Richard Smith: We don’t know what to eat

Richard SmithWHO is currently setting priorities for research in chronic or non-communicable disease, and generally the first research question is “Will what has worked in rich countries work in low and middle income countries?” We know, for example, what to do to reduce deaths from heart disease and how to reduce tobacco consumption. But interestingly when it comes to nutrition we don’t know what to recommend. The advice for rich countries may be wholly inappropriate for poor countries.Let’s start with fat. WHO recommends that fat should not be more than 15-30% of dietary energy and saturated fat 10%. These recommendations were made years ago, when fat accounted for well over 30% of the diet in rich countries. Those who made the recommendations knew well that lower fat consumption meant lower rates of heart disease right down to countries like India, where fat was well under 10%. Indeed, you need a certain level of fat consumption for smoking and hypertension to have their damaging effects—they needed fats to create the atheromatous plaques. Similarly intakes of saturated fat under 5% are good for health.

The 30% figure for total fat and 10% for saturated fat were pragmatic, much better than fat consumption in most rich countries but achievable. The lower figure for total fat was equally pragmatic: at that time many countries had a figure for total fat close to that and very little heart disease. Unfortunately these figures have become fixed in the heads of policy makers with them thinking that 30% fat and 10% saturated fat are targets and that there is no need to worry until they are reached. In fact low and middle income countries should probably aim for 15% total fat and 5% saturated fat, although we don’t know for sure.

Then there is the problem of sugar. WHO recommends that added sugar shouldn’t be more than 10% of dietary energy, but sugar and fat probably interact in ways that we don’t fully understand. Thus countries in the Caribbean that where sugar intakes are over 20% have obesity rates far higher than would be expected from their total fat intake. Probably what matters is the “energy density” of foods: fat and sugar both contribute to energy density as does refining foods. We don’t know what levels of energy density to recommend for poorer countries, but the level of sugar intake should probably be 5% of dietary energy not 10%.

Another complication is that many people in the poor world may be “supersensitive” to the effects of fat and sugar. We know that South Asians have much higher rates of diabetes and obesity than Europeans for the same intake of fat. It’s probably true for Mexicans and perhaps other populations as well. This may well be the result of the Barker hypothesis that those whose mothers were malnourished when pregnant are much more likely to develop diabetes, hypertension, and cardiovascular disease. The brutal reality is that until recently some 40-60% of people in the developing world were malnourished, and the very high rates of diabetes in China might be the result of extensive famine in China decades ago. Probably recommendations on fat, sugar, and salt intake should be more stringent in low and middle income countries.

There are many other unresolved issues in nutritional advice, and the subject is complicated further by usually very poor data on what people actually eat in low and middle income countries.
So the research issues around nutritional advice in low and middle income countries are much more complicated than simply finding ways to implement what we already know: there’s a great deal that is hugely important that we don’t know.