Another mechanism (perhaps among the five most important) of how obesity can lead to diabetes and recurrent sinus infections, articulated uniquely by CCIMHEALTH:

Excess fat --> excesses estrogen --> decreased levels of akkermansia and increased of strep --> more upper respiratory infections and more insulin resistance

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Long term estrogen treatment decreases akkermansia, increase Lactobacillus and strep levels https://www.sciencedaily.com/releases/…/06/180619173557.htm…

Long-term estrogen therapy changes microbial activity in the gut

Long-term therapy with estrogen and bazedoxifene alters the microbial composition and activity in the gut, affecting how estrogen is metabolized, a new study in mice found.
Source