The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 13 No. 6 • December 2010

Weight Gain: Eating at the Wrong Time of Day

Restricting Food Intake to the Active
(Dark) Phase Prevents Body Mass Gain in Mice

An interesting new study1 shows that exposing mice to dim light during the period when it is normally dark and when they normally eat most of their food results in a shift to more eating during the daytime (light) period and in excess weight gain.

It has already been shown that exposing humans to dim light during the night-time attenuates important biological effects that ordinarily take place after dark, particularly the release of melatonin. Night shift work has been shown to elevate body mass index in humans. 2 In the new study, mice (which are ordinarily active after dark and also do most of their eating at that time) were exposed to a circadian rhythm of light followed by dim light (16 hours light/8 hours of dim light), a standard light/dark cycle (16 hours light/8 hours dark), or continuous light.

Mice housed in either the continuous light or in light followed by dim light had significantly increased body mass and reduced glucose tolerance as compared with mice in a standard light/dark cycle. This was the case despite the fact that the mice in the two conditions had similar levels of total caloric intake and total daily activity! (Perhaps the mice hadn’t read the official FDA pronouncement that weight is determined only by calories and exercise.) The mice in the light/dim light group ate 55.5% of their food during the light phase, as compared to only 36.5% eaten during the light phase by the light/dark mice. In the light/dim light group, the increased body mass could be prevented by feeding the animals only during the dim light period when it would ordinarily be dark and the mice active. Moreover, mice that had their food access limited to the light period (when mice are normally inactive) had increased weight gain whether they were housed in light/dark conditions or were housed in light/dim light but fed only during the light period.

The results showed that dim light at a level as low as 5 lux “is sufficient to uncouple the timing of food consumption and locomotor activity, resulting in metabolic abnormalities.” (Our comment: Your computer monitor or TV is a lot brighter than 5 lux unless you turn the intensity way down.)

A hypothesis: Sandy wondered whether the effects of dim light on night-time eating and physical activity could be prevented or attenuated by taking melatonin earlier in the evening (e.g., after the start of the dark period but earlier than the normal bedtime) so as to induce circadian changes that would normally take place in the dark even when there is dim light present. Durk tried it (n=1) and it does seem to reduce the desire to eat after dark. If you have a night time eating problem, you might try this.


  1. Fonken et al. Light at night increases body mass by shifting the time of food intake. Proc Natl Acad Sci USA 107(43):18664-9 (2010).
  2. van Amelsvoort et al. Duration of shiftwork related to body mass index and waist to hip ratio. Int J Obes Relat Metab Disord 23:973-8 (1999); Parkes. Shift work and age as interactive predictors of body mass index among offshore workers. Scand J Work Environ Health 28:64-71 (2002).

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