Keto Dieters Should Skip the Cheat Day

The ketogenic diet is both popular and controversial. It’s proponents and those following it swear it provides a myriad of benefits. The claims include easy weight loss, improved joint health, better energy, better mood and even improved brain function and cognition. Detractors point to the very high levels of fat intake required to pursue the keto “holy grail” – the state of ketosis – as risky for human health in a number of ways.

One thing is certain. The keto diet isn’t going away anytime soon. If anything, it’s gaining in both popularity and general acceptance. Many keto dieters – like adherents of many other diet plans – incorporate a “cheat day” into their diet schedules and plans. These cheat days generally include much higher carbohydrate intake than the keto diet calls for. Dieters claim the cheat day “refeeds” their muscle glycogen, among other things.

However, if research from the University of British Columbia Okanagan is accurate, ketogenic dieters would do well to skip the cheat day. UBCO researchers believe that just one 75-gram dose of glucose can lead to blood vessel damage for folks on a keto diet. For reference, 16 ounces of grape juice has about 73g of sugar. A plate of french fries approaches the 75g level and an average-sized slice of vanilla cake with coconut frosting has about 65g of sugar.

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“The ketogenic — or keto — diet has become very common for weight loss or to manage diseases like type 2 diabetes,” says Jonathan Little, associate professor in the School of Health and Exercise Sciences at UBCO and study senior author. “It consists of eating foods rich in fats, moderate in protein, but very low in carbohydrates and it causes the body to go into a state called ketosis.”

Little reaffirms that the keto diet can get the body into a state of ketosis, thereby starving it of the preferred fuel source (glucose.) Because of this, the chemistry in the body begins to change, causing more aggressive burning of stored fat. Not only does this lead to weight loss, but can reverse the symptoms of certain metabolic diseases like type 2 diabetes.

“We were interested in finding out what happens to the body’s physiology once a dose of glucose is reintroduced,” says Cody Durrer, UBC Okanagan doctoral student and study first author. “Since impaired glucose tolerance and spikes in blood sugar levels are known to be associated with an increased risk in cardiovascular disease, it made sense to look at what was happening in the blood vessels after a sugar hit.”

Nine healthy young males were recruited as participants. They drank a 75-gram glucose drink before and after seven days of a high fat, low carbohydrate diet. The breakdown of the diet was 70 percent fat, 20 percent protein and 10 percent carbohydrates. This resembles the breakdown of some modern ketogenic diets.

“We were originally looking for things like an inflammatory response or reduced tolerance to blood glucose,” says Durrer. “What we found instead were biomarkers in the blood suggesting that vessel walls were being damaged by the sudden spike in glucose.”

The damage is most likely caused by the body’s metabolic response to the excess blood sugar. This response causes blood vessel cells to shed and may even kill them.


“Even though these were otherwise healthy young males, when we looked at their blood vessel health after consuming the glucose drink, the results looked like they might have come from someone with poor cardiovascular health,” adds Little. “It was somewhat alarming.”

By the researchers own admission, the small sample size of the study limits their ability to state conclusively that their findings are true across a broader population. While more work should be done to verify the findings, they believe that people on a ketogenic diet will want to reconsider their cheat days, based on these results.

“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,” he says. “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.”

So while many claim that the keto diet is easy to follow and allows flexibility, these results should inspire keto dieters to stick to the plan – all 7 days a week!

Keep the faith and keep after it!

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