Why the Keto Diet and Cheat Days Don’t Mix


Many people who commit to healthy eating also indulge in a cheat day, where they take a break from regimented eating. While some experts say they can help keep you on track (especially as part of an 80/20 mentality where you eat more nutrient-dense foods 80% of the time and enjoy indulgences the remaining 20%), other nutrition pros believe they can be more harmful — and that might be especially true if you’re on a keto diet.

“[Cheat days] are purely a mental game,” says Whitney Linsenmeyer, RD, PhD, assistant professor of nutrition at Saint Louis University and spokesperson for the Academy of Nutrition and Dietetics. “The idea is that you can stay motivated on the diet if you have those cheat days to look forward to, [but] there are no actual health benefits to the practice.”

What’s more, new research shows cheat days could have a negative effect on heart health, especially if you’ve been following the trendy keto diet. A recent study shows digging into a plate of nachos, tossing back a few beers or ordering an ice cream sundae on your day off from dieting may damage your blood vessels.


In the study, healthy adults consumed 75 grams of glucose (aka sugar) in a beverage (mimicking a high-sugar cheat day), and then again after following a ketogenic diet for one week. Researchers found that in the latter case, the body’s blood vessels had a harder time dilating, a marker of increased heart attack risk.

“We expected that healthy volunteers would become relatively intolerant to glucose if they followed a ketogenic diet for even a short period of time,” explains co-author Jonathan Little, PhD, assistant professor at the University of British Columbia. “Their bodies adapted to eating high amounts of fat and became bad at processing glucose and carbohydrates.” Thus, while the cells returned to full function once blood sugar levels dropped off, this indicates regular high-sugar cheat meals can lead to long-lasting damage, says Little.

Before following the keto diet, no biomarkers of damage were observed following spikes in blood glucose, leading Little to conclude the diet made blood vessels more susceptible to damage.


On cheat days, you might crave foods you’ve been restricting. In the case of the keto diet, which is low-carb, you’ll likely crave simple carbs, which cause greater spikes in blood sugar levels compared to slow-digesting complex carbs.

Linsenmeyer notes that cheat days may also lead to temporary water weight gain or gastrointestinal distress because your body is not used to processing foods that are high in sodium or sugar when you follow a restrictive diet.

Cheat days have other potential downsides: Obesity-prone dieters who exceeded their estimated calorie needs one day per week were less likely to engage in physical activity on their cheat days than those less prone to obesity, according to research published in the journal Obesity. Moreover, reducing cheat days helps remove the idea that any food is “off-limits,” which could result in foods you once craved no longer having such a pull.


It’s important to find an eating style that is sustainable for you long-term and more research is needed, says Little. “If a keto diet is helping you achieve your goals for weight loss or diabetes management and the occasional treat helps you stick with this restrictive eating approach, you don’t need to worry.” But if cheat days leave you feeling bloated and you’re consistently overeating, consider switching things up by aiming for a healthy source of protein, fat and carbs at every meal. If you need help getting started, contact a registered dietitian.


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