Eating steak and fries for dinner could make you ANXIOUS - the fat increases stress hormones, new research suggests

Indulging in a dinner of steak just as small as the palm of your hand and a side of French fries could increase stress and raise the risk of anxiety, new research shows. 

University of Colorado researchers tested mice who were fed either an average diet or one where almost half the daily calories came from fat found in junk food.

They found the latter group had more active genes known to alter levels of the 'feel good' neurotransmitter serotonin that had a direct influence on the mice's heightened anxiety. 

Those who ate a fat-rich diet also had less diversity in their gut bacteria, which aids in digestion, absorption of nutrients and is known to benefit one’s overall health.

Fat found in burgers, steaks, and fries is known to increase the risk of obesity, as well as damage to blood vessels that supply the heart, and has been strongly linked to a range of health issues, including heart disease, digestive issues and diabetes.

High-fat diets are known to increase the risk of obesity, heart disease, and type 2 diabetes

The mice were followed for nine weeks and divided into two groups — one group ate a diet consisting of 11 percent fat, while the other ate a diet of 45 percent fat, mostly saturated fat, the kind found in red meat. 

Researchers collected fecal samples and, after nine weeks, investigated how the diets affected the mice’s behavior by dropping them in a maze they had to escape from, placing them in a box separated by bright light and darkness - more time spent in darkness suggested more anxious behavior - and an open field to measure exploratory behavior and responses to a new environment. 

Researchers then injected the mice with a short chain of DNA that complements a certain genetic sequence to better understand how the genes involved in serotonin levels are activated. 

Measuring that level of expression of genes lets researchers know how changes there impacts serotonin function. 

The group that ate a high-fat diet not only gained more weight, they showed higher expression of three genes—tph2, htr1a, and slc6a4—all of which are involved in the production and signaling of the neurotransmitter serotonin, which plays a role in both anxiety and depression. 

These genes are particularly active in a region of the brainstem associated with stress and anxiety, indicating higher expression could be associated with higher levels of those emotions.

The average American diet is made up of about 36 percent fat, which would consist of around 80 to 120 grams of fat per day. Much of that daily amount of fat could come from eating one large serving of fries and and an eight ounce rib-eye steak.

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The recommended 2,000 to 3,000 calorie intake for the average American man, who weighs around 200lbs, should come from macronutrients that include 45 to 65 percent carbohydrates, 10 to 35 percent from protein, and 20 to 35 percent fat.

For the average American woman weighing about 170lbs, it is recommended to take in about 2,000 calories per day with a similar breakdown in macronutrients. 

The recommendation for fat intake is lower than both the average diet and the 45 percent-fat diet fed to mice.

Dr Christopher Lowry, a professor of integrative physiology at CU Boulder, said: ‘To think that just a high-fat diet could alter expression of these genes in the brain is extraordinary.

‘The high-fat group essentially had the molecular signature of a high anxiety state in their brain.’

While scientists do not fully understand how a high-fat diet affects anxiety-linked behaviors, changes in the connection between the gut and the brain are believed to be important.

The brain’s serotonin system is crucial for regulating emotions, including anxiety. The dorsal raphe nucleus (DR) is the brain's main source of serotonin, and its serotonin pathways influence various emotional behaviors and thinking processes.

When serotonin-producing neurons in specific parts of the DR are activated, they can increase anxiety-like responses.

The findings, published in the journal Biological Research, suggest the high-fat diet influenced the gut microbiome diversity and community composition across the nine weeks of diet treatment. 

The gut microbiome plays a key role in health and disease, including anxiety, both in experimental models and in humans.

Dr Lowry said: 'Everyone knows that these are not healthy foods, but we tend to think about them strictly in terms of a little weight gain.

'If you understand that they also impact your brain in a way that can promote anxiety, that makes the stakes even higher.' 

The gut microbiome is dominated by two types of bacteria – Firmicutes and Bacteroidetes. The study results showed an increase in the Firmicutes/Bacteroidetes (F/B) ratio in mice fed a high-fat diet.

A higher firmicute to bacteriodete ratio has been associated with the typical Western diet and higher rates of obesity. 

Firmicute growth outpacing that of bacteriodetes leads to less efficient extractions of nutrients from foods, leading to weight gain.

A high ratio also plays a role in metabolism and how food is stored as fat, leading to more fat accumulating in the body.