Is Keto Cheating Unhealthy?

A couple months ago, a study came out that seemed to show that cheating on your keto diet with a high-carb meal opened you up to severe blood vessel damage. Nine healthy, normal weight adults followed a keto diet (70% fat, 20% protein, 10% carbs). Then they ate a high-carb “cheat meal,” measured their blood sugar, and measured their endothelial microparticles—a marker of damage to the endothelial lining and potential harbinger of impaired vascular function. Their blood sugar went way up, and so did their endothelial microparticle count, leading researchers to conclude that keto dieting makes people more susceptible to hyperglycemia-induced endothelial damage.

So, is keto cheating unhealthy? Let’s take a closer look….

My Analysis Of the Study:

Here’s why I don’t think this study applies to most of you:

These people were on keto diets, but they weren’t keto-adapted (let alone fat-adapted). They’d only been doing the diet for a week. Bare minimum, it takes three weeks to a month for full keto-adaptation to occur—and often longer. We’d have to see what happens to endothelial microparticle count when someone who is fully keto-adapted is exposed to higher carb intakes.

The “cheat meal” was 75 grams of pure glucose. This is the oral glucose tolerance test—the disgusting, cloyingly sweet drink they give people to test for diabetes. It measures your ability to handle pure glucose. It’s not a meal. It’s not actually food even. There are no mitigating micronutrients. There are no other macronutrients included. It’s just a shot of pure sugar, down the hatch. I don’t know about you, but that’s not my preferred method of a high-carb cheat meal.

However, it does illustrate the importance of sticking with the diet—any diet—for way longer than a week before assessing the effects or stepping out to indulge.

Look at the big picture. Acute perturbations to endothelial homeostasis can look bad in the short term and good over time. Hell, when you ask overweight women to engage in a single bout of high intensity exercise, their endothelial microparticle count goes up just like it went up for the guys in this study who drank the glucose water. They “damage” their vascular function. But if they keep training regularly, their endothelial microparticle count goes down. Acute stressors can look bad when applied once and awesome when applied consistently. That’s not to say that drinking 75 grams of glucose consistently will suddenly become healthy. I’m just showing how looking at a single short term reaction doesn’t give the entire story, or even accurately portray the effects of the same stimulus applied consistently over the long term.

A Better Perspective On Cheat Meals

Cheat meals can actually help you lose more weight. In one study, women were placed on a cyclic diet consisting of three phases. For each phase, they reduced calories for 11 days followed by 3 days of ad libitum (i.e. at one’s pleasure) eating. After the three phases, they’d lost an average of 8 kg (about 17 lbs) of pure body fat. This surpassed the amount predicted by calories in, calories out. This study didn’t employ all-out cheat days, or call them cheat days, but the concept of “ad libitum” is pretty similar.

If you cycle in high carb days or high carb meals into your keto diet, and you end up getting leaner and performing better in the gym because of it, are you really hurting yourself? Are you really setting your vascular system up for impending doom? I doubt it. One of the best ways to improve endothelial function is to lose excess body fat. Whatever helps you get to that goal should also improve vascular function.

If You’re Going To Cheat On Keto:

Get fully adapted.

The people in this study were not keto-adapted. They’d only been eating the diet for a week before taking the test. Stay with the diet for two months—strictly—before venturing out with cheat days.

Don’t cheat with an oral glucose tolerance test.

While some folks undoubtedly get off on drinking 75 grams of pure glucose, there are better ways to cheat. Like with food. Also, food tends to include mitigating factors—phytonutrients, fiber, vitamins, minerals—that improve the metabolic response to the macronutrients contained therein. For instance, including some natural cocoa in the cheat meal can drop your endothelial microparticles by 60% alone.

Be relatively lean and experienced.

Cheat days are more effective for fairly lean-ish people to kickstart the loss of those last few pounds. They’re designed for long-time keto eaters to replenish glycogen stores and improve training. They’re designed for people who have been strict for long enough that they just need a break. They just aren’t going to work the same for obese people who’ve been keto for a little while who still have a lot of easy weight to lose on strict keto.

Cheat after a big workout.

Exercising increases insulin sensitivity. And if you lift heavy things, you increase something called non-insulin dependent glucose uptake in the muscles. That means your muscles can actually refill their glycogen content without using insulin to do it. If you’re keto and want to incorporate high carb meals/days or cheat meals, legitimate training is pretty much required. After all, why do you need the carbs if you’re not training?

Cheat if you need it.

If things are stalling, and you’ve tried being even stricter to no avail, perhaps momentarily loosening up with a cheat meal is exactly what you need. Read this post to get the lowdown on why carb refeeds can help break weight loss stalls and how to do them.

This study shouldn’t be ignored. Big boluses of sugar are never a good idea, especially when you’ve only been eating low-carb or keto for a week and have yet to adapt. I find it plausible that such excursions can induce acute damage to the vascular system in anyone with impaired glucose tolerance—even if that glucose intolerance is transient, as it is in short term keto dieters—but I don’t think it means much for people with good heads on their shoulders who do keto the right way.

What do you think, folks? Do you cheat on your diet, whether you’re keto or just Primal? What steps do you take to make sure you’re getting the most out of your dietary excursions?

Thanks for reading, everyone. Take care!


Durrer C, Robinson E, Wan Z, et al. Differential impact of acute high-intensity exercise on circulating endothelial microparticles and insulin resistance between overweight/obese males and females. PLoS ONE. 2015;10(2):e0115860.

Mcfarlin BK, Venable AS, Henning AL, et al. Natural cocoa consumption: Potential to reduce atherogenic factors?. J Nutr Biochem. 2015;26(6):626-32.

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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29 thoughts on “Is Keto Cheating Unhealthy?”

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  1. I give myself some latitude now and then. Went with friends for a “Cinco de Mayo” meal and enjoyed a quesadilla with the first tortilla I’ve eaten in 4 months. A few weeks back a friend invited me for dinner and she’d made a great bowl of chicken soup (including rice). I didn’t turn it down. Didn’t notice any effects from either “cheat.” I don’t need a full cheat day knowing I’m ok with just going off my usual eating plan a few times a month for social occasions or special events.

  2. I don’t really even consider this a cheat, but I enjoy potato salad once in awhile and have sourdough french toast (homemade) about 2-3 times a year. Popcorn a few times a year…yes. My body doesn’t even notice it.

  3. The evidence shows that high-fat diets induce insulin resistance and impair glucose tolerance, so obviously drinking sugar will cause a spike. I disagree with your comment that if the subjects were properly fat-adapted their response to the sugar load would be better. Based on the evidence, their glycemic response would be worse the more fat-adapted they become. I’m a type 1 diabetic. It happened to me.

    1. What evidence?.. you shouldn’t be eating a diet high in refined polyunsaturated…. that’s for damn sure.. or absolutely trans fats. Trans fats definitely cause insulin resistance….. So do branched chain amino acids…
      What’s the major cause of insulin resistance fructose..which we get in our diet through high fructose corn syrup and sucrose. Sucrose is table sugar which is one glucose molecule and one fructose molecule..

    2. By definition, if you’re a type 1 diabetic, your natural insulin response to glucose is zero, and will forever be zero. Until we find a way to fix the islet cells of the pancreas, Type 1 diabetes is not really a model for the keto diet. While many people with T1D do try keto and a few stay with it, it’s never going to be the case for any of them that their insulin response will ever improve.

      In the study mentioned in this post, they say: “Participants were excluded from the study if they (1) had a diagnosed metabolic disorder such as diabetes, metabolic syndrome, hypothyroidism, or any other condition known to affect metabolism”

      1. Actually, I have seen a couple of clues that type 1 diabetics CAN alter their diet to accommodate their condition without insulin. It involves ultra-low carb food, taken in small meals. Apparently, there is a mechanism involving glucagon that allows digestion to go forward with no insulin present. (I am just basing this on what I read here: )
        Metabolism is complicated.

    3. Drew is right. When you are fat adapted, your body goes into physiological insulin resistance ie spares glucose for brain, kidneys, red blood cells. Unlike pathological insulin resistance, this reverses easily when re-commencing carbs, but it’s not instant. it’s recommended that low carbers due for a glucose tolerance test up their carb intake gradually for 3 days to 150g per day to give the body time to reverse the resistance. if they took a test cold, they’d spike massively, but this 3 day period gives the body time to adjust. Cheat meals? I’d suggest building up over a couple of days prior.

  4. After years of being keto adapted my blood sugar response to sugar has gotten better and better. On ocasional carb meals, including desserts, I barely get any blood sugar spikes. It never goes beyond 110, even after a lot more than 75g of sugar. I do believe that a deep keto adaptation betters your flexibility, not worsens it. At least that’s what’s based on my experience.

  5. I would wonder if the answer to that question might depend (at least in part) on *why* someone is on a keto diet. It seems to me that if one is on a keto diet because he or she is already dealing with metabolic syndrome or diabetes, that person might have a greater risk if straying from the keto diet. But that is just my thought on that – I don’t have any citations to back it up. I don’t cheat on my keto diet, though.

    1. Jim, i think you’re absolutely right, that it depends why someone is on keto in the first place, but also on how long one has been on it and how low on the carbs.
      Why it matters would be logical – is because whatever disease is there as the reason for going on keto, it is created by some imbalance in the body’s hormonal system, and most often by inflammation.
      So until those imbalances and inflammation is eradicated and corrected in the body, it’s bound to have a negative effect if you suddenly go crazy on carbs.

  6. “Don’t cheat with an oral glucose tolerance test”

    LOL. Mark, you should award yourself the comment of the week for that one. 🙂

    1. It’s so funny, everytime they are making some ‘study’ thats going to make us believe that keto is bad, it’s always done with some kind of halfassed attempts, either using the wrong fats (to prove that highfat diets are bad), or like here with people who’d been on the diet for a week (what?) Such a ‘study’ is so ridiculous it’s impossible to take serious.
      I’m still laughing at it.
      I’m surprised you’d even bother, and love your explanation.

      I’ve had a long period off keto, and actually the weightgain is a lot slower than usual.
      Right now I’m back on the ketoroad, but still not fatadapted well enough, and if I eat or drink something highcarb, my heart starts racing, so I know it’s really bad.
      I don’t need a halfway one week study to tell me what my body knows – sugar is poison.

  7. In Australia part of the preparation for an OGTT is to eat at least 180g of carbs per day for 3 days before the test to prevent a false positive result.

  8. You’ve made some excellent points. I’ll add one… in ref to this part of the study: “Participants were provided with individualized meal plans and prepackaged food for the seven-day intervention and were instructed to only drink water during the study period.”

    Really? I mean, I guess I understand why they did that. They wanted to make sure they were comparing apples to apples. But where are the fresh greens? Were there any salads? Any cabbage or sauerkraut for vitamin C? What was the difference if you use a glucose tolerance test or a fresh organic kiwi? I would want to know more about exactly what they fed these people. Because it it’s a bunch of glyphosate sprayed GMOs plus an unhealthy dose of inflammatory vegetable oil, I’d say the glucose test wasn’t acting alone.

    I don’t like to cheat on the keto diet. It messes up my lovely calm balance. I use it for neurological reasons and it calms my jangly nerves right down. Why cheat and go back to anxious and uncomfortable? However, not everyone has such a good motivator.

  9. I just wanted to say, the fact that you allow comments alone is a sign I can trust what you say. You take responsibility for your words. Most of the “keto” articles out there, especially the negative ones, leave no space for comments. I find these are pretty damaging for people who are looking for info on keto and don’t know who are the “who’s who” out there. Like the study mentioned above, unless you understand how most studies are performed then you don’t know the potential flaws.

  10. I’d be interested to see if that much sugar would cause the same damage to someone who was not on a “Keto” diet. ( I agree, a one week Keto diet is not enough) or what the long term damage of elevated sugar levels do, which I think has already been established. Are they suggesting that eating a high card or SAD diet protects us from this damage of taking that much glucose? Interesting…

  11. It seems that maybe this silly fad is just that, and that everyone with a need to be “special” should think about why they have this need in the first place. Half of the discussions about keto are about cheating: how often can I? With what foods? Should I? Etc, etc. If you even need to ponder this, maybe it’s a clue?
    Fat people are fat because they’re lazy and eat too much. Try eating real food, and not too much of it. Work out intensely and often. MOVE throughout your day – a lot. Do not discuss your diet or goals with anyone, but rather keep them internal. You’ll get all the attention you want when you’ve transformed yourself.
    If you need to keep finding ways to turn cauliflower into pizza crust, well…

    1. That’s a bit of an ignorant blanket statement suggesting all day people are fat because they eat too much and are lazy. Metabolic disorders, medication side effects, heredity, lifestyle choices, life pressures all contribute to how well an individual is able to maintain an “ideally healthy” body. Additionally, people sharing and discussing diets and/or how it’s effecting them (good or bad) isn’t them grabbing for attention, it’s called being well informed. It’s how information is passed on. I would check my biases before suggesting that any blanket group is “just lazy”

      1. He’s an alt right guy … makes posts to get a rise out of people. Anyone who does not have their world view is a “snowfake” engaging in “identity politics” blah blah blah.

        1. Unless you’ve seen something from him that proves that, I wouldn’t assume his politics. I’ve seen people on the alt-right (and center, who also hate identity politics) eat keto and primal, and leftists who think it’s all fads and attention seekers. Attitudes like this guy’s cross political lines.

          1. Well Said!!!
            Keep the density politics off this Site!


    People get so bent out of shape about things like this. Your sane, rational, and down-to-earth perspective is a much, much needed counterbalance to the neuroticism and zealotry in the keto world these days. Thank you for always being a voice of reason.

    1. Mark.
      Has you caloric breakdown(F,P,C %’s) and daily diet foods and philosophy changed much/at all from your May 14, 2008 posting on your daily diet. I’m curious as we are nearly the same age and I couldn’t find any new posts that updated with any changes so I hoped to ask you.
      Thank you.

  13. I’m not particularly keto (but basically maintain a strict paleo low carb although very high non starch veg based diet)

    I do however love to indulge in dolmades, almost everyday. They are homemade and from a beautiful Turkish restaurant that only uses olive oil. I have about 3-4 daily. What are your thoughts on traditional rice and herb stuffed dolmades Mark? How bad are these for my health?

  14. It’s so funny, everytime they are making some ‘study’ thats going to make us believe that keto is bad, it’s always done with some kind of halfassed attempts, either using the wrong fats (to prove that highfat diets are bad), or like here with people who’d been on the diet for a week (what?) Such a ‘study’ is so ridiculous it’s impossible to take serious.
    I’m still laughing at it.
    I’m surprised you’d even bother, and love your explanation.

    I’ve had a long period off keto, and actually the weightgain is a lot slower than usual.
    Right now I’m back on the ketoroad, but still not fatadapted well enough, and if I eat or drink something highcarb, my heart starts racing, so I know it’s really bad.
    I don’t need a halfway one week study to tell me what my body knows – sugar is poison.

  15. For me it’s part of the plan, so I don’t like the word cheat. Make a calculated decision and own it, and it’s not cheating. Every Friday at 4 pm, an hour after a heavy, intense lifting session, I destroy as many carbs as I can until bed without feeling sick. Obviously I took the time to get very far adapted years ago, but this has become the best way for me to be both lean and strong over the years.

  16. I up my carbs before a mountain bike ride, otherwise I can’t keep up… hopefully I am not hurting myself!

  17. I have been working hard at eating primally and low carb since January! I typically fast until 1130 AM. I work out a fair amount about 3-5 times a week 1 hour kickboxing or rowing classes. Prob a little more than recommended but it is my long term lifestyle so I don’t think it is uber cortisol stimulating. I eat zero complex carbs…. typically I consume about 40-60 carbs a day. All from veggies and almonds. I feel great- I have lost close to 15lbs- I am 38, I have not had my monthly cycle in 4 months. Prior to this I was very regular. Wondering if I should try carb refeeding. Body fat is likely around 20 percent. Would love to drop a few more pounds and I have been holding at my current weight for about 1 month. Just feel nervous about adding in complex carbs since I have become completely accustomed to going without!

  18. When I was 10 days into keto I cheated and ate pizza… a lot of pizza lol. I literally felt like I was having a heart attack. I thought keto was killing me. Donnnnn’t cheat during keto flu!