Obesity, high blood pressure, and diabetes being risk factors for complications with C19 and every other ordinary virus, I would say he just got smart about lifestyle choices to get healthy. Every other Secretary of State has looked like hell while they served due to the demands of the office, and then suddenly, dramatically began to look healthier after leaving the State Department. It is something I noticed with Madeleine Albright and HRC. All the international travel, disrupted sleep schedules, jet lag, long hours of sedentary work, heavy meals at state dinners as well... I have seen a couple friends achieve similar results with Keto and disciplined workouts.