Ask the doctors: New study attempts to link keto diet, anxiety

Dear Doctors: I’ve been thinking about trying a keto diet. A friend had good results when she used it to lose weight. I was already worried so much fat would be bad for my health. Now I’ve read that a high-fat diet can cause anxiety. Is that true?

Dear Reader: The keto diet has been one of the most popular diet strategies in the United States for several years. It is based on strictly limiting carbohydrates, which forces the body to change how it obtains energy. With carbs largely out of the picture, the preferred source of energy, which is glucose, is no longer available. The body is forced to turn to its alternative method of obtaining fuel, which is burning fat. That process results in compounds known as ketone bodies, which give the keto diet its name.

It is possible to trigger ketosis with a diet high in protein, but the high-fat version of keto is the one most commonly followed. In this approach, up to 90% of daily calories come from fat. Although this diet is associated with improved blood glucose control, the long-term health effects, including on blood lipid levels, are not yet clear.

There is also a great deal of interest in the potential effects of a keto diet on mood and mental health. In a recent column, we explored research that suggests a keto diet can help modulate the extremes of mood associated with bipolar disorder. Other studies have linked the keto diet to improvements in the symptoms of depression.

Now, however, researchers in Colorado have linked a high-fat diet to an increase in anxiety. However, there are several factors to consider. One is that the study looked at rats, not humans. The other is that the diet the rats consumed consisted almost exclusively of saturated fats. (The percentage of saturated fats came close to that of the typical American diet.) Yet it was not a keto diet. The researchers were interested in how large amounts of saturated fat would affect the gut microbiome, and thus the gut-brain axis. That’s the biochemical pathway that allows communication between the gastrointestinal tract and the brain.

When compared to a control group, which ate a healthful diet throughout the nine-week study, the high-fat rats had a marked drop in the diversity of their gut microbiomes. They also gained weight and exhibited behaviors associated with increased anxiety. Fecal analysis found an increase in microbes associated with obesity. In addition, the rats underwent metabolic changes that are associated with the rise of a subset of serotonin.

We typically hear about serotonin, which helps to regulate mood, as the feel-good chemical. However, the subset of serotonin that was identified in the rats is known to trigger a response of anxiety. The increase in that subset was particularly evident in an area of the brain stem linked to stress and anxiety. It’s true that the rats ate a diet high in fat, but they were not in a metabolic state of ketosis. As a result, the findings here can’t be used to draw conclusions about potential effects in a keto diet.

Send your questions to askthedoctors@mednet.ucla.edu.