“Most clinicians, and even experts in the sleep apnea world, have not typically focused on fat in the tongue for treating sleep apnea,” said Richard Schwab, MD, chief of Sleep Medicine. “Now that we know tongue fat is a risk factor and that sleep apnea improves when tongue fat is reduced, we have established a unique therapeutic target that we’ve never had before.”

https://www.sciencedaily.com/releases/2020/01/200110101035.htm

From the research article abstract:

Conclusions:

Weight loss reduced volumes of several UA soft tissues in persons with obesity and OSA. Improved AHI with weight loss was mediated by reductions in tongue fat. New treatments that reduce tongue fat should be considered for patients with OSA.

Journal Reference:

1. Stephen H. Wang, Brendan T Keenan, Andrew Wiemken, Yinyin Zang, Bethany Staley, David B. Sarwer, Drew A. Torigian, Noel Williams, Allan I Pack, Richard J Schwab. Effect of Weight Loss on Upper Airway Anatomy and the Apnea Hypopnea Index: The Importance of Tongue Fat. American Journal of Respiratory and Critical Care Medicine, 2020; DOI: 10.1164/rccm.201903-0692OC

Wait for it.  A plethora of diet and weight loss books for your tongue.