Malnutrition is an "invisible crisis" - ignored by development agencies and governments. Taken more seriously, argues Lawrence Haddad, Director of the Institute of Development Studies in Sussex, it could be eradicated in 20 years.

I was in India and I asked a group of journalists, "In your opinion, what percentage of the children in your country are malnourished?" They said 20%. The rate is, in fact, twice as high.

This surprised them.

They were alarmed when I told them that India's celebrated economic growth is not doing much to reduce child malnutrition.

And they were speechless when I told them India has a higher rate of child malnutrition than sub-Saharan Africa.

Sub-Saharan Africa has not done any better in terms of progress on child malnutrition. In fact, the rates of child malnutrition have been stuck at about 40% for the past 30 years.

We have to get more political about malnutrition reduction

I want to tell you what malnutrition is, why I believe it matters so much, why it is so persistent - even in countries experiencing rapid economic growth - and what we can do about it.

Most people think malnutrition is all about not having enough food or enough of the right kind of food to eat. This is a big part of the story. But there are many other links in the chain.

If children are drinking dirty water or are playing in areas where people are defecating in the open, diarrhoea will ensure that the nutrients are not absorbed and that appetite will be depressed.

If children do not receive enough attention from parents and carers, they will fail to receive the stimulation and interaction that helps convert food intake into growth.

So dealing with malnutrition means fixing all the links in the chain - food, health, sanitation, water and care.

The problem starts for some children even before they are born. Their mothers are malnourished and their bodies cannot cope with the demands of pregnancy leaving their babies malnourished in the womb. These babies are born malnourished. And the deprivations that children face early on, if not corrected within the first 1000 days after conception, will be locked in for life.

This is because in pregnancy, and during a child's first two years, the key software of life is being laid down - the immune system and cognitive functions to name but two.

For example, we know that children who are malnourished at the age of three go on to do less well in school and are more likely to die from infection. As adults they earn lower wages, are much more likely to live in poverty, and are at greater risk of the diseases of middle age such as diabetes, heart disease and hypertension.

Most malnourished children appear healthy - there is no obvious distress

At a human level, this is tragic. At a national level this has serious consequences for economic growth, poverty reduction and social mobility. In essence, countries that pursue routes to development that neglect nutrition are building on quicksand.

So we need to focus on what works to reduce malnutrition.

Broad-based economic growth helps, but is not a panacea. Nutrition will not just take care of itself. Rising income needs to be guided towards investment in policies that work.

We know that breastfeeding is vital for child growth in environments where water is not clean, and where nutrients are in short supply.

We know that handwashing with soap helps prevent diarrhoea. We know that fortifying flour and salt with key vitamins and minerals bolsters nutrient intake for those with low quality diets. We know that deworming improves nutrient absorption by the gut.

So if we know the causes of malnutrition, the terrible toll it exerts on people and on societies, and what to do about it, then we may wonder why it is so persistent.

A major reason is that malnutrition is an invisible crisis.

We are all familiar with pictures of children who are obviously malnourished - we can see their bones through tightly-stretched skin, their eyes are glazed, their hair thinning, their stomachs bloated. They are in obvious distress and seeing them first hand is a chastening experience.

But the truth is that most malnourished children appear healthy. There is no obvious distress and they do not seem thin.

Image caption Haddad's children are from Cambodia - where malnutrition is a big problem

My wife and I adopted our daughter from an orphanage in Cambodia 11 years ago. At that time our daughter was malnourished, but not in ways that were obvious to her excellent carers or to us.

When we went back to Cambodia 18 months later to adopt our son, the orphanage staff who remembered our daughter couldn't believe how much she had grown in 18 months. Most forms of malnutrition are invisible.

This invisibility means that parents, community health workers and politicians are unaware of the extent of the problem.

Find out more Lawrence Haddad's essay is part of the BBC Radio 3 series Why Poverty

It will be broadcast on Thursday 29 November at 22:45 GMT, Listen to the programme on iPlayer

Another reason for malnutrition's persistence is that many things need to fall in place to reduce it. Giving children better-quality diets is undermined if they have chronic diarrhoea.

Breastfeeding is difficult to do if women are expected to work long hours in garment factories. If children are more likely to get sick rather than better when they visit a low-quality health facility, then the impact of better sanitation is going to be blunted.

So, every link in the nutrition chain needs to be strong. And this is a massive challenge. Nutrition often gets left out of the equation.

This was really reinforced by a presentation I attended by a dynamic non-governmental organisation operating in South Asia.

I asked the head of the NGO why they it wasn't doing more in nutrition. He said: "We would like to, but there is no one to argue with". Nutrition is everybody's business, but nobody's responsibility.

So in the face of all these challenges, is the lack of progress in reducing malnutrition inevitable? Absolutely not. There are success stories to inspire and sustain us.

Image caption Clean water is part of the package of what's needed to reduce malnutrition

Fundamentally we have to make nutrition visible, we have to help governments become more responsive and we have to find ways to act in concert for nutrition.

Ultimately we have to get more political about malnutrition reduction.

And the success stories point the way.

Brazil's Zero Hunger programme was driven by the values of that country's labour movement, by electoral politics, and by the personal conviction of then President Lula, someone who had known poverty and hunger as a youngster.

We can eradicate malnutrition in 20 years - I really believe that with all my heart

In Vietnam, the success in reducing malnutrition was fuelled by economic growth, but also by an ethos that reducing inequality mattered and this led to important investments for the poorest.

In Mexico, a successful cash transfer programme made the receipt of money conditional on visits to health centres, generating a doubly positive impact on nutrition.

But Peru is my favourite inspiration because it is a citizen-led story. In 2006, a group of Peruvian and international NGOs got together to challenge the presidential candidates to sign a pledge to do something about malnutrition if they were elected.

The NGOs were so effective, even the candidates who had never thought about the malnutrition (and there were plenty of those) had to sign up to the pledge. And when Alan Garcia was elected as president, money, laws and policies were quickly committed to malnutrition reduction.

But governments have many priorities, and not all face elections. Their attention needs to be dragged towards malnutrition.

Image caption It's often hard to tell if a child is malnourished or not

This means recruiting people to social movements - people who will stand up for nutrition, who will not let it drop, who will assume responsibility for leading efforts to reduce it. The Scaling Up Nutrition Movement (SUN) is leading the way.

It is a movement of individuals and organisations who are determined to make nutrition more visible, to raise resources for it, to support governments which do something about it. To not let it drop. It involves many organisations worldwide, including my own.

SUN has been going for two years now, and is beginning to make a difference to policies, thinking and spending. The true test will be whether malnutrition rates actually fall.

There are about 170 million young children who are malnourished, and there are many more adults who are suffering from the terrible legacy of malnutrition early in their own lives.

But we can eradicate malnutrition in 20 years. I really believe that with all my heart.

Why Poverty? on BBC Radio 3 features five speakers on different aspects of the subject of poverty. Lawrence Haddad's essay is broadcast on Thursday 29 November at 22:45 GMT, or listen again on iPlayer

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