Human body energy balance

At least three peptides are implicated in the regulation of food intake, energy expenditure, and whole-body energy balance in both rodents and humans and are found both peripherally as hormones and centrally. These are galanin, neuropeptide Y, and... 

The first law states that energy is neither created nor destroyed, which applies to the human body as to any other system. Thus the body mass represents a balance between energy intake (i.e. food) and that expended in various processes in the body, especially physical activity. Thus the law is particularly relevant in weight-reducing diets to overcome obesity or to maintain normal body weight. The subject of obesity is discussed in Appendix 1.5. The general principles of energy intake and expenditure are now discussed. 

The pathways of amino acid catabolism, taken together, normally account for only 10% to 15% of the human body s energy production these pathways are not nearly as active as glycolysis and fatty acid oxidation. Flux through these catabolic routes also varies greatly, depending on the balance between requirements for bio-... 

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. 

Bjomtorp, P. (1985). Regional patterns of fat distribution. Ann. Intent. Med. 103,994r-995. Bouchard, C-, and Tremblay, A. (1997). Genetic influences on the response of body fat and fat distribution to positive and negative energy balances in human identical twins. /. Nutt. 127, 943S-947S. 

Unfortunately for overweight humans, the complex homeostatic mechanisms that regulate energy balance, which we have just reviewed, are much more effective in defending a low body weight from any further... 

The mean human body core temperature fluctuates very little ( 1.0 C). A compensated heat balance is thus a prerequisite for the ability of the organism to function and stay alive. Since man, when performing physical labor, attains a thermic efficiency of less than 10%, it is safe to assume that in excess of 90% of the energy expended (physical labor) will be in the form of heat which must be transmitted to the environment. A brief overproduction of body heat because of especially intensive muscular work may be absorbed by a temporary increase of the body core temperature. In keeping the body heat balanced, heat conduction, convection, radiation, and perspiration play important parts (Figure 6.52). 

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. 

Though we frequently use the word equilibrium in our life, equilibrium is not a common state for any real system. The common thermodynamic state is called steady state when a system s parameters are not changing because the output and input fluxes of energy and mass are balanced. For example, the temperature of a human body is remarkably constant due to a delicately balanced steady state, and this temperature, 36.6°C, is quite different from any common temperature in the surroundings. 

Two-node thermal models tend to divide the entire human body into two concentric shells of an outer skin layer and a central core representing internal organs, bone, muscle and tissue. The temperature of each node is assumed to be uniform. The energy balance equations are usually developed for each node and solved to produce the skin and core temperature and other thermal responses. 

The early two-node models were not widely used by people due to the lack of sufficient consideration of the complicated physiological phenomena of the human body. Gagge et al. [19] introduced a more complete two-node model for the entire body, which includes the unsteady-state energy balance equation for the entire human body and two energy balance equations for the skin node and core node, as listed in the following ... 

Multi-node models divided the entire human body into more than two nodes and developed energy balance equation for each node as well the control functions for blood flow rate, shivering metabolic rate, and so on. Stolwijk et al. [20] presented a more complex multi-node mathematical thermal model of the entire human body, in which many efforts are made to flie statement of the thermal controller. This model firstly divided the body into six cylindrical parts of head, trunk, arm, hands, legs and feet and a spherical body part comprising the head. Each part is further... 

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