Editors' ChoiceObesity

Yet Another Reason Rats Don’t Take Day Jobs

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Science Translational Medicine  26 Jan 2011:
Vol. 3, Issue 67, pp. 67ec11
DOI: 10.1126/scitranslmed.3002146

Late-night feeding has been well established to associate with weight gain in humans. However, eating when you’re supposed to sleep, particularly eating fatty meals, has implications for adverse health effects that are not mediated through weight gain. In order to clarify potential mechanisms underlying these adverse health outcomes, Glad et al. conducted an investigation in a rat model of “reverse feeding,” which is defined as feeding during the normal sleep period.

There is evidence that altered patterns of food intake may lead to changes in the biological clock. Rats, which normally eat during the “dark phase” because of their nocturnal nature, have been shown to not only have an inverted biological clock but also have inverted gene activation in peripheral tissues. This activity may depend on the hypothalamus-pituitary-axis, specifically the axis involving growth hormone. To examine this, Glad et al. studied the effects of both transient (6 hours) and prolonged (1 month) night-time food deprivation on male rats. They learned that growth hormone, which is critical in skeletal growth and fat breakdown, was suppressed in those rats that underwent transient food deprivation. Prolonged reverse feeding was associated with prolonged growth hormone suppression and diminished growth of skeletal, pituitary, liver, and kidney mass, but did not increase white adipose tissue. They also observed an increase in liver- and muscle-specific expression of genes associated with clock regulation and an increase in body weight gain and efficiency of fat storage in the reverse-feeding rats.

This study provides an elegant demonstration in the rat of the multifaceted way by which altering the normal dietary pattern by day and night cycles can affect growth and development of multiple organ systems beyond body weight gain. These findings provide the basis for further examination of these effects in humans who work, and likely eat, at night.

C. A.-M. Glad, et al. Reverse feeding suppresses the activity of the GH axis in rats and induces a preobesogenic state. Endocrinology, 5 Jan 2011 (10.1210/en.2010-0713). [Abstract]

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