The inference chains four arm-level facts into a mechanism attribution. (1) The egg arm delivered ~467 mg choline and the choline-bitartrate arm ~411 mg — comparable choline doses. (2) Free choline (bitartrate) raised fasting TMAO ~6-fold (O-63), establishing that the assay and the gut-microbial TMA pathway are responsive at this dose. (3) Eggs did not raise TMAO (O-62); crucially, this is not because the choline was not consumed/absorbed — plasma choline rose comparably in the egg arm (O-65), ruling out non-compliance and mal-absorption as confounds. (4) Phosphatidylcholine capsules, delivering choline in the same phospholipid form as egg yolk but without the whole-egg matrix, also failed to raise TMAO (O-64), which points past “the whole-egg food matrix” to the phospholipid-bound form of choline itself as the operative variable. The only remaining variable that separates the TMAO-raising arm from the two null arms is the chemical form of choline (free vs phosphatidylcholine-bound), so the data force the form/bioavailability conclusion (supporting H-28) and, applied to whole eggs specifically, the egg-null harm-pathway conclusion (H-29). The controlled contrast (same dose, absorption confirmed) is what makes this a valid deduction rather than a bare association.
Validity (step 6): approved / checked. Reconstructed step: three candidate explanations for the egg TMAO-null are under-dosing, non-compliance/malabsorption, and choline form. The matched doses (~467 vs ~411 mg) close off under-dosing; the confirmed plasma-choline rise in the egg arm closes off non-compliance/malabsorption; the free-choline arm’s ~6-fold TMAO rise proves the assay and the gut TMA pathway are responsive at this dose, so a null is informative rather than a floor effect. With those alternatives eliminated, the sole variable separating the one TMAO-raising arm (free choline) from the two null arms (egg, phosphatidylcholine capsule) is chemical form/bioavailability — a clean four-arm eliminative contrast, not a bare association. I probed one undercutting defeater that does not deny the premises: TMAO generation depends on choline reaching colonic microbiota, and a systemic plasma-choline rise confirms absorption but not equal colonic delivery — however the statement’s conclusion is explicitly “form/bioavailability,” which is precisely the form-dependent colonic-availability channel, so this refines rather than breaks the step. The PC-capsule arm (same phospholipid form as yolk, no whole-egg matrix, also null) correctly pushes the conclusion past “food matrix” to the phospholipid-bound form itself. Conditional on the four observations, the isolation of form as the determinant follows; approved as stated. (Whether egg truly does not raise TMAO — small-trial, high-variance TMAO — is a premise-truth question priced downstream, not a validity flaw.)