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Chapter: Introduction to Human Nutrition: Energy Metabolism

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Energy requirements in disease and trauma

The DLW technique has been used in various studies to assess the energy requirements of hospitalized patients.

Energy requirements in disease and trauma

 

The DLW technique has been used in various studies to assess the energy requirements of hospitalized patients. Information on energy requirements during hospitalization for disease or trauma is important because:

 

      energy expenditure can be altered by the disease or injury

 

      physical activity is often impaired or reduced

 

      both underfeeding and overfeeding of critically ill patients can lead to metabolic complications; there-fore, correct assessment of energy requirements during recovery is an important part of therapy.

 

The metabolic response during recovery from a burn injury includes an increase in RMR, although this is not necessarily a function of the extent of the burn. The widely used formulae to predict energy needs in burn patients are not based on measurement of energy expenditure and estimate that most patients require 2–2.5 times their estimated RMR. However, using the DLW technique, total energy expenditure was 6.7 + 2.9 MJ/day in 8 year old children recovering from burn injury, which was equivalent to only 1.2 times the onfasting RMR. The lower than expected values for total energy expenditure in children recov-ering from burns suggest that RMR is not as elevated in burn patients as previously speculated, and that RMR is not a function of burn size or time after the injury, probably owing to improvements in wound care which reduce heat loss. In addition, energy requirements in patients recovering from burn injury are reduced because of the sedentary nature of their hospitalization.

In a study of patients with anorexia nervosa, total energy expenditure was not significantly different than controls (matched for age, gender, and height). However, physical activity-related energy expendi-ture was 1.3 MJ/day higher in anorexia nervosa patients, which was compromised by a 1.3 MJ/day lower RMR. Thus, energy requirements in anorexia nervosa patients are normal, despite alterations in the individual components of total energy expenditure. In infants with cystic fibrosis, total energy expendi-ture was elevated by 25% relative to weight-matched controls, although the underlying mechanism for this effect is unknown.

 

Developmental disabilities appear to be associated with alterations in energy balance and nutritional status at opposite ends of the spectrum. For example, cerebral palsy is associated with reduced fat mass and FFM, whereas half of patients with myelodysplasia are obese. It is unclear whether the abnormal body com-position associated with these conditions is the end-result of inherent alterations in energy expenditure and/or food intake, or whether alterations in body composition are an inherent part of the etiology of the specific disability. In addition, it is unclear how early in life total energy expenditure may be altered and whether reduced energy expenditure is involved with the associated obese state. Nevertheless, pre-scription of appropriate energy requirements may be a useful tool in the improvement of nutritional status in developmental disabilities.

Total energy expenditure has been shown to be lower in adolescents with both cerebral palsy and myelodysplasia, partly owing to reduced RMR but primarily to reduced physical activity. Based on measurements of total energy expenditure, energy requirements of adolescents with cerebral palsy and myelodysplasia are not as high as previously specu-lated. In nonambulatory patients with cerebral palsy, energy requirements are estimated to be 1.2 times RMR, and in the normal range of 1.6–2.1 times RMR in ambulatory patients with cerebral palsy.


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