Metabolic effects of physical inactivity and intermittent energy restriction
Publication Date
August 4, 2021
Creator
Abstract
The modern obesogenic environment favouring passive overfeeding and a diminished level of physical activity makes optimal health notoriously difficult to achieve. The overarching aim of this thesis was to investigate the effects of physical inactivity and 5:2 intermittent energy restriction (5:2 IER) on basal and postprandial metabolism.
Physical Inactivity (Chapter 3)
The Physical Inactivity study extended the findings of published research by evaluating the effects of two-days of physical inactivity, with (SIT=E) and without (SIT+E) a proportional decrease in energy intake, compared with a CONTROL arm (two consecutive days of standardised daily levels of moderate physical activity and matched energy intake) on basal and postprandial metabolism utilising a randomised crossover design. A physical inactivity model was used in which step counts were reduced by 80%. There was a strong tendency towards a significant difference in incremental area under the curve (iAUC) for serum inulin over 180 min postprandially between the groups (P = 0.05, η2p = 0.35). This was driven by the difference between the CONTROL vs. SIT+E trials. Compared with the CONTROL trial, the mean iAUC insulin was 25% higher in the SIT+E (P = 0.02) and 8% higher in the SIT=E (P = 0.39) trials. There were no differences in iAUC insulin between the SIT+E and SIT=E trials (P = 0.09). Thus, two-days of step reduction without the compensation of reduced energy intake tended to elevate postprandial insulinaemic excursion; this effect tended to be ameliorated, when accompanied by a compensatory reduction in energy intake to maintain energy balance.
5:2 Intermittent Energy Restriction (Chapters 4 and 5)
Intermittent energy restriction (IER) may overcome poor long-term adherence with continuous energy restriction (CER), for weight reduction. In a two-week randomised, parallel trial, 16 young, healthy-weight participants, were assigned to either CER (20% below estimated energy requirements (EER)) or 5:2 IER (70% below EER on two non-consecutive days; five days at EER, per week). Metabolic and appetite regulation markers were assessed before and for three hours after a liquid breakfast; followed by an ad libitum lunch; pre- and post-intervention. Weight loss 2 was similar in both groups: -2.5 (SEM 0.37) kg for 5:2 IER vs. -2.3 (SEM 0.26) kg for CER. There were no differences between groups for postprandial iAUCs for serum insulin, blood glucose or subjective appetite ratings. Compared with CER, 5:2 IER led to a reduction in fasting blood glucose concentrations (treatment-by-time interaction, P = 0.018, η2p = 0.14). Similarly, compared with CER, there were beneficial changes in fasting composite appetite scores after 5:2 IER (treatment-by-time interaction, P = 0.0003, η2p = 0.35) which may help to reduce the desire to eat.
Collectively, these findings highlight the important role of overfeeding in the negative effects of physical inactivity and provide novel insights into the metabolic effects of 5:2 IER. Replication and mechanistic assessments across different population groups and for longer periods of time are warranted.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Subjects (LC)
Associated Schools / Departments
School of Life Sciences
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eprints ID
65931
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