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White and brown adipose tissues have long been considered as two distinct and independent entities, underestimated by researchers.

Body silhouette is defined by skeleton framework, muscle masses and fat distribution All these anatomical components are genetically fixed, related to growth hormones and sex hormones, and modified by extrinsic factors such as age, physical exercise, diet, constrictive garments, way of living and general health conditions.

Extreme loss of body tissue in association with severe illness has been observed by physicians since ancient Greek times. The term ‘cachexia’ was the label for a ‘signum mali ominis’ in various, mostly fatal, diseases. Observing the chronicity of the course of a disease, cachexia was recognised as a severe complication indicating end-stage disease and poor quality of life. As modern treatment helps to prevent early death for an increasing number of chronic diseases, growing interest is focussed on chronic complications such as cachexia. Nevertheless, observation and clinical documentation of this condition go back as long as medical science itself. Pioneering studies on the reasons and mechanisms of cachexia were performed several decades ago. These studies provide fundamental insights and guidance towards a better understanding of cachexia.

The interrelationships between clinical diseases and malnutrition have long been recognised. Malnutrition due to starvation, disease or injury is a very common phenomenon, even in current times. Our predecessors in medicine were more familiar with clinical malnutrition than we are, since observation and physical examination played a much greater role in diagnosis in the past. Century-old textbooks provide detailed descriptions of physical changes that occur with malnutrition. Classic studies document the complex adaptations that occur in response to starvation as well as the metabolic alterations associated with stress and trauma.

The human organism, like other higher animal organisms, derives the energy needed for its essential vital functions from the oxidation of organic substrates. In effect, the only form of energy that humans are able to utilise is the chemical energy contained in C-C or C-H bonds, while plants and vegetables can utilise solar energy in order to synthesise the complex molecules needed for their growth and survival [ 1 ].

Since the time of Lavoisier, it has been known that the ingestion of foods by animals and humans produces an increase in oxygen consumption. This increase in metabolic rate, originally called ‘specific dynamic action’ (SDA) is now widely referred to as the ‘thermic effect’ (TE) of food or ‘diet-induced thermogenesis’ (DIT) [ 1 ]. This effect starts generally 1 h after ingestion, reaches a maximum after 3 h later, and continues at this level for several hours [ 2 ]. The DIT is a component of the total energy expenditure, which includes energy expenditure required for performance of cellular and organ functions (basal metabolism [BM]), physical activity, and thermorégulation of body temperature. Supplementary energy is required for metabolic processes taking place during growth, pregnancy, and lactation [ 3 ]. In quantitative terms DIT represents about 10% of total energy expenditure (15% together with cold-induced thermogenesis).

Nutrition is an important factor in the aetiology and management of several major causes of death and disability. The nutritional status of a person is the result of a balance between the intake and the requirement of nutrients. Optimal nutritional status is achieved when sufficient nutrients are consumed to support day-to-day body needs. This status promotes growth and development, maintains general health, support activities of daily living, and assists in protection from diseases. Several variables can influence the intake of food: economical, emotional, developmental and cultural factors, dietary patterns, unbalanced self-imposed diets, anorexia, bulimia, etc. The intake of food also varies in relation to many physiological situations, such as growth, pregnancy, breast-feeding and physical activity. Dysphagia, dyspepsia, malabsorption, loss of nutrients (vomit, diarrhoea, wounds, fistulas, drainage, etc.), alterations in metabolic and nutritional requirements, and drug interactions can be present in different pathological situations.

Nitrogen is a main body component and is required for both tissue protein synthesis and the production of several nitrogenous compounds involved in a variety of functions (hormones, immune mediators, neurotransmitters, antioxidant defences, etc.)Thus, the body nitrogen content should be both quantitatively and qualitatively normal, as well as normally maintained, to ensure normal body functions.

In the adult organism, maintenance of body protein stores is the result of changes linked to a diurnal rhythm of catabolic and anabolic phases [ 1 ]. In physiological states a net loss of body proteins occurs in the periods between meals, particularly at night-time, and during exercise [ 2 ]. Conversely, a net protein gain occurs during meal absorption, both in the entire body and at muscle level [ 3 ]. Recently, the recovery phase after exercise has also been recognised as anabolic [ 4 ].

Malnutrition is not invariably diagnosed by physical findings of nutritional deficits. Malnutrition is a deviation (in excess or defect) from a complex of ideal scores. Paradoxically, a plump, flourishing patient may be affected by malnutrition if he or she exceeds this ideal score.