As developing countries struggle to reduce hunger, some are also facing the growing problem of obesity.

A 1999 United Nations study found that obesity was increasing in all developing regions, even in sub-Saharan Africa, where hunger is still rife. In China, the number of overweight people rose from less than 10 per cent to 15 per cent in just three years. In Brazil and Colombia, the figure is around 40 per cent - on a par with several European countries.

Unfortunately, weight gain can mask underlying deficiencies in vitamins and minerals, which afflict both the underfed and the overfed. Two of the most common are iron deficiency anaemia and vitamin A deficiency, which continues to cause widespread blindness in children under five years old.

To try and counter this, the Food and Agricultural Organization of the UN (FAO) stresses that nutrition is a question of quality as much as quantity, and aims to promote a diverse diet including traditional foods, which are generally balanced.

Why is obesity a problem in the developing world?

Obesity in the developing world is a result of a series of changes in diet, physical activity, health and nutrition, collectively known as the 'nutrition transition'.

For a start, increasing import of foods from the industrialised world means that traditional diets featuring grains and vegetables are giving way to meals high in fat and sugar.

Urban areas have higher rates of obesity because cities offer a greater range of food choices, generally at lower prices. And as more and more women work away from home, they may be too busy to shop for, prepare and cook healthy meals at home.

In rural areas, increased mechanisation on farms has reduced physical activity. Moreover, many farmers have given up subsistence farming of multiple crops that provide a more balanced diet in favour of a single, high-yielding cash crop.

In many countries, being overweight has now reversed its meaning. In Mexico and Brazil, overweight used to be a sign of wealth, but now that the poor have access to a diet high in fat and sugar it often signals poverty. The elite, who have better access to nutrition education, healthy foods and exercise facilities, tend to be slimmer.

But cultural context is important: in South Africa it has been suggested that overweight people may be deterred from losing weight because thinness is associated with HIV/AIDS, a disease with a high degree of social stigma attached to it.