The proportion of adults who fall below the cut-off for underweight (BMI < 17) and above the cut-off point for obesity (BMI ≥ 30) is shown in Table 13.2. The poorest countries are therefore still grappling with underweight and the developed countries with overnutrition issues such as obesity. Despite the widespread efforts to reduce the extent of obesity and its associated diseases, their prevalence continues to increase.

Table 13.2 Percent below and above BMI cut-offs: adults in 2000

	BMI < 17 (underweight)	BMI ≥ 30 (obese)
Least developed (n = 45)	8.9	1.8
Developing (78)	6.9	4.8
Transition (27)	2.4	17.1
Developed market (24)	1.6	20.4

Source: WHO 2002 (http://www.who.int/nut/db_bmi.htm; accessed 9 September 2002)

The major micronutrient deficiencies worldwide are iron, iodine, and vitamin A. Approximately 2 billion individuals worldwide are iron deficient, 750 million are iodine deficient and 160 million are vitamin A deficient. In developed countries certain other potential micronutrient deficiencies have become more of a concern in recent years. These include folate deficiency in women in relation to spina bifida in a small percentage of newborns, but also in men and women in relation to elevated plasma levels of homocysteine levels related to coronary heart disease.

Anaemia prevalence is used as a proxy for iron deficiency. In industrialized countries this is likely to be a close approximation, but in the developing world anaemia can occur due to factors other than iron deficiency such as malaria, other parasitic infections, current infectious diseases and other pathologies. Anaemia is a serious problem throughout the lifecycle, both in industrialized and developing countries where the prevalence is over 10% and 14% respectively. It is a particular problem for pregnant women who have high haematinic needs, with a prevalence of almost 20% in industrialized countries and almost 60% in developing countries (see chapters 5 & 8).

One of the most visible manifestations of iodine deficiency is goitre (see chapter 5) and this is used as one indicator of deficiency. The overall world prevalence of goitre is 13%, highest in the African region (20%), followed by Europe (15%), SE Asia (12%), Western Pacific (8%) and the Americas (5%)

Severe vitamin A deficiency (VAD) manifests itself clinically as night blindness and corneal xerosis (see chapter 5). Sub-clinical vitamin A deficiency in pre-school children is defined as serum retinol level <0.7 μmol/L. While clinical signs of vitamin A deficiency are relatively rare (estimated 3 million pre-school children), subclinical deficiency, which increases the likelihood of morbidity and mortality in pre-schoolers, is estimated to be widespread (75–250 million) in developing countries only, and most likely found in South Asia and sub-Saharan Africa.

In addition to anthropometric data and patchy micronutrient status data, food balance sheet data are available for most developing countries for most years. These data are compiled by the UN’s Food and Agriculture Organization (FAO) from food production, food trade and food aid flows. The foods are converted into calories and divided by population size to give the dietary energy supply (DES) in calories per capita. The DES numbers are converted to estimates of the percentages of individuals without adequate access to food: 17% in developing countries, with the highest in sub-Saharan Africa (33%), and 7% in countries in transition.

Some of the factors behind the tragic decline in nutrition status in sub-Saharan Africa include: closed markets in the developed world (especially the EU) for their exports; HIV/AIDS generating a health and development crisis and undermining the ability to respond to the crisis; wars and refugee movements; military expenditure; drought; crop and livestock disease; many ecosystems making technology diffusion and adaptation difficult; under-investment in agricultural research; no economy serving as regional driver (Nigeria and South Africa’s under-whelming economic performance); low levels of human capital in terms of literacy; declining terms of trade for natural resources on world markets; low population densities leading to thin infrastructure and market institutions.

Analysis of causes

Figure 13.1 summarizes the causes of undernutrition in children, but much of this scheme is also relevant to adults. The causes lie at several levels (immediate, underlying and basic) and in many sectors (agriculture, health, water, education, and employment, etc). It is important to understand the causes of malnutrition to guide the interventions needed to improve nutrition status. The following examples focus first on undernutrition, followed by similar analyses that can be made for the chronic nutrition related diseases (overnutrition).

Figure 13.1 The food–care–health model of undernutrition.

Immediate causes

The most immediate causes of malnutrition in young children (and also adults) are poor diet and infection (see chapters 6 & 8). If the child is not able to ingest enough food, both in terms of quantity and quality that can be used for growth and development, then malnutrition occurs. Infection and an inadequate diet reinforce each other as infection reduces the intake of nutrients by diminishing appetite, inhibiting nutrient absorption, and increasing nutrient requirements for combating infection while poor diet reduces the effectiveness of the immune function.

Equivalent immediate causes of diseases of affluence are excess intake of food, eg through bottle feeding, snacking, high fat foods, and lack of exercise.