|Chronic Energy Deficiency : Consequences and Related Issues (International Dietary Energy Consultative Group - IDECG, 1987, 201 pages)|
|Seasonality in energy metabolism|
The phenomenon of seasonality has recently attracted a lively interest, as testified by the rapidly expanding body of literature on this topic. In spite of this, the evidence gathered so far is inconclusive, often incomplete or contradictory or anecdotal.
In reviewing the literature on seasonality, it has been difficult in several cases to separate occasional from regularly recurring climatic or biological fluctuations, the two merging almost insensibly. The lack of distinction between the two situations might lead to unwarranted generalizations regarding the severity, frequency and geographic distribution of seasonal cycling of energy metabolism. In the context of this paper, seasonality refers to a regularly recurring set of conditions leading to approximately annual alternations of restricted and unrestricted access to food energy, often coinciding with periods of variable demand for physical labour. With this definition in mind, situations resulting either from chronic food deprivation or from acute famine have been left out.
The first part of this paper deals with the environmental characteristics conducive to seasonal cycling in food availability and workloads. The second part is a review of the literature on the actual impact of seasonality on energy metabolism and has been divided into two sections. The first comprises studies describing the occurrence of body weight changes, taken as a proxy of energy imbalance. The second section includes studies describing seasonal fluctuations of BMR and energy expenditure, with or without concomitant body weight changes. Studies on the fluctuation in food availability and energy intake have been omitted, unless evidence is presented that these functions resulted in energy imbalance.