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Fifty-six participants were included in our study, filtered by VAS questionnaire of familiarity, 14 subjects in each group. The subjects' height, weight, waist circumference, hip circumference, BMI, waist-to-hip ratio and energy intake during breakfast in first study day were described in Table 1. There was no significant difference in these parameters between OF and OS groups, as well as between LF and LS groups.
Items LF (n = 14) LS (n = 14) OF (n = 14) OS (n = 14) Age (y) 20.7 ± 0.8 20.9 ± 1.2 21.1 ± 1.0 20.8 ± 1.1 Height (cm) 172.2 ± 4.2 173.3 ± 5.1 173.1 ± 5.3 173.6 ± 7.0 Weight (kg) 64.2 ± 2.9 65.6 ± 3.3 80.2 ± 6.1 79.9 ± 7.2 BMI (kg/m2) 21.7 ± 0.6 21.9 ± 0.8 26.7 ± 1.5 26.5 ± 1.3 Body fat (%) 17.1 ± 0.8 17.5 ± 1.6 23.1 ± 3.2 23.4 ± 3.7 Waist circumference (cm) 79.3 ± 4.4 81.5 ± 4.4 91.3 ± 5.9 90.8 ± 6.7 Hip circumference (cm) 95.1 ± 3.7 96.9 ± 3.9 102.8 ± 4.0 103.4 ± 5.2 Waist-to-hip ratio 0.83 ± 0.03 0.84 ± 0.03 0.89 ± 0.04 0.88 ± 0.03 Food intake in first day (g) 292 ± 48 289 ± 45 311 ± 53 306 ± 49 Energy intake in first day (kcal) 1, 489 ± 242 1, 472 ± 228 1, 586 ± 269 1, 563 ± 250 Note. LF: lean friends; LS: lean strangers; OF: overweight friends; OS: overweight strangers. Data are expressed as means ± SD. Table 1. Basic Characteristics of the Lean and Overweight Participants
As shown in Table 2, a significant difference of familiarity VAS values was found between friends and strangers groups (P < 0.01) both in lean and overweight participants. Preprandial appetite VAS, glucose and insulin concentration, and dietary satisfaction VAS were not significantly different between familiar and unfamiliar peers of both weight statures.
Items Lean Overweight LF (n = 14) LS (n = 14) OF (n = 14) OS (n = 14) Familiarity VAS (mm) 85.7 ± 14.9 26.0 ± 12.9## 87.5 ± 10.4 13.7 ± 8.4** Dietary satisfaction VAS (mm) 69.9 ± 13.2 67.6 ± 9.9 73.3 ± 11.7 70.0 ± 10.8 Preprandial hunger VAS (mm) 64.6 ± 9.4 67.0 ± 9.2 70.9 ± 9.8 68.6 ± 8.4 Preprandial satiety VAS (mm) 35.4 ± 9.0 33.9 ± 8.7 34.1 ± 8.8 33.2 ± 8.1 Preprandial glucose (mmol/L) 5.3 ± 0.4 5.2 ± 0.4 5.8 ± 0.4 5.9 ± 0.3 Preprandial insulin (μIU/mL) 1.3 ± 0.3 1.1 ± 0.3 3.2 ± 1.1 3.5 ± 1.0^^ Note. LF: lean friends; LS: lean strangers; OF: overweight friends; OS: overweight strangers. **Significantly different from OF group, P < 0.01; ##Significantly different from LF group, P < 0.01. ^^Significant difference between lean and overweight groups, P < 0.01. Data are expressed as means ± SD. Table 2. VAS, Glucose and Insulin Concentration in the Lean and Overweight Participants
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Main effects of status (P = 0.010) and familiarity (P = 0.001) were observed, but no significant interaction between status and familiarity (P = 0.137) on energy intake during breakfast was observed (Figure 2). Regardless of status, familiar subjects' energy intake was higher than unfamiliar dyads' during their breakfast (mean ± SD: energy intake, 1, 829 ± 339 vs. 1, 548 ± 266 kcal, P = 0.001). Compared with OS group, the subjects' energy intake was significantly higher in OF group when they had breakfast with companions (mean ± SD: energy intake, 1, 989 ± 365 vs. 1, 592 ± 297 kcal, P = 0.004, Figure 2). However, no difference was found in the LF and LS groups (mean ± SD: energy intake, 1, 670 ± 228 vs. 1, 505 ± 233 kcal, Figure 2).
Figure 2. Mean ± SD energy intake by friends and strangers in lean (lean friends, n = 14; lean strangers n = 14) and overweight (overweight friends, n = 14; overweight strangers n = 14) subjects when they had breakfast with companions. A 2-factor ANOVA showed significant main effects of status (P = 0.010) and familiarity (P = 0.001) but no significant status · familiarity interaction (P = 0.451) on energy intake. **Significant difference between overweight friends and strangers (P = 0.001).
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As shown in Table 3, a significant difference in meal duration (F = 0.189, P = 0.67; t = 0.85, P = 0.001), talking time (F = 6.10, P = 0.02; t = 9.63, P < 0.01), and chewing frequency per 10 g food (F = 0.39, P = 0.54; t = -3.89, P = 0.001) was found between OF and OS groups. However, in the same situation, only talking time was shown to exhibit significant difference between LF and LS groups (F = 19.89, P < 0.01; t = 6.79, P < 0.01).
Items Lean Overweight LF (n = 14) LS (n = 14) OF (n = 14) OS (n = 14) Meal duration (s) 436 ± 54 411 ± 54 482 ± 51 403 ± 59** Talking time (s) 98 ± 36 30 ± 10## 124 ± 31 35 ± 16** Chews/10 g 19.1 ± 1.9 20.5 ± 3.2 15.3 ± 1.9 17.9 ± 1.6** Note: LF: lean friends; LS: lean strangers; OF: overweight friends; OS: overweight strangers. **Significantly different from OF group, P < 0.01; ##Significantly different from LF group, P < 0.01. Data are expressed as means ± SD. Table 3. Influence of Familiarity on the Food Intake Parameters
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Postprandial CCK-8 concentration rapidly increased and peaked at 30 min, and then slowly decreased. Compared with that in the OS group, the plasma concentration of CCK-8 was significantly lower in OF group at 30 (F = 4.71, P = 0.039), 60 (F = 5.73, P = 0.024), and 90 min (F = 4.87, P = 0.036), but not at 120 min. In the lean subjects, no significant differences were found between LF and LS groups at all time points (Figure 3A). Among all participants, plasma GLP-1 concentration rapidly increased and then decreased. The OS group had higher GLP-1 concentration than the OF group, and significant difference was found at 60 (F = 5.63, P = 0.025) and 90 min (F = 4.58, P = 0.042). The LS group had higher GLP-1 concentration than the LF group, but no significant differences were found at all time points (Figure 3B). Postprandial ghrelin concentration decreased for a brief period, and then increased thereafter. Plasma ghrelin concentration was significantly higher in the OF group than in the OS group at 90 (F = 5.54, P = 0.026) and 120 min (F = 4.66, P = 0.040). Compared with the LS group, no significant difference was found at all time points in the LF group (Figure 3C).