Changes in Body Fluids and Tissue Components in Lean and Obese Rats During Starvation

Abstract

distribution), intracellular fluid volume, water intake, urine output, insensible water loss, and serum and urinary sodium potassium, and osmolality. Glomerular filtration rate (51Cr-EDTA clearance), hemoglobin, hematocrit, erythrocyte count, serum glucose, cholesterol, urea nitrogen, and ketones were also determined. . The great majority of studies concerning the physiologyof human starvation have been reported within the last 15years. The cause of this recent interest is the popular use of fasts of varying duration as a technique in the correction and control of intractable obesity. Presently, opinion on the safety of therapeutic fasting falls into three main categories: 1) prolonged fasting is an extremely useful and relatively safe method of treatment for the massively obese; 2) prolonged fasts are an unnecessary risk since substantial weight losses can be achieved by repeated fasts of shorter duration; and 3) fasts of any duration expose the patient to unjustifiable hazards. The question of benefit to be achieved versus risk involved in therapeutic fasting has not been answered conclusively. Moreover, studies of body fluids in man during starvation have yielded somewhat contradictory results. Although rapid decreases in total body water (TBW) during the initial days are well documented, it is not clear which fluid compartments are diminished, or whether these decreases result from urinary or insensible water loss.An ideal weight-reduction program should yield 2 loss of fat while sparing lean body mass. In addition to the loss of water, decreases in body weight must be composed largely of fat or protein becausecarbohydratestores in the body of man represent only about 840 calories. Unfortunately, losses of lean tissue during fasting are of such magnitude as to be of concern for a number of authors. Benoit, Martin, and Watten (2) estimated that 65% of an average 9.6-kg loss during 10-day fasts in seven obese men was lean tissue, with only a 3.4-kg decrease in body fat. Ball et al(1) reported that five obese patients, fasted for 16 days, lost 563 g of lean tissue and only 202 g of fat daily. The lean tissue loss represented almost 75% of the total weight decrease.Employing lean and obese rats as a model, investigations were made to elucidate the tissue components of weight loss and the influence of excess adipose tissueon body fluidsand renal function during fasting. The results of some of these studies will be summarized briefly.MATERIALS AND METHODS Three hundred male Charles River CD outbred albino rats were offered ground Purina Laboratory Chow (PLC) and water ad libitum. At approximately 6 weeks of age, the anima!s were separated randomly into two groups. One group was offered a diet containing 42.5% fat, and the other group cqntinued to receive PLC. The fasting (no chow; water ad libitum) periQd began when the.,rats were 22 weeks old.The following' parameters were evaluated prior to and throughout prolonged fasts: body weight, body fat (extraction with chloroform/methanol), lean dry mass, total body water...