7.5 What causes different forms of malnutrition?


  • Diets deficient in calories lead to undernutrition.
  • Diets deficient in calories are also often deficient in essential macro-/micro-nutrients, often made worse by poor sanitation and high prevalence of disease – factors that undermine nutrient absorption.
  • Diets adequate in energy but deficient in essential micronutrients have various health consequences including for example night blindness (vitamin A deficiency) and anaemia (iron deficiency).
  • Diets that are high in fats and sugar but low in fruit and vegetables are usually high in energy and therefore associated with obesity.
  • Such diets are also, independent of obesity, associated with non-communicable diseases such as heart disease, and Type 2 diabetes.
  • The links between overconsumption and poor health need to be seen in the context of the diet as a whole, and other lifestyle and socio-economic influences on health.

7.5.1 Undernutrition

Undernutrition is a consequence of energy deficiencies

Hunger is generally a consequence of poverty and insufficient disposable income.

Inadequate food energy leads to low body weight and hunger.

Diets that are inadequate in energy may be inadequate in important macro-nutrients (e.g. protein) and are usually deficient in micronutrients.

Diets leading to hunger and undernutrition are usually:

  • Overwhelmingly grain or tuber based.
  • Lacking in other foods – e.g. fruits and vegetables, legumes, animal products.
  • Lacking in diversity.
  • As discussed at the start of this chapter, inaccessibility of healthy food is only one factor in nutritional problems. Insufficient health care in general and other socio-economic factors such as lack of clean drinking water can exacerbate these problems. For example, diarrhoea-related illnesses can inhibit nutrient uptake, increasing vulnerability to the effects of undernutrition.

7.5.2 Nutrient deficiencies

Nutrient deficiency leads to various problems including, for e.g. anaemia (iron deficiency), night blindness (vitamin A deficiency), goitre (iodine deficiency) neural tube defects (folate), osteoporosis (calcium deficiencies).

Nutrient deficiencies often occur alongside undernutrition, but may also occur when energy intakes are adequate or excessive

7.5.3 Obesity

Overconsumption: diets high in fat, salt and sugar are associated with obesity, Type 2 diabetes and other diseases

High intake of (saturated) fat, salt and sugar are associated with high Body Mass Index (i.e. overweight or obesity), raised cholesterol and raised blood pressure.

Which increase risks of developing:

  • Type 2 diabetes
  • Heart disease
  • Strokes
  • Some cancers

Overconsumption arises from excess energy consumption and can lead to obesity.

Poor diets (independent of obesity) that are high in saturated fats, salt, and sugar, but low in fruit and vegetables are also associated with non-communicable diseases such as chronic heart disease. For more on healthy diets, see Chapter 9.

As such, people can suffer from obesity, from both obesity and non-communicable diseases, or from non communicable diseases (such as heart disease and Type 2 diabetes).

Diets high in meat, especially processed meat, can be high in fat, sugar and salt and have consequently been associated with such diseases.

High intake of sugar is common in many processed foods and has also been linked to obesity and Type 2 diabetes.

However, an association does not mean causation nor does it mean that, for example, meat or processed food consumption are necessarily and/or solely responsible.

Meat can be rich in nutrients and energy and the health risk is relative to consumption levels. In other words, moderate levels of meat can be part of a healthy diet. However increasingly research indicates that processed meats should be avoided and red meat intakes limited.

The links between overconsumption and poor health need to be seen in the context of the whole diet and other lifestyle, socio-economic and genetic factors

Eating habits
High consumption of energy dense foods such as some meats, oils and fats, and sugars is often characteristic of poor eating habits general. As such, the association between these foods and obesity and non communicable diseases must be seen in the context of the diet as a whole. See Chapter 8 for a more in-depth discussion of the links between meat consumption and health.

Socio-economic factors
Lack of access to healthy foods and socio-economic factors such as education can contribute to poor eating habits.

Price gaps between healthy and unhealthy food are increasing in some parts of the world (for example in the UK), potentially making healthy food less affordable for poorer people.

Lifestyle factors
Sedentary lifestyles, smoking and alcohol consumption also contribute to obesity and non communicable diseases. People with unhealthy lifestyles also tend to have poor diets.

Some research has shown that the ill-health effects associated with red meat and processed meat consumption are confounded by lifestyle factors such as generally unhealthy eating patterns, lack of exercise, other negative lifestyle habits, and socio-economic factors.

Processed meats and sugars are often found in fast food and pre-prepared foods, and increasingly these have been shown to be cheaper sources of energy than healthy balanced diets.

Urbanisation is increasing globally, with more people now living in urban environments than rural. On the one hand, obesity prevalence has been show to be higher in cities than rural areas. On the other hand, urban populations are sometimes better educated and there is some evidence (in high income countries) that this leads to lower BMIs and healthier eating habits. However, strong differences exist between high and low income contexts and trends are in flux.