Why poor will pay for fatter world

THE RAPID expandsion of the world’s population raises the problem of how to feed all of these extra mouths. The statistics that are usually presented in this debate concentrate on the numbers of mouths to be fed but take no account of the fact that some mouths eat much more than others.

This latter aspect has now been addressed in research published by Sarah Walpole and others in BioMed Central Public Health . The calculations show that increasing levels of global fatness have dramatic implications for resources needed to cope with the projected increase in world population.

The energy needs of the human body are supplied by the food we eat. The body expends energy both in maintaining the living condition and also in powering physical activity and both of these energy expenditures increase with body mass – an increase in body fat is automatically accompanied by metabolically active (energy-consuming) lean tissue, while the energy required to move the body around obviously increases with body mass.

Walpole and colleagues point out that in ecological studies generally the energy requirements of a species are calculated based on the total biomass of the species, but this aspect has not been emphasised in calculating the consequences of human population growth for the energy (food) required to grow and maintain this extra human biomass. They address this deficiency based on an analysis of the world population in 2005. Body Mass Index and height distribution data were used to calculate average adult body mass for each country. Total human biomass is a product of population size and average adult body mass.

BMI is a number calculated from a person’s weight and height that provides a reliable index of fatness for most people and is used as an index of weight categories that correlate with various health problems. BMI is calculated simply by dividing your weight in kg by the square of your height in metres. Normal BMI range is 18.5 to 25, overweight is 25 to 30 and obese is categorised as a BMI over 30.

The results reported in the paper are as follows (I quote directly because the authors are so eminently concise): “In 2005, global adult human biomass was approximately 287 million tonnes, of which 15 million tonnes were due to overweight , a mass equivalent to that of 242 million people of average body mass .

Biomass due to obesity was 3.5 million tonnes, the mass equivalent of 56 million people of average body mass . North America has 6 per cent of the world population but 34 per cent of biomass due to obesity. Asia has 61 per cent of the world population but 13 per cent of biomass due to obesity.