Hidden hunger includes both low weight for age (excluding acute malnutrition, which cannot be considered hidden), and micronutrient deficiency, which is very often associated to low weight for age. The scale of the problem is huge: one out of six children in developing countries is underweight, that is, 100 million children in total suffer from hunger .
What are the consequences? To start with, 3.1 million children still die of malnutrition every year . The picture is bleak: a shocking 45  to 55%  of childhood deaths worldwide are attributable to under-nutrition. Hunger remains the biggest killer of under-five children. Furthermore, malnourished children are both more likely to contract diseases and to die from them. Of childhood deaths from disease, the following percentages can be attributed to under-nutrition  :
It is important to note that this is not limited to children who are extremely underweight. Though the effect is more pronounced in such cases, if we combine the risk associated with moderate malnutrition with its high prevalence rates, we find that much of the burden of deaths as a result of under-nutrition in young children is attributable to moderate, rather than to severe, malnutrition.
But perhaps the most invisible form of hunger is micronutrient deficiency, which, though not even necessarily associated to low body weight, can seriously reduce span and quality of life. These are some of the consequences of particular micro-nutrient deficiencies :
As for the economic consequences of hunger, start by noticing that it is the main factor in causing childhood stunting, which affects a quarter of all children worldwide . This has got consequences to motor and cognitive development, and to educational achievement, which in turn reduce productivity in adulthood. This and the increased health costs it causes make hunger a heavy burden on the economy. Under-nutrition and micronutrient deficiency cost up to USD2.1 trillion a year to the global economy , and it is estimated that childhood malnutrition costs USD25 billion a year to Africa alone . In contrast, it is estimated that addressing childhood and maternal hunger worldwide would cost only USD10 million .
There has been some progress in reducing hunger over the last decades, with the number of undernourished people having decreases by 17% in the last two decades  but this is widely acknowledged to be unsatisfactory. For example, the stunting of early childhood growth as a result of malnutrition has decreased only 1%  in the last two decades. In comparison, TB cases have declined by 40% , and malaria cases by 30% . Also, the improvements there have been are unevenly distributed geographically: for instance, in North Africa and South Asia the improvements have been modest, and in West Africa, the situation has actually worsened .
Solving this problem will have to involve agricultural partners, governments, and NGOs, and will likely require economic growth and improved social policy in the affected countries. As components of a solution for this problem, the following have been suggested :
Assessing the cost-effectiveness of interventions in these areas is possibly worth investigating. But for now the best opportunity for effective giving to target hidden hunger is micronutrient fortification, as Giving What We Can has acknowledged in recommending Project Healthy Children . Adding important nutrients such as folic acid, iodine, iron, vitamin A, and zinc to staple foods is very cheap, at just a few cents per year per person, and greatly contributes to eliminating the problems caused by micronutrient deficiency. The Copenhagen Consensus has estimated that every UDS1 spent on food fortification results in USD9 benefits to the economy .
Micronutrient fortification is not a complete solution to the problem of hunger, but it seems to be the best place to start. The problem has a large scale and, when we consider the suffering it causes, much more should be done to alleviate it. Hidden hunger needs to be brought to light and approached integrating economic and agricultural policy, education, and large-scale health interventions like micronutrient fortification. If you want to start making a difference today, you can donate to Project Healthy Children here.