Methodological issues relating to the measurement of food, energy and nutrient intake in human laboratory-based studies

Abstract

The relevance of measuring intake to the nutritional and behavioural sciencesUnderstanding the mechanisms controlling human appetite and energy intake (EI) is fundamental to nutritional science since it is through a balance between EI and energy expenditure (EE) that body weight and composition are maintained and functional integrity is sustained. The recent resurgence of interest in the study of feeding behaviour and the physiological control of food intake (FI) is mainly due to the rapidly increasing proportion of overweight and obese individuals in Western society (White et al. 1991; Department of Health, 1995). It is widely accepted that the uncoupling of EI from EE is largely responsible for these secular trends in body weight. The ability to measure food, energy and nutrient (FEN) intake is critical to our understanding of the processes producing these secular trends. The mechanisms controlling feeding are multifactorial and complex in nature and are generally characterized by an on-going interaction between physiology and behaviour. In recent years an increasing number of studies have incorporated both behavioural and nutritional measures of intake in attempting to understand the quantitative importance of a number of factors (e.g. diet composition, exercise, disease) thought to exert important influences on appetite and energy balance (EB). The measurement of intake in the laboratory is also critical in establishing mechanistic links between other aspects of diet and disease. The relationship between dietary antioxidant intake and oxidative damage to somatic DNA, the effects of dietary lipid profile on immune function and the influence of fibre on mineral bioavailability are three of many possible examples. Such carefully controlled laboratory protocols are crucial in establishing the existence and importance of diet in the promotion of health and the development of disease.There are, thus, two basic forms of intake measurement in the laboratory. The first allows subjects to control their own FEN intake within the constraints of the experimental design. Under these conditions measures of FEN intake result from the subject's behavioural response to the experimental manipulation and any other factors which may influence their behaviour at the time. The second type of FEN intake measurement in the laboratory is a measure of a fixed mandatory intake (termed 'fixed-intake' studies here). In such studies the subject's feeding behaviour has been clamped and the measurement is not as susceptible to 'behavioural noise' provided the subject is compliant with the protocol and the experiment is rigorously designed. Fixed-intake studies are therefore less fraught with methodological difficulties relating to the effects of the experimental environment on behaviour. The majority of errors under these conditions will be of a technical nature, while studies which allow subjects to alter their own intakes are subject to both technical and behavioural errors. Because behaviourally-oriented studies are subject to both type...

Description and evaluation of an experimental model to examine changes in selection between high-protein, high-carbohydrate and high-fat foods in humans

“…The reason why a certain selection of foods is offered to human subjects is not often stated, beyond the general notion that foods comprise an ad libitum diet from which subjects can select, usually in response to some prior manipulation. The relative advantages and disadvantages of these approaches for measuring the amount of food and energy eaten by subjects in response to various experimental manipulations has been reviewed elsewhere (Hill et al, 1995;Stubbs et al, 1998).…”

Food-conditioned odour rejection in the late stages of the meal, mediating learnt control of meal volume by aftereffects of food consumption

“…This learnt link between amount of food eaten and the aftereffects of eating has recently become acknowledged again as the explanation of increased energy intake on high-fat or energy-dense diets (Blundell et al, 1995;Poppitt & Prentice, 1996;Stubbs et al, 1998). Clearly, such caloric over-consumption is far from passive when an unfamiliar increase in the energy content of meals results in increased intake of energy by active performance of the learnt control of volume eaten.…”

Visualising future behaviour: Effects for snacking on biscuit bars, but no effects for snacking on fruit

“…Ogden, 1998), or by self-reward, resulting in the selection of a more desirable snack as perceived payment for involvement in the study (e.g. Rogers, 1987;Stubbs et al, 1998), although study snacks were specifically selected to try and avoid this perception.…”

“…Apples and bananas are two of the most commonly consumed fruits in the United Kingdom (Billson et al, 1999), and other snacks were selected based on their fruit content, or their lack of fruit and chocolate. Care was taken to select non-fruit snacks that were unlikely to be perceived or selected by participants as treats or rewards (Rogers, 1987;Stubbs et al, 1998), and fruit-based biscuit bars were also included as an intermediary between fruit and biscuit bars. Three pieces of each item were presented, participants were free to take one snack while the researcher was occupied elsewhere to avoid effects due to demand characteristics, and snack choice was covertly recorded after the participant had left the test situation.…”