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9.2. The response to semistarvation

When energy intakes are reduced substantially, a number of mechanisms are normally considered to be affected, and estimates of the changes are given in Table 4, which reproduces the summary of the physiological changes provided in the Minnesota monograph (KEYS et al., 1950). It should be noted that physical activity has been calculated as the difference between intake and the sum of other measured components of energy output, and that the specific dynamic action (SDA) is assumed to fall in proportion to the reduced energy intake. These assumptions are incorrect and will be considered in detail later.

Table 5. Populations on low energy intakes

Reproduced from DURNIN (1979), where no references are provided.

Included in Table 4 are recalculated values from data provided by NORGAN, FERRO-LUZZI and DURNIN (1974) on free-living New Guinea Kaul males. The same assumptions in calculating physical activity and SDA have been made in presenting their data for this Table as were made in the Minnesota experiment (TAYLOR et al., 1945). Energy turnover in the Norgan study is taken to be equivalent to the calculated energy expenditure and not to the lower figure of 8.1 MJ (1936 kcal) per day for energy intake. It is clear that the Kaul males are metabolizing very much more than the semistarved volunteers in Minnesota and that their "basal" metabolic rate was appreciably higher when expressed either in absolute terms or in relation to the fat-free mass. On this basis it is doubtful whether the Kaul men could be considered to be adapted to restricted intakes, although their data have been included amongst those groups quoted as seeming able "to exist in energy balance on astonishingly low energy intakes".

Table 5 reproduces a Table given by DURNIN (1979) to indicate some of the populations whom he describes as living on low energy intakes. The references are not given in this article, but the Jamaican data relate to Ashworth's studies and the New Guinea data to Durnin's own data from NORGAN, FERRO-LUZZI and DURNIN (1974). The data on the New Guinean coastal women, i.e., the Kaul women, suggest that their energy intakes, as quoted by DURNIN (1979), were indeed low and in the same range as those found in the other studies shown in Table 5. Since Durnin's own investigations can be considered as some of the best work conducted on energy balance in free-living individuals on "low" intakes, it would seem reasonable to examine these data in detail.

Table 6. The estimated energy turnover of Kaul women in the coastal region of New Guinea

⁺ Both intake and output measurements were made on this group but no separate details of the intake of this particular group were given. The lying metabolic rates were not measured under basal conditions but on a table in the village laboratory - presumably sometimes after a meal.

* Non-pregnant, non-lactating women with weight calculated from authors' Table 7.

FFM = Fat-free mass calculated from Table 4 by taking the value of 22% for the body fat content of all Kaul women.

Data from NORGAN et al. (1974) on New Guinea women and unpublished data from DAVIES et al. on Cambridge women. In the Cambridge study, the lying metabolic rate is the average value of a series of measurements made in the home in the morning and afternoon with no restriction on meals. Fat-free mass in the Cambridge women taken from body fat estimated from the sum of the four standard skinfold thickness measurements and equations from DURNIN and WOMERSLEY (1974).

Table 6 compares the energy intake and expenditure values as given by NORGAN and his colleagues (1974) with those of Cambridge women (DAVIES, unpublished; DURNIN and WOMERSLEY, 1974). The slightly different size of the groups listed in the intake and expenditure columns does not affect the comparison because the authors themselves note that there was an appreciable discrepancy between intake and output. They discuss this discrepancy in detail without coming to a conclusion. The possibility of the lying metabolic rates being enhanced by anxiety is one possibility suggested by the authors since the subjects were measured lying on a table in a village laboratory. However, the villagers were accustomed to the investigators undertaking the practical work. The explanation may well be wrong, therefore, particularly as data for other groups proved to be consistent. By recalculating the authors' data on lying metabolic rates and expressing it as a 24-hour value it seems much more probable that the food intake data are in error. The individuals were described as moderately active, and the energy cost of the various activities measured was appreciable, so it would be unrealistic to expect the intake values to be as low as they are. If a third of the 24 hours was spent in bed at a theoretical basal rate and the energy cost of the rest of the day, i.e., 16 hours, is calculated at only a sitting metabolic rate, then a sedentary output of 5.94 MJ is obtained which leaves only 206 kJ for all major physical activity in a day. All these conclusions point to there being a systematic error in the intake measurement rather than a systematic error in measuring energy expenditure.

Table 7. Energy turnover in farmers from the Upper Volta

Mean ± SEM
From BLEIBERG et al. (1981).

Table 6 includes values for energy output measured in normal-weight Cambridge women using techniques comparable to those of Durnin's group. It is clear from the comparison of New Guinea and Cambridge women that there is nothing remarkable about the data on energy output in the Kaul women, particularly when these are expressed in terms of fat-free mass. On a fat-free mass basis the observed metabolic rates at rest during the day are the same in the Cambridge and the Kaul women. On this basis we have suggested elsewhere (JAMES and SHETTY, 1982) that the findings on low energy intakes in less developed countries simply reflect the differences in body size, with some female (but not male) groups having surprisingly low intakes.

A further example of the discrepancy between energy intake and output measurements in developing countries has been published by BLEIBERG et al. (1981) and their data on farmers in the Upper Volta are shown in Table 7. In this case differences are seen only in the women and not in the men.

It seems then that the observed "low" intakes in developing countries, or in some groups in developed countries, may well be spuriously low. Intakes may be tower in these countries than in affluent societies, but many differences are readily explained by differences in body size.

Table 8, taken from APFELBAUM (1973), shows that in controlled experiments the range of adaptation is similar in men and women and that the extent of adaptation in lean and obese individuals seems to be comparable.

All these studies point to the conclusion that changes in metabolic efficiency occur with appreciable decreases in food intake and that body weight loss accompanies the fall in dietary energy. Those individuals in good health supposedly subsisting in an adapted state on what appears to be a low energy intake, in practice show little evidence of metabolic adaptation. There are therefore few, if any, good physiological examples from field work of Sukhatme's adapting individuals; changes in metabolic efficiency only occur as weight loss progresses.

Table 8. Weight loss and decrease of basal oxygen consumption during restricted diets M = Male; F = Female; N = Normal; O = Obese; U = Undernourished

(1) Decrease in basal VO₂ referred to the post-refeeding value; (2) The subject was Zuntz in person; (3) The subject was Loewy in person; (4) Decrease referred to BOOTHBY et al. (5) Diabetic, (6) Normal subjects with an experimental restricted diet of 1600 kcal for 6 days succeeding to a 3-year unquantifiable restricted diet; (7) Ambulatory subjects having gone off their diet on Sundays and holidays; (8) 19% with Benedict's apparatus, 20% in metabolic room; (9) Preceded by a 1-month restricted diet.

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