People in the villages surrounding Ndélélé in Cameroon cannot afford many of the foods sold in the market, so to supplement themselves they rely on the eru leaf and insects gathered from the forest nearby.

In the early 2000s, this caught the attention of Amy Ickowitz, a scientist doing her dissertation research in the area.

"I was struck by how well-fed people were despite extreme poverty," said Ickowitz. "The children seemed very well nourished in comparison to other places where I had traveled."

More than a decade later, she and a team of scientists from the Center for International Forestry Research used her initial observation to study how living near forests affected nutrition in 21 African countries.

They found a correlation between children's nutrition and how close they lived to areas with tree cover. Although their work is the first of its kind and the findings are preliminary, the researchers suggest that living near forests may mean a more varied diet—one that provides essential nutrients. If the findings hold up, some experts say they suggest interesting possibilities for future research and policy.

"Nutrition clearly contributes to health, and thus a narrative about the importance of land use and management to health could be an interesting one," said Jules Pretty, professor of environment and society at the University of Essex.

Hidden hunger

Malnutrition is the biggest humanitarian problem today, affecting more people than war. Worldwide, about 852 million people — 12 percent of global population — do not consume enough calories, according to the Food and Agriculture Organization.

And calories are only part of the problem. The World Health Organization estimates that 2 billion people, 29 percent of the world's population, are not receiving vital nutrients including iron, vitamin A, and iodine, which come from eating fruits, vegetables and nuts. The organization refers to this form of malnourishment as the "hidden hunger." Its devastating effects have been well-documented.

Hidden hunger can have severe effects on the physical and cognitive development of children and is a major cause of child mortality, according to the World Health Organization. For instance, 100 to 140 million children do not get enough vitamin A. Lack of vitamin A can weaken immunity and delay growth. Lack of iodine, one of the most common forms of hidden hunger, affects 187 million people. The deficiency can cause brain damage.

"One thing that research has shown is that child nutrition, especially during the first one to two years of life, can have large effects on learning," said Paul Glewwe, professor of economics at the University of Minnesota. "If we can design policies that improve child nutrition in the first years of life, we can have big 'payoffs' in terms of higher learning and other life outcomes later in life."

The solution to this problem is not just more food, but more variety. Forests, it turns out, may help provide that variety.

Why trees change the equation

Ickowitz and her team combined two kinds of data in their study: Demographic Health Studies conducted by the U.S. Agency for International Development (USAID), which gathers information about population and diet in Africa, and tree cover data from the Global Land Cover Facility at the University of Maryland. They saw that children living in landscapes with high tree cover tended to have more varied diets.

But improving nutrition is not as simple as growing or saving forests.

"Dependence on wild foods is a viable strategy for people when population density is low," said Ben Phalan, a research fellow in the Conservation Science Group at Cambridge University. "However, it is not possible in most cases to support high human population densities without switching at least partly to agriculture, not least because harvesting wild species often becomes unsustainable beyond relatively low levels of exploitation."

Because the research is based on correlations, Ickowitz and her team could not determine the exact cause, if any, of the relationships between tree cover and increased fruit and vegetable consumption. However, they propose three possible explanations why tree cover might lead to more varied diet.

First, children who live near forests may have increased access to wild foods, including fruits and leafy greens such as the vitamin rich Safou fruit. Second, farmers who practice agro-forestry may get increased nutritional benefits from planting fruit and nut trees. Finally, the types of agricultural practices that are more common near forests, like shifting cultivation, tend to favor a wider variety of crops.

"It is not clear how much of the effect is due to tree cover in farms, agroforests and plantations, and how much to tree cover within forests," said Phalan. "So it tells us something about the relationship between tree cover and diets, but not about the relationship between forests and diets."

Ickowitz and her team are now studying where people in African countries get their fruits and vegetables to understand the pattern they observed. Markets and wealth may play a role.

For now, though, the team suggests that approaches to food security that focus solely on calories and staple foods may fall short. Further research on the different factors that contribute to increased dietary diversity could help scientists and policy makers decide where funding needs to go to fight malnutrition.

It could also help inform decisions about land use. About 36 football fields worth of forests are cleared every minute to make room for agriculture, according to the World Wildlife Fund, and this study suggests that solutions to malnutrition are complex and should be better understood before clearing forests.

"[We hope] that policy makers will start valuing forests as part of the solution to problems of food security and as not an obstacle to food security," said Ickowitz.

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