“High Fat Diet” Controversy

The words that we use are important. If we don’t all understand the words we’re using in the same way, how can we communicate effectively? I’ve been thinking about this a lot lately. If you’re wondering what this has to do with nutrition and wellness, the answer is: a lot.
Here’s one example of a poorly defined word that leads to untold confusion and pain: Fat.
The word fat has two entirely distinct definitions in the nutrition and wellness context.
  1. Fat is one of the three macronutrients found in food that we eat.
  2. Fat is also what we call the adipose tissue cells that store triglycerides, and if we accumulate enough of them, can change the shape of our body.

It’s not always clear which “fat” is being referred to by health experts, and over time, most people have stopped acknowledging any difference between them. The macronutrient fat is generally understood to automatically become the adipose tissue fat when eaten.

This is wrong for several reasons that I won’t go into here, (see this article for a little more on that) but one could see how this confusion could have happened innocently and organically. Foods contain fat and our bodies contain fat. While I’m personally frustrated by this misleading homonym on a daily basis, it’s nowhere near as devastating for our collective health as a similarly ill defined phrase I’ve started noticing a lot lately, “high fat diet”.

High Fat Diet

Certain high fat diets (often referred to as ketogenic or low-carb-high fat, LCHF) are currently quite popular among people interested in their health, from high performance athletes to weight loss communities. Many people swear that switching to a diet higher in fat content (and lower in other macronutrients) has not only helped them lose weight, but has also improved every function of their body. The Reframe Lifestyle is high fat as well and consistently brings not just weight loss, but a reduction in pain and basically all other measurable health outcomes.

Meanwhile, nutrition research and nutrition advice still uses the phrase “high fat diet” as the opposite of a “healthy” or “balanced” diet in nutrition studies, and these “high fat diets” invariably correlate with worsening health outcomes. Literally any chronic condition you can imagine, you can find a study linking it to a “high fat diet”. Labs routinely use “high fat diets” to induce diabetes in rats. Just look at the results on PubMed when you search for the term “high fat diet”. The results are terrifying. Despite millions of people around the world thriving on a low carb high fat diet, the nutrition establishment continues to tell us that a high fat diet causes heart disease, obesity, cancer, and everything else that ails us.

So what’s going on here?

When you see a news article, a nutrition study, or any health claim that includes the phrase “high fat diet”, they don’t ever mean low carb high fat. When they are referring to a low carb high fat diet, they will specify that, or use the term “ketogenic”. A more accurate definition of the mainstream use of “high fat diet” would be, “high sugar, high junk food, high carb, high everything you can get your hands on diet”. 

In a research context, a high fat diet is defined as any diet that contains more than 35% of calories from fat. That’s certainly stretching the definition of the word “high”, but okay, let’s grant that definition.

There are two reasons why these “high fat diets” lead to terrible outcomes in studies.

Reason #1: This kind of research is often done on lab animals that aren’t meant to eat fat.

The research community is well aware that nutrition studies on humans can rarely, if ever, provide useful information on anything at all. See #2 below for more on this. That’s why nutrition studies are often carried out on rats or mice first, for many reasons, not the least of which being the fact that you can actually separate the rat subjects into two groups and fully control what they eat. In human subjects, you cannot control for much of anything. Sometimes, health related studies on rats and mice can be very compelling, but not for studies centered around fat.

In the wild, both rats and mice eat a diet consisting of about 5% fat, mostly from the occasional seed or nut. Rats do not even have a gallbladder, which is a really good biological sign that they aren’t meant to eat much fat. Obviously an animal that evolved to eat only a tiny amount of fat and lacks a bile concentration organ, is going to have consistently bad health outcomes when it’s forced to eat high amounts of fat. The rat’s body is not equipped to digest fat well. It’s not clear to me what this has to do with humans, who have always eaten fat and have a gallbladder to help us digest large amounts of it.

Every species is going to be the most healthy eating in a way that it is most adapted to eating. Small, mostly plant eating rodents may be easier to monitor in a lab, but they aren’t always going to give us information that exactly translates to humans.

Reason #2: Dietary studies in humans can only find correlations. 

When dietary studies are attempted in humans, as we already mentioned, the researchers cannot lock down half of the participants and force feed them something specific for the rest of their lives. They really only have two options. They can recommend a certain kind of diet for one group and allow the other group to eat however they want, or alternatively, they can just send everyone questionnaires on a regular basis and attempt to correlate long-term health outcomes with the self-reported data. Both of these formats are relying on everyone being honest (fat chance, haha) and regardless of the honesty of participants, they can never tell us anything particularly useful, especially not any causal relationships between foods and outcomes.

So do we choose to believe studies done on animals who aren’t meant to eat fat, or poorly designed correlation studies on people with every incentive to lie? In nutrition, these are often our only options.

The research definition of “high fat diet” as fat content over 35% remains true for human studies, but don’t forget that it’s also a whole lot of other things besides just over 1/3 fat. The research definition of “high fat diet” for humans should just be called the standard American diet, or SAD, because that’s what it always is.

When studies find correlations between a “high fat diet” and obesity, diabetes, cancer, heart disease, an unhealthy microbiome, and every other chronic condition, do you really think they’re referring to a diet high in avocados, coconut, and chicken thighs? Of course not.

They’re referring to a diet high in fast food, convenience food, processed meats, stuff fried in canola oil, and of course, lots of sugar. I wouldn’t even call that a high fat diet. It’s almost always still highest in carbohydrates, and the fats it does contain are overwhelmingly artificially produced seed fats and trans fats.

This incredible flaw is always easy to see if you have the time and ability to access the full text of any human diet study, but of course these nutrition-focused researchers blame all the negative health correlations on the fat content of the diet, because fat contains more calories than other nutrients, and therefor they think it makes people fat, which they then think leads to other chronic health conditions.

It’s all so backwards. 

All of those assumptions are wrong, and all of the advice that comes out of them is wrong. On the rare occasions when studies are conducted using actual high fat, low carbohydrate diets, the correlated outcomes are always markedly different than those of a “high fat diet”. Both meet the definition of high fat, so why are the HFLC diets not correlated with any worsening health outcomes, while “high fat diets” are?

Well now you know, it’s because the “high fat diets” aren’t just high fat, they’re also high everything else, and it’s all those other things that are doing the most damage.

A diet high in natural fats is healthy. A diet high in indiscriminate processed grease and sugar is unhealthy. This isn’t rocket science, yet we are still given the wrong advice. Even when the studies are done, they continue to be interpreted by ignorant nutritionists as confirming their previous beliefs that too much fat of any kind is bad. We shouldn’t all need to be PhDs to understand how to not kill ourselves with food. It’s not that complicated! We just need to get back to the basics and return to trusting our own outcomes over the Featured Snippet advice endorsed by Google.

Join the Reframe movement.

Get early access to upcoming events, insider content, and more.

“However beautiful the strategy, you should occasionally look at the results.”

— Winston Churchill
This error message is only visible to WordPress admins

Error: No feed found.

Please go to the Instagram Feed settings page to create a feed.

Before You Go...We'd love to stay in touch! Sign up to get Reframe blog posts, news, tips, and recipes!