It's a scenario that, given the current austerity drive and soaring fuel prices, could easily become a reality in the UK.

In 1990 the Cuban economic crisis – triggered by the collapse of the Soviet Union – meant food and fuel were in short supply; millions went hungry, most had to abandon their cars and, gasp, walk.

Cars and buses virtually disappeared from the roads as fuel supplies dried up, and farmers had to abandon motorised machines and work the fields manually. The government issued one million bicycles to keep the population on the move.

And guess what? The people got leaner and fitter. Because they were expending more calories than they were consuming, over five years or so each person lost an average of 5kg, or 10lbs. It's a no-brainer. Eating less and exercising more is the fundamental rule of weight loss. Some bright spark has calculated that 2.5 billion calories were wiped off the national diet – the equivalent of eight million fewer cheeseburgers consumed over the same period.

Further benefits emerged. Deaths from diabetes began to fall in 1996, five years after the start of the weight-loss period, and remained low for six years. Deaths from heart disease reduced by one-third.

Could we do the same now? It would be nice to think so. It sounds easy: all we'd each need to do is consume 50 calories fewer each day for five years.

The trouble for modern obesity-cursed countries like ours is that the national Cuban weight loss was the result of a natural experiment. It wasn't enforced by public health do-gooders, whose advice, it has been all too graphically proven, is easy to ignore.

You never know. If the economic situation gets worse, it might well boost the country's vital statistics.