Editor's note: This story contains detailed descriptions of how starvation affects the body.

Famine has been a threat to humanity since ancient times.

But it wasn't until the end of World War II that scientists began to investigate what starvation actually does to a person's body.

Now aid advocates are calling for those lessons to be applied to today's food emergencies including the crises in Sudan, Gaza and Haiti.

Lessons from World War II

To understand why, Alex de Waal, a social scientist at Tufts University who specializes in famines, says you need to go back to an episode that sparked modern study of the subject: The moment at the end of World War II when Allied forces liberated the concentration camps that the Nazis had set up to exterminate Jews and kill millions of others.

The survivors of these camps were emaciated.

"American and British soldiers rushed to feed [them]," says de Waal. "Then had seen to their dismay that many of them actually perished."

It turned out starvation had thrown the survivors' biological functions so out of whack, their bodies couldn't handle starting up regular eating.

"It's called the re-feeding syndrome," says de Waal.

In the years since, researchers have uncovered a lot of the reasons behind it. For instance, when someone is suffering from severe acute malnutrition, "blood sugar levels and electrolyte levels can be volatile," says de Waal. "And simply feeding regular foodstuffs can actually upset those balances" – with sometimes deadly consequences.

Scientists also discovered some long term impacts of extreme malnutrition by studying another grim chapter of the Second World War: A famine during Germany's occupation of the Netherlands that's often referred to as the Dutch "hunger winter," when the Nazis blocked food supplies. Many of the survivors participated in follow-up studies for decades. The findings, says de Waal: "The children who were very young when they suffered malnutrition grew up stunted — they were appreciably shorter than their elder or younger siblings."

They also showed cognitive deficits, did less well in school and went on to have more health problems as adults.

By the 1980s additional research on brain development helped explain why young children are so vulnerable to this kind of lasting effect, says Anu Narayan, a senior adviser at UNICEF who coordinates its response to food emergencies affecting children.

"We now know that, really for children, under two years of age is when you're forming most of your neural pathways," says Narayan.

And a young child's stomach is very small.

"So the frequency with which they need to eat, and the quality of nutrition with each of the foods that they're eating, needs to be higher."

This means that even in the earliest stages of a food crisis, as families shift from consuming vegetables and proteins toward grains that are cheaper but less nutritious, "the child starts losing weight pretty rapidly."

It's the symptom of acute malnutrition often referred to as "wasting."

"That's when we see the quietness in the children. They'll become very, very quiet," says Narayan.

Their bodies are reserving energy for only the most basic functions.

Soon, even those bodily functions start to break down – often beginning with the regulation of fluid, says Narayan. "Children's bellies will get distended. There is accumulation of fluid in their feet and their extremities."

Their immune system also begins to suffer, and children often succumbs to diarrheal and respiratory infections.

They become too weak to stand up.

"At that stage," says Narayan, "they absolutely need medical care."

And aid groups have gotten really skilled at providing that kind of care.

For example, de Waal notes, in 1974 there was a massive famine in Bangladesh. In the aftermath, "nutritionists in South Asia developed very low-cost technologies for providing therapeutic feeding and salts and sugars for malnourished children." By the 1990s, he adds, clinicians had developed sophisticated protocols for how to use them.

Why help is now harder to give

Today, says de Waal, there's a new challenge: In an increasing number of hunger crises, aid workers who can provide that kind of specialized care are unable to get in due to ongoing conflicts.

UNICEF's Narayan agrees. Right now, she says, "the largest number of children at risk is in Sudan."

World experts project that in Sudan, nearly 4 million children under age 5 will suffer from acute malnutrition this year. And 730,000 of them will reach the life-threatening stage.

Also worrying, says Narayan is Northern Gaza, because of how quickly malnutrition has spread through the population. A data team led by UNICEF estimates that more than 21,000 young children there are now acutely malnourished — with about 4,400 at a point where, without medical intervention "they will not survive."

In short, says Narayan, for all the scientific progress on bringing people back from the brink of starvation, "when our access is limited, those are the children that we're likely to lose."

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