Body composition and energy balance

To the clinician, the accurate measurement of total body water (TBW) can provide indirect information concerning whole body composition and energy balance. Desiccation measurements performed on eviscerated guinea pigs in 1945 [270] led to the almost universal acceptance of the fact that lean body mass (LBM) was of constant composition — and additionally, contained all of the body water. Thus the extracellular water associated with adipose tissue was neglected and the water content of lean body mass taken as 73.2%. The following simple formula, which was readily applied to man, provided an indirect estimate of body fat  

Credance was given to this formula from 6 whole body chemical analyses performed on adult cadavers where the mean water content of LBM was 72.5% (67.4-77.5%) [271]. That the use of this formula, even for subjects of normal body composition, may be an over-simplification leading to significant errors has been stressed [272]. Certainly it is inapplicable to individuals exhibiting oedema, malnutrition, obesity or during pregnancy. The study of obesity with respect to body composition, has prompted the development of a new model for calculating adipose tissue and adipose-free masses [261]. The model still requires the measurement of total body water and its application to 4 normal and 5 obese individuals has been presented [273]. 

Water uptake from the stomach has been investigated using deuterium oxide [277]. In eight normal subjects the disappearance rate of administered label was found to be 2.5% per min giving 95% disappearance at approximateiy 54 min. In a separate study [278], it was calculated that the net absorption of water from the stomach amounts to 230 ml per h. It was also demonstrated that this water movement is somewhat reduced in patients exhibiting gastric atrophy. 

In terms of the whole body, the dynamics of distribution of deuterium oxide between blood and extravascular water have been determined following the intravenous injection of the label [259]. The plasma pre-equilibrium concentration curve plotted semi-logarithmically with respect to time was composed of 2 exponentials, described by the equation - 

Finally in this broad area of study two isolated and unrelated applications of deuterium oxide may be briefly mentioned. Haemodialysis constitutes the normal treatment used as a prelude to renal transplantation. Peritoneal dialysis, however, provides a method for alleviating temporary renal faflure. Deuterium oxide has been used to determine the kinetics of water equilibration between the body water and dialysis fluid in an attempt to improve the efficiency of peritoneal dialysis [280]. 

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Anderson EJ, Lavoie HB, Strauss CC, Hubbard JL, Sharpless JL, Hall JE. Body composition and energy balance lack of effect of short-term hormone replacement in postmenopausal women. Metabolism 2001 50(3) 265-9. 

Weight gain is widely believed to be a common consequence of HRT, and the desire to avoid obesity is a major reason why some women decline treatment. However, the potential effects of HRT need to be distinguished from effects that could be due to changing lifestyle or ageing. The effects of short-term hormone replacement and age on alterations in weight, body composition, and energy balance have therefore been studied in a prospective... 

Assessing the outcome of EN includes monitoring objective measures of body composition, protein and energy balance, and subjective outcome for physiologic muscle function and wound healing. 

This chapter will review the relative contributions of exercise and food intake to changes in body weight and more specifically body composition. The emphasis of this chapter is on exercise as a modality for fat reduction and fat-free weight maintenance with the focus on aerobic exercise which has greater potential to modify body composition due to larger effects on energy balance. The first section reviews the effects of aerobic exercise on body composition in humans. The second section addresses techniques for measurement of body composition and limitations of these measurements in humans. The third section examines the use of experimental animals for studies of exercise and body composition, and the fourth section examines the interactions of diet and exercise. 

Normal assumptions about body composition and activity may not be true for subjects with a FAOD. Further research on energy balance in a wider patient population is needed. For clinical... 

It is generally accepted that the primary etiology of obesity concerns problems of energy balance as a consequence of nutritional excess and physical inactivity with less than 1% of cases associated with endocrine dysfunction (13). Changes in body weight or body composition depend on the relationship of energy intake to energy... 

Grande, F. (1968) Energy balance and body composition changes a critical study of three recent publications. Int. Med. 68, 467-480. 

It is important to evaluate body composition in the context of safety. Ultimately the goal of assessment is to identify levels of difference in body composition that are associated with immediate or long-term disease risk. The relevant component of body composition to measure will depend on the nature of the added ingredient. Eor example, if an ingredient is likely to have metabolic effects, it will be important to assess the relative contribution of fat and fat-free mass since these components may differentially reflect underlying factors related to energy and protein balance. In contrast, for other ingredients, bone mineral content may be more relevant. 

Long term recording of body weight and possibly body composition would result in data for the substrate flow to or from body stores. The dietary food intake can be assessed by questionnaires or prediction formulas, provided by earlier measurements. So energy expenditure and substrate oxidation rates can be calculated from energy and substrates balances. All these approaches would not need calorimetry at all it could however be used to verify some of the results of these methods. Body composition can be assessed by various established methods like dual energy X-ray analysis (DEXA), skin fold measurements, underwater weighing and body impedance measurements. 

Earlier sections of this chapter have emphasized that, in addition to their use as energy sources, fatty acids have a number of roles that are essential to cell and tissue function (Figure 5). A range of fatty acids is required for membrane composition, integrity and function to be retained. This means that a supply of the correct balance of fatty acids to cells and tissues is essential for the optimal functioning of those cells and tissues. Furthermore, different cells and tissues may require a different balance of fatty acids (i.e. they may have different demands for fatty acids). Although many fatty acids can be synthesized in the human body, some caimot (linoleic and a-linolenic acids) and so these fatty acids must be consumed in the diet. In the absence of significant dietary intakes, synthesis of some other fatty acids (e.g. arachidonic acid) requires the provision of a preformed precursor fatty acid (e.g. linoleic acid). This means that dietary supply of some fatty acids is very important to meet the demands imposed by optimal ceU and tissue function. Thus, an inadequate or unbalanced supply of fatty acids may impair cell and tissue function and lead to ill health and disease. Therefore, dietary fatty acids can influence human health. 

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