Stephen J. Synowski

Relation of cognitive appraisal to cardiovascular reactivity, affect, and task engagement

The relation of primary cognitive appraisals to cardiovascular reactivity, affect, task engagement, and perceived stress was examined in 56 men (ages 18–29). Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate, preejection period, stroke index, cardiac index, and total peripheral resistance were assessed at rest and during performance of a computerized mental arithmetic task. Extending on prior investigations, threat and challenge appraisals were assessed independently from one another and from secondary appraisals. Positive and negative affect, task engagement, and levels of perceived stress were also assessed. Results indicated that threat (R2 = .08, p = .01), challenge (R2 = .14, p = .003), and their interaction (R2 = .11, p = .006) independently predicted DBP reactivity; DBP responses were greatest among participants with a high threat/low challenge pattern of appraisal. Threat appraisals predicted greater negative affect (R2 = .32) and perceived stress (R2 = .48), whereas challenge appraisals were related to greater positive affect (R2 = .44) and task engagement (R2 = .40, ps < .0001). Greater positive affect was correlated with increased SBP and DBP reactivity, and greater levels of task engagement with increased DBP response (ps ≤ .002). Results suggest that primary cognitive appraisals are more potent predictors of affect and task engagement than cardiovascular reactivity.

Independent effects of diet palatability and fat content on bout size and daily intake in rats

Although considerable evidence attests to the hyperphagic effects of high-fat (HF) diets, the attribute(s) of these diets (e.g., palatability, caloric density, and postingestive effects) which promote overeating is still unclear. The present studies investigated the independent effects of diet palatability and macronutrient composition on intake using the self-regulated intragastric infusion paradigm. In Experiment 1, rats were infused with either HF or high-carbohydrate (HC) diet while drinking either saccharin (Sacc) or a more palatable saccharin-glucose (SaccGlu) test solution for 9 days. HF elicited greater daily intake than HC; lick pattern analysis revealed that HF produced larger but not more frequent bouts. Test solution was not related to intake, possibly due to the relatively modest palatability manipulation. Experiment 2 provided a more sensitive test: The palatability manipulation was strengthened and diet infusion made optional by provision of chow. HF again elicited larger bout size and total daily intake (diet+chow) than HC. Rats given the more palatable solution significantly increased intake (via larger bouts) and thus the amount of diet infused, but chow intake decreased such that total kilocalorie intake was not significantly related to solution palatability. The reliable observation that HF promoted larger bout size and greater total kilocalorie intake than HC provides additional evidence that fat sends weaker feedback signals relevant to controls of both satiation (suppression of ongoing eating, behaviorally manifest in meal size) and satiety (suppression of subsequent intake, reflected in total daily intake).

Effect of food deprivation and maintenance diet composition on fat preference and acceptance in rats.

High-fat diets typically elicit greater kcal intake and/or weight gain than low-fat diets. Palatability, caloric density, and the unique postingestive effects of fat have each been shown to contribute to high-fat diet hyperphagia. Because long-term intake reflects the sum of many individual eating episodes (meals), it is important to investigate factors that may modulate fat intake at a meal. The present studies used high-fat (hi-fat) and high-carbohydrate (hi-carb) liquid diets (both 2.3 kcal/mL) to assess the effect of hunger level (0 versus 24-h food deprivation) and fat content of the maintenance diet (12 versus 48%) on fat preference (when a choice among foods is offered in a two-bottle test), and acceptance (only one food offered) in male rats. Preference for hi-fat relative to hi-carb (two-bottle test) was enhanced by 24-h food deprivation, and by a high-fat maintenance diet. In contrast, neither deprivation nor maintenance diet composition influenced relative meal size (one-bottle test) of hi-fat and hi-carb: irrespective of test conditions, meal size of hi-fat was bigger than meal size of hi-carb.

Learned suppression of intake based on anticipated calories : Cross-nutrient comparisons

Following training with distinctively flavored solutions which differ in calories and thus in their postingestive effects, rats demonstrate flavor-postingestive consequence learning by preferentially consuming one of the flavors in two-bottle tests (both flavors presented in nutrient-identical solutions). The direction of the preference--for the flavor previously paired with more calories (F-hi) or for the flavor previously paired with fewer calories (F-lo)--depends critically upon the magnitude of postingestive effects experienced during training. The most frequent and more thoroughly investigated observation has been preferential consumption of F-hi (conditioned flavor preference). However, when relatively concentrated solutions (e.g., 5% and 30% sucrose) are used as the training nutrients, F-lo is preferentially consumed in two-bottle tests. This lesser intake of F-hi presumably reflects its previous association with the more potent satiating effect of the highly concentrated nutrient: conditioned satiety. The present series of experiments explored conditioned satiety across nutrient types. In each experiment, rats consumed 30 mL of distinctively flavored nutritive solution per day, alternating between a distinctively flavored high-calorie (1.6 kcal/mL) solution and a lower calorie (0.2 kcal/mL) solution containing a different flavor. Two-bottle testing evaluated whether conditioned satiety was evident. Experiment 1 found that rats trained with sucrose, fructose, glucose, maltodextrin, or saccharin-sweetened medium-chain triglyceride oil emulsion preferentially consumed F-lo in two-bottle tests. In contrast, rats trained with corn oil emulsions tended to preferentially consume F-hi. In Experiment 2, increasing the number of corn oil calories associated with F-hi produced a tendency toward preferential intake of F-lo in two-bottle tests. In Experiment 3, rats consumed a high-fat maintenance diet; sucrose-trained rats again consumed more F-lo than F-hi, whereas rats trained with corn oil emulsions showed a tendency (nonsignificant) to consume more F-lo in two-bottle tests. In Experiment 4, however, adding saccharin to corn oil emulsions did produce conditioned satiety. These findings demonstrate conditioned satiety as a robust phenomenon across various nutrient types; however, corn oil calories entrain conditioned satiety only under certain conditions.

Meal size of high-fat food is reliably greater than high-carbohydrate food across externally-evoked single-meal tests and long-term spontaneous feeding in rat

A series of studies in rat using isoenergetic (kcal/ml) liquid diets differing in fat content has previously found dietary fat to dose-dependently increase daily caloric intake. In single-meal tests in which meal initiation was externally evoked in feeding-associated environments, the behavioral expression of this overeating was found to be larger meal intake. The present studies confirmed the ecological validity of this larger meal size of high-fat diet (HF) relative to high-carbohydrate diet (HC): meal size of HF>HC in home-cage testing (Experiment 1), and during undisturbed, spontaneous feeding in which ingestive behavior was continuously monitored (Experiments 2 and 3). These findings demonstrate that single-meal paradigms yield results consistent with spontaneous feeding of high-fat and high-carbohydrate liquid diets, thus supporting the use of single-meal studies to better understand the physiological bases of elevated caloric intake associated with chronic consumption of a high-fat diet.

Flavor-Cued Modulation of Intake in Rats: Role of Familiarity and Impact on 24-h Intake

Following training with distinctively flavored nutritive solutions that differ in concentration and thus in caloric value, rats demonstrate flavor-postingestive consequence learning by preferentially consuming one of the flavors in two-bottle tests (both flavors in nutrient-identical solutions.) Experiment 1 investigated whether the relative familiarity of the flavor-nutrient combinations encountered in two-bottle tests contributes to the observed preference. One of the training concentrations (rather than the customary intermediate concentration) was used to present the flavors in testing; thus, one of the flavors was in a familiar context while the other was in an unfamiliar context. The results of two independent trials (rats trained with 1 and 5% sucrose; rats trained with 5 and 40% sucrose) confirmed that two-bottle test preference was not a preference for the familiar flavor-nutrient combination. Experiment 2 examined whether caloric expectancies based upon a previously learned flavor-postingestive consequence association would affect total daily intake. On alternating days, rats consumed 30 mL of dilute (5%) and concentrated (40%) sucrose, each distinctively flavored. When given 30 mL of 22.5% sucrose containing each of the flavors on separate test days, they ate less chow and thus fewer total calories over 24 h when given the flavor previously paired with concentrated sucrose. Experiment 3 replicated the design of Experiment 2 except that fat calories were used instead of sucrose; no significant adjustment of chow intake in extinction tests was noted, even when the number of fat calories used in training was increased (Experiment 4). Thus, rats did not exhibit flavor-cued modulation of chow intake when trained with fat, in contrast to responsivity to flavor cues when trained with sucrose. This differential responding to fat versus carbohydrate calories is consistent with previous observations, in a variety of paradigms, that modulation of caloric intake is less energetically appropriate when ingested foods are high in fat relative to high-carbohydrate foods.

Effects of glucose ingestion on autonomic and cardiovascular measures during rest and mental challenge

BACKGROUND High levels of dietary sugar consumption may result in dysregulated glucose metabolism and lead to elevated cardiovascular disease risk via autonomic nervous system and cardiovascular dysfunction. Altered cardiovascular function can be examined using perturbation tasks such as mental challenge. This study examined the effects of controlled glucose intake on cardiovascular measures at rest and in responses to mental challenge in a laboratory setting. METHOD Using a double blind within-subjects design, participants were monitored at baseline, following ingestion of a glucose or taste-control solution, during structured speech (SS), anger recall (AR) and recovery (N=24, 288 repeated measures; age = 21±2 years). Pre-ejection period (PEP), heart rate (HR), stroke index (SI), cardiac index (CI), blood pressure and total peripheral resistance (TPR) were measured throughout the protocol. RESULTS Glucose resulted in sustained decreased PEP levels compared to control condition (Δ=11.98±9.52 vs. 3.27±7.65 m·s, P<.001) and transient increases in resting HR (P=.011), CI (P=.040) and systolic blood pressure (P=.009). Glucose did not result in increased cardiovascular reactivity to mental challenge tasks, but was associated with a delayed HR recovery following AR (P=.032). CONCLUSION Glucose intake resulted in a drop in PEP indicating increased sympathetic nervous system activity. No evidence was found for glucose-related exaggerated cardiovascular responses to mental challenge. Dysregulated glucose metabolism may result in elevated cardiovascular disease risk as a result of repeated glucose-induced elevations of sympathetic nervous system activity.