Malnutrition remains a scourge on the planet. Over 800 million people do not have enough food. If they don't die, they are more prone to disease and they have less energy to work. Extreme malnutrition in children causes long-term brain damage, making it harder for them to earn a living.

Poverty and hunger go hand in hand. Often poor people cannot afford sufficient food, which undermines their capacity to sustain a livelihood, leaving them even more under-fed.

There is much more to food, of course, than feeding the poor. It is central to consumer lifestyles, and as such – in the West – a significant source of identity.

Arguably, though, food insecurity is the most important moral challenge facing the world. Using the UN Food and Agriculture Organisation's definition, food insecurity occurs when people at some time do not have 'physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.'1Quoted by P. J. Gregory, J. S. I. Ingram & M. Brklacich, 'Climate change and food security', Philosophical Transactions of the Royal Society, 360 (2005), p. 2141.

World population growth has been slowing, which has eased the pressure on food resources. In 1965-70 the growth rate reached an all-time high of about 2.0% a year, and then declined to 1.2%. This decline has been unprecedented because it has been caused largely by voluntary reductions in procreation.2Joel E. Cohen, ‘The Future of Population’ in Richard N. Cooper & Richard Layard (eds.), What the Future Holds. Insights from Social Science, Cambridge, Massachusetts: MIT, 2003, p. 36.

By the late 1990s it became clear that across the world people were choosing to have fewer children. Families of five, six or eight were becoming less common.

UN demographers suggest that if the percentage rate of population increase continues to fall as it has since the early 1970s, after 10,000 years of almost uninterrupted, exponential growth, the world population will stabilise by around 2050. We are witnessing the 'most staggeringly important shift' in world demographic trends.3Colin Tudge, So Shall We Reap, London: Penguin, 2003, p. 25.

Despite the slower pace of growth, current trends are adding 77 million people to the global population a year – equivalent to a country larger than the UK. The world's population grew from a little over 2.5 billion in 1950 to just under 6.7 billion in 2007 (see chart above).

Six countries will account for half the annual increase in global population from 2005 to 2010 – India, China, Nigeria, Pakistan, the USA, Indonesia and Bangladesh. The American figure is due mainly to high immigration, which puts the US on a different demographic path to most of the developed world.4World Population Prospects: The 2006 Revision, New York: United Nations, 2007.

The planet has been unable to feed its growing population. True, agricultural output has more than kept up with population growth – due, for example, to:

The global supply of food calories per person rose from 2420 kilocalories (kcal) per day in 1958 to 2808 kcal in 1999.5Bernard Gilland, 'World population and food supply. Can food production keep pace with population growth in the next half-century?', Food Policy, 27 (2002), pp. 47-48. The proportion of undernourished people in the developing world fell from 20% to 17%.

Yet despite this huge achievement, the figures are not as encouraging as they might seem:

For years the world had been making slow headway against hunger. Has the trend now been reversed?

The International Food Policy Research Institute's Hunger Index shows that since the mid 1980s large parts of the Andean region in South America, African countries like Ghana, Mozambique and Angola, and South Asia have begun to escape the vicious cycle of poverty and hunger. But trends have been less encouraging in sub-Saharan Africa as a whole.7Doris Wiesmann, 2006 Global Hunger Index. A Basis for Cross-Country Comparisons, http://www.ifpri.org.

The rich have been over-eating while the poor have starved. Is this significant? Some argue that poverty is the root cause of hunger. If you could get rid of poverty you would eliminate hunger. The eating habits of the rich have little to do with it. Others say that over-eating by the rich makes it much harder to reduce both poverty and hunger.

Over 1 billion adults are overweight, 25% more than the number of people who are under-fed. Among the overweight are at least 300 million who are clinically obese.8'Overweight and obesity', World Health Organisation, http://www.who.int (accessed 13 December 2006).

In the USA, for example, the number of overweight adolescents trebled between 1980 and the early 2000s. Thirty percent of US adults aged 20 and over – some 60 million people – were clinically obese in the mid 'noughts'.9'Overweight and obesity', 4 December 2006, Centers for Disease Control and Prevention, http://www.cdc.gov.

Obesity is not just a problem for the West. Ten percent of Chinese were judged overweight or obese in 1995: by 1999 the figure was 15%.10Colin Tudge, So Shall We Reap, London: Penguin, 2003, p. 111.

Excessive body weight is largely a 'disease of affluence', even though many of those afflicted are among the poor in wealthier countries. It stems partly from lack of exercise, as more people do sedentary jobs in the service sector.

But it is also due to changes in diet. As poor people grow richer, they eat more meat. 'The general shift towards meat (and the saturated fat that comes along with it) is the greatest transition of modern times both in nutrition and in agriculture.'11Colin Tudge, So Shall We Reap, London: Penguin, 2003, p. 139.

As a rule of thumb (though experts are divided), an individual requires an average of at least 40 grams of animal protein per day. Almost three-quarters of the world's population live in countries where animal protein consumption is less than 30g. Just 16% of people are in countries – mainly the West – where consumption averages 50 to 80g.12Bernard Gilland, 'World population and food supply. Can food production keep pace with population growth in the next half-century?', Food Policy, 27, 2002, pp. 50-51.

Richer countries are eating more meat than they need. Land is being used to support this surplus livestock instead of growing crops for human consumption. If land was switched from meat to grains for human food, many more people could be fed. Food prices would be kept lower, helping the poor.

It is often pointed out that the world already produces enough to feed its population. The global supply of food calories (around 2800 kcal per person per day) would be sufficient for everyone if the food was equally distributed. But because more affluent people tend to eat more than they need, the poorest go without.

Tackling food shortages has become an international priority. In 1996 the Rome World Food Summit set a target of halving the number of undernourished people by 2015. The United Nations Millennium Summit, in September 2000, set a less ambitious – but still stretching – target of halving the proportion of people who suffer from hunger by 2015.

With the other Millennium goals (including targets for extreme poverty, education, gender equality and health), this has galvanised action to meet the needs of the poor.

Though there is plenty of debate over specific strategies, communities of experts are widely agreed on what should be done about hunger. A twin-track approach is necessary.13State of Food Insecurity in the World 2006, Rome: Food and Agriculture Organisation, 2006, p. 6.