When You Eat Is As Important As What You Eat!

November 15, 2012

If you’re one of those people always keeping an eye on what you’re eating, you might want to consider also when you’re eating.
In a study published this week in
Nature Medicine, two researchers at the University of Pennsylvania by investigating fat cells in mice, were able to identify the existing link between daily rhythm and metabolism.
In particular, their findings showed that when a species' typical daily rhythm is thrown off, changes in metabolism also happen. These results shed light on the complex causes of obesity in humans.

The findings

The Penn studies are surprising in two respects. "The first is that a relatively modest shift in food consumption into what is normally the rest period for mice can favor energy storage," says Georgios Paschos PhD, a research associate in the lab of Garret FitzGerald, MD, FRS director of the Institute for Translational Medicine and Therapeutics, Perelman School of Medicine. "Our mice became obese without consuming more calories." Indeed, the Penn researchers could also cause obesity in normal mice by replicating the altered pattern of food consumption observed in mice with a broken clock in their fat cells.
This behavioral change in the mice is somewhat akin to night-eating syndrome in humans, also associated with obesity and originally described by Penn's Albert Stunkard in 1955.
For example, in people, night shift workers have an increased prevalence of obesity and metabolic syndrome, and patients with sleep disorders have a higher risk for developing obesity. Also, less sleep means more weight gain in healthy men and women.
Daily intake of food is driven by oscillating expression of genes that drive and suppress appetite in the hypothalamus. When the clock was broken in fat cells, the Penn investigators found that this hypothalamic rhythm was disrupted to favor food consumption at the time of inappropriate intake – daytime in mice, nighttime in humans.
The second surprising observation relates to the molecular clock itself. Traditionally, clocks in peripheral tissues are thought to follow the lead of the "master clock" in the SCN of the brain, a bit like members of an orchestra following a conductor. "While we have long known that peripheral clocks have some capacity for autonomy – the percussionist can bang the drum without instructions from the conductor – here we see that the orchestrated behavior of the percussionist can, itself, influence the conductor," explains FitzGerald.

Balancing act

Balancing energy levels in the body requires integrating multiple signals between the central nervous system and outlying tissues, such as the liver and heart.
Fat cells not only store and release energy but also communicate with the brain about the amount of stored energy via the hormone leptin. When leptin is secreted, it causes more energy to be used and less eating via pathways in the hypothalamus.
The Penn team found that only a handful of genes were altered when the clock was broken in fat cells and these governed how unsaturated fatty acids were released into the bloodstream.
The findings point to a role for the fat cell clock molecules in organizing energy regulation and the timing of eating by communicating with the hypothalamus, which ultimately affects stored energy and body weight.
Taken together, these studies emphasize the importance of the molecular clock as an orchestrator of metabolism and reflect a central role for fat cells in the integration of food intake and energy expenditure.
"Our findings show that short-term changes have an immediate effect on the rhythms of eating," says FitzGerald. "Over time, these changes lead to an increase in body weight. The conductor is indeed influenced by the percussionist."

The Iron You

The above story is reprinted from materials provided by University of Pennsylvania School of Medicine, via Eurekalert!


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