The use of visual analogue scales to assess motivation to eat in human subjects: a review of their reliability and validity with an evaluation of new hand-held computerized systems for temporal tracking of appetite ratings.

This present paper reviews the reliability and validity of visual analogue scales (VAS) in terms of (1) their ability to predict feeding behaviour, (2) their sensitivity to experimental manipulations, and (3) their reproducibility. VAS correlate with, but do not reliably predict, energy intake to the extent that they could be used as a proxy of energy intake. They do predict meal initiation in subjects eating their normal diets in their normal environment. Under laboratory conditions, subjectively rated motivation to eat using VAS is sensitive to experimental manipulations and has been found to be reproducible in relation to those experimental regimens. Other work has found them not to be reproducible in relation to repeated protocols. On balance, it would appear, in as much as it is possible to quantify, that VAS exhibit a good degree of within-subject reliability and validity in that they predict with reasonable certainty, meal initiation and amount eaten, and are sensitive to experimental manipulations. This reliability and validity appears more pronounced under the controlled (but more artificial) conditions of the laboratory where the signal:noise ratio in experiments appears to be elevated relative to real life. It appears that VAS are best used in within-subject, repeated-measures designs where the effect of different treatments can be compared under similar circumstances. They are best used in conjunction with other measures (e.g. feeding behaviour, changes in plasma metabolites) rather than as proxies for these variables. New hand-held electronic appetite rating systems (EARS) have been developed to increase reliability of data capture and decrease investigator workload. Recent studies have compared these with traditional pen and paper (P&P) VAS. The EARS have been found to be sensitive to experimental manipulations and reproducible relative to P&P. However, subjects appear to exhibit a significantly more constrained use of the scale when using the EARS relative to the P&P. For this reason it is recommended that the two techniques are not used interchangeably.

The degree of saturation of fatty acids influences post-ingestive satiety.

Two studies were designed to compare the effects on post-ingestive satiety of manipulating the degree of saturation of fatty acids, at a fixed chain length (18 C atoms), in a fixed energy (5.68 MJ for males; 3.97 MJ for females), high-fat (55% energy) lunch meal. Two different groups of twenty subjects (ten males and ten females) took part in each study. All forty subjects were of normal weight and aged between 18 and 36 years. Study 1 compared the effects of fat A (oleic blend, high in monounsaturated fatty acids (MUFA)) with those of fat B (linoleic blend, high in polyunsaturated fatty acids (PUFA)) and fat C (stearic-oleic blend, high in saturated fatty acids (SFA)). Study 2, which was designed to confirm and extend the findings of Study 1, compared the effects of fats A, B and C with those of fat D (a linoleic-oleic blend). Energy and nutrient intakes were monitored for the rest of the day and for the following day. Profiles of hunger, fullness and other sensations were monitored by continuous tracking and end-of-day questionnaires. In each meal the fat content was exclusively composed of one particular type (A, B, C or D) and was divided equally between the main course and dessert. Study 1 revealed a significant effect of fat type (degree of saturation) on intake of nutrients at the following (dinner) meal (smallest F[2,36] 3.38, P < 0.05), on post-ingestive ratings of motivation to eat (smallest F[2,36] 4.18, P = 0.02) and on energy intake over the whole test day (F[2,36] 3.39, P < 0.01). Subjects consumed significantly more energy after consumption of the lunch containing fat A than after the lunches containing fats B or C and there was a trend for these effects to continue into the second day. In Study 2, fat C produced more similar effects on appetite to fat A and there was a tendency for subjects to consume more over the whole test day when they had consumed the lunch containing fat A than when they had consumed the lunch containing fat B. Furthermore, when the data from fat conditions A and B in both studies were combined (n 40) the results of Study 1 were confirmed. Overall, the results of these short-term studies indicate that PUFA may exert a relatively stronger control over appetite than MUFA and SFA.

The effects of high-carbohydrate vs high-fat breakfasts on feelings of fullness and alertness, and subsequent food intake.

Fourteen subjects consumed four realistic isoenergetic (2035 kJ) breakfasts, varying in macronutrient content (two fat-rich, two carbohydrate-rich (low- and high-fibre)), in random order on separate mornings. After breakfast, subjects left the laboratory and completed appetite and alertness ratings at specific times and recorded all subsequent fluid and food intake for the rest of the day. The high-fibre, carbohydrate-rich breakfast was the least palatable but most filling meal and was associated with less food intake during the morning and at lunch. Hunger returned at a slower rate after this meal than after the low-fibre, carbohydrate-rich meal. Both fat-rich breakfasts were more palatable but less satiating than the carbohydrate-rich meals and were followed by greater food intake during the morning, which may be a compensatory response to ingest a sufficient amount of food and/or carbohydrate to match the level of fullness produced by the subjects' habitual breakfasts. By the end of the day, the average total energy intake was significantly greater after the fat-rich EB meal than after the high-fibre, carbohydrate-rich meal (P < 0.05). Total day fat intakes were also significantly greater when the high-fat breakfasts were eaten. For every individual test, alertness ratings increased immediately after breakfast was consumed. On average, the high-fibre carbohydrate-rich meal was associated with the highest post-breakfast alertness ratings and with the greatest cumulative amount of alertness during the period between breakfast and lunch (AUC). Alertness AUC values up until lunch correlated positively with fullness AUC values (r = 0.36, P < 0.01, n = 56). The results confirm the relatively weak satiating power of fat-rich meals observed in controlled laboratory-based studies and indicate that a high-fibre, carbohydrate-rich breakfast may assist weight control efforts by maintaining fullness. Further research is required to determine whether satiety directly enhances alertness and whether low-GI carbohydrate-rich meals enhance alertness to a greater degree than high-GI meals.

A medium-term intervention study on the impact of high- and low-fat snacks varying in sweetness and fat content: large shifts in daily fat intake but good compensation for daily energy intake.

Thirty-six normal-weight, habitual snackers (eighteen males, eighteen females) completed a medium-term intervention study designed to examine the tendency of four different types of snacks, varying in nutrient (low- (LF) or high-fat (HF) and sensory properties (sweet (SW) or non-sweet (NSW)), to influence the control of appetite and to adjust daily energy intake. Subjects were exposed to each snack category for a 3-week period and were asked to consume a minimum number of snacks each day so that at least 25% of their daily energy intake would be derived from the test snacks. Energy and macronutrient intakes from the test snacks were calculated every day and also from other eating episodes (using 3 d food diary records) during the third week of snack exposure. Subjects consumed more energy/d from the SW snacks than from the NSW snacks, with most energy being consumed from the HF/SW snacks (3213 kJ) and least energy from the LF/NSW snacks (1628 kJ). This differential snack intake remained stable across the whole snack exposure period. Total daily energy intake did not differ significantly during exposure to any of the four snack types. Furthermore, the encouragement to eat freely from the test snacks did not lead to daily overconsumption of energy when compared with pre-study intakes. Hence, the level of snack consumption was largely compensated for by the energy consumed from the rest of the eating pattern. Although daily energy intake during exposure to the HF snacks was an average of 364 kJ higher (NS) than that during exposure to the LF snacks, the clearest and most significant effect of snack consumption was on daily macronutrient intake. Appreciable consumption of the HF snacks raised the percentage of total daily energy intake consumed as fat from 37 to 41% (P < 0.01). In contrast, the LF snacks reduced daily fat intake to 33.5% (LF/SW, P < 0.05; LF/NSW, NS) of total daily energy. The results, therefore, suggest that, in habitual snackers, generous consumption of LF snacks, when compared with HF snacks, is an effective strategy to reduce fat intake so that it approaches the recommendations of dietary guidelines without increasing total daily energy intake.

Effects of amount and type of dietary fibre (soluble and insoluble) on short-term control of appetite.

Fibres which are soluble or insoluble in water have different physiochemical properties and may therefore be expected to exert different effects on post-ingestive satiety signals. This study compared the effects on short-term (24 h) appetite of two equienergetic high (22 g) fibre breakfasts, an equienergetic low fibre breakfast and a low energy, 'light' breakfast. Psyllium gum (the soluble fibre) and wheat bran (the insoluble fibre) were incorporated into breakfast cereals and consumed at breakfast by sixteen healthy, normal weight males after an overnight fast using a repeated measures, counterbalanced design. Ad libitum energy intake was assessed at a test snack 1.5 h after breakfast, later in the day using food boxes and the following day using food diaries. Motivation to eat and gastrointestinal sensations were tracked for the next 24 h. Hunger ratings showed a trend towards the subjects being less hungry and they consumed significantly less energy at snack time after the high insoluble than after the high soluble fibre breakfast cereal. The soluble fibre breakfast produced a greater suppression of snack intake than the light breakfast, but smaller suppression than the other breakfasts. Interestingly there was a trend toward reduced hunger and voluntary energy consumption following the soluble fibre compared with the insoluble fibre much later in the day (9.5-13.5 h after breakfast) although this was not significant. There was no significant effect of breakfast type on total day energy intake. The results suggest that different types of fibre modulate the timecourse of appetite control and may produce alterations in the experience of motivation and patterns of eating without necessarily effecting total energy intake.

A satiety quotient: a formulation to assess the satiating effect of food.

This paper introduces a satiety quotient (SQ) to assess the satiating effect of an eating episode. This procedure constitutes an improvement on previous measures by considering the satiating effects of the eating episode over time. A satiety quotient was calculated from data obtained from several studies involving the presentation of a preload/meal to young lean male and female subjects. Subjects were presented with preloads/meals of varying composition, and motivation to eat immediately prior to, and periodically following, the eating episode were measured. Food and fluids were not consumed whilst motivation to eat was measured in the post preload/meal period. The SQ was calculated by dividing the difference between ratings of motivation to eat before and after the eating episode (pre minus post) by the weight or energy content of intake during the episode. This quotient relates intake to the rate of return of motivation to eat in the post-ingestive period, a relationship which is not apparent on separate examination of the amount consumed or ratings of motivation to eat. Development of this satiety quotient is a further contribution to the evolution of the concept of quantifying satiating effects of foods, and provides additional information on the effects of food attributes on short-term appetite control.

Plasma prednisolone concentrations and kinetics in renal transplant patients.

Plasma prednisolone concentrations were measured in 26 renal transplant (RT) patients and five control subjects. A linear relationship was found between prednisolone dosage in mg/kg and area under the plasma concentration time curve in seven stable RT patients (r = 0.98) and in all subjects (n = 19) with estimated prednisolone clearance rates (CLp) between 0.075 and 0.11 L/kg/hr (r = 0.96). The greatest deviation from this occurred in five patients having reduced CLp with prolonged prednisolone half life (t1/2p) and in one having increased CLp while taking phenytoin. Three of the five with reduced clearance had steroid induced diabetes and one a Cushingoid appearance. There was some correlation between peak plasma prednisolone and dosage (r = 0.77) in all subjects, but none between creatinine clearance and t1/2p or CLp.