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.
One tonne of human biomass corresponds to approximately 12 adults in North America and 17 adults in Asia. If all countries had the BMI distribution of the USA, the increase in human biomass of 58 million tonnes would be equivalent in mass to an extra 935 million people of average body mass and have energy requirements equivalent to that of 473 million adults”.
The average adult body mass (kg) in different regions in the world in 2005 was as follows: Asia 57.7, Europe 70.8, Africa 60.7, Latin America/Caribbean 67.9, North America 80.7, Oceania 74.1, World 62.0. The percentage of people overweight (BMI>25) in these regions was: Asia 24.2 per cent, Europe 55.6 per cent, Africa 28.9 per cent, Latin America/Caribbean 57.9 per cent, North America 73.9 per cent, Oceania 63.3 per cent, World 34.7 per cent.
Over one billion people worldwide are currently overweight and the entire population distribution of body mass is increasing in all regions of the world. If this trend is left unchecked, by 2050 increasing population fatness could have the same implications for world food energy demands as an extra half billion people of average body mass living on Earth. On the other hand, if everyone had a BMI under 25, global energy (food) consumption would reduce by an amount equivalent to the food consumption of 298 million average adults.
Increased global demand for food because of body mass increase will probably lead to higher food prices. The more affluent nations have greater purchasing power and therefore the authors speculate that the worst effects of increased food prices will fall on the world’s poor.
Increasing global demands on food are not just caused by increasing population, but also by lifestyle. The biggest increase in population in the coming years will be in sub-Saharan Africa, which is not an area characterised by a high BMI. So, there is little doubt about it – growing fat is not only bad for you, it is bad for everyone.
William Reville is an emeritus professor of biochemistry and public awareness of science officer at University College Cork. See understandingtscience.ucc.ie
