Biology of the drive to eat1

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Peer-Reviewed | Manuscript received: November 23, 2017 | Revision accepted: March 23, 2018

Implications for understanding human appetite and obesity

Food selection and the drive to eat

It is a key feature of appetite control that food selection and the drive to eat are quite separate processes which are influenced by distinct clusters of socio-cultural and biological factors. One of the most salient features of appetite in humans depends on the fact that humans are omnivores. Unlike herbivores or carnivores whose feeding habits are biologically programmed for restricted types of foods, omnivores have a much greater range of potentially edible items.

One consequence of this has been to enable humans to colonise and exploit many different types of environments sustaining quite distinctive nutritional repertoires. It follows that, for humans, the type of food that is put into the mouth is not heavily programmed biologically but depends on the local culture, geography, climate, religion, ethnic principle and social forces. This means that the processes of food intake control have to be geared to a variety of dietary scenarios and the control mechanisms have to be sufficiently adaptable to deal with a huge range of food types.

Although food is basically comprised of fats, proteins and carbohydrates (CHOs), it is put into the mouth in a large number of forms and associated with a multitude of tastes and textures. The behavioural act of putting a selected type of food into the mouth is a precursor of eating. This means that food choice depends on the environment. In certain environments rational food choice can be undermined by an environment in which nutritional value (and therefore biological value) of specific food items can be concealed or confused. This can easily happen in technologically advanced societies in which synthetic foods can be readily manufactured and which contain arbitrary and unlikely combinations of composition, textures and tastes. This can lead to quantitatively and qualitatively inappropriate eating habits.

¹ Article based upon the keynote talk by John Blundell during 54. DGE-Congress 2017, March 1–3, Kiel/Germany.

Abstract

Understanding the drive to eat is a fundamental issue that can throw light on the aetiology of obesity and the inexorable surge of the obesity epidemic. It is proposed here that energy expenditure (EE) is a driver of energy intake (EI). Surprisingly this is a neglected area of thinking in this field. Theoretical writings about obesity often focus on the idea of ‘regulation’ and refer casually to a matching of energy intake and energy expenditure as if this happens automatically and there is nothing to explain. However, biological processes do not happen by accident, and the way in which EE is related to EI requires a justification and an explanation.

It is frequently written that nothing in biology makes sense without the theory of evolution; the processes linking EE and EI are based on an evolutionary perspective. It is proposed that the energy required to maintain vital organs (heart, liver, brain, kidneys, skeletal muscle) represents an irresistible metabolic drive for food (the drive to eat). Much attention in this field has been directed to the inhibition of eating (or lack of it), with formulations lacking a mechanism for driving food behaviour. The evidence that fat free mass and resting metabolic rate constitute major determinants of energy intake has implications for understanding the aetiology and management of obesity.

Keywords: appetite, obesity, energy balance, food selection

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