Compared to a normal diet, both high-fat and high-sugar diets cause changes in gut bacteria that may be associated with significant loss of cognitive flexibility, which is the ability to adapt to changing situations, according to a study published in Neuroscience.
This effect was most pronounced on the high-sugar diet, which also showed an impairment of early learning for both long-term and short-term memory.
The findings are consistent with some other studies about the impact of fat and sugar on cognitive function and behavior, and suggest that some of these problems may be linked to alteration of the microbiome.
The research was done with laboratory mice that consumed different diets and then faced a variety of tests, such as water maze testing, to monitor changes in their mental and physical function, and associated impacts on various types of bacteria. The findings were published in the journal Neuroscience, in work supported by the Microbiology Foundation and the National Science Foundation.
"It's increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain," Kathy Magnusson, DVM, PhD, of the Oregon State University College of Veterinary Medicine, said in a press release. "Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions. We're not sure just what messages are being sent, but we are tracking down the pathways and the effects."
After four weeks on a high-fat or a high-sugar diet, the performance of mice on various tests of mental and physical function declined compared with animals on a normal diet. One of the most pronounced changes was in cognitive flexibility.
What's often referred to as the "Western diet," or foods that are high in fat, sugars, and simple carbohydrates, has been linked to a range of chronic illnesses in the United States, including the obesity epidemic and an increased incidence of Alzheimer's disease.
"We've known for a while that too much fat and sugar are not good for you," Magnusson said in the press release. "This work suggests that fat and sugar are altering your healthy bacterial systems, and that's one of the reasons those foods aren't good for you. It's not just the food that could be influencing your brain, but an interaction between the food and microbial changes."
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Western diets are high in fat and sucrose and can influence behavior and gut microbiota. There is growing evidence that altering the microbiome can influence the brain and behavior.
This study was designed to determine whether diet-induced changes in the gut microbiota could contribute to alterations in anxiety, memory or cognitive flexibility. Two-month-old, male C57BL/6 mice were randomly assigned high-fat (42% fat, 43% carbohydrate (CHO), high-sucrose (12% fat, 70% CHO (primarily sucrose) or normal chow (13% kcal fat, 62% CHO) diets.