The scourge of hidden hunger, also known as vitamin and mineral deficiencies, has been highlighted by a major international research group.
In its Global Hunger Index report, which identified 16 countries with "extremely alarming" or "alarming" hunger levels, the International Food Policy Research Institute also stressed the challenge of fighting the often overshadowed form of malnutrition that occurs when people do not absorb enough nutrients.
"More than two billion people worldwide suffer from hidden hunger, more than double the 805 million people who do not have enough calories to eat," the Washington-based institute said in its report.
"This shortage in essential vitamins and minerals can have long-term, irreversible health effects as well as socioeconomic consequences that can erode a person's well-being and development."
"By affecting people's productivity, it can also take a toll on countries' economies."
Hidden hunger can be caused by a poor diet, health problems such as diseases, infections or parasites, and increased needs for micronutrients during certain life stages, such as pregnancy or infancy, the report said.
Many developing countries face the so-called "triple burden" of malnutrition -- undernourishment, micronutrient deficiencies and obesity.
The problem also exists in higher income countries and even an obese child can suffer from hidden hunger.
According to the report, nutrient deficiencies cause an estimated 1.1 million of the 3.1 million child deaths that occur each year as a result of undernutrition.
And nearly 18 million babies are born with brain damage annually due to iodine deficiency.
The report offered a number of solutions to the problem, such as diversifying diets or adding tiny amounts of vitamins and minerals to commercial staple foods or condiments during processing.
Biofortification -- breeding food crops using conventional or transgenic methods to increase their micronutrient content -- is another solution, it said.
"Biofortified crops that have been released so far include vitamin A orange sweet potato, vitamin A maize and cassava, iron beans and pearl millet, and zinc rice and wheat."
Providing vitamin supplements to children could also help reduce hidden hunger, the report said.
Aside from this form of malnutrition, the report said hunger levels in the world were still "serious", despite a marked improvement in developing countries.
Burundi and Eritrea were both classified as having "extremely alarming" hunger levels, while most of the countries with "alarming" scores were in Africa, south of the Sahara.