January 2000, Volume 24, Issue 1, Pages 101 - 107

Paper

Loss of total body potassium during rapid weight loss does not depend on the decrease of potassium concentration in muscles. Different methods to evaluate body composition during a low energy diet M Krotkiewski1, K Landin2, D Mellström3 & J Tölli4 1Department of Rehabilitation Medicine, Sahlgrenska University Hospital, Göteborg     2Department of Endocrinology, Sahlgrenska University Hospital, Göteborg     3Department of Geriatrics, Sahlgrenska University Hospital, Göteborg     4Department of Radiation Physics, Sahlgrenska University Hospital, Göteborg, Sweden     Correspondence to: M Krotkiewski , Department of Rehabilitation Medicine, Sahlgrenska University Hospital, Guldhedsgatan 19 111 tr, 413 45 Göteborg, Sweden. E-mail: mpab@algonet.se .

Keywords

skeletal muscle potassium;   skeletal muscle glycogen;   body composition;   weight reduction

Abstract

OBJECTIVE: The aim of the study was to elucidate whether combustion of skeletal muscle glycogen during a very low calorie diet (VLCD) was associated with decreased muscle potassium content. A comparison between different methods was also performed to evaluate body composition during a VLCD and a low calorie diet (LCD). DESIGN: Dietary treatment of obese women by VLCD and LCD. Measurements after 1 and 2 weeks of VLCD and 6 months of LCD. SUBJECTS: Fifteen perimenopausal obese women aged 46.5±1.3 y and 15 of 48.0±0.7 y of age. MEASUREMENTS: Skeletal muscle biopsies under local anaesthesia. Body composition measurements by means of deal-energy X-ray absorptiometry (DEXA), and measurements of total body potassium (40K) and total body nitrogen (TBN). Measurements of electrolytes and glycogen concentration in muscle samples. RESULTS: In the first study (1 week of VLCD) skeletal muscle glycogen decreased (P<0.01), but muscle potassium increased (P<0.01). Muscle sodium decreased (P<0.01), while muscle magnesium was unaltered. Body weight decreased by 2.9±0.5 kg and 40K decreased. Fat-free mass (FFM) calculated from 40K and DEXA decreased by 2.7 vs 1.9 kg (P<0.001). Body fat measured with DEXA decreased by 1.1 kg (P<0.01), but not body fat calculated from 40K. TBN decreased by 0.03±0.01 kg (P<0.05) and FFM calculated from TBN by 2.9±0.5 kg (P<0.002). In the second study, 6 months on the LCD resulted in 17.0±2.0 kg weight reduction and this was mainly due to reduced body fat, 14.0±2.0 kg measured with DEXA and from 40K (P<0.001). The decrease in FFM was slight. CONCLUSION: One week of VLCD resulted in muscle glycogen depletion but increased muscle potassium content in spite of decreased total body potassium. FFM contributed to the main part of body weight loss during short periods of severe energy restriction, but remained unchanged during long-term dietary treatment. Body fat became mostly responsible for the body weight loss during long-term LCD. Calculations of changes of FFM from 40K and TBN seem to overestimate the FFM decrease associated with short-term VLCD. International Journal of Obesity (2000)24, 101-107

Received 9 November 1998; Revised 5 May 1999; Accepted 27 July 1999

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