Obesity is becoming more common among poor city dwellers in Africa because of easier access to cheap, high fat, high sugar foods, scientists said on Tuesday.

Researchers looking at data from seven African countries found the number of people overweight or obese increased by nearly 35 percent between the early 1990s and early 2000s and the rate of increase in obesity was higher among poor people.

Given the chronic nature of most diseases associated with obesity and by extension the huge cost of treatment, the prospects look grim for the already under-funded and ill-equipped African health care systems unless urgent action is taken, said Abdhalah Ziraba, who worked on the research with the African Population and Health Research Center in Nairobi.

The study, published in the BioMed Central Public Health journal, found that while rich people in urban areas of Africa were more likely to be overweight or obese than others, the rate of increase in obesity was higher among the poor.

The data chimes with findings from the World Health Organization, which said in October that being overweight has now overtaken being underweight among the world's leading causes of death.

Despite being the least urbanized continent, Africa's population is becoming increasingly urban and its cities are growing at unprecedented rates, Ziraba said in the study.

In spite of rampant poverty in urban areas, access to cheap foods with a high content of fat and sugar is commonplace.

Obesity levels are rising across the world and threatening to overwhelm health care systems and government health budgets with the costs of handling the high number of cases of diabetes, heart disease and cancer that being overweight can cause.

The number of people with diabetes -- one of the major chronic diseases caused by excess weight -- is already reaching epidemic levels, with an estimated 180 million people suffering from it around the world.

A second study published on Tuesday focusing on the problem in England found one in 10 children there will be obese by 2015, with the poorest at far greater risk than the rich.

Researchers said the gap between the most and least well off sectors of society was set to widen, with more children from poor and less educated households caught in the obesity trap.

If trends continue as they have been between 1995 and 2007 in 2015 the number and prevalence of obese young people is projected to increase dramatically, and these increases will affect lower social classes to a larger extent, Emmanuel Stamatakis, of the epidemiology and public health department of University College London said in the study.

Stamatakis and fellow researchers looked at obesity trends in England from 1995 to 2007 in children and young people and then predicted obesity levels in 2015.

Obesity among all boys aged 2 to 10 in 2015 was forecast at 10.1 percent, but the worse case scenario could see a prevalence of 13.5 percent. Among girls the figures were 8.9 percent and 9.3 percent respectively, the researchers said in their study in the Journal of Epidemiology and Community Health.

For comparison, in the United States, which has a severe obesity problem, more than 26 percent of Americans are obese and nearly a third rated as overweight.