Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...Tell Me More
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….
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.
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.
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.
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.
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.
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?
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.