Researchers: Keto Cheat Days Might be Deadly

Posted in: Diet & Nutrition

Susan Ohtake, CPT

You’ve heard of “cheat days,” right?

That’s when you get to take a break and eat whatever you want (within reason, of course).

I mean…you can’t go crazy…

…but you can take one day a week and eat a few more calories.

If you’re on keto, it’s common to take a “cheat day” to eat carbs.


Well, according to research conducted at the University of British Columbia…

…if you’re on the keto diet, you might want to think twice about taking a “cheat day.”

(and not because cheat days hurt your fat loss efforts).

Before we go any further, let me get this out of the way:

I am NOT against the keto diet.

It’s worked for many people—men and women alike.

But the reality is: Women struggle to see results on the keto diet (much more than men do).

Cutting carbs, eating enough fats, and staying in ketosis is difficult for anyone. But, when you’re going without and you’re not seeing much of a difference when you look in the mirror…it gets even harder.

But even aside from diet considerations: Overall, it’s just harder for women to lose weight. There are TONS of considerations that go into this…beyond which type of diet you’re on.

All this aside:

I generally DO NOT recommend the keto diet to women.

One of the key reasons is that out bodies are very good at storing dietary fat in our lower bodies.

Did you know that dietary fat and body fat have the exact same composition?

And it’s super easy for your body to mobilize dietary fat, put it into your bloodstream, and send it right to empty fat cells just waiting to fill up. Compared to men, our bodies are more efficient at mobilizing fat, using fat, and storing fat.

That’s just the way it is!

(blame your hormones).

Now, this isn’t even the #1 reason I don’t recommend keto. I’ll share that in a minute. First, we need to talk cheat days…

What is “Cheat Day” on a Keto Diet?

One of my friends who recently started a keto diet (and she actually saw great success with it…down 20+ lbs in 12 weeks) loves the “cheat day.”

I don’t know what plan she’s following, but it’s working!

For her, the keto cheat day happens every 2 weeks.

Every 2 weeks she gets to have a day off of keto. It’s filled with plenty of carbs.


Once every 14 days, burger buns, French fries, and all those deserts you can’t eat on keto make a comeback.

I can see why it’s so easy to look forward to cheat day.

Unfortunately, some startling new research from the University of British Columbia has me worried for her…

Keto Cheat Days: Bad for Your Heart?

A study published in the academic journal Nutrients in early 2019 has me worried about the increasingly common keto “cheat day.”

Researchers at the University of British Columbia set out to see what actually happens during a cheat day.

They wanted to know:

What happens when you take a cheat day on a keto diet?

I know most people are worried about “won’t a cheat day take me out of ketosis?” and “will it hurt fat loss if I take a cheat day?”

(by the way…the answer to both of those questions is YES)

But their inquiry was different…

What does a cheat day do to your health?

Take weight loss and results out of it. Is a cheat day healthy?

To find out, researchers put test subjects on a 70% fat, 10% carb, and 20% protein diet. These are typical keto “macros.”

Initially, they wanted to look for “inflammatory resource or reduced tolerance to blood glucose” by having participants consume a 75-gram glucose drink once per week. Researchers were interested in what happens inside your body once carbs are re-introduced after you’ve been in ketosis.

Just One Sugary Drink Damaged Blood Vessels

The alarming result?

Just ONE 75-gram sugary drink…about the same as two cans of soda…damaged the blood vessels of study participants.

Blood vessel walls were damaged when glucose was re-introduced.

Not days later. Not a week later. Not after months of cheat days adding up.

Blood vessels were damaged within hours of cheating.

Sugary Soda.jpg

It doesn't have to be a sugary drink, either. This 75-grams of carbs during a "cheat day" could be any carb-rich food: French fries, potato chips, a bowl of rice...

After the 75-grams of glucose was introduced, doctors said the blood vessels of young, healthy study participants looked like they came from a person with poor cardiovascular health. The damage was same-day.

I’m not surprised they found damage.

The truth is, the ketogenic diet was never intended to be a long-term diet for weight loss purposes. It was developed almost 100 years ago as a medical treatment for epilepsy. The diet itself is 100-year-old science, recently adopted for weight loss.

As more and more people without medical issues (and just fat to lose) try keto, we’ll learn more about what it actually does to our health.

For now, know that you shouldn’t cheat on a keto diet.

Why You Shouldn’t Cheat on a Keto Diet

This study suggests that you might want to re-consider cheat days if you’re following a keto diet.

Blood vessel damage was caused by just a single sugary drink, just one day per week.

Study participants stuck to a strict keto diet 6 days per week. Just one day per week, they drank a single sugary drink (with 2 cans of soda worth of sugar).

The result was same-day blood vessel damage.

Doctors do not know what this damage will do long term.

In the study, they suggested avoiding cheat days if you’re following a keto diet. They didn’t judge the overall safety of ketogenic dieting.

Is Keto the Best Choice for You?

The high protein, higher fat, low carb ketogenic diet was developed as a medical treatment for epilepsy.

But that doesn’t mean it’s medically a healthy choice for people who do not have epilepsy.

When you go on a keto diet and stick to it, you are tricking your body into believing you are starving so it is forced into burning fat.

That’s the why and how behind it.


You eat fat to become “fat adapted.” At the same time, you go without carbs so your body only has the option to burn fat as fuel.

Insulin levels also drop on keto, which increases fat breakdown (turning stored fat into fatty acids). Even though keto speeds up lipolysis, turning fat cells into fatty acids, you still need to burn off these fatty acids. They can always be re-stored as fat.

That means you still have to keep track of calories on keto—keeping a calorie deficit is the only way you will ever burn stored fat (keto or not).

Honestly, I feel like that’s the point everyone misses when it comes to keto.

You still need to keep track of calories in and calories out. Just going super low on carbs and upping fat intake isn’t going to take off weight if you’re still overeating (compared to energy expenditure.

But my bigger point is this:

What if the Damage is WORSE than Just “Cheat Day?”

Blood vessel damage caused by “cheat days” is easy to fix:

You just cut out cheat days!

That might be easy for you. It might be difficult. I know, for many, occasional cheat days are what make keto bearable.

What I’m worried about is what we do not know about keto—and the potential damage it can do to your body.

This is just one study, looking into one specific aspect of keto.

As more studies are conducted, we’ll learn more about how our bodies respond to ketosis. My hope is that the dangers of keto are limited. I know keto has helped many people take off stubborn fat.

But I also know:

There are safer, proven ways to lose stubborn fat that DO NOT trick your body into believing it’s starving.

My recommendations for fat loss typically involve lower carb intake and higher protein intake, pared with high intensity workouts that stimulate fat metabolism, and an increase in overall total energy expenditure.

I do not think it’s a good idea to go to extremes with diets like Keto, simply because we don’t know what such a high fat intake does to our body…although it’s clear we are learning. It’s too early to tell if keto is safe.

  • Short-Term Low-Carbohydrate High-Fat Diet in Healthy Young Males Renders the Endothelium Susceptible to Hyperglycemia-Induced Damage, An Exploratory Analysis:

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