Fasting and flying

As seen in the science newswire: new sleep research from Cliff Saper's lab at Harvard suggests a possible mechanism to moderate the effects of jetlag: fast before you fly, and eat (early in the day) when you get to your destination. They examined which parts of the circadian circuitry in the brain controls light-entrainable versus food-entrainable circadian rhythmicity, focusing on the hypothalamus:



Using knockout mice carrying a deletion of the clock gene Bma1, which lack circadian rhythmicity, they restored Bma1 function to specific hypothalamic nuclei using viral vector injection and show that different brain regions control light (suprachiasmatic nuclei) and food (dorsomedial hypothalamic nucleus) entrainable rhythmicity.

Figure 2 from Fuller et al. 2008. Mice heterozygous for Bma1 show normal food entrainment (A), seen as a rise in body temperature before feeding (gray bar), as well as light entrainment, seen as elevated body temperature during the presumptive dark cycle (12-24h). Both types of rhythmicity are abolished in -/- mice (B), but reintroduction of Bma1 to the DMH restores the preprandial increase in body temperature (C).

The general idea is that fasting induces a state where food consumption is prioritized, causing the body to entrain to periods of food availability. In the authors' words:

For a small mammal, finding food on a daily basis is a critical mission. Even a few days of starvation, a common threat in natural environments, may result in death. Hence, it is adaptive for animals to have a secondary "master clock" that can allow the animal to switch its behavioral patterns rapidly after a period of starvation to maximize the opportunity of finding food sources at the same time on following days.

In actuality, the fact that circadian rhythms are entrainable by food availability was already known (see Krieger 1974; more recently Gooley et al 2006 implicated the dorsomedial hypothalamic nucleus in the process), so the idea that fasting can prevent jetlag is newer to the news media than to the field. However, the positive identification of specific brain region control suggests mechanistic sources for the separability of different kinds of circadian entrainment.