Book: Nutrition: A Very Short Introduction (Very Short Introductions)

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Severe under-nutrition is generally associated with developing countries where food is in short supply, affecting some 162 million people worldwide. In India, 40 per cent of the population is underweight, and a further 10 per cent is severely malnourished. In sub-Saharan Africa, 10 to 20 per cent of the population of different countries is underweight. Even in developed countries, about 2 per cent of the population (a total of 11 million people worldwide) is significantly undernourished, and can be classified as having moderate protein-energy malnutrition.

Three conditions are classified as protein-energy malnutrition: marasmus, which affects adults and children; kwashiorkor, which affects young children; and cachexia, which is associated with advanced cancer and other chronic diseases, and involves increased metabolic rate as well as reduced food intake.

The term protein-energy malnutrition does not imply that there is a deficit of protein per se, rather that there is a lack of food, so that much of the dietary protein is being used as a metabolic fuel rather than for tissue protein synthesis. A body mass index (BMI) between 17 and 18.4 is classified as moderate, 16 to 17 as moderately severe, and less that 16 as severe protein-energy malnutrition. BMI between 18.5 and 20 is considered to be underweight, but is not associated with any adverse outcomes.

Through the last quarter of the 20th century there was an increase in food availability in almost all countries, largely as a result of increased yields of staple cereals, due to the ‘green revolution’. Since then the condition has worsened in many countries, for a variety of reasons. Droughts, floods, and wars have led to considerable losses of crops, and what should be food crops such as maize and soya are increasingly used to produce biofuels to replace oil. There is increasing loss of agricultural land by desertification in sub-Saharan Africa and elsewhere. At the same time, the world population has increased from 5 billion in 1997 to 7 billion in 2010, and is predicted to increase to 11 billion by the end of the 21st century. Finally, increasing affluence in fast developing countries such as China, India, and Brazil has led to demands for a more Western style of diet, with more meat and less reliance on cereals and root crops as the dietary staples. This means that more of the cereals, legumes, and root crops are used to feed livestock. Although the animals are eaten by human beings, this is considerably less efficient in terms of utilization of the crops than if they were eaten directly.

Marasmus

The name ‘marasmus’ comes from the Greek for wasting, and this is the most obvious feature of the severely underfed person—severe wasting of muscle with negligible fat reserves. The condition is the predictable outcome of a prolonged inadequate intake of food. Adipose tissue reserves of fat are used as the main metabolic fuel, but there is a need to maintain a supply of glucose for the brain, by use of amino acids from protein turnover for synthesis of glucose. The rate of tissue protein breakdown continues at a more or less normal rate, but replacement synthesis is severely reduced, both because of the use of amino acids for glucose synthesis and also because of the high energy cost of protein synthesis. Once adipose tissue reserves are more or less exhausted, there is a considerable increase in the rate of protein loss, and eventually essential tissue proteins are lost, leading to death.

The reduced rate of protein synthesis leads to impaired immune system responses, so that resistance to infection is low, and what might be considered to be a mild infection may be fatal. There is also a reduction in the rate of tissue cell proliferation. This especially affects cells in the gastro-intestinal tract, which turn over rapidly. As a result there is considerable flattening of the intestinal villi (the finger-like projections of the intestinal wall where most nutrients are absorbed) and loss of the normal absorptive area in the gut. This leads to diarrhoea and failure to absorb much of such food as is available.

Cachexia

‘Cachexia’ comes from the Greek for ‘in a bad state or condition’. Superficially, this condition resembles marasmus, in that the patient is severely emaciated, with negligible fat reserves and considerable muscle loss. The condition is seen in patients with advanced cancer, AIDS, tuberculosis, and chronic heart and lung disease.

To some extent the condition can be attributed to reduced food intake—the patient’s appetite may be poor because of illness, and many of the drugs used cause nausea (so reducing appetite) or distort the senses of taste and smell, so that many foods become aversive. At the same time, many of the drugs used in cancer chemotherapy inhibit cell division, so that there is flattening of the villi in the small intestine that normally provide the large surface area for absorption of nutrients. This leads to failure to absorb nutrients.

There are two differences between marasmus and cachexia: the cachetic patient has a high metabolic rate, and in addition to reduced protein synthesis there is an increased rate of protein breakdown. Both are responses to hormones and other factors produced either by the body in response to the disease or, in the case of cancer, to factors produced by the tumours. The increased metabolic rate in cachexia leads to fever and an increased need for metabolic fuels, so hastening the development of malnutrition.

Kwashiorkor

Kwashiorkor was first described in Ghana in 1935, and the word is the Ga name for the disease affecting undernourished children. Traditionally it develops when the child is weaned (which may be as late as age 2 to 3 years), and the early hypothesis was that kwashiorkor developed because the child was fed on a starchy gruel with little or no protein. However, kwashiorkor is not the result of an adequate energy intake with inadequate protein, but the result of lack of food overall. Protein-deficient children show stunted growth, but children with kwashiorkor are less stunted than those with marasmus. Furthermore, the condition begins to resolve when the child is given an adequate supply of energy (often in the form of sugar solution), before the protein intake is increased.

Kwashiorkor is frequently precipitated in an undernourished child by an infection, and it is likely that the precipitating factor is tissue damage by radicals produced by white blood cells (macrophages) that are activated to fight the infection.

Kwashiorkor differs from marasmus in that there is considerable retention of fluid under the skin. This oedema masks the muscle wasting, so that the child with kwashiorkor may appear to be chubby. There is also fatty infiltration of the liver, leading to a pot belly. The child’s hair is thin, wispy, and underpigmented, and the child has a characteristic miserable facial expression and a sunburn-like dermatitis.

A child who is 60 to 80 per cent of expected weight for age without oedema is considered to be undernourished; if there is also oedema, the problem is kwashiorkor. If the child is less than 60 per cent of expected weight for age without oedema, this is marasmus. If there is also oedema, this is marasmic kwashiorkor, which is the most serious condition. In emergency situations, it is children with marasmic kwashiorkor who have the first priority for treatment.

Malnutrition in developed countries

Even in developed countries, where obesity is the main cause for concern, a significant number of people are undernourished. In the UK, 5 per cent of adults have a BMI of less than 20, and 2 per cent below 18.5, which is moderate protein-energy malnutrition. Three per cent of older men and 6 per cent of women living in their own homes and looking after themselves are undernourished. For elderly people living in care homes, the situation is worse, with 16 per cent of men and 15 per cent of women significantly undernourished. One study showed that 40 per cent of consecutive patients admitted to hospital were undernourished, and two-thirds of those staying in hospital for more than a week lost weight, even those who were undernourished on admission. The cost to the National Health Service of treating the consequences of malnutrition in UK is estimated at around £7 billion a year—almost twice the cost of treating the consequences of obesity.

Malnutrition leads to impaired immune responses, predisposing the individual to infection. The loss of muscle may result in increased fatiguability, inability to work, and falls. Inactivity as a result of loss of muscle predisposes individuals to blood clots and also leads to further muscle loss. Loss of respiratory muscle strength leads to poor cough pressure, which creates a predisposition to chest infections, poor recovery from chest infections, and increased risk under general anaesthesia. The healing of wounds is impaired, and recovery from illness is prolonged, leading to an increased length of stay in hospital and delayed return to work.

Even when not accompanied by physical illness, malnutrition leads to apathy, depression, self-neglect, loss of libido, and deterioration in social interactions.

The most vulnerable sections of the population are those living at or below the poverty line; those who are outside the welfare net for one reason or another; and the bereaved elderly, who may have little motivation to cook and eat. There are also problems in care homes and hospitals.

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