The apparent cause:
[D]uring the period of the economic crisis [first half of the 1990s]…Cubans, who were walking and bicycling more after their public transportation system collapsed, and eating less (energy intake plunged from about 3,000 calories per day to anywhere between 1,400 and 2,400, and protein consumption dropped by 40 percent). They lost an average of 12 pounds.
The apparent effect:
[D]eaths from cardiovascular disease and adult-onset type 2 diabetes fell by a third and a half, respectively. Strokes declined more modestly, and overall mortality rates went down.
Then, a reversal:
This enforced fitness regime lasted only until the Cuban economy began to recover in the second half of the 1990s…Eventually people in Cuba were eating even more than they had before the crash…”by 2011, the Cuban population has regained enough weight to almost triple the obesity rates of 1995.”