BACKGROUND AND AIMS
It has been hypothesised that prolongation of the nocturnal low insulin state that is achieved through early day fasting1 or a zero carbohydrate breakfast2 results in greater mobilisation of adipose tissue stores. The aim of this study was to investigate this hypothesis further in comparison to two different approaches of early day nutritional strategies.
MATERIALS AND METHODS
In this cross-over study, 10 lean, healthy volunteers (females: 7; males: 3) aged 28.6±4.3 years with a mean BMI of 22.9±1.4 kg/m2 underwent three 6-hour morning sessions after an overnight fast: A: fasting; B: 500 kilocalorie (kcal) zero carbohydrate breakfast;3 and C: 500 kcal Mediterranean-type breakfast. Fasting duration before the experiments was reported. Insulin resistance (Homeostatic Model Assessment of Insulin Resistance [HOMA-IR]) was measured at baseline. Plasma glucose and insulin measurements, as well as Visual Analogue Scales (VAS) for hunger, were obtained every 30 minutes during the study. Plasma β-hydroxybutyric acid (bHB) concentrations were used as an index of adipose tissue mobilisation,2 and were measured via a colorimetric assay on an hourly basis. The trapezoidal rule was used to calculate the area under the curves (AUC) during the study for all obtained parameters.
The unadjusted AUC [bHB] was not significantly different between the three sessions (p=0.089). After controlling for session type, linear regression analysis demonstrated that the AUC [bHB] correlated positively with fasting duration (β=0.416; p=0.018) and negatively with HOMA-IR (β=-0.398; p=0.024). The AUC [bHB], after adjustment for fasting duration and HOMA-IR, was significantly higher after session A versus B (p=0.021) and A versus C (p=0.008), but it did not differ (p>0.05) between session B versus C (6.08±0.55 versus 4.14±0.55 versus 3.76±0.60 mmol/hour/L, for sessions A, B, and C, respectively). The AUC [insulin] was significantly lower for session A versus C (p=0.001), session A trended lower than B (p=0.067), and session B trended lower than C (p=0.081), while the AUC [glucose] was similar among the three sessions (p=0.907). The AUC [VAS-hunger] was significantly higher in session A compared with either B or C (p<0.01) and similar between B and C. AUC [VAS-hunger] in the second half of each session was significantly higher in session C compared with session B (p<0.01).
Greater mobilisation of adipose stores, as indexed by increased [bHB], may be achieved through intermittent fasting in the morning compared with either a zero carbohydrate or a Mediterranean-type breakfast eaten by lean individuals. Carbohydrate restriction in the morning and a Mediterranean-type breakfast constitute equal choices in terms of adipose tissue mobilisation, while a zero-carbohydrate breakfast provides a more prolonged hunger suppression. Further studies are needed to examine the long-term metabolic effects of fasting in the morning.