Failure of dietary fat intake to promote fat oxidation: a factor favoring the development of obesity

Article Abstract:

Obesity is a major health problem in affluent societies. In part this is considered to result from both low physical activity and the high fat content of Western diets. Previous work has shown that the ingestion of carbohydrate elicits a complex metabolic response that acts to increase utilization of carbohydrate and elevates basal energy expenditure. When diets are supplemented with fat there is no increased utilization of the fat as would be the case in carbohydrate supplementation. Thus, it appears that regulation of metabolism is significantly more dependent on carbohydrate consumption than on dietary fat. However, these studies have only followed the metabolic rate for nine hours after meals; the experimental design described in this research allows for the possibility that an adjustment in metabolism from fat ingestion could occur later. The current study expands the period of study to 24 hours following a fat supplement. Seven healthy, nonsmoking males aged 20 to 26 were included in the study. All had stable body weights and no family diabetic history. The subjects were placed in a respiration chamber where they were provided with the facilities of a one-room suite. They could communicate with investigators through a window and by intercom. All urine was collected and analyzed for nitrogen (urea). Subjects exercised on a treadmill for one hour each day and their general movements were monitored by radar. Temperature and humidity were maintained at constant levels and the air of the chamber was constantly evaluated for oxygen and carbon dioxide concentration. The measurements of oxygen, carbon dioxide and urinary nitrogen allowed the calculation of basal energy expenditure. During the first 24 hour period total energy expenditure measured 2,783 kcal per day. When 987 kcal of dietary fat was added to the diet there was no change in 24 hour energy expenditure. Thus the previously collected data on the inability of fat supplementation to shift energy expenditure appears valid when the length of observation is extended to include a 24 hour period of supplementation.

Health aspects, Obesity, Carbohydrates, Metabolism, Fat metabolism, Carbohydrate metabolism, Veterinary physiology, Animal physiology, Carbohydrates in the body

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Twenty-four-hour energy expenditure and basal metabolic rate measured in a whole-body indirect calorimeter in Gambian men

Article Abstract:

Many research studies concerning the energy intake and energy expenditure of people in developing countries have suggested that they may adjust to habitually low caloric intake by reducing their metabolic rate, or burning less energy. Women living in the Gambia have been found to consume very low energy intakes while remaining active; in theory they should have lost weight, but they were able to maintain their weight. It is a mystery how certain populations continue to function while chronically undernourished. A study was conducted in which the metabolic rate of young Gambian men was measured over a 24-hour period. Energy expenditure while sleeping, exercising, and after meals (when additional calories are lost due to increased heat production) was measured. The 20 young Gambian men were individually studied while they stayed in a respiration chamber for 24 hours. This chamber is an airtight room in which the consumption of oxygen and release of carbon dioxide (indicators of metabolic rate) can be quantified. The study was conducted during the 'hungry season' when most Gambian men are engaged in strenuous farming work, and the food supply from the previous season is almost gone. A comparison group of 16 European men, matched for body composition, was also studied in the same manner. The results revealed that all measures of metabolic rate were lower in the Gambian men than the European subjects, meaning that the Gambian men were burning fewer calories; this difference held during sleep, while exercising, after meals, and for the basal metabolic rate (the energy needed to fuel basic body processes, such as breathing and heart rate). It was concluded that the Gambian men exhibited increased energy efficiency during all activities, which allowed them to tolerate the marginal food intake of the hungry season. (Consumer Summary produced by Reliance Medical Information, Inc.)

Measurement, Developing countries, Food and nutrition, Basal metabolism, Malnutrition, Gambia

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Protein turnover and thermogenesis in response to high-protein and high-carbohydrate feeding in men

Article Abstract:

The thermic effect of feeding (TEF) is the well-established phenomenon in which the energy expenditure of the body increases after a meal. Part of this energy expenditure is a direct result of the digestion, processing and storage of the ingested food, and part of the TEF has not been accounted for. Although both high-protein and high-carbohydrate meals induce a thermic effect, the TEF of protein is greater and seems to last longer. In an effort to clarify the factors which contribute to the thermic effect, the investigators measured TEF after seven male subjects ate either high-protein or high-carbohydrate meals every hour throughout the day. After eating, the body manufactures new proteins at a greater rate than while fasting. The results indicated that 36 percent of the TEF which results from a carbohydrate meal is due to increases in protein synthesis in response to that meal. In the case of the high-protein meal, not only was the thermic effect greater, but a greater proportion of the effect was accounted for by the synthesis of new body proteins. After the high-protein meal, 68 percent of the observed increase in energy expenditure could be accounted for by the increase in protein synthesis. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, Protein metabolism, Thermogenesis

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