Effect of extended morning fasting upon ad libitum lunch intake and associated metabolic and hormonal responses in obese adults

Background/Objectives: Breakfast omission is positively associated with obesity and increased risk of disease. However, little is known about the acute effects of extended morning fasting upon subsequent energy intake and associated metabolic/regulatory factors in obese adults. Subjects/Methods: In a randomised crossover design, twenty-four obese men (n=8) and women (n=16) extended their overnight fast by omitting breakfast consumption or ingesting a typical carbohydrate-rich breakfast of 2183 ± 393 kJ (521±94 kcal), before an ad libitum pasta lunch 3 hours later. Blood samples were obtained throughout the day until 3 hours post-lunch and analysed for hormones implicated in appetite regulation, along with metabolic outcomes and subjective appetite measures.Results: Lunch intake was unaffected by extended morning fasting (difference=218 kJ, 95 % CI -54 kJ, 490 kJ; p=0.1) resulting in lower total intake in the fasting trial (difference=-1964 kJ, 95 % CI -1645 kJ, -2281 kJ; p<0.01). Systemic concentrations of peptide tyrosine-tyrosine (PYY) and leptin were lower during the afternoon following morning fasting (p≤0.06). Plasma acylated ghrelin concentrations were also lower following the ad libitum lunch in the fasting trial (p<0.05) but this effect was not apparent for total ghrelin (p≥0.1). Serum insulin concentrations were greater throughout the afternoon in the fasting trial (p=0.05), with plasma glucose also greater 1 hour after lunch (p<0.01). Extended morning fasting did not result in greater appetite ratings after lunch, with some tendency for lower appetite 3 hours post-lunch (p=0.09).Conclusions: We demonstrate for the first time that, in obese adults, extended morning fasting does not cause compensatory intake during an ad libitum lunch nor does it increase appetite during the afternoon. Morning fasting reduced satiety hormone responses to a subsequent lunch meal but, counterintuitively also reduced concentrations of the appetite-stimulating hormone acylated ghrelin during the afternoon relative to lunch consumed after breakfast.