Diet composition and energy intake in humans

Abstract

Absolute energy from fats and carbohydrates and the proportion of carbohydrates in the food supply have increased over 50 years. Dietary energy density (ED) is primarily decreased by the water and increased by the fat content of foods. Protein, carbohydrates and fat exert different effects on satiety or energy intake (EI) in the order protein > carbohydrates > fat. When the ED of different foods is equalized the differences between fat and carbohydrates are modest. Covertly increasing dietary ED with fat, carbohydrate or mixed macronutrients elevates EI, producing weight gain and vice versa. In more naturalistic situations where learning cues are intact, there appears to be greater compensation for the different ED of foods. There is considerable individual variability in response. Macronutrient-specific negative feedback models of EI regulation have limited capacity to explain how availability of cheap, highly palatable, readily assimilated, energy-dense foods lead to obesity in modern environments. Neuropsychological constructs including food reward (liking, wanting and learning), reactive and reflective decision making, in the context of asymmetric energy balance regulation, give more comprehensive explanations of how environmental superabundance of foods containing mixtures of readily assimilated fats and carbohydrates and caloric beverages elevate EI through combined hedonic, affective, cognitive and physiological mechanisms. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

Keywords: energy balance regulation; energy density; energy intake; hedonics; macronutrients; obesity.

Figure 1.

Relationship between percentage of energy from dietary macronutrients and water (in grams) (predictor variables) and energy density (kcal 100 g⁻¹) of 66 070 ready to eat foods, taken from the Slimming World UK database of commercially available foods to consumers. Nutritional information is derived from food labels. All associations were significant at p < 0.001. (Online version in colour.)

Figure 2.

Relationship between percentage of EI from dietary macronutrients and water (expressed in g 100 g⁻¹) and energy density of the diet (kcal g⁻¹) (predictor variables) and total energy intake (kcal d⁻¹). Analysis was derived from 6155 subjects self-recording their food intake by 24 h dietary recall over 4 days [77,78]. No corrections for plausibility of dietary energy intake were made. Sloping lines were a random sample of 40 individual regression lines, based on 4 days, to give an indication of inter-individual variation. All associations were significant at p < 0.001. (Online version in colour.)

Figure 3.

Relationship between dietary energy density (expressed in kcal g⁻¹) (predictor variable) and energy intake (kcal d⁻¹) and total food intake (g d⁻¹). Analysis was derived from 6155 subjects self-recording their food intake by 24 h recall over 4 days [77,78]. No corrections for plausibility of dietary energy intake were made. Sloping lines were a random sample of 40 individual regression lines, based on 4 days, to give an indication of inter-individual variation. All association were significant at p < 0.001. (Online version in colour.)

Figure 4.

The central axis of eating behaviour, which like other goal-oriented motivated behaviours, operate in cycles of anticipation, consummation and termination. Directly linked to these cycles (in animals and humans) are reactive processes of learned habitual behaviours and response to environmental (e.g. food availability, palatability) and somatic cues such as stress and emotional reactivity. The neurobiological architecture of eating behaviour (i.e. selection and consumption of different foods) in turn, influences energy balance through the effects of eating behaviour on energy intake. The diagram acknowledges that components of the system exert feedback to influence both cycles of goal-oriented eating behaviour and the prompts and cues that influence reactive components of eating behaviour. Strategies of behaviour change, which involve cognitive modification of beliefs, attitudes, intentions and plans, aimed to reshape eating behaviour are often less influential than we would hope, particularly if they oppose reactive and/or homeostatic and hedonic factors. This schema assumes that the asymmetry of regulation evolved to align homeostasis and hedonics in resource-limiting environments, e.g. selection of energy-dense foods occurs because they are highly palatable, and pleasure is a central cue that links food reward to ecologically adaptive patterns of learned ingestive behaviour. (Online version in colour.)