Stress responses to repeated exposure to a combined physical and social evaluative laboratory stressor in young healthy males.

Repeated exposure to homotypic laboratory psychosocial stressors typically instigates rapid habituation in hypothalamic-pituitary-adrenal (HPA) axis-mediated stress responses in humans. However, emerging evidence suggests the combination of physical stress and social evaluative threat may be sufficient to attenuate this response habituation. Neuroendocrine, cardiovascular and subjective stress responses following repeated exposure to a combined physical and social evaluative stress protocol were assessed to examine the habituation response dynamic in this context. The speech task of the Trier social stress test (TSST; Kirschbaum et al., 1993) and the socially evaluated cold pressor task (SECPT; Schwabe et al., 2008) were administered in a combined stressor protocol. Salivary cortisol, cardiovascular and subjective stress responses to a non-stress control and repeat stressor exposure separated by six weeks were examined in males (N=24) in a crossover manner. Stressor exposure resulted in significant elevations in all stress parameters. In contrast to the commonly reported habituation in cortisol response, a comparable post-stress response was demonstrated. Cortisol, heart rate and subjective stress responses were also characterised by a heightened response in anticipation to repeated stress exposure. Blood pressure responses were comparatively uniform across repeated exposures. Findings suggest a combined physical and social evaluative stressor is a potentially useful method for study designs that require repeated presentation of a homotypic stressor.

No effects of ingesting or rinsing sucrose on depleted self-control performance.

Self-control tasks appear to deplete a limited resource resulting in reduced subsequent self-control performance; a state of ego depletion. Evidence of reduced peripheral glucose by exertion of self-control, and attenuation of ego depletion by carbohydrate metabolism underpins the proposition that this macronutrient provides the energetic source of self-control. However, the demonstration of positive, non-metabolic effects on ego depletion when merely sensing carbohydrates orally contradicts this hypothesis. Recent studies have also failed to support both metabolic and non-metabolic accounts. The effects of ingesting or rinsing a carbohydrate (sucrose) and an artificially sweetened (sucralose) solution on capillary blood and interstitial glucose, and depleted self-control performance were examined in older adults. Forty, healthy, adults (50-65years) ingested and rinsed sucrose and sucralose solutions in a 2 (method)×2 (source), fully counterbalanced, repeated measures, crossover design. Capillary blood and interstitial glucose responses were assayed. Depleted self-control performance (induced by the Bakan visual processing task) on an attention switch task was assessed under each study condition. Ego depletion had no consistent effects on peripheral glucose levels and no significant effects of ingesting or rinsing sucrose on self-control were observed. The act of rinsing the solutions, independent of energetic content, resulted in a small, non-significant enhancement of performance on the attention switch task relative to ingesting the same solutions (RT: p=.05; accuracy: p=.09). In conclusion, a metabolic account of self-control was not supported. Whilst a positive effect of rinsing on depleted self-control performance was demonstrated, this was independent of energetic content. Findings suggest glucose is an unlikely physiological analogue for self-control resources.

A step-by-step introduction to vegetables at the beginning of complementary feeding. The effects of early and repeated exposure.

Breastfeeding (BF) is associated with willingness to accept vegetables. This may be due to the variety of flavours delivered via breast milk. Some mothers add vegetables to milk during complementary feeding (CF) to enhance acceptance. The present study tested a step-by-step exposure to vegetables in milk then rice during CF, on intake and liking of vegetables. Just before CF, enrolled mothers were randomised to an intervention (IG, n = 18; 6 BF) or control group (CG, n = 18; 6 BF). IG infants received 12 daily exposures to vegetable puree added to milk (days 1-12), then 12 × 2 daily exposures to vegetable puree added to rice at home (days 13-24). Plain milk and rice were given to CG. Then both received 11 daily exposures to vegetable puree. Intake was weighed and liking rated on days 25-26 and 33-35 after the start of CF in the laboratory, supplemented by the same data recorded at home. Vegetables were rotated daily (carrots, green beans, spinach, broccoli). Intake, liking and pace of eating were greater for IG than CG infants. Intake and liking of carrots were greater than green beans. However, at 6m then 18m follow up, vegetable (carrot > green beans) but not group differences were observed. Mothers reported appreciation of the structure and guidance of this systematic approach. Early exposure to vegetables in a step-by-step method could be included in CF guidelines and longer term benefits assessed by extending the exposure period.

Resistance and susceptibility to weight gain: individual variability in response to a high-fat diet.

An obesigenic environment is a potent force for promoting weight gain. However, not all people exposed to such an environment become obese; some remain lean. This means that some people are susceptible to weight gain (in a weight-promoting environment) and others are resistant. Identifying the characteristics of appetite control and food motivation in these two groups could throw light on the causes of weight gain and how this can be either treated or prevented. We have investigated the issue experimentally by identifying people who habitually consume a high-fat diet (greater than 43% fat energy). These individuals have been termed high-fat phenotypes. We have compared individuals, of the same age (mean=37 years old) and gender (male), who have gained weight (BMI=34) or who have remained lean (BMI=22). The susceptible individuals are characterised by a cluster of characteristics including a weak satiety response to fatty meals, a maintained preference for high-fat over low-energy foods in the post-ingestive satiety period, a strong hedonic attraction to palatable foods and to eating, and high scores on the TFEQ factors of Disinhibition and Hunger. The analysis of large databases suggests that this profile of factors contributes to an average daily positive energy balance from food of approximately 0.5 MJ. This profile of characteristics helps to define the symptomatology of a thrifty phenotype.