Back to "All values were always in the normal ran..."
Claim
Strong Support
descriptive
Analysis v3

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...

31
Pro
0
Against

Mechanism

Synthesis from 1 study

How it works

After surgery that stops fat digestion, the body makes less of its active thyroid hormone because it can't convert the stored form properly. At the same time, burning more protein for energy tells the brain to keep the thyroid control signal steady, so the main hormone and the brain's signal stay...

Most probable mechanism

In Simple Terms

After surgery that blocks fat digestion, the body can't make enough active thyroid hormone from its stored form, so levels of the active hormone drop. At the same time, the body starts burning more protein for energy, which signals the brain to keep the thyroid control signal steady even though the active hormone is low. This keeps the main thyroid hormone and the brain's signal normal, even as the active hormone falls.

Causal chain
1

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

Verified by multiple studies
which leads to
2

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

Verified by multiple studies
which leads to
3

Lower deiodinase type 1 activity reduces conversion of thyroxine (T4) to triiodothyronine (T3), causing sustained reduction in circulating free triiodothyronine (FT3).

Verified by multiple studies
which leads to
4

Shift in substrate utilization toward protein oxidation increases amino acid catabolism, generating metabolic signals that modulate hypothalamic-pituitary-thyroid axis feedback.

Verified by multiple studies
which leads to
5

Pituitary thyrotrophs adjust TSH secretion based on protein oxidation rates, maintaining TSH within normal range despite low FT3 and stable FT4.

Verified by multiple studies

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.

Sign up to see full verdict

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

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 these stable TSH levels are linked to the rate at which the body breaks down protein during fasting.

31
0
89%

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
81%

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
0
78%

After thyroid removal, some patients have high TSH and high FT4 but low FT3, which suggests their bodies are not efficiently converting the available thyroid hormone (T4) into its active form (T3).

44
0
70%