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close this bookChronic Energy Deficiency : Consequences and Related Issues (International Dietary Energy Consultative Group - IDECG, 1987, 201 pages)
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View the documentIntroduction
close this folderResearch relating to energy adaptation in man
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View the document1. General introduction
View the document2. The Sukhatme-Margen hypothesis
View the document3. Is energy balance regulated in man?
View the document4. The time basis of energy regulation
View the document5. Altered metabolic rate
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View the document7. Problems in testing the Sukhatme-Margen hypothesis
View the document8. The reproducibility of metabolic rates in man
close this folder9. Adaptation to underfeeding
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View the document9.1. The range of adaptation
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close this folder10. Overfeeding studies
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View the document10.1. Early studies
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close this folderSeasonality in energy metabolism
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close this folder3. Seasonal body weight fluctuations
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View the document3.1. Children
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close this folder4. Seasonal fluctuations of energy expenditure
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close this folderChronic energy deficiency and the effects of energy supplementation
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View the document2.1. Chronic energy deficiency
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close this folder4. Supplementation studies
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View the document4.1. The INCAP study
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close this folder5. Some possible explanations for the small effects
View the document5.1. Are the recipients really malnourished?
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View the document6. Contemporary models
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close this folderA critical view of three decades of research on the effects of chronic energy malnutrition on behavioral development
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View the document1. Background
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View the document3.1. Outcomes of primary and secondary malnutrition
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close this folderEffects of chronic energy deficiency on stature, work capacity and productivity
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close this folder1. Studies in adults
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View the document1.1. Malnutrition and VO2 max
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close this folder2. Studies in children
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View the document2.1. Anthropometry, sexual maturation and body composition in boys
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View the document3.3. Efficiency of economy of submaximal work in malnutrition
View the document3.4. Reduced physical activity in chronic energy deficiency
View the document3.5. Work performance in large and small individuals
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close this folderThe energy requirements of pregnancy and lactation
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close this folderMethodology of field studies related to socioeconomic effects of chronic energy deficiency
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View the documentAppendix
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close this folderPregnancy, lactation and childhood: Report of working group 1*
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View the document1. Introduction
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close this folder4. Children
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View the document4.1. Energy supply and physical growth of infants and children
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View the document4.3. Chronic energy deficiency and development
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close this folderWork capacity, work performance: Report of working group 2*
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close this folder1. Definitions
View the document1.1. Physical work capacity
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View the document4. Relationship of the proposed research activities to developing countries
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close this folderSocial and economic development: Report of working group 3*
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View the document1. Introduction
close this folder2. Designs for studying the effects of low energy intake on behavior
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View the document2.1. Naturalistic designs
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2. Reasons of seasonal variations in energy metabolism

Climatic-environmental conditions have an enormous influence on the vegetative cycle of the food and cash crops on which the whole economy of rural households in Less Developed Countries (LDC) depends. The same factors that regulate the agricultural cycle can therefore be expected to impinge on the energy metabolism of the individuals. Essential factors are: temperature, water availability, nature and structure of the soil, solar radiation, and variation in the photoperiod.

In equatorial or tropical areas, where temperature, solar radiation and photoperiod do not undergo substantial seasonal fluctuations, the only factor that limits vegetal development is water availability. For example, even sorghum, a drought-resistant vegetal species, needs about 250,000 L of water per ton of total dry matter produced. Since artificial irrigation is rarely possible in LDC, rain and other factors which limit or increase the loss of water through percolation, evaporation and/or transpiration (i.e., the nature of the ground) are critical. Therefore, the best indicators of agricultural production potential in equatorial and tropical areas are absolute and relative seasonality, derived from pluviometric data.

Absolute seasonality is the proportion of dry months among all months of a year. Dryness is not an absolute value depending only on pluviometric data; it is corrected for the evapotranspiration in relation to the culture, temperature, exposure to winds, relative humidity, nature and granulometrical structure of the soil, direct and indirect radiation, etc. The range of absolute seasonality extends from 0 (sufficient rains all year long) to 1 (total lack of a period favouring the optimal growth of plants).

Relative seasonality is the ratio between the amount of rain in different months and annual pluviosity. This index ranges from 0 (no seasonality) to 1.8 (extreme seasonality).

By combining data on annual rainfall with values of absolute and relative seasonality, we have constructed a rough, global index; it describes the likelihood and intensity of seasonal fluctuations on simultaneous demand and availability of food energy (Figure 1). Desert areas, characterized by permanent shortage, represent a peculiar and extreme situation and have not been included in this analysis. The remaining areas are subdivided into three categories.

In the very low seasonality category are areas with annual rainfall of more than 1000 mm, reasonably distributed throughout the year, and with an index of absolute seasonality of less than 0.40. No seasonal interference with the energy balance of the population is expected.

In the moderate seasonality category are areas with an annual rainfall between 500 and 1000 mm, an absolute seasonality between 0.40 and 0.75, and a relative seasonality between 0.8 and 1. The high absolute pluviosity or a bimodal distribution of rains ensures that the vegetative cycle is prolonged. In these areas, the likelihood of seasonal fluctuations of energy metabolism of individuals is very limited. Since agricultural work is spread throughout the year and food crops are harvested on a semicontinuous basis, energy is available at all times, without occurrence of a "hungry season", except in particular situations such as rain failure in unusually dry years.

In the severe seasonality category are areas with an annual pluviosity of less than 500 mm, an absolute seasonality index higher than 0.75, and values of relative seasonality higher than 1. In these areas, the vegetative period is very brief, and farmers are forced to concentrate all their physical efforts on a time usually coinciding with depleted food stores. Furthermore, the shortage of water imposes wide spacing between furrows, and the brevity of the vegetative period creates the need to utilize seed cultivars which have a short cycle and are less productive than those with a longer cycle. All this leads to a reduced potential for food production in these areas. BAYLISS-SMITH (1981) calculated that, in one year, a hectare of soil in an area with an absolute seasonality index below 0.5 and a relative seasonality index below 0.6 will theoretically produce 40 to 44 tons of total dry matter. An area where the two indexes are above 0.8 can, in the same period and for the same unit of surface, produce at most a theoretical quantity of 10 tons of total dry matter.


Figure 1. Grading of climatic seasonality of some areas of the world (see text for explanation).

The conclusions are obvious:

1. In LDC areas with an essentially agricultural economy, climatic seasonality is undoubtedly the overriding cause of seasonal energy imbalance of the population, either through its impact on energy expenditure or on food energy availability, or on both.

2. The statement that seasonality is "... the rule among adults in rural areas of developing countries" (TEOKUL, PAYNE and DUGDALE, 1986) represents an unwarranted generalization.

3. In areas with non-seasonal or bimodal climatic conditions, major fluctuations of human energy balance are not to be expected.

4. As climatic seasonality increases, physical labour demand - and thereby energy expenditure - tends to concentrate in a brief annual bout. Food availability is limited in a similar seasonal manner. The two fluctuations are often asynchronous, compound each other's effect and cause marked seasonal imbalances of energy metabolism.