Appetite, feeding behaviour and energy balance in human subjects

Abstract

Since the Second World War there has been a secular trend of increased overweight and obesity in societies where people have ad libitum access to Westem-type diets (Royal College of Physicians, 1983;Gregory et al. 1990;White et al. 1991; Department of Health, 1995). Over this time period the economic costs of obesity and the personal costs of being overweight (in terms of reduced quality of life, increased morbidity and mortality) have been well documented (Seidell, 1995). Throughout this period scientific efforts have intensified in attempting to understand the cause of overweight and obesity and in endeavours to produce effective approaches to sustained body-weight reduction. Ironically, the increased governmental, public health and biomedical research efforts aimed at understanding how to reverse current secular trends in body fatness have been accompanied by an escalation of those very trends. We have now reached the remarkable situation in the UK whereby more that half of the adult population has been categorized as collectively overweight and obese (Department of Health, 1995). By considering research trends in the area of human energy balance (EB) over the last two decades it should become apparent that current research has grown out of and built on the research that went before it. Several of the hypotheses of the 1970s and 1980s have been rejected as inoperable in human subjects in the light of the evidence that was collected to evaluate them. It is worth remembering that disproving an hypothesis does not reduce the contribution it has made to scientific understanding. The very process of disproving the hypothesis actually advances science and leads to new avenues of investigation. It is unfortunate that the meticulous process of hypothesis-testing necessarily proceeds at a somewhat slower rate than the problem that we are trying to address: a large prevalence of excess body weight. However, considerable progress has been made over the last two decades in understanding the major factors most likely to alter EB in man and the types of model which are likely to explain how some people become overweight and obese. These insights have proved invaluable in helping us address current issues pertinent to the control of EB and in targeting key research areas for the future. In order to fully illustrate this point it is worth considering the direction of research into obesity and EB over the last couple of decades.

Associations between energy density and macronutrient composition in the diets of pre-school children: sugars vs starch

“…2 Given the cross-sectional nature of this survey, no direct conclusions can be drawn between diet composition (or energy density) and obesity or BMI in these children. The positive association of ED with EI is consistent with short-term experimental studies 9,19 showing that energy-dense diets induce high energy intakes, and is only partly explained by the 6 month age difference between groups. Children with a high energy requirement may preferentially choose energydense foods, which ful®l their metabolic needs within a limited eating capacity.…”

“…6 For example, in a recent study that controlled for the potential effect of both macronutrient composition and palatability, Bell concluded that energy intake was driven by the energy density of the meals provided. 9 A series of investigations using covert manipulations of energy density and macronutrient composition 7,19,24 and general reviews of the issue 10,19 have arrived at similar conclusions.…”

“…It is now becoming apparent that the main reason high-fat diets induce over-consumption of energy is because they are energy dense. 6,9,19 The lower satiety value of fat compared with carbohydrate 20,21 and the high palatability and sensory attributes of fat-containing foods 22 undoubtedly contribute, but energy density may be the prime determinant of passive over-consumption. 6 For example, in a recent study that controlled for the potential effect of both macronutrient composition and palatability, Bell concluded that energy intake was driven by the energy density of the meals provided.…”

The Geometry of Human Nutrition

“…The extent to which weight gain occurs following ingestion of excess nutrients depends on what happens to such excesses once they enter the body. There is a clear relationship between the priority with which surplus nutrients are voided from the body through being metabolised and excreted, and the extent to which they are stored [10]. Excess carbohydrates are readily metabolised and excreted, and stores are minimal (in the form of glycogen in the liver and muscles).…”

“…Partly for this reason, it remains contentious whether humans are able to regulate their intake of different macronutrients [10][11][12]. There are, nonetheless, three sources of information that suggest that we can regulate the intake of specific nutrients.…”