The hard times experienced by the people of Cuba in the early 1990s – when food was short and petrol almost unobtainable owing to the tightening of the US embargo and loss of Russian support – led to falling rates of heart disease and diabetes, say doctors.

Researchers studied the so-called "special period" between 1991 and 1995, when people resorted to donkeys to transport loads and the government imported 1.5m bicycles from China, to see whether eating less, walking, cycling and manual labour made a difference to the health of the population as a whole.

Unusually for a scientific study, the researchers, from eminent universities in the US as well as Spain and Cuba, put on record their condemnation of the political activity that caused the crisis and their admiration of the way the Cuban people coped. "We would like to acknowledge our great respect and admiration for the Cuban people who faced extremely difficult social and economic challenges during the special period – and by making common cause against this tragedy held up with courage and dignity. This tragedy was 'man made' by international politics and should never happen again to any population," they write.

Cuba, which has a much-admired healthcare system based on the "barefoot doctors" who provide comprehensive primary care, has excellent data on the health of its people as well as complete and publicly accessible death records. The researchers, publishing their findings in the British Medical Journal, say they were able to track what happened to the weight of the population and look at the subsequent death rates from coronary heart disease, stroke and diabetes from 1980 to 2010, focusing on the city of Cienfuegos.

Led by Dr Manuel Franco, associate professor at the University of Alcalá in Madrid, the team found the population lost an average of 5.5kg (12lb) in weight during the five years of the economic crisis. That had a real impact on health, cutting deaths from diabetes by half and from coronary heart disease by a third.

"Marked and rapid reductions in mortality from diabetes and coronary heart disease were observed in Cuba after the profound economic crisis of the early 1990s," the doctors write. "These trends were associated with the declining capacity of the Cuban economy to assure food and mass transportation in the aftermath of the dissolution of the former Soviet Union and the tightening of the US embargo. Severe shortages of food and gas resulted in a widespread decline in dietary energy intake and increase in energy expenditure [mainly through walking and cycling as alternatives to mechanised transportation."

But as the economic crisis ended in 1996 and Cuba began to become more prosperous again, the weight started to go back on. From 2000, the economy has had sustained growth. From 1996, physical activity levels have declined, although only slightly. But energy intake – the amount of food and drink consumed – had increased above pre-crisis levels by 2002.

As a result, write the researchers, "by 2011, the Cuban population has regained enough weight to almost triple the obesity rates of 1995".

Diabetes levels had dropped during the five hard years, but from 1995 they began to surge. With economic recovery, the incidence of the disease peaked in 2004 and again in 2009. From 2002 to 2010, death rates from diabetes were rising again every year at the same rate as before the crisis. Deaths from coronary heart disease and stroke were declining, as they have done elsewhere with better treatment, but only at the same rate as before 1991.

What this shows, say the authors, is that interventions to bring down the weight of whole populations – as opposed to leaving it up to individuals – can have real benefits. But, they say, "so far, no country or regional population has successfully reduced the distribution of body mass index or reduced the prevalence of obesity through public health campaigns or targeted treatment programmes".

Franco, in a video explaining the study, says that one of the lessons from Cuba for governments is that "transportation policies are fundamental – therefore we should encourage walking and bicycling as means of transportation. The results also highlight the need for physical activity and diet changes to happen at the same time, involving the whole population."

But he doubts whether the Cuban crisis holds out any hope for a beneficial health outcome from the current economic crisis afflicting European countries like his own. Europe is far more heterogeneous than Cuba, which has around 11 million people mostly of the same racial background and similar social circumstances.

In a commentary supporting the call for government action, Walter C Willett, professor and chair department of nutrition at Harvard School of Public Health in Boston, says the study offers "powerful evidence that a reduction in overweight and obesity would have major population-wide benefits. To achieve this is perhaps the major public health and societal challenge of the century. Medical treatment of people at high risk for disease will have limited impact on mortality rates if the primary causes of disease are not dealt with, and reviews agree that solutions will require multi-sectoral approaches."

Potential strategies include "educational efforts, redesign of built environments to promote physical activity, changes in food systems, restrictions on aggressive promotion of unhealthy drinks and foods to children, and economic strategies such as taxation."