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Physiological and biochemical responses to diet and exercise Noble, Rosemary Jane

Abstract

The purpose of this study was to investigate work performance on a semi-defined, low calorie diet during daily periods of light and moderately heavy activity. Four male graduate students volunteered for the ten week study which was divided into five experimental periods. During Period 1 (control) the subjects received a balanced, normal diet of usual foods providing approximately 3600 calories per day and meeting the Canadian Dietary Standards for all nutrients. During this two week period, a "normal" level of activity was maintained. Period 2 consisted of ten days on a semi-defined low calorie diet with continued "normal" activity. The low calorie diet provided, approximately 1800 calories daily, plus one multiple vitamin pill. It met the Canadian Dietary Standards for all nutrients. Period 3 was a repeat of Period 1, two weeks during which the subjects received approximately 4000 calories, per day, of the control diet. Again, "normal" activity was maintained. Period 4 consisted of ten days of the same low calorie semi-defined diet as Period 2, with an additional daily energy expenditure, per subject, of approximately 500 calories. Period 5 was the same as Periods 1 and 3, two weeks of the control diet with "normal" activity. Several physiological variables were measured during the last two days of each experimental period to ascertain the effects of the treatment conditions on the cardiorespiratory and general fitness of the subjects. Strength measurements and maximal oxygen uptake determinations remained unchanged for the duration of the study, whereas, physical work capacity (PWC 170) decreased continually, beginning in the third experimental period. Total body weight decreased during Periods 2 and 4. Period 4, which involved increased physical activity caused slightly more weight loss than Period 2. Anthropometric measurements, body composition, and body density were only slightly changed, the changes paralleling the changes in body weight. Pasting blood samples were taken twice during each experimental period; midway through the period and on the last day. Twenty-four hour urine samples were also collected on the final day of each study period. Although some minor changes did occur, most biochemical parameters remained within normal limits. The blood glucose concentrations decreased during Periods 2 and 4 and plasma free fatty acid levels increased. Plasma cholesterol levels decreased during Periods 2 and 4, as did the hematocrit, hemoglobin, total serum protein, serum albumin, and blood urea nitrogen concentrations. Plasma Vitamins A and E, as well as the serum Vitamin C levels also decreased during Periods 2 and 4. Urinary thiamine excretion increased, possibly in response to the greater percentage of calories derived from endogenous fat stores Generally speaking, the low calorie diet situations were well tolerated by the subjects. Physiological measurements indicated a change only in physical work capacity, which decreased during the study. Biochemical determinations revealed definite alterations; however, most parameters remained within the normal limits.

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