Influence of nutritional and non-nutritional dietary components on appetite, motivation to eat and body weight

In the context of the rising obesity epidemic, understanding the role of eating patterns and diet composition on calorie intake and body weight is clearly important for the development of dietary strategies that encourage body weight control. It is now accepted that there are many nutritional and non-nutritional factors that will influence energy intake (EI) and eating behaviour.   Non-nutritional factors include palatability of food, portion size, sensory variety and meal patterns (e.g. snacking). It is accepted that these factors can contribute to the passive overconsumption of calories, at least in the short term, and that these attributes have a major contribution to the reward value of food. Examining the non-nutritional influences on eating behaviour tends to focus on what we eat (food choice), whereas the physiological or metabolic aspects focus on how much we eat (calories or weight of food intake). The sensory (odour, texture, taste, appearance) aspects of a food or meal can significantly alter our choice, at least in the short term. These sensory or hedonic parameters influence the reward aspects of eating behaviour and much research focuses on assessing responses to changing single parameters.   The main nutritional factors are macronutrient composition and energy density (ED). The mechanisms linking energy intake and expenditure are unclear, but it seems reasonable to believe that appetite (sensations that promote food ingestion or rejection) is central to the maintenance of energy balance and body weight. In this context, isoenergetic amounts (same energy content) of the dietary macronutrients are not equal in terms of their effect on appetite and motivation to eat, with laboratory and free-living studies highlighting protein as the most satiating macronutrient, independent of ED, relative to carbohydrate and fat. Recent findings suggest that an elevated protein intake seems to play a key role in body-weight management, through :   (i)      increased satiety related to increased diet-induced thermogenesis, (ii)    its effect on thermogenesis, (iii)   body composition, (iv)  decreased energy-efficiency   Supported by these mechanisms, a relatively larger weight loss and stronger body-weight maintenance thereafter have been observed with protein-enriched diets. Protein-induced satiety has been shown acutely, within single meals that contain between 25% to 81% of energy from protein, with reductions in subsequent energy intake. Protein-induced satiety has been shown with high protein ad libitum diets, lasting from 14d up to 6 months.   The role of energy density and fibre are also discussed in the context of appetite control. Fibre may be useful in the treatment of obesity by facilitating compliance to low-calorie intake. Fibre can impact satiety in several ways, it increases food volume, decreases ED, increases gastric volume, retards gastric emptying, which maximizes early satiety signals, and influences satiety hormones in the gut. Increasing fibre intake during weight maintenance, however, has a limited impact on body weight control.   People do not always eat in response to a physiological hunger cue and common psychological influences on eating behaviour are discussed, for example, the role of stress and food addiction. Dietary interventions based on caloric restriction or macronutrient manipulation can promote weight loss, as can exercise-induced energy deficit. In theory, weight loss is easy, whereby calorie intake is less than expenditure. However, in practice, this is often difficult to achieve in the medium to long term by obese subjects. One of the main reasons for failure to adhere to a diet is feeling hungry. We do not understand the variability in psychological and behavioural parameters of hunger/satiety and food preference during energy deficit (exercise or diet-induced) across the life course, and how these manipulations relate to gut hormones, neural activation and energy metabolism. The psychological, behavioural and endocrine/neurological bases of these effects and their applicability across age, gender and phenotype remain to be determined.   Dr Alexandra Johnstone, Rowett Institute of Nutrition & Health, University of Aberdeen, from the EU funded project ‘SATIN’ is chairing a session on ‘Identifying key consumer attitudes to weight management’