FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS	ESN:FAO/WHO/UNU/ EPR/81/6 August 1981
	WORLD HEALTH ORGANIZATION
	THE UNITED NATIONS UNIVERSITY

Item 2.2.2. of the Provisional Agenda

Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements

Rome, 5 to 17 October 1981

EFFECT OF ENVIRONMENTAL FACTORS ON ENERGY AND PROTEIN REQUIREMENTS

by

Reynaldo Martorell

Food Research Institute
Stanford University

I. Introduction

Most researchers find a coefficient of variation of 15 % for obligatory nitrogen losses in urine and faeces. An allowance of 30% (twice the C.V.) was therefore added to the estimated obligatory losses to compensate “for the effects of ordinary sources of stress of daily life such as minor infections and trauma, pain, anxiety and loss of sleep” by the last FAO/WHO Committee on Energy and Protein Requirements (FAO/WHO, 1973). There is no firm basis to date for altering this empirically derived factor and much less for assigning variable factors by occupation, social status, age, sex or any other variable.

The 1973 report considered the effect of climate on requirements concluding that “there was no quantifiable basis for correcting the resting and exercise energy requirements according to climate” (FAO/WHO, 1973). Protein requirements were also not corrected for climatic factors. Some new information has come to light since the last meeting and this is reviewed in this report. The effects of high altitude on energy requirements are also discussed.

This report also deals with the effects of infection on protein and energy requirements. While the 1973 report noted the significance of these effects, it did not specify any correction factors for infections.

The final section of this report considers whether the recommendations of the 1973 report regarding the effects of climate and infection on requirements ought to be changed.

II. Literature review

A. Nitrogen losses in sweat

The work of Mitchell and Hamilton (1949) and later of Consolazio et al. (1963) suggest heavy sweating results in nitrogen losses as high as 3 to 4 g. per day. These findings cannot be extrapolated to native populations of hot environments because the subjects in both studies were not acclimatized to heat. One important aspect of acclimatization is the gradual reduction in the N concentration in sweat as suggested by the very studies of Consolazio and colleagues.¹ During 16 days of experimentation at 100°F, the N concentration in sweat fell from 1.00 to 0.53 mg/g in the subjects included in Consolazio et al.'s 1963 study. A later study confirmed these findings (Consolazio et al., 1975) as did a study by Bass et al. (1955). Ashworth and Horrower (1967) reported that Jamaican subjects have low N concentrations in sweat and also noted that there was an inverse relationship between sweat volume and N concentration.

Acclimatization could also involve a reduction in urinary N loss to compensate for the N loss in heavy sweating. The literature on this issue is conflicting as some authors find no evidence of renal compensation (Consolazio et al., 1963; Weiner et al., 1972; Consolazio et al., 1975) while others do (Ashworth and Horrower, 1967; Huang et al., 1972).

¹ Another reason why Consolazio's values may be high is because sweat was collected in arm bags. Arm sweat is more concentrated than sweat from the whole body (Ashworth and Horrower, 1967). Also, protein intakes in Consolazio's study were high. Some investigators have shown that the nitrogen loss in sweat is increased at higher protein intakes (Howat et al., 1975; Calloway et al., 1971; Ashworth and Horrower, 1967; Consolazio et al., 1975).

The nitrogen losses in sweat in tropical environments do not appear to be excessive. In Tanzanian subjects, the N lost in sweat would not exceed 1 g/day on a good diet or 0.5 g/d on a low protein diet (Weiner et al., 1972). Ashworth and Horrower (1967) estimated Jamaican men lost 0.5 g N/day in approximately 3 L of sweat. These values exceed those allotted for skin and miscellaneous losses in the 1973 FAO/WHO report (i.e., 0.5 mg N/kg/day for skin and miscellaneous losses or 0.35 g N/day for a 70 kg man) by a small amount. A joint FAO/WHO Memorandum (1979) concluded the nitrogen cost in sweat was trivial.

B. Energy expenditure in hot environments

Another issue of importance is whether work capacity and energy expenditure are affected by heat. Since blood flow from the body core to its surface is increased in heat stress, one would expect that during heat stress less blood would be available to exercising muscle. While one would not necessarily expect the energy cost of submaximal work to be affected, work capacity would clearly be diminished by heat stress. Gupta et al. (1977) found that the oxygen consumption of Indian soldiers during sub-maximal work decreased in hotter temperatures. However, the total oxygen cost of the submaximal work remained the same because increased anaerobic metabolism compensated for the reduced blood flow to muscle. Williams et al. (1962) and Sengupta et al. (1979) also reported similar findings. Brun et al. (1979) found, in Iranian agricultural workers, no significant differences between the energy cost of standardized activities at high summer temperatures and moderate temperatures. Consolazio et al. (1962), on the other hand, reported no changes in oxygen consumption in moderate and heavy activity when the temperature was increased from 70°F to 85°F, though at 100°F oxygen consumption values increased by over 11 percent. Other authors also observed a rise in oxygen consumption with increased temperature (Durnin and Haisman, 1966) though others reported no effect of temperature (Saltin et al., 1972).

Reports about work capacity or rather, maximal oxygen consumption (VO₂ max) in a hot environment are also conflicting. Williams et al. (1962) reported that the VO₂ max of subjects was not significantly different in hot compared to comfortable environments. Matsui et al. (1978) report no significant differences in VO₂ max at three different temperatures. Similar findings were reported by Pirnay et al. (1970) in coal miners; however, when a group of students was exposed to hot temperatures for 20 minutes prior to performing the same work done by the miners, VO₂ max did decrease. Mostardi et al. (1974) found no changes in VO₂ max with increases in body temperature. Saltin et al. (1972) reported that exercising to exhaustion in a warm environment influences work performance time without altering VO₂ max. They reasoned that anaerobic metabolites accumulated in the exercising muscles in the warmer environment causing the subjects to stop earlier. Like Pirnay et al. (1972), Saltin et al. (1972) found significant reductions in both work performance and VO₂ max when the subjects were preheated prior to performing the maximal exercise at 40°C. Gupta et al. (1977) found a significant fall in VO₂ max with increased environmental temperatures, with the fall being greater in hot humid environments. The latter would be expected to impose a greater thermoregulatory strain than dry heat because high humidity limits sweat evaporation.

C. Energy expenditure in cold environments

Some primitive people must cope with very cold temperatures, particularly at night.² The aborigines of central Australia and the Bushmen of the Kalahari Desert wear no clothing except for a genital cover and during winter nights may be exposed to moderately cold temperatures (e.g., average minimum temperature of 3–5°C in July). That these people manage to sleep well under such conditions while foreigners cannot at all is indicative of adaptive physiological processes. Most peoples inhabiting cold regions are apparently able to maintain high skin and extremity temperatures by increasing the basal metabolic rate.³ These efforts to maintain body temperatures obviously increase energy requirements. The biological and cultural adaptations of primitive people to the cold are discussed extensively by Frisancho (1979) and LeBlanc (1975).

² Environmental stress in a cold climate is primarily a function of ambient temperature and wind speed. The resulting wind chill index is a better representation of cold stress.

On the other hand, with proper housing and clothing, modern man is essentially unexposed to the cold.⁴ Most authors find lower temperatures do not appear to influence basal or resting metabolism in Europe and North America (McCarroll et al., 1979; Petrasek, 1978; Dauncey, 1979; Bray and Atkinson, 1977). Investigations in the Artic and Antartic show none or only small seasonal variations in BMR (Discussion, 1966). Yet, Japanese investigators have for years claimed to observe a small seasonal variation in basal metabolism arguing that Japanese are not as insulated from cold stress as North Americans (Sasaki, 1966; Yoshimura et al., 1966; Matsui et al., 1978).⁵

³ Other groups such as the Australian aborigines apparently cope with the cold by decreasing insulation of the body shell through vasoconstriction and by tolerating moderate cooling of the skin and extremities without raising the basal metabolic rate (Scholander et al., 1958; Hammel et al., 1959).

⁴ In breathing, cold air is warmed to values well above temperatures associated with tissue freezing before reaching the trachea or bronchi (Buskirk, 1978). The energy cost of warming air has not apparently been assessed.

⁵ Basal metabolism was increased by 35% in the winter when water temperatures fall to 10°C in women divers from the Korean peninsula of Ama. The degree of cold exposure to which these women subject themselves has no parallel in human populations (Hong, 1963).

Energy expenditures may be increased in properly clothed men working outside. It has been estimated that artic clothing may increase energy expenditure by 16 percent over desert clothing, and 8 percent over temperate clothing (Gray et al., 1951). Some argue that the “hobbling” effect of bulky multiple clothing layers adds 15 percent to the total energy cost of movement, in addition to the cost of the weight of the clothing (Goldman and Teitlebaum, 1972). The minimal weight of clothing and equipment in soldiers in cold environments is over 40 pounds and counting skis and magnesium shoes, some 55 pounds (McCarroll et al., 1979). The difficulty of the terrain will also affect energy expenditures. Relative to a black-top road, the energy expended in walking is increased by 30 percent in hard-packed snow and by as much as 500 percent in very deep snow (Pandolf et al., 1976).

In summary, energy expenditures are increased in primitive peoples exposed to cold environments. Proper clothing and shelter, rather than energy for basal metabolism, would seem to be the more pressing need. The situation in modern man is succinctly summarized by McCarrol et al. (1979, p. 609):

It is clear that temperature per se does not increase basal metabolism in properly clothed individuals. The only adjustment to food intake that is necessary is that which is required by increased activity (work).

D. Nutritional effects of high altitude

Acute exposure to high altitudes, especially over 3500 m, leads to anorexia, reduced food consumption and weight loss. These are temporary effects; appetite for example, returns to normal within two weeks of high altitude residency (Hannon et al., 1976; Ward, 1975; Surks et al., 1966; Johnson et al., 1969; Whitten et al., 1968).

New comers to high altitude also show decreased maximal oxygen uptakes (Buskirk, 1976; Blatteis, 1978; Consolazio et al., 1966; Dill and Adams, 1971). Some authors have found a gradual improvement in the aerobic capacity in subsequent weeks as the oxygen carrying capacity improves (e.g. increased hematocrit and hemoglobin) but since cardiac output is reduced, the VO₂ max is never restored to its pre-altitude value (Grover, 1978; Blatteis, 1978).⁶

On the other hand, Blatteis (1978) found that while the O₂ cost of submaximal standarized exercises is increased upon arrival to high altitude, no differences relative to sea values can be demonstrated one week after arrival. Blatteis' (1978) interpretation of his work and that of others is that submaximal exercise is not affected by altitude.

E. Infection and nutritional status

The most common infectious diseases in developing countries are those of the gastrointestinal and the respiratory tract. Children under three years of age are by far the group most likely to be more frequently and more severely ill.

⁶ Some authors find that the VO₂ max of Quechua Indians tested at high altitude equals that of lowlanders tested at sea level and exceeds that of lowlanders acclimatized and tested at high altitude (Frisancho, 1979; Grover, 1978). Perhaps, adaptations acquired during the developmental period (e.g. enlarged lung volume, chest size and right ventricle of heart) account for the findings.

1. Field studies of infection and growth

The results of studies of illness and physical growth are summarized in Table 1 for developed countries and in Table 2 for developing countries. The separation according to area of origin reveals constrasting results. While most of the studies from developed nations report no associations between illness and physical growth, those from developing nations report that common childhood ailments, in particular diarrheal diseases are clearly associated with poor physical growth.⁷

Differences in methodology may explain the results. The measurement of illness was more direct in developing countries and greater reliance in the studies done in wealthier nations on school records and on lengthy recall interviews with parents may have obscured existing associations. However, it may be that the findings reflect contrasting ecological settings. The disease load experienced by children in developed countries is light in comparison to that of malnourished populations. Another obvious difference is the superior nutritional status of children from developed nations. Perhaps no associations were evident in the wealthier countries because such children, with ample nutritional resources, quickly made up the losses which the infrequent episodes of illness may have caused.

⁷ Parasitic infections are more common than diarrheal diseases but far less important. For example, most studies have been unable to show that treatment of intestinal parasites with antihelminthic or antiprotozoal drugs on growth in pre-school children improves growth rates (Salomons and Keusch, 1981).

The magnitude of the impact of illness on physical growth can be estimated from the results of studies carried out in four rural Guatemalan villages (Martorell et al., 1975a, 1975b). Children who were relatively free from diarrhea from birth to 7 years of age grew significantly better than children not so fortunate. The differences in growth at 7 years of age between both groups were 3.5 cm in height and 1.5 kg in weight. These differences are of large magnitude if we consider that 7-year-old children from such communities differ from well-nourished children from the U.S.A. by about 13 cm in height and 5 kg in weight.⁸

Table 1 --Illness and physical growth indicators of nutritional status: developed nations

Table 2 --Illness and physical growth indicators of nutritional status: developing nations. All samples are from the rural area

¹ The Guatemalan samples studied by Guzmán et al. (1968), Mata et al. (1971, 1972), and Martorell et al. (1975a, 1975b) were independent studies carried out in separate communities.

2. Effects of infection and food untakes

One of the mechanisms through which infections affect nutritional status is by reducing food intake. Anorexia and even nausea and vomiting frequently accompany even the mildest of infections in children. These effects may be compounded by cultural practices which restrict the child's solid and fluid intake.

Recent findings provide estimates of the extent to which food intake is reduced by infections. Hoyle et al. (1980) found that total calorie intakes in children with diarrhea were 40 percent lower than in healthy children. Molla et al. (1981) reported that diarrheal diseases reduced food intake by 30 percent. These two studies from Bangladesh show greater intake reductions than what have been observed in Guatemala by Mata et al. (1980) and Martorell et al. (1980). Mata et al. (1980) showed children consumed 93 percent of estimated requirements (i.e. 1250 kcal/day) when healthy but only 80 percent when ill with diarrhea. Relative to intakes observed when healthy, intakes were reduced by 14 percent by diarrheal diseases.⁹ Martorell et al. (1980) reported diarrheal diseases reduced intakes by about 19 percent. Reductions were similar for energy and protein.¹⁰ Combining all studies, diarrheal disease can be said to lower food intakes by 15 to 40 percent.

⁸ The vulnerability of malnourished children to infection is also illustrated by the fact that immunizations with live agents (BCG, smallpox, polio, DPT + polio), which are innocuous experiences to most well-nourished children, can lead to substantial weight loss, particularly in children less than 6 months of age or with a poor initial status (Kielman, 1977).

⁹ Children consumed 1161 k cal/day when healthy and 996 k cal when ill with diarrhea. When sick, intakes were 86 percent of normal (996/1161).

The impact of infectious diseases on dietary intakes can be estimated for populations if the frequency of illnesses and their average impact on diets are known. Martorell et al. (1980) found that twenty-three percent of pre-school children (i.e. 1 to 5 years of age) in Guatemala were sick every day with any of several symptoms included in a summary variable (i.e. diarrhea, apathy, fever, vomiting, rash, and confined to bed). The average effect of the summary variable was 175 kcal/day. Thus, the group's intake was lower by 40 kcal/day (.23 × 175) on account of the effects of the summary variable. The children of this study had intakes that were lower, for their age and body size, than the FAO/WHO requirements by 225 kcal/day. In other words, at least 18 percent (i.e. 40/225 kcal/day) of the apparent energy deficit may be explained by the effect of the summary variable on intakes.

¹⁰ Martorell et al. (1980) found the effect of respiratory infections on energy intakes to be much less (-67 kcal/day) than that of diarrhea (-160 kcal), apathy (-175 kcal/day) or a summary indicator of common but important symptoms (-175 kcal).

3. Effects of illnesses on nutrient utilization.

Diarrheal diseases are accompanied by malabsorption of sugars, nitrogen, fats and micronutrients (Rosenberg et al., 1977). Illnesses also have profound effects on nutrient metabolism and utilization. A variety of infectous agents, including bacteria, ricketsia, and viruses, have been shown to produce similar but marked alterations in virtually all aspects of nutrient metabolism. The nature and sequence of these responses from the moment of exposure through the incubation phase and the febrile period to convalescence have been extensively studied by Beisel (1977). Foremost among the changes are the disturbances in protein metabolism. Infections bring about protein catabolism and, if the illness is severe and prolonged, lead to a depletion of the lean body mass stores.¹¹

4. Estimates of the nutritional cost of illness.

Brisco (1979) attempted to estimate the quantitative effect of infection on the use of food by children. In spite of the limitations of the data, Brisco (1979) was able to conclude that anorexia during infection and mortality (i.e. the food consumed by those who died was “wasted”) were the principal factors contributing to food inefficiency in a cohort of children who survive to their fifth birthday in Bangladesh. Brisco estimated the amount of food that is not used effectively may be reduced from 9 percent to 3 percent in a hypothetical situation where all sources of infection are eliminated but other conditions remain unchanged.

Preliminary data from Martorell and Yarbrough (1981) allow for an indirect estimate of the nutritional cost of infections. From 12 to 36 months of age, the Guatemalan children they studied grew 4.09 kg while children from Denver, U.S.A. grew 4.53 kg (Hansman, 1970) a difference of 440 g. These rather adequate growth rates are partly explained by the fact these children were participating in a food supplementation program. Martorell and Yarbrough (1981) estimated that 100 kcal provided daily from 12 to 36 months resulted in 261 g greater growth in weight during the same period.¹²

¹¹ See Mata et al. (1980) Chen (1981) and Brisco (1979) for an expanded discussion of the mechanisms through which infectious diseases, and particularly diarrheal diseases, affect growth.

¹² Apparently, only a small portion of the calories provided were used for tissue synthesis and for the maintenance of this new tissue. Perhaps physical activity (which was not measured) was increased appreciably.

In the same population and age range, the authors estimated the average child failed to gain 305 g on account of the summary variable explained above.¹³ The effects of infection and of supplement were found to be independent. From the above, it can be calculated that in theory, the negative effects of infection on growth, 305 g, could be made up by 116 daily supplement calories (305/261). Whether 116 kcal/day is a fair estimate of the energy cost of infection in these children is not clear. It is an estimate, however, of what it would take to undo the deleterious effects of infection.

¹³ This figure represents the long term effects of acute illnesses. While present, infections lead to weight loss, including lean body mass, fat and water. During convalescence, hydration is restored and catch up in tissue loss and perhaps in growth rates may take place. The figure of 305 g is therefore, the amount which compensatory mechanisms failed to make up.

III. Concluding remarks

The losses of nitrogen in heavy sweating appear to have been underestimated in the 1973 report. The level of correction as pointed out, is however trivial.

The issue of whether resting and exercising metabolic rates vary with environmental temperature and altitude is a far more important question. In reviewing the literature, one is confronted with many inconsistencies which are difficult to reconcile because of methodological differences between studies (e.g. different levels of physical condition and of acclimatization in subjects; different intensities, duration and types of work; varying manners of inducing heat, cold or hypoxic stimuli, and different measurement techniques). An important fact to keep in mind is that most people work and exercise at a submaximal level. Most of the studies reviewed indicate that the energy cost of standarized and short interval tasks performed at submaximal level are not affected by heat, cold, or altitude. The evidence also suggests that as the conditions become extreme (e.g. preheating of subjects, high hot-humid conditions) and as the intensity of work approaches maximal levels, working capacity (i.e. VO₂ max is reduced) is impaired. What this means is that hard, strenuous work is difficult to sustain in extreme environmental conditions. Extreme environments appear therefore, to limit total energy expenditures but whether these are different than they would have been under more moderate conditions is an open question. More research should be carried out in workers going about their daily routines and less, it would seem, on laboratory exercises.

Without proper clothing and housing, there is no question that a cold environment will increase energy requirements. Except for some primitive (e.g. Australian aborigines) or impoverished peoples (e.g. Quechua Indians), most people protect themselves appropriately. Where metabolic rates are significantly raised to cope with cold stress, proper clothing and shelter, rather than food, should be the corrective measure. Though heavy and bulky clothing increases energy expenditures, activity patterns are likely to change in winter (e.g. outdoor recreational activities) with the end result that total energy expenditures may in fact decrease. Again, studies of energy expenditures in normal people under normal circumstances throughout the year are required.

No allowances for temperature or altitude should therefore be recommended. Rather, adjustments should be based on actual patterns of energy expenditure in specific occupations in specific environmental conditions.

There appears to be no doubt that infectious diseases have important adverse nutritional effects in developing countries, particularly in young children. Indeed, Mata et al. (1977, 1980) eloquently claim infectious diseases may overshadow the lack of food per se as causes of malnutrition. While the “nutritional cost” of infections such as diarrheal diseases may be roughly estimated, it would not be appropriate to use these estimates for adjusting energy and protein requirements. The problems of infection must be dealt with, not through food, but rather through health education, environmental sanitation and preventive medicine. Further, it is unlikely that children can be fed while the anorexic effects of illnesses last, though better appetites would be expected during convalescence. Finally, though infections may be less severe in well-nourished children, incidences will remain high regardless of dietary intakes. Strategies for improving nutritional status must include therefore aggressive measures for controlling infectious diseases.

REFERENCES

1. Ashworth, A. and A. D. B. Harrower. Protein requirements in tropical countries: nitrogen losses in sweat and their relation to nitrogen balance. Br. J. Nutr. 21 : 833–843, 1967.

2. Bass, D. E., C. R. Kleeman, M. Quinn, A. Henschel and A. H. Hegnauer. Medicine. 34 : 323, 1955.

3. Beaton, G. H., D. H. Calloway and J. Waterlow. Protein and energy requirements: a joint FAO/WHO memorandum. Bull. World Health Org. 57 : 65–79, 1979.

4. Blatleis, C. M. Oxygen uptake and blood lactate in man during mild exercise at altitude. In Environmental Stress: Individual Adaptations. L. A. Folinsbee et al (Eds) New York : Academic Press, 1978, pp. 351–369.

5. Bray, G. A. and R. L. Atkinson. Factors affecting basal metabolic rate. Prog. Fd. Nutr. Sci. 2 : 395–403, 1977.

6. Brun, T. A., C. A. Geissler, I. Mirbagheri, H. Hormozdiary, J. Bastani and H. Gedayat. The energy expenditure of Iranian agricultural workers. Amer. J. Clin. Nutr. 32: 2154–2161, 1979.

7. Buskirk, E. R. Work performance of newcomers to the Peruvian Highlands. In P. T. Baker and M. A. Little (Eds) In Man in the Andes: A Multidisciplinary Study of High-Altitude Quechua Natives. Stroudsburg, Pa.: Dowden, Hutchinson & Ross, Inc., 1976.

8. Buskirk, E. R. Cold stress: a selective review. In L. J. Folinsbee et al. (Eds) Environmental Stress: Individual Adaptations. New York: Academic Press, 1978, pp. 249–266.

9. Calloway, D. H., A. C. F. Odell and S. Margen. Sweat and miscellaneous nitrogen losses in human balance studies. J. Nutrition 101 : 775–786, 1971.

10. Cole, T. J. and J. M. Parkin. Infection and its effect on the growth of young children: a comparison of the Gambia and Uganda. Transactions of the Royal Society of Tropical Medicine and Hygiene 71 : 196–198, 1977.

11. Condon-Paoloni, D.,J. Cravioto, F.E. Johnston, E. R. de Licardie, and T. O. Scholl, Morbidity and growth of infants and young children in a rural Mexican village. Amer. J. Pub. Health. 67 : 651–656, 1977.

12. Consolazio, C. F., H. L. Johnson, R. A. Nelson, J. G. Dramise and J. H. Skala. Protein metabolism during intensive physical raining in the young adult. Amer. J. Clin. Nutr. 28 : 29–35, 1975.

13. Consolazio, C. F., L. O. Matoush and R. A. Nelson. Energy metabolism in maximum and sub-maximum performance at high altitudes. Fed. Proc. 25: 1380–1387. 1966.

14. Consolazio, C. F., L. R. O. Matoush, R. A. Nelson, J. B. Torres and G. J. Isaac. Environmental temperature and energy expenditures. J. Appl. Physiol. 18 : 65–68, 1963.

15. Dauncey, M. J. Energy metabolism in man and the influence of diet and temperature: A Review. J. Human Nutri. 33: 259–269, 1979.

16. Dill, D. B. and W. C. Adams. Maximal oxygen uptake at sea level and at 3,090 maltitude in high school champion runners. J. Appl. Physiol. 23 : 555–560, 1967.

17. Discussion. Federation Proceedings. 25 : 1175–1176, 1966.

18. Draper, K. C., and C. C. Draper, Observations on the growth of African infants: with special reference to the effects of malaria control. J. Trop. Med. Hyg. 63 : 165–171, 1960.

19. Durnin, J. V. G. A. and M. F. Haisman. The effects of hot environments on the energy metabolism of men doing standardized work. J. Physiol. 183 : 75P, 1966.

20. Evans, M. E. Illness history and physical growth. II. A comparative study of the rate of growth of preschool children of five health classes. Amer. J. Dis. Child. 68 : 390–394, 1944.

21. FAO/WHO. Energy and Protein Requirements. Rome: FAO, 1973.

22. Frisancho, A. Roberto. Human Adaptation: A Functional Interpretation. St. Louis: C. V. Mosby Company, 1979.

23. Goldman, R. F. and A. Teitlebaum. Increased energy cost and multiple clothing layers. J. Appl. Physiol. 33 : 181–183, 1972.

24. Grover, R. F. Adaptation to high altitude. In. Environmental Stress: Individual adaptations. New York: Academic Press, 1978.

25. Gray, E. L., F. C. Consolazio and R. M. Kark. Nutritional requirements for men at work in cold, temperate and hot environments. J. Appl. Physiol. 4 : 270–275, 1951.

26. Gupta, J. Sen, G. P. Dimri and M. S. Malhotra. Metabolic responses of Indians during sub-maximal and maximal work in dry and humid heat. Ergonomics 20 : 33–40, 1977.

27. Guzman, M. A., N. S. Scrimshaw, H. A. Bruch, and J. E. Gordon. Nutrition and infection field study in Guatemalan villages, 1959–1964. IIV. Physical growth and development of preschool children. Arch. Environ. Hlth. 17 : 107–118, 1968.

28. Hammel, H. T., R. W. Elsner, D. H. LeMessurier, H. T. Anderson and F. A. Milan. Thermal and metabolic responses of the Australian aborigine exposed to moderate cold in summer. J. Appl. Physiol. 14 : 605–615, 1959.

29. Hannon, J. P., G. J. Klain, D. M. Sudman, and F. J. Sullivan. Nutritional aspects of high-altitude exposure in women. Am. J. Clin. Nutr. 29 : 604–613, 1976.

30. Hansman, C. Anthropometry and related data. In Human Growth and Development. R. H. McCammon (Ed) Springfield, Illinois: Charles C. Thomas, 1970, pp. 101–154.

31. Hardy, M. C. Frequent illness in childhood, physical growth and final size. Amer. J. Phys. Anthrop. 23 : 241–246, 1938.

32. Hewitt, D., D. K. Westropp, and R. M. Acheson, Oxford child health survey: effect of childish ailments on skeletal development. Br. J. Prev. Soc. Med. 9 : 179–186, 1955.

33. Hong, S. K. Comparison of diving and nondiving women of Korea. Fed. Proc. 22 : 831–833, 1963.

34. Howatt, P. M., M. K. Korslund, R. P. Abernathy and S. J. Ritchey. Sweat nitrogen losses by and nitrogen balance of preadolescent girls consuming three levels of dietary protein. Amer. J. Clin. Nutri. 28 : 879–882, 1975.

35. Hoyle, B., M. Yunus, and L. C. Chen. Breast feeding and food intake among children with acute diarrheal disease. Amer. J. Clin. Nutr. 33 : 2365–2371, 1980.

36. Huang, P. C., H. E. Chong and W. M. Rand. Obligatory urinary and fecal nitrogen losses in young Chinese men. Journal of Nutrition. 102 : 1605–1614, 1972.

37. Johnson, H. L., C. F. Consolazio, L. O. Matoush and H. J. Krzywicki. Nitrogen and mineral metabolism at altitude. Federation Proc. 28 : 1195–, 1969.

38. Kielman, A. A. Weight fluctuations after immunization in a rural preschool child community. Amer. J. Clin. Nutr. 30 : 592–598, 1977.

39. Kubat, K., J. Kourim, M. Novahova, M. Moderova, and M. Stloukalova. The relation of acute morbidity in preschool age to the weight and height in six years old children. Ceskoslovenska Pediatrie. 26 : 105–106, 1971

40. LeBlanc, J. Man in the Cold. Springfield, Ill. Charles C. Thomas, 1975.

41. Mardsen, P. D. The Sukuta project. A longitudinal study of health in Gambian children from birth to 18 months of age. Transactions of the Royal Society of Tropical Medicine and Hygiene, 58 : 455–489, 1964.

42. Martens, E. J. and H. V. Meredith. Illness history and physical growth I. Correlation in junior primary children followed from fall to spring. Amer. J. Dis Child. 64 : 618–630, 1942.

43. Martorell, R., J-P, Habicht, C. Yarbrough, A. Lechtig, R. E. Klein, and K. A. Western, Acute morbidity and physical growth in rural Guatemalan children. Amer. J. Dis. Child. 129 : 1296–1301, 1975a.

44. Martorell, R., C. Yarbrough, A. Lechtig, J-P, Habicht, and R. E. Klein Diarrheal diseases and growth retardation in preschool Guatemalan children. Amer. J. Phys. Anthrop. 43 : 341–346, 1975b.

45. Martorell, R., C. Yarbrough, S. Yarbrough, and R. E. Klein. The impact of ordinary illnesses on the dietary intakes of malnourished children. Amer. J. Clin. Nutr. 33 : 345–350, 1980.

46. Martorell, R. and C. Yarbrough. The energy cost of diarrheal diseases and other common illnesses in children. Paper prepared for the workshop. “Interactions of diarrhoea and malnutrition,” Bellagio, Italy, May 1981.

47. Mata, L. J., J. J. Urrutia, and A. Lechtig, Infection and nutrition of children of a low socioeconomic rural community. Ameri. J. Clin. Nutr. 24 : 249–259, 1971.

48. Mata, L. J., J. J. Urrutia, C. Albertazzi, O. Pellecer, and E. Arellano. Influence of recurrent infections on nutrition and growth of children of Guatemala. Amer. J. Clin. Nutr. 25 : 1267–1275, 1972.

49. Mata, L. J., R. A. Kronmal, J. J. Urrutia, and B. Garcia. Effect of infection on food intake and the nutritional state: perspectives as viewed from the village. Amer. J. Clin. Nutri. 30 : 1215–1227, 1977.

50. Mata, L. J., R. A. Kronmal and H. Villegas. Diarrheal diseases : a leading world health problem. In Cholera and Related Diarrheas O. Ouchterlony and J. Holmgren (Eds) Goteborg: S. Karger, Basel, 1980, pp. 1–14.

51. Matsui, H., K. Shimaoka, M. Miyamura and K. Kobayashi. Seasonal variation of aerobic work capacity in ambient and constant temperature. In Environmental Stress: Individual Adaptations. L. J. Folinsbee et al., Eds. New York: Academic Press, 1978, pp. 279–291.

52. Meredith, H. V. and V. B. Knott. Illness history and physical growth. III. Comparative anatomic status and rate of change for schoolchildren in different long-term health categories. Amer. J. Dis. Child. 103 : 146–151, 1962.

53. McCarroll, J. E., R. F. Goldman and J. C. Denniston. Food intake and energy expenditure in cold weather military training. Military Medicine. 144 : 606–610, 1979.

54. Mitchell, H. H. and T. S. Hamilton. J. Biol. Chem. 178 : 345, 1949.

55. Molla, A. M., A. Molla, S. A. Sarker, and M. M. Rahaman. Intake of nutrient during and after recovery from diarrhoea in children. Paper prepared for the workshop “Interactions of diarrhoea and malnutrition,” Bellagio, Italy, May 1981.

56. Morley, D., M. Woodland, and W. J. Martin. Whooping cough in Nigerian children. Tropical and Geographical Medicine. 18 : 169–182, 1966.

57. Morley, D., J. Bicknell, and M. Woodland. Factors influencing the growth and nutritional status of infants and young children in a Nigerian village. Transactions of the Royal Society of Tropical Medicine and Hygiene. 62 : 164–195, 1968.

58. Mostardi, R., R. Kubica, A. Veicsteinas and R. Margaria. The effect of increased body temperature due to exercise on the heart rate and on the maximal aerobic power. Europ. J. Appl. Physiol. 33 : 237– 245, 1974.

59. Noack, R. Regulation of body temperature. Prog. Fed. Nutr. Sci. 2 : 473–481, 1977.

60. Palmer, C. E. The relation of body build to sickness in elementary school children. Amer. J. Phys. Anthrop. (Supplement), 21 : 7–8, 1936.

61. Pandolf, K. B., M. F. Haisman and R. F. Goldman. Metabolic energy expenditure and terrain coefficients for walking on snow. Ergonomics. 19 : 683–690, 1976.

62. Petrasek, R. Influence of climatic conditions on energy and nutrient requirements. Prog. Fd. Nutr. Sci. 2 : 505–514, 1978.

63. Pirnay, F., R. Deroanne and J. M. Petit. Maximal oxygen consumption in a hot environment. J. Applied Physiol. 28 : 642–645, 1970.

64. Rowland, M. G. M., T. J. Cole, and R. W. Whitehead. A quantitative study into the role of infection in determining nutritional status in Gambian village children. Br. J. Nutr. 37 : 441–450, 1977.

65. Salomons, N. W. and G. T. Keusen. Nutritional implications of parasitic infections. Rev. 39 : 149–161.

66. Saltin, B., A. P. Gagge, U. Bergh and J. A. J. Stolwijk. Body temperatures and sweating during exhaustive exercise. J. Applied Physiol. 32 : 635–643, 1972.

67. Sasaki, Takashi. Relation of basal metabolism to changes in food composition and body composition. Federation Proceedings. 25 : 1165–1168, 1966.

68. Scholander, P. F., H. T. Hammel, J. S. Hart, D. H. LeMessurier and J. Steen. Cold adaptation in Australian aborigines. J. Appl. Physiol. 13 : 211–218, 1958.

69. Sengupta, A. J., D. N. Sarkar, S. Mukhopadhyay and D. C. Goswami. Relationship between pulse rate and energy expenditure during graded work at different temperatures. Ergonomics. 22 : 1207– 1215, 1979.

70. Surks, M. I., K. S. K. Chinn and L. O. Matoush. Alterations in body composition in man after acute exposure to high altitude. J. Appl. Physiol. 21 : 1741–1746, 1966.

71. Turner, C. E., W. W. Longee, K. Saravia, and R. P. Fuller. Rate of growth as a health index. Research Quarterly, 6 : 29–40, 1935.

72. Valadian, I., R. B. Reed, H. C. Stuart, B. S. Burke, S. I. Pyle, and J. C. Cornoni. Interrelationships between protein intake, illness, and growth as manifested by children followed from birth to 18 years. unpublished manuscript.

73. Ward, W. Mountain Medicine. A clinical study of cold and high altitude. Van Nostrand Reinhold Co., New York.

74. Weiner, J. S., J. O. C. Willson, H. El-Neil and E. F. Wheeler. The effect of work level and dietary intake on sweat nitrogen losses in a hot climate. Br. J. Nutr. 27 : 543–552, 1972.

75. Whitten, B. K., J. P. Hannon, G. T. Klain and K. S. K. Chinn. Effect of high altitude (14,100 ft.) on nitrogenous components of human serum. Metabolism 17 : 360- , 1968.

76. Williams, C. G., G. A. G. Bredeel, C. H. Wyndham, N. B. Strydom, J. F. Morrison, J. Peter, P. W. Fleming and J. S. Ward. Circulatory and metabolic reactions to work in heat. J. Applied Physiology. 17 : 625–638, 1962.

77. Yoshimura, M., K. Yukiyoshi, T. Yoshioka and H. Takeda. Climatic adaptation of basal metabolism. Federation Proceedings. 25 : 1169–1174, 1966.