• Breakfast consumption suppresses appetite but does not increase daily energy intake or physical activity energy expenditure when compared with breakfast omission in adolescent girls who habitually skip breakfast: a 7-day randomised crossover trial

      Zakrzewski-Fruer, Julia K.; Seall, Claire; Tolfrey, Keith; ; University of Bedfordshire; Loughborough University (MDPI, 2021-11-26)
      With concerns that adolescent girls often skip breakfast, this study compared the effects of breakfast consumption versus breakfast omission on free-living physical activity (PA) energy expenditure (PAEE) and dietary intakes among adolescent girls classified as habitual breakfast skippers. The participants went through two 7-day conditions in a trial with a crossover design: daily standardised breakfast consumption (energy content: 25% of resting metabolic rate) before 09:00 (BC) and daily breakfast omission (no energy-providing nutrients consumed) until 10:30 (BO). Free-living PAEE, dietary intakes, and perceived appetite, tiredness, and energy levels were assessed. Analyses were linear mixed models. Breakfast manipulation did not affect PAEE or PA duration. Daily fibre intake was higher (p = 0.005; d = 1.31), daily protein intake tended to be higher (p = 0.092; d = 0.54), post-10:30 carbohydrate intake tended to be lower (p = 0.096; d = 0.41), and pre-10:30 hunger and fullness were lower and higher, respectively (p ≤ 0.065; d = 0.33–1.01), in BC versus BO. No other between-condition differences were found. Breakfast-skipping adolescent girls do not compensate for an imbalance in energy intake caused by breakfast consumption versus omission through subsequent changes in PAEE but may increase their carbohydrate intakes later in the day to partially compensate for breakfast omission. Furthermore, breakfast can make substantial contributions to daily fibre intake among adolescent girls.
    • Effect of breakfast omission and consumption on energy intake and physical activity in adolescent girls: a randomised controlled trial

      Zakrzewski-Fruer, Julia K.; Plekhanova, Tatiana; Mandila, D.; Lekatis, Y.; Tolfrey, Keith; University of Bedfordshire; Loughborough University (Cambridge University Press, 2017-09-13)
      It is not known if breakfast consumption is an effective intervention for altering daily energy balance in adolescents when compared with breakfast omission. This study examined the acute effect of breakfast consumption and omission on free-living energy intake (EI) and physical activity (PA) in adolescent girls. Using an acute randomised crossover design, forty girls (age 13.3 ± 0.8 y, body mass index 21.5 ± 5.0 kg∙m-2) completed two, 3-day conditions in a randomised, counter-balanced order: no breakfast (NB) and standardised (~1962 kJ) breakfast (SB). Dietary intakes were assessed using food diaries combined with digital photographic records and PA was measured via accelerometry throughout each condition. Statistical analyses were completed using repeated measures analysis of variance. Post-breakfast EI was 483 ± 1309 kJ/d higher in NB vs. SB (P=0.025), but total daily EI was 1479 ± 1311 kJ/d higher in SB vs. NB (P<0.0005). Daily carbohydrate, fibre and protein intakes were higher in SB vs. NB (P<0.0005), whereas daily fat intake was not different (P=0.405). Effect sizes met the minimum important difference of ≥0.20 for all significant effects. Breakfast manipulation did not affect post-breakfast macronutrient intakes (P≥0.451) or time spent sedentary or in PA (P≥0.657). In this sample of adolescent girls, breakfast omission increased post-breakfast free-living EI, but total daily EI was greater when a standardised breakfast was consumed. We found no evidence that breakfast consumption induces compensatory changes in PA. Further experimental research is required to determine the effects of extended periods of breakfast manipulation in young people.
    • Metabolism and exercise during youth

      Tolfrey, Keith; Zakrzewski-Fruer, Julia K.; Smallcombe, J.; Loughborough University; University of Bedfordshire (HUMAN KINETICS PUBL INC, 2017-02-01)
      Three publications were selected based on the strength of the research questions, but also because they represent different research designs that are used with varying degrees of frequency in the pediatric literature. The first, a prospective, longitudinal cohort observation study from 7 to 16 years with girls and boys reports an intrinsic reduction in absolute resting energy expenditure after adjustment for lean mass, fat mass, and biological maturity. The authors suggest this could be related to evolutionary energy conservation, but may be. problematic now that food energy availability is so abundant. The second focuses on the effect of acute exercise on neutrophil reactive oxygen species production and inflammatory markers in independent groups of healthy boys and men. The authors suggested the boys experienced a "sensitized" neutrophil response stimulated by the exercise bout compared with the men; moreover, the findings provided information necessary to design future trials in this important field. In the final study, a dose-response design was used to examine titrated doses of high intensity interval training on cardiometabolic outcomes in adolescent boys. While the authors were unable to identify a recognizable dose-response relationship, there are several design strengths in this study, which was probably underpowered.
    • Physical activity duration but not energy expenditure differs between daily and intermittent breakfast consumption in adolescent girls: a randomized crossover trial

      Zakrzewski-Fruer, Julia K.; Wells, Emma K.; Crawford, Natasha S.G.; Afeef, Sahar M.O.; Tolfrey, Keith (Oxford University Press, 2018-02-27)
      Background: It is not known whether breakfast frequency affects physical activity (PA) in children or adolescents. Objective: This study examined the effect of daily compared with intermittent breakfast consumption on estimated PA energy expenditure (PAEE) in adolescent girls. Methods: Using a randomized crossover design, 27 girls (age 12.4 ± 0.5 y, body mass index 19.3 ± 3.0 kg∙m-2) completed two, 7-day conditions. A standardized breakfast (~1674 kJ) was consumed every day before 09:00 in the daily breakfast consumption (DBC) condition. The standardized breakfast was consumed on only three days before 09:00 in the intermittent breakfast consumption (IBC) condition alternating with breakfast omission on the remaining four days (i.e., only water consumed before 10:30). Combined heart rate-accelerometry was used to estimate PAEE throughout each condition. Statistical analyses were completed using condition by time of day repeated measures analysis of variance. The primary outcome was PAEE and the secondary outcome was time spent in PA. Results: Daily estimated PAEE from sedentary, light, moderate and vigorous intensities and total PAEE were not significantly different between the conditions. The condition by time of day interaction for sedentary time (P = 0.05) indicated that the girls spent 11.5 min/d more time sedentary in IBC compared with DBC during 15:30-bedtime (P = 0.04). Light PA was 19.8 min/d higher during DBC compared with IBC (P = 0.05), which was accumulated during wake-10:30 (P = 0.04) and 15:30-bedtime (P = 0.03). There were no significant differences in time spent in MPA or VPA between the conditions. Conclusions: Adolescent girls spent more time in light PA before 10:30 and after school and spent less time sedentary after school when a standardized breakfast was consumed daily compared with intermittently across seven days. However, breakfast manipulation did not affect estimated daily PAEE. 
    • Postprandial glucose responses to standardised meals consumed after moderate- and high-intensity exercise bouts across standard school days in healthy adolescents

      Afeef, Sahar M.O.; Barrett, Laura A.; Zakrzewski-Fruer, Julia K.; Tolfrey, Keith; Loughborough University; King Abdulaziz University; University of Bedfordshire (Lidsen Publishing, 2022-08-15)
      Exercise-induced moderation of postprandial glycaemia in adolescents is unclear and has not been examined under free-living conditions. We assessed the effect of moderate-intensity exercise (MIE) and high-intensity intermittent exercise (HIIE) bouts on subsequent postprandial glycaemic responses across three standard school days. Fourteen healthy adolescents (13 ± 1 years) completed three conditions in the following order across consecutive days: MIE, 30-min continuous brisk walking; CON, no-exercise control; HIIE, 30- min of 10 × 30-s sprints interspersed with 2.5-min brisk walking bouts. Participants consumed three standardised meals (breakfast, lunch and dinner) at standardised times. Interstitial glucose, energy intake, sedentary time and physical activity were assessed under free-living conditions. Linear mixed models compared glucose outcomes between conditions, and Cohen’s d effect sizes were calculated. Although non-significant, the reduction in postbreakfast glucose iAUC was moderate for MIE (-0.24 mmol·L -1 ; P = 0.59; d = 0.77) and large for HIIE (-0.26 mmol·L -1 ; P = 0.44; d = 0.86) compared with CON. Non-significant, moderate (0.37 mmol·L -1 ; P = 0.22; d = 0.70) and large (0.42 mmol·L -1 ; P = 0.20; d = 0.81) increases in postlunch glucose iAUC were observed for MIE and HIIE compared with CON. Nevertheless, the 24-h mean glucose was stable at ~5.4 mmol·L -1 across conditions. The glycaemic variability indices calculated over 24-h after the onset of exercise for each condition including standard deviation (P = 0.59) and mean amplitude of glycaemic excursion (P = 0.82) were not different between conditions. Thirty-minute bouts of MIE and HIIE did not change postprandial glycaemia or 24-h glycaemic variability significantly in the small sample of healthy adolescents. However, the moderate and large effect sizes suggest both MIE and HIIE reduced breakfast glucose iAUC compared with CON, yet led to increases in post-lunch iAUC in the two exercise conditions. The mismatch between the probability values and effect sizes was a consequence of our COVID-reduced sample. The ramifications of these exercise effects are unclear and need to be confirmed in a larger sample of adolescents.