A high-fat diet may increase anxiety, according to research published in the journal “Biological Research”. Scientists explain how eating large amounts of saturated fat from animal products affects the brain.
As experiments on rats have shown, a high-fat diet affects intestinal bacteria and, indirectly, also chemicals in the brain. – Everyone knows that it is not healthy food, but we tend to think about it only in terms of weight gain – said the lead author of the new publication, Prof. Christopher Lowry from the University of Colorado in Boulder, quoted on ScienceDaily. “If we understand that it also affects our brain in ways that can cause anxiety, the stakes are even higher,” he added.
How the experiment went
The study was conducted on adolescent rats. Lowry's team divided them into two groups: Half were on a standard diet containing about 11 percent for nine weeks. fat, the remaining rats were on a high-fat diet containing 45 percent. fat, mainly saturated fat from animal products. According to the Centers for Disease Control and Prevention, the typical American diet contains about 36 percent. fat. During the study, scientists analyzed stool samples to assess the animals' microbiome, or gut bacteria. After nine weeks, the rats were subjected to behavioral tests.
Unhealthy food – how it affects the brain
As expected, the high-fat diet group gained weight compared to the control group. In addition, they had a much lower diversity of intestinal bacteria, whereas a greater diversity of bacterial flora is generally associated with better health. Another difference was the numerical predominance of Firmicutes bacteria over Bacteroidetes bacteria in fat-eating rats. This advantage appears to be related to the typical highly processed diet and obesity.
Additionally, the high-fat diet group showed higher expression of three genes (tph2, htr1a and slc6a4) involved in the production and signaling of the neurotransmitter serotonin – particularly in an area of ​​the brainstem known as the dorsal raphe nucleus (cDRD), which is associated with stress and anxiety.
High-fat diet and the “happiness hormone”
Serotonin is sometimes called the “happy hormone,” but as Lowry pointed out, certain subsets of serotonin neurons can, when activated, trigger anxiety-like responses in animals. It is known that increased expression of tph2, or tryptophan hydroxylase, in cDRD has been associated with mood and stress-related mental disorders in humans.
“The idea that a high-fat diet alone can change the expression of these genes in the brain is extraordinary,” said Lowry, quoted on DailyScience. “The high-fat group essentially had a molecular signature of high anxiety in their brain,” he explained.
Lowry suspects that an unhealthy microbiome compromises the gut lining, allowing bacteria to enter the circulatory system and communicate with the brain via the vagus nerve, which is the pathway from the digestive tract to the brain. – If we think about human evolution, it makes sense – said the scientist. “We are programmed to really notice the things that make us sick so that we can avoid those things in the future,” he noted.
Fats – which ones are worth eating?
As he emphasized, not all fats are bad. Healthy fats, such as those found in fish, olive oil, nuts and seeds, may have anti-inflammatory effects and benefit the brain. Therefore, he advises to eat as many different types of fruits and vegetables as possible, fermented foods that support a healthy microbiome, and to avoid pizza and french fries. There are studies that show that “good” fat can counteract some “bad” fat – so if someone has to eat hamburgers, Lowry advises adding a piece of avocado.
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