Should You Have a Cheat Day on Keto?
Chocolate cake, cheesecake, and pizza easily qualify as three of the all-time cheat meals for lifters serious about their diet, training, and physique. They’re also three meals that’ll kick you out of ketosis faster than you can say bulletproof coffee or fat bomb.
To be in a state of ketosis generally requires consuming a ketogenic diet.
Related - What is the Ketogenic Diet?
In case you’ve been in a cave on a deserted island for much of the past couple of years (thereby sparing yourself from the endless ramblings of keto zealots), a ketogenic diet entails consuming:
- 70-75% of your calories from fat,
- 20% from protein, and
- a scant 5-10% from non-starchy carb sources (i.e. green veggies).
Much has been made about the benefits that come from adopting a very low carb or ketogenic diet, including weight loss, reduced hunger, and increased satiety. However, the keto diet isn’t without its drawbacks.
Specifically, the ketogenic diet is somewhat “high maintenance” in that it mandates individuals closely watch their carbohydrate and protein intake, as consuming too much of either macronutrient can easily kick a person out of ketosis.
As with any diet, you’re bound to need a break (both mentally and physically). These “breaks” usually come in the form of a cheat meal, carb refeed, and/or a return to maintenance calories for a short time before returning to the rigors of calorie restriction.
If you’re presently following a ketogenic diet, chances are you’ve taken a break here and there to indulge in a sweet treat and kill you carb cravings as ketogenic diets tend to be more restrictive than other diets.
After “scratching” your carb itch, you likely returned to your high-fat feasting.
However, the findings of a new study may temper your desire for a high-carb cheat day the next time you’re looking for a break from keto.
Published in the journal Nutrients, the new piece of research finds that having just one sugary cheat meal while living la vida low carb could do some serious damage to your blood vessels.
Nine healthy young men (BMI 23.2 ± 2 kg/m2) participated in the study. For seven days, each male consumes an iso-energetic high-fat diet consisting of:
- ~70% energy from fat
- ~20% energy from protein
- ~10% energy from carbohydrates
Researchers were primarily interested in determining the effects of an acute, high glucose intake on markers of endothelial damage before and after a short-term, low-carb, high-fat diet. 
The reason subjects needed to consume the low-carb, high-fat diet for the purposes of the trial is that high-fat diets have been noted to induce glucose intolerance and insulin resistance in animal models.  Additionally, several human studies have documented that short-term high-fat diets (like the one here) promote glucose intolerance in healthy subjects. [3,4]
Prior to adopting the ketogenic diet, subjects consumed a 75g glucose drink (roughly the amount of sugar in ~23.08oz of sugary soda) in order for researchers to get a baseline measurement of its impact on a variety of endothelial-related markers, including:
- Flow-mediated dilation (FMD)
- arterial stiffness
- Arterial diameter
- Arterial velocity,
Following seven days on the high-fat diet, researchers again had the men consume a sugary drink containing 75 grams of glucose and found that flow-mediated dilation was significantly reduced. They also documented several blood biomarkers indicative of endothelial damage. 
It’s also worth mentioning the men also experienced a reduction in flow-mediated dilation when they ingested the sugary drink during baseline testing prior to adopting the high-fat diet.
Essentially, pounding back 75g of pure sugar at one time with no other food in your system is not a good idea regardless if you’re on a high-fat diet or not. Doing so leads to a state of hyperglycemia which increases oxidative stress, reduces nitric oxide bioavailability, and ultimately impairs endothelial function. [5,6]
But, before you start completely condemning carbs, it’s also important to realize that researchers have documented reductions in flow-mediated dilation after a single high-fat meal (59.9 grams fat, 30.7 g protein, and 50g carbohydrate) in humans due to the same factors that reduced dilation in hyperglycemic individuals -- oxidative stress and blunted NO bioavailability. [7,8]
This begs the question if it’s the combination of high fat and high carbs in the same meal leading to reductions in FMD. Would individuals still experience reductions in FMD had they consumed a meal of only fat and protein with no carbohydrate or one in which there was minimal fat but predominantly carbohydrate and protein?
Taken together, the findings of the study suggest that those weekend binges on carbs likely aren’t a good idea if you’re eating low-carb, high-fat diets the rest of the week.
Note: sugary food binges aren’t a good idea in general, but might be that much more hazardous to your health if you’re typically eating a very low carb, high-fat diet.
The researchers do state that the study population is rather small and more research needs to be conducted.
However, this study was carried out using healthy males in the “normal” BMI range.
Therefore, if the effects of a high-carb binge in healthy high-fat dieters were this noticeable, just imagine how much worse the damage might be for an overweight or obese individual that is undertaking a ketogenic diet during the week and then going high-carb on the weekends.
Study co-author Dr. Jonathan Little said:
“My concern is that many of the people going on a keto diet—whether it's to lose weight, to treat Type 2 diabetes, or some other health reason—may be undoing some of the positive impacts on their blood vessels if they suddenly blast them with glucose. Especially if these people are at a higher risk for cardiovascular disease in the first place. Our data suggests a ketogenic diet is not something you do for six days a week and take Saturday off."
What do you think?
Do you currently follow a ketogenic diet?
And, if so, do the findings of this study give you pause about having occasional high-carb cheat days or trying cyclical ketogenic diets?
Leave your comment down below.
1) Cody Durrer et al, Short-Term Low-Carbohydrate High-Fat Diet in Healthy Young Males Renders the Endothelium Susceptible to Hyperglycemia-Induced Damage, An Exploratory Analysis, Nutrients (2019). DOI: 10.3390/nu11030489
2) Short term feeding of Ketogenic Diet induces more severe Hepatic Insulin Resistance than obesogenic High Fat Diet, Journal of Physiology (2018). DOI: 10.1113/JP275173
3) Lovejoy, J.C.; Windhauser, M.M.; Rood, J.C.; de la Bretonne, J.A. Effect of a controlled high-fat versus low-fat diet on insulin sensitivity and leptin levels in African-American and Caucasian women. Metabolism 1998, 47, 1520–1524.
4) Wan, Z.; Durrer, C.; Mah, D.; Simtchouk, S.; Robinson, E.; Little, J.P. Reduction of AMPK activity and altered MAPKs signalling in peripheral blood mononuclear cells in response to acute glucose ingestion following a short-term high fat diet in young healthy men. Metabolism 2014, 63, 1209–1216.
5) Mah, E.; Noh, S.K.; Ballard, K.D.; Matos, M.E.; Volek, J.S.; Bruno, R.S. Postprandial Hyperglycemia Impairs Vascular Endothelial Function in Healthy Men by Inducing Lipid Peroxidation and Increasing Asymmetric Dimethylarginine: Arginine–3. J. Nutr. 2011, 141, 1961–1968
6) Ceriello, A.; Esposito, K.; Piconi, L.; Ihnat, M.; Thorpe, J.; Testa, R.; Bonfigli, A.R.; Giugliano, D. Glucose “peak” and glucose “spike”: Impact on endothelial function and oxidative stress. Diabetes Res. Clin. Pract. 2008, 82, 262–267
7) Cuevas, A.M.; Guasch, V.; Castillo, O.; Irribarra, V.; Mizon, C.; San Martin, A.; Strobel, P.; Perez, D.; Germain, A.M.; Leighton, F. A high-fat diet induces and red wine counteracts endothelial dysfunction in human volunteers. Lipids 2000, 35, 143–148.
8) Bae, J.-H.; Bassenge, E.; Kim, K.-B.; Kim, Y.-N.; Kim, K.-S.; Lee, H.-J.; Moon, K.-C.; Lee, M.-S.; Park, K.-Y.; Schwemmer, M. Postprandial hypertriglyceridemia impairs endothelial function by enhanced oxidant stress. Atherosclerosis 2001, 155, 517–523.