Meal times differ from culture to culture. These differences may influence energy regulation and, consequently, body weight. Current studies support the notion that not only "what" but also "when" the investigators eat may have a significant role in obesity treatment. Recently, it has been shown that eating the main meal of the day, lunch in Spain, late in the day is predictive of difficulty in weight loss and decreased insulin sensitivity. Furthermore, it has been shown that eating late at night when plasma melatonin concentrations are elevated, impairs glucose tolerance, particularly in MTNR1B risk allele carriers.