Gilbert B. Forbes

Adult lean body mass declines with age: Some longitudinal observations

Abstract Lean body mass, as estimated from 40 K counting, declines progressively during adult life. The rate of decline tends to speed up in later years, and is somewhat greater in the male. By age 65–70 the average male has 12 Kg. less LBM than at age 25; the female has 5 Kg. less. Longitudinal observations show that this trend is for the most part biological, not secular in origin. The magnitude of the decline is such, and the sex difference in LBM great enough to suggest that age and sex should both be taken into account in such matters as drug dosage and nutritional requirements.

HUMAN BODY COMPOSITION

Although it is self-evident that the study of human nutrition has as its goal the optimal nutrition of man, the nutritional status of the body best suited to optimal performance, i.e., optimal nutrition, has unfortunately not yet been satisfactorily defined. Body composition of animals may be measured by direct chemical analysis and correlated with dietary intake and with the various aspects of performance; studies of body composition of living man, on the other hand, must rely on indirect measure ments. The following two reports, which give an account of the current status of the attack on the difficult task of measuring body composition in living man, are sponsored by the Committee on Nutrition to call attention to the resurgence of effort in this field during recent years. A fuller knowledge of the gross composition of the human body and its relation to preceding diet will constitute a significant step towards realization of the ultimate goal of nutritional science. Even then, a particular body composition will be of importance primarily in terms of functional performance. The availability of newer techniques should do much to stimulate physicians and nutritionists in defining body composition as an essential step in arriving at a more exact definition of optimal nutrition.

ESTIMATION OF TOTAL BODY FAT FROM POTASSIUM-40 CONTENT

On the assumption that the potassium content of the lean body mass is constant, it should be possible to estimate fat content in living man from a measurement of potassium-40 activity in the whole-body scintillation counter. A series of such measurements on children and young adults shows good correlations with skin-fold thickness and weight/height ratio as indices of fatness.

Deliberate overfeeding in women and men: energy cost and composition of the weight gain.

1. Thirteen adult females and two males were overfed a total of 79-159 MJ (19,000-38,000 kcal) during a 3-week period at the Clinical Research Center, Rochester. The average energy cost of the weight gain was 28 kJ (6.7 kcal)/g, and about half the gain consisted of lean body mass (LBM) as estimated by 40K counting. 2. A survey of the literature disclosed twenty-eight normal males and five females who had been overfed a total of 104-362 MJ (25,000-87,000 kcal) under controlled conditions: twenty-five of these had assays of body composition, and three had complete nitrogen balances. 3. When these values were combined with those from our subjects (total forty-eight), there was a significant correlation between weight gain and total excess energy consumed (r 0.77, P less than 0.01) and between LBM gain and excess energy (r 0.49, P less than 0.01). Based on means the energy cost was 33.7 kJ (8.05 kcal)/g gain and 43.6% of the gain was LBM; from regression analysis these values were 33.7 kJ (8.05 kcal)/g gain and 38.4% of gain as LBM. 4. Individual variations in the response could not be explained on the basis of sex, initial body-weight or fat content, duration of overfeeding, type of food eaten, amount of daily food consumption or, in a subset of subjects, on smoking behaviour. 5. The average energy cost of the weight gain was close to the theoretical value of 33.8 kJ (8.08 kcal)/g derived from the composition of the tissue gained.

AGE AND SEX TRENDS IN LEAN BODY MASS CALCULATED FROM K40 MEASUREMENTS: WITH A NOTE ON THE THEORETICAL BASIS FOR THE PROCEDURE.

The availability of modem techniques for the assessment of body composition in living subjects has brought about a renewed interest in this field of human physiology. This report is concerned with one such modern approach; namely the estimation of lean body mass,+ and its derived parameter fat, from the body content of potassium. Analyses of adult human carcasses, together with data reported in the literature,’ indicated the relative constancy of the potassium component of the lean body mass. Other investigators2 had found that water and nitrogen content (in animals) were also constant. All of these data lent strong support to the concept, first proposed many years ago: that the fat-free portion of the body is for practicable purposes invariant

ESTIMATION OF TOTAL BODY SODIUM BY ISOTOPIC DILUTION. I. STUDIES ON YOUNG ADULTS

, and that changes in overall composition are the result of alternations in fat. On this basis, any parameter of lean body mass can be used to derive an estimate of the quantity of lean tissue; and indeed the total body water and densitometric methods, now in common use, are based on this principle. Three groups of investigators have proposed that the potassium method could be used for this p u r p o ~ e . ~ . ~ , ~ The scintillation counter measures the K40 activity of the body, whence chemical potassium can be calculated from the isotopic abundance of the naturally occurring radionuclide. This technique offers the advantage of being nontraumatic to the subject, and without hazard.

Effects of starvation in infancy (pyloric stenosis) on subsequent learning abilities

Although the amount of sodium contained within the human body has been determined in a number of fetuses and newborns by direct chemical analysis, no such data are available for the adult. This value has been estimated (by means which are not clear) to be 63 Gm. by Shohl (2), 56 Gm. by Hackh (3), and 105 Gm. by Sherman (4) for a 70 Kg. man. The literature contains reports of the chemical analysis of one adult carcass, but unfortunately values for sodium are not given (5). The importance of sodium in the electrolyte economy of the human body prompted us to undertake a study of the feasibility of determining total body sodium by the isotopic dilution method. In vAtro applications of isotopic dilution analysis are well known, and present no particular difficulties under conditions wherein the system to be studied is a closed one. The method was applied to man for the determination of total body water in 1934 by Hevesy and Hofer (6) who used deuterium, a stable isotope, in their experiments. More recently radioactive hydrogen has been used for the same purpose (7). Although Kaltreider and his co-workers (8) made the suggestion several years ago that they were measuring total body sodium in experiments aimed at determination of extracellular fluid volume, F. D. Moore (9) was the first to emphasize the potentialities of the isotopic dilution method for the measurement of total body sodium and potassium in addition to total body water in man, and re-

Effects of body size on potassium-40 measurement in the whole body counter (tilt-chair technique).

The model of starvation in this study was the medical condition of congenital hypertrophic pyloric stenosis. Pyloric stenosis involves a period of brief starvation in early infancy, is unrelated to socioeconomic conditions, and is easily correctable. A number of specific learning abilities together with the general adjustment of 50 subjects, 5 to 14 years old, who had PS were studied and compared to those of 44 siblings and 50 matched controls. Learning ability was negatively correlated with the degree of severity of the starvation. Starvation resulting in reduction of more than 10% of the expected body weight in infancy was associated with poorer learning abilities, especially those involving short-term memory and attention.

Long-term administration of antiepileptic drugs and the development of rickets

Abstract The precision of 40K determination in man by the tilt-chair technique is compromised by geometrical and self absorption factors. In an attempt to improve calibration accuracy simultaneous measurements of 40K and total body water (deuterium dilution) were made in 50 subjects of widely varying body size. The results show that neither height nor weight per se affects the observed body ratio of 40K/H2O, and that the principal systematic error concerns the relative fat content of the subject. Correction of the observed 40K values for this factor improves the accuracy of the measurement.

The assessment of muscle mass in progressive neuromuscular disease

Two young children developed rickets as a complication of anticonvulsant therapy and were subsequently cured by vitamin D therapy. They are the youngest patients thus far reported, and the first to be reported in the United States. On the basis of clinical studies, rickets and osteomalacia can be added to the list of toxic effects of anticonvulsant therapy. Although the exact mechanism of pathogenesis remains to be elucidated, it appears likely that these drugs alter the metabolism of vitamin D in certain patients. Special attention should be paid to the status of calcium and phosphorus metabolism in children who are receiving such drugs, and to their intake of vitamin D.