Resistance and susceptibility to weight gain: Individual variability in response to a high-fat diet
Section snippets
Background
A large number of factors have been shown to be associated with high BMI or an increase in body weight. These include factors associated with food itself, for example, high-energy density, high-fat, portion size, sweet-fat combination, sugary drinks, etc., and features of the food environment, for example, eating in fast-food restaurants, food eaten outside the home, snacking and TV viewing, and others. The obesigenic environment is also characterised by abundant availability, easy
Risk factors for weight gain—via appetite
Most researchers do not have any trouble accepting the idea that the state of a person's metabolism constitutes a major risk for developing weight gain and becoming obese. However, as obesity develops, metabolic characteristics change so that the state of obesity itself is associated with a different metabolic profile to that accompanying the process of weight gain. This makes it important to do longitudinal studies (whilst weight is increasing) as well as cross-sectional studies (comparing
Components of susceptibility
The notion that some people are more susceptible to weight gain than others is a truism. The issue is how to characterise the features of susceptibility and then, to decide how these features can be used to deal with the epidemic of obesity. Susceptibility can be identified at various levels—genetic, physiologic and metabolic, behavioural and psychological. Identifying specific genes or allelic variations that are associated with obesity or body weight gain is already well advanced [3], [4]. A
Functional phenotype approach
There exist many mechanisms through which an individual could gain weight and become obese. As noted above, this diversity is reflected at the level of analysis of genetics, central and peripheral physiology, and the behavioural and psychological profile. It is also clear that a great number of environmental features can exploit intrinsic risk factors (see Table 1) to induce susceptibility. In recent years, dietary features, such as high-energy dense foods, high-fat, high-carbohydrate, high-GI,
Experimental approach
The functional phenotype approach, as applied here, is designed to limit the number of possible variables that could potentially influence susceptibility. Even restricting the study to individuals habitually consuming a particular diet, the situation remains complicated, but the dietary contribution to this complexity is largely eliminated. In a comparison of high- and low-fat phenotypes (individuals habitually consuming a 43% or greater fat diet, or 32% or less fat diet), there was a greater
Dual assessment: laboratory and natural environment
The methodology was based on two different procedures—termed probe days and free-living days. In the probe days, subjects were intensively investigated within the laboratory, during which time they received test meal challenges during full-day exposures to either high-fat or low-fat foods, completed profiles of ratings for hunger, fullness and other sensations, performed food preference and forced-choice food selection tests and made hedonic ratings of foods consumed. The food preference
Experimental outputs
The results of the investigation indicate that four or more characteristic features could account for an elevated energy intake in susceptible people. First, the probe day nutritional challenges indicated a specific post-ingestive response to high-fat, but not to low-fat, challenges in susceptible people. Although susceptible subjects had higher daily energy intakes than resistant for both high-fat and low-fat probe days (expected because of the greater body weight of susceptible subjects), the
Summary
Taken together the various measurable outputs from this experimental approach have identified clear differences between the susceptible and resistant subjects. These differences are apparent in both states and traits, and in the homeostatic and hedonic influence over eating. The state differences are interesting because they signify a weak post-ingestive satiety response that is specific to fat intake. The careful monitoring of peri-prandial sensations has indicated a suppression of hunger (an
Acknowledgements
The work described above was funded by the European Commission, Framework V, Quality of Life and Management of Living Resources Programme. Number: QLK1-CT-2000-00515.
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