This "abrupt downward trend" in illness does not appear to be because of Cuba's barefoot doctors and vaunted public health system, which is rated amongst the best in Latin America. The researchers say that it has more to do with simple weight loss. 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.

It wasn't only the amount of food that Cubans ate that changed, but also what they ate. They became virtual vegans overnight, as meat and dairy products all but vanished from the marketplace. People were forced to depend on what they could grow, catch, and pick for themselves-- including lots of high-fiber fresh produce, and fruits, added to the increasingly hard-to-come-by staples of beans, corn, and rice. Moreover, with petroleum and petroleum-based agro-chemicals unavailable, Cuba "went green," becoming the first nation to successfully experiment on a large scale with low-input sustainable agriculture techniques. Farmers returned to the machetes and oxen-drawn plows of their ancestors, and hundreds of urban community gardens (the latest rage in America's cities) flourished.

"If we hadn't gone organic, we'd have starved!" said Miguel Salcines Lopez in the journal Southern Spaces. Salcines is an agricultural scientist who founded "Vívero Alamar," one of Cuba's best known organopónicos, or urban farms, in vacant lots in Havana.

During the special period, expensive habits like smoking and most likely also alcohol consumption were reduced, albeit briefly. This enforced fitness regime lasted only until the Cuban economy began to recover in the second half of the 1990s. At that point, physical activity levels began to fall off, and calorie intake surged. Eventually people in Cuba were eating even more than they had before the crash. The researchers report that "by 2011, the Cuban population has regained enough weight to almost triple the obesity rates of 1995."

Not surprisingly, the diseases of affluence made a comeback as well. Diabetes increased dramatically, and declines in cardiovascular disease slowed to their sluggish pre-1991 levels. (Heart disease did decline slightly in the 1980s due to improved detection and treatments.) By 2002, "mortality rates returned to the pre-crisis pattern," according to the authors of the study. Cancer deaths, which fell in the years after the crash, also started inching up after the recovery, rising 5.4 percent from 1996 to 2010.

While the study's author's are cautious about attributing all of these changes in disease rates exclusively to changes in weight, Professor Walter Willett, of the Harvard School of Public Health, Boston wrote in an editorial that the study does provide "powerful evidence [that] a reduction in overweight and obesity would have major population-wide benefits."