Do High-Fat Diets Cause Depression?

woman worked up about mouse chow

Fat-phobia strikes again

Earlier this month, the following headline showed up in my inbox:

"High-Fat Diet Linked to Anxiety, Depression"

It was distributed by Medscape (a widely-read e-news source geared towards medical professionals), as well as a variety of other media outlets, including Science Daily.

The study itself was published in the British Journal of Pharmacology and is entitled "High fat diet-induced metabolic disorders impairs serotonergic function and anxiety-like behaviours in mice."

We have been (wrongly) told for decades by public health officials that dietary fat is unhealthy, so we tend to take articles that support this belief at face value, without question.

But before you clear your cupboards of all fatty foods, hoping for eternal happiness and tranquility, let me tell you why the results of this MOUSE study need not cause you any additional depression and anxiety.

Of mice and mental health

Researchers fed one group of mice a low-fat chow and another group a high-fat chow. After twelve weeks, the mice eating high-fat chow had gained more weight. They had also developed high blood sugars, high insulin levels, and glucose intolerance. Sixteen weeks into the study, these mice also showed more signs of emotional distress.

Poor meeces.

Furthermore, when the high-fat mouse group was treated with the antidepressant Escitalopram (brand name Lexapro), the antidepressant failed to work.

The study’s authors concluded that high-fat diets may lead to type 2 diabetes, and that type 2 diabetes may then lead to depression and anxiety symptoms which respond poorly to antidepressants.


As a psychiatrist with a special interest in nutrition, I understand how important dietary fat is to the health of the brain, and I know that fat doesn’t cause type 2 diabetes. So, I took a peek behind the headlines to see if this study would confirm or challenge my beliefs.

What I discovered is that the researchers who conducted this study THINK their experiment is about fat, when in reality, it’s about SUGAR.

The proof is in the chow, my friends.

Show me the chow

I hunted down the ingredients and macronutrient composition for each of the mouse chows used in the experiment:

Low-fat chow (STDA04, SAFE diets) main ingredients: barley, wheat, corn, soja meal, wheat bran, and hydrolyzed fish protein. Macronutrient composition: 43.5% starch, 16.1% protein, 3.9% fiber, 3.2% sugars, 3.1% fat and 2,791 kcal/kg.

High-fat chow (D12451, Research Diets) main ingredients: casein, lard, sucrose, maltodextrin, corn starch, cellulose, and soybean oil. Macronutrient composition: 41% carbohydrate, 24% protein, 24% fat, and 4,730 kcal/kg. The carbohydrate in this chow consists of 21% corn starch, 29% maltodextrin, and 50% sucrose!!! Are you rolling your human eyes at these mouse researchers yet?

Yes, the high-fat chow was indeed higher in fat than the control chow (24% vs 3%), I’ll grant you that. However, it also contained 50% more protein, 70% more calories, and THIRTEEN TIMES the amount of refined carbohydrate, HALF of which was pure sugar! The control chow contained only 3% sugar and no refined starches at all.

But wait, there’s more.

The manufacturer of the high-fat chow, Research Diets Inc, makes a low-fat chow that it specifically instructs researchers to use as a well-matched control, yet this was not done. Here is a direct quote from the high-fat chow manufacturer’s product information sheet:

“We recommend that you use a matched, purified ingredient diet and not a grain-based ‘chow’ diet. There are many, many differences between purified diets and chow diets and these variables make it difficult to interpret your data from a study in which one group was fed a purified ingredient high-fat and the other a low-fat chow diet. Differences between your groups could be due to the level of fat, but could also be due to differences in fiber type and level, source of carbohydrate, and the presence or absence of plant chemicals (such as phytoestrogens), just to name a few.”

Instead of doing as they were told, the researchers went rogue. They used chows made by two different manufacturers, so their ingredients were almost completely different.

The protein in the high-fat chow was casein (milk protein), whereas the low-fat chow contained soy and fish proteins. The high-fat chow contained two kinds of fat: lard and soybean oil. The low-fat chow, made of whole grains, soy meal and fish protein, is FAR healthier in general for a mouse than the high-fat chow, which is essentially the mouse version of a really bad ice cream cone, loaded with highly processed ingredients.

With so many variables, how are we to know which differences were responsible for the results?

mouse eating ice cream cone

Don’t be fooled

Please think twice (or maybe even a few hundred times) before taking this fat-phobic headline seriously. High-fat diets do not cause diabetes. High-SUGAR diets (whether they are high-fat or low-fat) can, and frequently do. This poorly-conducted mouse study, if it tells us anything at all, simply confirms that well-established connection. To see the evidence for yourself, please read my post "Why Sugar Is Bad for You: A Summary of the Research."

Maybe this sorry study is trying to tell us that mice who eat too much sugar, dairy, and refined starches not only develop type 2 diabetes, but that they get depressed and anxious as well. Now THAT would be a potentially very interesting result, with profound implications for mouse psychiatrists worldwide.

High-fat diets and depression

So, what about the role of fat in depression and anxiety disorders? When it comes to brain conditions, high-fat, low-sugar diets are GOOD. While there is very little scientific research available to tell us whether a high-fat diet could be helpful in treating depression, it is well-established that ketogenic diets, which are very high in fat, have uniquely powerful healing properties when it comes to other serious brain conditions such as epilepsy and neurodegenerative diseases. Time will tell if depression will be counted among them. [For more information, please see my post about ketogenic diets and bipolar disorder].

There is, however, excellent science demonstrating a clear connection between high-sugar diets and anxiety—in humans. More about that in a new post coming up later this season . . . sign up below if you’d like to be notified when it becomes available.

To learn more about the history, politics, and science of the dietary fat myth which continues to inspire so much bad research, I highly recommend Nina Teicholz’s book The Big Fat Surprise and Gary Taubes’ book Good Calories, Bad Calories.

  • Big Fat Surprise
  • Good Calories, Bad Calories

Until then, question the headlines! It is very common to see proclamations that high-fat diets cause disease, death, and worldwide destruction, but every anti-fat study I’ve ever read failed to take the amount and quality of carbohydrate in the diet into consideration. I know of no properly conducted study demonstrating a connection between whole-food sources of fat and human disease.

The single most important thing you can do for your health is to replace the bad carbohydrates (sugars and refined starches) in your diet with healthy fats!

Don’t let your good health be destroyed by bad information.

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