Nairobi — What is hunger? To most people hunger is just a minor physical sensation felt a few times a day.

But to over a billion people worldwide, it's a lot more than that. It's a chronic state. That is, each of these people feel hungry almost all the time, every day. But it's even more than that. The "trap" of hunger and poverty means most of these people have to undergo an enormous struggle to break from this cycle of perpetual hunger.

If they are severely undernourished, their cognitive and physical capacity is affected, making it much harder for them to develop the skills needed to overcome hunger.

Almost every factor confronts these people: Their natural environment, their social and political environments, and the economic structures functioning around them. Their struggle becomes one of mental endurance as well as sustenance. I once went five days without eating, but I always knew I'd be able to eat at the end of it, so while I became very thin and tired, I was never mentally weakened.

Chronic hunger leaves no such comfort; it's an unending sufferance. Chronic hunger is as psychologically debilitating as it is physically emaciating. Next month, the UN will meet in New York to review progress on the Millennium Development Goals. MDG 1, to halve between 1990 and 2015 the proportion of people suffering from hunger, has already been an embarrassing failure.

There were 817 million hungry people in 1990. Today there are over a billion. So why have we failed so spectacularly to solve the problem of hunger? What has caused hunger? How can we solve global hunger?

Humans have never conquered hunger. Look back through the records of ancient Rome, China, the Mayans -- all were beset by food crises that led to famine and starvation.

But today, as rich countries' supermarket shopping aisles are stuffed with thousands of foodstuffs, a phantasmagoria of branded edible products, our race has walked on the moon and we have instantaneous communication technology, how can we still have failed to master hunger?

The problems lie in our social, political and economic systems; most were not designed for the purpose of sharing goods equitably. The "smaller" our world appears to have become through miraculous transport and communications achievements, the more tragically evident this fact becomes.

And despite the supposed dominance of liberalism in the international system, we nevertheless remain unable to re-organise these systems according to all peoples' equal needs. This failure is ultimately an ethical one.

Before trying to prescribe solutions to it, we should understand that hunger is not a distinct entity; there is no single hunger, but multiple hungers, of diverse forms, severity, duration, origin and consequence.

Hunger can be seen as a nested concept, within the larger bracket of "food insecurity," and part of a process that leads to undernutrition, or clinical forms of hunger, resulting from serious deficiencies in one or a number of nutrients (protein, energy, vitamins and minerals).

A food insecure person can become hungry if their food availability, access or utilisation fails. This is likely to happen if they are vulnerable, given that physical, environmental, economic, social and health risks threaten the availability, access or utilisation of food.

Decades of research and indeed the lessons of history have shown that hunger does not necessarily stem from inadequacy of food output and supply, as alarmists from the production side and neo-Malthusian development theorists are prone to propagate.

The warnings that world food output is falling behind population growth not only fail to address the causes of hunger, but also blind us to the complex range of causes that demand our attention. Steve Wiggins from development think tank ODI says, "It's never about food availability [production]. The big issue is distribution." Wiggins adds, "People go hungry because they are poor."

Wiggins proposes poverty reduction and a focus on child healthcare as macro and micro level solutions to hunger. Wiggins' first proposition is questionable, given that macro increases in income have not translated into proportional decreases in hunger.

Oxfam's Chris Leather describes political will, community-based participation, good governance, fulfilment of ODA pledges, social protection, appropriate humanitarian assistance, international systems, multilateral collaboration and accountability mechanisms as priority areas for solving hunger.

The list is exhaustive, and narrated with weariness, so as to make these concepts mundane, like a shopping list. These are the axioms of nucleated development policy sects, whose mantras become obtuse tautologies, devoid of meaning. Hunger is always highly localised; such all-encompassing prescriptions serve little purpose.

Amartya Sen, perhaps the world's most renowned student of hunger, has maintained the need for a nuanced analytical approach, yet even he veers into prescriptive overload.

Economic growth, expansion of gainful employment, diversification of production, enhancement of medical and health care, safety nets for vulnerable women and children, increasing basic education and literacy, strengthening democracy and the media and reducing gender inequalities are, he argues, the right causal avenues to address when tackling hunger. But where do you start?

Sometimes I think it simply boils down to ethics. Gandhi once said there is more to life than increasing its speed. Our political, economic and ethical systems incentivise technological development and individual wealth over genuine human equality. If we really wanted to address people's hunger, we would change these systems, and the systems of thought that underpin them.

Hunger is becoming one of the great moral failures of the 21st century.

Harry Johnstone is a policy officer for the World Food Programme in Kampala, Uganda. The views expressed here are his own and should not be attributed to WFP.