Weight changes and health in CubaBMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f1777 (Published 09 April 2013) Cite this as: BMJ 2013;346:f1777
- Walter C Willett, professor and chair
Changes in food supplies and reductions in physical activity are fueling increases in overweight and obesity, diabetes, and cardiovascular disease worldwide.1 We have had few opportunities to see a reversal of this process, which is continuing inexorably almost everywhere. One such opportunity was provided by the well developed public health surveillance systems in Cuba, which were maintained during a period of serious economic hardship in the early 1990s. In a linked study (doi:10.1136/bmj.f1515), Franco and colleagues used these systems to look at the effects of reduced energy intake and increased physical activity on body weight and the occurrence of diabetes, cardiovascular disease, cancer, and death.2
In Cuba, decreased food availability and increased physical activity, supported by the distribution of more than a million bicycles during 1991 to 1995, led to an average 5.5 kg reduction in weight over five years, shifting the whole population distribution of weight downwards. Predictably, a profound and almost immediate reduction in the incidence of diabetes occurred, and a striking decline in cardiovascular mortality began, with a lag of about five years. These findings are consistent with those of the many epidemiologic and clinical studies that have examined the incidence of diabetes, cardiovascular disease, and cancer.3 4 5 6
The economic crisis was followed by a slow recovery, increased food intake, reduction in activity, and an increase in the prevalence of obesity to three times higher than before the crisis. With weight regain, the trend in incidence of diabetes rapidly reversed, and a decade after the period of weight loss, the decline in cardiovascular disease had greatly slowed. Most troublesome, the continued rapid increase in obesity and diabetes predicts that the decline in cardiovascular disease, and thus total mortality, will be reversed because the full impact of diabetes on incidence of cardiovascular disease is not seen until several decades after diagnosis.5 The apparent lack of effect of weight loss on death from cancer seen in the current study is not surprising. Only some cancers are associated with obesity and disease latency can be decades.7 More detailed analyses by specific types of cancer would be useful.
Franco and colleagues’ findings are consistent with many analyses of body mass index and mortality, including two recent ones that pooled data on about 2.5 million participants from cohort studies, which showed optimal body mass index to be less than 25.8 9 These results are at odds with another recent analysis,10 which suggested a U-shaped relation between body mass index and mortality, with overweight (body mass index 25-30) being optimal. However, that study included participants with serious underlying illnesses, heavy smokers, Asian populations burdened with undernutrition and chronic infections, and frail older people who had lost weight. Leanness may therefore have been due to illness so that, by comparison, mortality was lower in overweight people.
Franco and colleagues are appropriately cautious in their conclusions and avoid attributing all the changes in disease rates to changes in weight. Consumption of cigarettes declined during the same period and changes in dietary quality, including consumption of red meat, fruits, and vegetables, might also have had some effect. However, these variables could not account for all the trends in disease rates, and there is no question that the current increases in obesity are associated with major adverse effects.
The current findings add 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 multisectoral 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.11 12 Although these solutions must extend far beyond our healthcare systems, physicians can help by monitoring weight and counseling patients who gain weight before they become overweight. Recent evidence indicates that clinic based weight loss programs can be effective.13
Physicians can help promote healthy social norms by visibly engaging in healthy behaviors. On a recent trip to Cuba, I had hoped to see Havana by borrowing one of the million bicycles that had been distributed. However, there were virtually no bikes, bike riders, or bicycle lanes to be seen; and several people told me that bicycles reminded them of earlier economic hardships. In many countries, walking and bicycle riding are regarded as lower class behaviors. Boston celebrates the example set by Paul Dudley White, probably the most famous cardiologist in America and personal physician to President Eisenhower, who rode his bicycle daily to Massachusetts General Hospital into his 80s. The city named a bike path in his honor, and it is currently expanding its bicycle parking facilities. Dr White may have saved more lives by his bike riding than by putting stethoscope to flesh.
Cite this as: BMJ 2013;346:f1777
Competing interests: The author has completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned; not externally peer reviewed.