Physiology & Behavior, Vol. 25, pp. 313-315. Pergamon Press and Brain Research Publ., 1980. Printed in the U.S.A.

Does the Lee Obesity Index Measure General Obesity?

D. N. S T E P H E N S

Department of Child Health, The Medical School, Manchester M13 9PT, England

R e c e i v e d 13 M a r c h 1980

STEPHENS, D. N. Does the Lee obesity index measure general obesity? PHYSIOL. BEHAV. 25(2) 313-315, 1980.- Obesity, defined as increased percentage body fat, was correlated with the Lee index (weight °WNaso-Anal Length) in three groups of adult rats. One group had been fed laboratory chow and served as controls. Another group had been made obese by feeding a palatable diet, and the third group made lean by a period of undernutrition during their suckling period. Although the three groups differed significantly in percentage body fat, there were no significant differences in their Lee indices. Further, the Lee index did not correlate significantly with percentage fat in any of the groups. It is postulated that the reason for the lack of correlation between obesity and the Lee index in intact rats is that length is a relatively weak predictor of fat free mass in animals of a similar age and nutritional history.

Lee index Obesity Body fat Dietary obesity Early life undernutrition

A COMMON problem in studies of body weight regulation is in providing an estimate of body fat content without having to perform a laborious chemical extraction of the carcass. Not only is such an extraction time consuming and unpleas- ant to carry out, but necessitates killing the experimental animal. Many investigators have attempted to overcome the difficulty by expressing the relative obesity of the animal in terms of the Lee Index (weight°.Wnaso-anal length), which is often quoted as a reliable indicator of obesity (e.g., [3,8]). Little evidence is available on this point, however, and the index, was never intended by Lee as a measure of obesity, but rather, as an indication of whether the animal was in a healthy state of nutrition [5].

The use of the Lee Index as an obesity index stems from the work of Szentagothai, Flerko, Mess and Halasz [12] and was subsequently taken up by Bernardis and his colleagues [1,2]. While these workers established that the index was significantly correlated with body fat content in rats given ventromedial hypothalamic lesions either as adults or wean- lings, they emphasised that significant correlations did not exist in their sham-operated control groups. Furthermore, a recent study of obesity in mice questioned the use of the Lee index even in animals made obese by chemical (gold thioglu- cose) lesions of the hypothalamus [6]. From these studies, it is premature to use the index as a general measure of obesity and, therefore, it seemed useful to compare the Lee index with measured fat content in rats whose body fat was varied by means other than hypothalamic lesions.

METHOD

Subjects

The rats were of the Lister hooded strain, and were the relevant groups from a study reported elsewhere [ 10]. Lit ters were removed from well fed mothers at birth, and cross fos- tered to other well fed mothers, or to mothers fed daily with a food ration equal to half that eaten by ad lib fed controls.

This latter procedure is known to produce rats which are both smaller in size, and which have a reduced body fat content in adulthood [9,13]. At 21 days of age, all the mothers were given free access to food, and the pups were weaned at 30 days. At weaning, a Lean Group (n= 11) was provided by taking one male pup from each of the under- nourished litters, and this group was then fed standard lab- oratory diet (PMD, RHM Labsure, England) for 100 days. Two male pups were taken from each of the well fed litters, and one from each litter allocated to a Control Group (n= 11) which was also fed ad lib for 100 days. The other well fed pup was allocated to a Fat Group (n= 11) and fed, in addition to the standard diet, a palatable and varied ' supermarket ' diet for 100 days. The supermarket diet consisted of various foods such as sausage, banana, cake, cereals, biscuits and canned pet foods [10,11].

Procedure

At 130 days of age, body water was estimated by the tritium dilution method and body fat calculated [7] using equations determined in our laboratory relating fat content to body water content [10]. Rothwell and Stock [7] reported that fat estimated by this means shows a good correlation (r=0.868; p<0.001) with fat measured by chloroform- methanol extraction, and in this laboratory a correlation of r=0.950 (p<0.001) between the two measures has been found. At the same time, the rats were weighed and naso- anal lengths (NAL) measured under ether anaesthesia.

RESULTS AND DISCUSSION

Table 1 shows that rats fed the palatable diet were fatter, and rats undernourished in early life leaner than the controls. Nevertheless, there were no significant differences between the values of the Lee index between the experimental and control groups. Further, there was no significant correlation between the Lee index and percentage body fat content

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314 S T E P H E N S

T A B L E 1

SPEARMAN RANK-ORDER CORRELATION COEFFICIENTS, r, AND THEIR ASSOCIATED PROBABILITIES FOR VARIOUS PARAMETERS CORRELATED WITH BODY FAT EXPRESSED

AS A PERCENTAGE OF BODY WEIGHT

Control group Fat group Lean group Overall

% F a t 18.4 ± 0.9 26.5 ± 1.5¢ 13.6 ± 0.8:~ 19.5 _+ 1.1 Lee lndex 340.4 _+ 4.1 345.0 ± 2.2 332.6 ± 4.0 339.3 ± 2.2 r .150 .518 - . 100 .432 p NS <0.1 NS <0.05

Weight (g) 436.1 ± 11 .1 523.1 ± 16.35 309.0 _+ 7.7~; 419.6 ± 17.1 r - . 114 .539 .109 .758 p NS d0.1 N S <0.001

Length(mm) 223.1 + 2.9 233.4 ± 2.2t 202.2 _+2.0~: 219.5 ± 2.7 r - .018 .092 .191 .706 p NS NS NS <0.001

Weight/length 2.00 ± 0.05 2.19 ± 0.07* 1.53 _+ 0.035 1.91 _+ 0.06 r .032 .618 - .063 .726 p NS <0.05 NS <0.001

*different from corresponding value for control group, p <0.05. ~p<0.01. +p<0.001.

wi th in any of the indiv idual g roups , and on ly a weak corre la- t ion w h e n all t h r ee groups were c o n s i d e r e d toge ther . F o r the pu rpose of d i s t inguish ing b e t w e e n the t h r ee g roups , body weight or body length, i.e. N A L , were of more va lue t han the Lee index. Thus , empir ica l ly , the L ee index is not a rel iable ind ica to r of obes i ty .

W h y should this be? One poss ib le exp lana t ion of the weak cor re la t ions b e t w e e n Lee index and pe rcen t age fat is tha t ra ts of a g iven naso-ana l l eng th might va ry in fat free mass (FFM) . The t e rm for Lee index can be wr i t t en

L ee index = (Fa t + F F M ) °'~3 N A L

or (Lee index) '~ = Fa t + F F M ( N A L ) 3 ( N A L ) 3

Thus , Lee index = 3q, Fa t + F F M ( N A L ) 3 ( N A L ) 3

F r o m this , it fol lows tha t the L ee index will vary as m u c h due to changes in F F M as to changes in fat , and for the index to be a good measu re of obes i ty , the t e rm F F M / ( N A L ) 3 mus t be re la t ively invar iab le c o m p a r e d to the t e rm F a t / ( N A L ) 3. T~ble 2 shows tha t length is a poo r p red ic to r of F F M wi th in r~ ~ .~ same age and nu t r i t iona l h i s tory , a ccoun t ing for, at bes t , only ha l f the va r i ance , i .e. , F F M / N A L 3 is no t con- s tant . Thus , it is not surpr is ing tha t the Lee index does not cor re la te well wi th pe rcen t age body fat wi th in a g roup o f ra ts showing a fair a m o u n t of var ia t ion in F F M .

W h e n the p ropor t ion of weight occup ied by fat is high re la t ive to F F M , howeve r , t hen the va r ia t ion in F F M will a s s u m e less impor t ance , and the index would t hen be ex-

T A B L E 2

SPEARMAN RANK ORDER CORRELATIONS BETWEEN NASO-ANAL LENGTH, AND FAT FREE MASS FOR GROUPS OF RATS MADE

OBESE OR LEAN

n r p

Control group I l .785 <0.01 Fat group 11 .679 <0.05 Lean group 11 .409 NS Overall 33 .907 < 0.001

pec t ed to reflect the obesi ty . Ra ts wi th ven t romed ia l les ions a p p e a r to mee t this cr i ter ion [1,2] and the index is, t he re fo re , useful in compar ing groups of ven t romed ia l obese and con- trol rats . E v e n in this case , howeve r , it seems likely tha t the s impler ra t io of weight d iv ided by length would be as good an ind ica t ion of obes i ty as would the index. All such m e a s u r e s , of course , will be mis leading w h e n the expe r imen t a l t reat- m e n t gives rise to fat a ccumula t i on which is no t a ssoc ia ted wi th inc reased body weight [4]. Thus , if conc lus ions are to be d rawn as to a t r e a t m e n t ' s ef fects on obes i ty , the re is a lways d a n g e r in fail ing to measu re fat , e i the r d i rect ly by ex t rac t ion , or, whe re it is i m p o r t a n t to ma in t a in an in tac t an imal , by some indirect m e t h o d such as tha t used in the p r e sen t repor t .

ACKNOWLEDGEMENTS

This work was supported by grants to Professor John Dobbing from the Medical Research Council and from the National Fund for Research into Crippling Diseases. I thank Professor Dobbing, Dr. J. L. Smart and especially Mr. C. J. Whittaker for helpful discussion, and Mrs. G. Bourdillon for assistance with the body water meas- urements.

L E E I N D E X A N D O B E S I T Y 315

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