Meal pattern has been identified as a factor influencing the thermic effect of food (TEF) and metabolic status, and therefore health. This thesis investigated the effects of an irregular meal pattern, with a controlled energy intake, in normal-weight (n=11) and obese with insulin resistance (n=9) females over a 14-day period. Measurements were made of the TEF, circulating glucose, insulin, lipids concentration and appetite regulation, using a crossover design. The irregular intervention period led to a significant reduction in the TEF following a test drink consumption in both normal-weight and obese participants. Glucose iAUC responses to the test drink measured over 3h were higher after the irregular compared with the regular intervention with no difference in the insulin response in the normal-weight study. In the obese study, glucose responses were unaffected by the regular and irregular intervention periods, whilst there was a main effect of meal pattern in insulin responses. In the normal-weight study, fasting GLP-1 decreased after both interventions. In contrast, fasting GLP-1 increased after both interventions in the obese study. Furthermore, in the obese study, the regular intervention produced a higher GLP-1 iAUC compared with the irregular intervention, but there were no such effects in the normal-weight study. The normal-weight study showed that fasting PYY was lower after the interventions compared with before. Moreover, iAUC for PYY increased after the interventions compared with before. However, there were no significant differences in fasting and iAUC PYY responses between the two interventions in the obese study. A regular meal pattern appears to be associated with greater TEF, which might result in more favourable energy balance for weight maintenance. Also, it is likely that a regular meal pattern improved insulin sensitivity in healthy normal-weight females. Therefore, a regular meal pattern could be a lifestyle factor that may promote an individual’s health.