Food Utilization and Nutrition

Although a primary purpose of food is provision of dietary energy, and widely used undernourishment indicators such as FAO's lean heavily on estimates of calorie consumption to estimate food security trends, food is of course much more than just energy. Food also provides protein and various nutrients essential for bodily function, and there is increasing recognition of the important role insufficient intake of these nutrients plays in global illness and death from infectious disease (Black 2003). Importantly, prevalence of micronutrient deficiencies around the world is generally higher than estimates of caloric deficiencies, and alleviating these deficiencies has become a major public health priority.

Table 2.3 lists major micronutrient deficiencies, some of their health effects, and the most recent estimates of their global prevalence. It reveals that estimated prevalences for deficiencies in nutrients such as iodine and zinc are more than twice the FAO benchmark estimates for number of global undernourished. As a result, added together these micronutrient deficiencies account for one of the largest sources of global health loss (Lopez et al. 2006).

Table 2.3 Global prevalence of micronutrient deficiency (http://www.who.int/vmnis; (Ezzati 2004))

Number of global

Percent of population

Micronutrient

Effects of deficiency

deficient (billion)

deficient (%)

Iron

Child and maternal

1.6

25

mortality, reduced

cognitive development

Iodine

Reduced cognitive

1.9

31

development, deformation,

goiter

Vitamin A

Blindness, immune deficiency

0.6 (children

20

<5 yrs)

0.1 (women 15-44)

6

Zinc

Immune deficiency

1.9

31

Most poor households receive what micronutrients they do get through the consumption of plants, with vitamins sourced largely from fruits and leafy greens, and minerals from cereals. For instance, some estimates suggest that 80% of African and Southeast Asian intake of vitamin A comes through fruit and vegetable consumption (Ruel 2001). Meat and dairy products are a primary source of many nutrients in the developed world, but are often too expensive for poor households, and are thus a minor source of micronutrients throughout much of the developing world.

Climate change could directly affect micronutrient consumption in three main ways: by changing the yields of important crop sources of micronutrients, by altering the nutritional content of a specific crop, or by influencing decisions to grow crops of different nutritional value.

There is little published evidence on the effects of climate change on micronutrient content of crops, and also much less evidence on the potential effects of climate change on fruits and vegetable yields compared to that available for cereals. Some studies show that higher CO2 concentrations can lower protein content in various food crops, particularly in the context of low nitrogen inputs (Taub et al. 2008). While the estimated reductions could be relatively modest in magnitude - 10-15% decrease in grain protein content by around the end of century - such declines would be amplified by any yield losses, and would hit hardest in poor areas where nitrogen application rates are low and where crops constitute a primary source of dietary protein.

Beyond direct effects on yields, climate can also shape the decisions farmers make about what crops to grow (Rosenzweig and Binswanger 1993), and thus could potentially alter planting decisions in ways that alter micronutrient availability. For instance, in the poor soils and highly variable climates of much of central and western Africa, starchy tubers such as cassava and yam often dominate cropping systems, in no small part because of their ability to achieve at least some yield in the worst weather years. Unfortunately, such crops are also very poor sources of both protein and micronutrients, and to the extent that they are favored in future climate relative to cereals as a source of dietary energy, nutrient consumptions could decline.

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