Nutrient balance in humans: effects of diet composition

Article Abstract:

Body weight and body composition are related to the amount of calories consumed, the type of calories consumed (such as fat versus carbohydrate), and the amount of energy expended (used) during daily activities. In order for body weight and body composition to remain constant over time, the energy intake has to be equal to the amount of energy that is expended. It has been suggested that obesity may result when the amount of fat consumed is greater than the amount of fat that is oxidized (used for fuel) by the body. This article describes the results of a study designed to determine whether altering the composition of the diet (the proportions of fat and carbohydrate) influences the amount of energy expended and the amount of fat and carbohydrate that are oxidized by the body. Eight adults followed a diet containing 60 percent of calories as carbohydrate for one week, and followed a diet containing 60 percent of calories as fat during another week. Six adults followed a diet containing 45 percent fat for an additional week. Body composition and the amount of energy expended during a 24-hour period were measured. The results of this study show that the composition of the diet does not affect the amount of energy expended. However, the amount of fat oxidized, or used as fuel, by the body was greatest when the high-fat diet was consumed and the amount of carbohydrate oxidized was greatest when the high-carbohydrate diet was consumed. These findings indicate that the amount of fat and carbohydrate consumed in the diet can influence the amount of fat and carbohydrate that are oxidized by the body. (Consumer Summary produced by Reliance Medical Information, Inc.)

Energy metabolism, Metabolic regulation

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Evaluation of an alternating-calorie diet with and without exercise in the treatment of obesity

Article Abstract:

Obesity may be associated with changes in the metabolic state of individuals that allows them to lose weight more easily than to maintain the loss. In part this could be due to decreases of the resting metabolic rate such that the person requires less food to maintain body composition as weight decreases. Two important variables in the production of a dietary regimen for weight loss are the level of caloric intake (or restriction) and the degree of energy burning exercise. The current study examines these parameters in 40 moderately obese women, defined as 130 to 160 percent of their ideal weight. Subjects were required to prepare a complete two week eating diary to qualify for admission to the study. Body weight was recorded at the onset of the treatment and at weekly group meeting. Body composition measurements were also made by weighing individuals underwater as a measure of their lean body mass (density measurement). All subjects participated in a life-style modification program. The subjects' metabolic rate was also measured both before the start of the experiment and at its conclusion. Subjects were placed in one of several groups. In one group the level of dietary intake was varied between 600 and 1,800 kcal per day, in the other group the patients were placed on a straight 1,200 kcal per day diet for the 12 week period. Subgroups of both diet strategies either increased their caloric output through aerobic exercise or did not participate in this exercise program. Both calorie reducing diets were equally successful in achieving a weight loss, and had no effect on resting metabolic rate. Exercise was seen as clearly helpful in weight-loss strategies.

Research, Measurement, Women, Reducing diets, Food and nutrition, Aerobic exercises

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Energy content of diets of variable amino acid composition

Article Abstract:

Frequently, a therapeutic diet is prescribed to contain a certain level of calories, or energy. For this reason, it is important to know the energy content of particular food constituents such as carbohydrates or amino acids, the building blocks of proteins. The first step in determining energy content of a compound is to ascertain the extent to which it is absorbed or retained by the body. The energy content of the absorbed nutrient is then equal to the total energy obtained from its combustion minus the energy of its metabolites, breakdown products, which are not fully used by the body. Carbohydrates are almost completely used by the body, and thus the biological energy content is equivalent to its energy of combustion. However, amino acids contain nitrogen in addition to a carbohydrate constituent, and various nitrogenous metabolites are not completely used, so that the biological energy content and combustion energy of amino acids are different. Furthermore, the biological energy content of the 20 amino acids differs according to the proportion of nitrogen to non-nitrogenous content, and each amino acid thus has a different caloric content. The chemical basis and the calculations used to determine the energy value of diets containing differing amino acids, and different levels thereof, are described in this article. A computer program was written to perform these calculations, and its use and availability are discussed. The application of the program for analysis of diets of varied composition is described and sample calculations are performed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Food, Amino acids in nutrition

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