High-fat diets may lead to anxiety and impaired memory, says a new study. Find out if that includes the healthy fats, like the ones in your high-fat, low-carb diet

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Before you start ordering bar food tonight, you should know that those french fries are doing way more than just adding some mass to your middle: Mice who were fed a high-fat diet had higher anxiety levels, impaired memory, and more markers of inflammation in both their brain and body, according to a new study in Biological Psychiatry. (Try these 6 Foods to Fix Your Mood.)

Researchers attribute this effect to a high-fat diet changing the mix of bacteria in the gut. What does your gut have to do with your brain? There are two promising theories.

"The intestines have almost an entire brain within them," explains Annadora Bruce-Keller, Ph.D., associate professor of inflammation and neurodegeneration at Pennington Biomedical Research Center in Louisiana. The system is comprised of neurometabolites-neurons and chemicals similar to those in the brain. Fat disrupts the chemical harmony in your intestines, including what and how many of these neurometabolites are produced. Since this category includes mood stabilizers like serotonin and norepinephrine-and since neurometabolites travel from the intestines and function seamlessly in the brain-altered chemicals in the gut lead to altered chemicals in the brain.

The other viable explanation is that a high-fat diet compromises the integrity of the intestines. "Our intestines contain a highly volatile environment for the rest of the body, so if there is even a low-grade disruption, toxic chemicals can seep out," she explains. The fats create inflammation and negative bacteria, which can weaken the system's lining. And once inflammatory markers are in your blood, they can travel to your brain and inhibit the tiny blood vessels from expanding, compromising your cognitive abilities. (Yikes! 6 Signs You Need to Change Your Diet.)

And, while mice are not humans, previous research has shown that depressed people have a different mix of gut bacteria as well, so we do know that altered microbiomes can mess with your mood, Bruce-Keller points out.

Luckily, these effects are more than likely limited to unhealthy fats. The mice's diet was based on lard, and the bulk of research suggests it's only saturated fats that cause inflammation and mess with your metabolism, Bruce-Keller adds. (Ask the Diet Doctor: Are You Eating Too Many Healthy Fats?) That means if you're on a Mediterranean diet or the high-fat, low-carb kick favored by so many celebs and athletes right now, your mood and memory are probably safe.