Bad news for people who moderate their healthy diets with designated "cheat days" -- capping off a week's worth of healthy eating by eating junk food could be almost as bad as eating straight junk without the healthy days.
Junk food wreaks havoc on the microbial cells in the gut regardless of how rarely it's eaten, according to Margaret Morris, head of pharmacology at the University of New South Wales, Australia.
"A relatively healthy but complex community is living together peacefully, until an unruly mob of hooligans begins unsettling the community’s residents and disturbing the peace every weekend," Morris wrote. "This scenario could be playing out in the human gut every time you go on a junk food binge. Yo-yoing between eating well during the week and bingeing on junk food over the weekend is likely to be just as bad for your gut health as a consistent diet of junk."
To understand why junk food has such a detrimental effect, Morris says, it's important to understand "microbiota," the vast swamp of up to 100 trillion microbial cells that inhabit the gut of every person. Recent research has revealed microbia play a much more important role in human health than previously thought, and scientists say microbia impact everything from mental health to immune function and metabolism.
It's the latter that matters when it comes to junk binges, Morris says. In an experiment, researchers put groups of rats into three groups: The first was kept on an all-healthy, all-the-time diet; the second group was given healthy food during the week, and junk on the weekends; and the last group feasted on junk food all the time.
Disturbingly, the experiment showed the mostly healthy group that became weekend warriors of junk food suffered consequences almost as severe as their friends who were eating the rat equivalents of pizza and hamburgers all week. While the weekend warrior rats were slightly slimmer than the consistent junk-gobblers, they were still 18 percent heavier than their healthy-eating counterparts.
Researchers realized that "any exposure to the junk food was sufficient to shift the gut biota profile."
"In other words," Morris says, "the microbiota of cycled rats was almost indistinguishable from rats fed a constant diet of junk."
On the bright side, the study doesn't conclusively prove humans are impacted the same way rats are. While research scientists use rats often because of their similarity to humans -- particularly when it comes to adverse impacts on the body -- scientists won't be able to say for sure whether junk food has the same impact on human microbia until they conduct further studies.
And as further consolation, Morris writes, "the gut biota profile can change relatively quickly, so we have the capacity to introduce healthy lifestyle measures in order to improve intestinal health." In other words, as quickly as microbia can be disturbed by an influx of empty calories and artery-clogging food, recent studies show the damage to the gut can also be undone rapidly by sticking to a healthy diet.