Scientists show connection between darkness and metabolic fuel switch.

Stop blaming an inability to burn fat on petty scapegoats like “adulthood” and start faulting the true culprit: the sun.

As we go about our bright days and dark nights, our bodies create cellular energy, primarily by consuming glucose—burning fat is a last resort. But, according to a paper in the January 19th edition of Nature, extended periods of darkness cause a state similar to hibernation, turning the body into a fat-burning machine. At least, that’s what happens in mice.

Researchers at the University of Texas Health Science Center at Houston propose that darkness acts as a metabolic signal.  Extended periods of darkness cause the release of an enzyme, switching the body from being glucose-fueled to being fat-fueled.

“If this mechanism is conserved in humans, I have proposed that it could provide new strategies to treat obesity and type-2 diabetes,” senior author Cheng Chi Lee said via e-mail. “I think the most likely immediate effect is the regulation of core body temperature during major surgery and during trauma response.”

Lee, a biochemistry professor and expert in circadian rhythms, examined the genes of two groups of mice: one that was kept in darkness for 48 hours, and one that was exposed to a normal light-dark cycle. When he examined the livers of the constant-darkness group, he found highly elevated levels of a gene involved in the degradation of dietary fat.

The study stemmed from Lee’s investigation into what triggers hibernation. Previous studies have focused on food, environmental temperature and photo-period; however, not one of these factors is common to all animals that hibernate.

“We asked, ‘What is the common environmental factor faced by hibernating mammals?’” Lee said. “I can only think one consistent environmental factor, and that is constant darkness.”

In a further study, Lee and postdoctoral student Jianfa Zhang found that darkness not only affected the liver gene, it increased levels of a chemical called 5’-AMP, a byproduct of cellular energy (ATP) production. The increased levels of 5’-AMP, a “garbage” byproduct, baffled Lee, who expected to see a change in ATP levels instead.

“It then occurred to me that a CEO of a large company can monitor how well they are doing by looking at their sales, i.e. consumption,” Lee said. “Similarly, a head of household will know what the family consumed if you look at the garbage.”

“The organism must be doing the same thing,” he continued. “To determine its energy requirement, it must determine how much ATP has been consumed, [using] the 5’-AMP level.”

The level of the chemical acts as a feedback mechanism, indicating how much energy the body needs, based on how much 5’-AMP has been produced. The body responds to the level by either going into a glucose-burning normal state or a fat-burning, hibernation-like state.

Rejoice, carb counters! You can now try supplementing pasta with shots of 5’-AMP. Just prepare for a food coma unlike any other.

Originally published January 23, 2006


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