and triiodothyronine levels drop significantly.

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After bilio-pancreatic bypass surgery, reduced fat absorption is linked to persistently lower levels of free triiodothyronine in obese adults, even when weight no longer changes, suggesting that nutrient absorption directly affects thyroid hormone levels independently of weight loss.

31
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After bilio-pancreatic bypass surgery in severely obese adults, levels of the active thyroid hormone FT3 drop by 10.5% within three months and stay 11.2% lower for up to three and a half years, even when body weight stops changing.

31
0
78%