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On the keto diet? Ditch the cheat day: Just one dose of carbohydrates can damage blood vessels -- ScienceDaily

"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." For their test, the researchers recruited nine healthy young males and had them consume a 75-gram glucose drink before and after a seven-day high fat, low carbohydrate diet. The diet consisted of 70 per cent fat, 10 per cent carbohydrates and 20 per cent protein, similar to that of a modern ketogenic diet. "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." Little says the most likely culprit for the damage is the body's own metabolic response to excess blood sugar, which causes blood vessel cells to shed and possibly die. "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."

The case against carbohydrates gets stronger

We started the participants on a calorie-restricted diet until they lost 10%-14% of their body weight. After that, we randomly assigned them to eat exclusively one of three diets, containing either 20%, 40% or 60% carbohydrates. For the next five months, we made sure they didn’t gain or lose any more weight, adjusting how much food they received, but keeping the ratio of carbohydrates constant. By doing so, we could directly measure how their metabolism responded to these differing levels of carbohydrate consumption. Participants in the low (20%) carbohydrate group burned on average about 250 calories a day more than those in the high (60%) carbohydrate group, just as predicted by the carbohydrate-insulin model. Without intervention (that is, if we hadn’t adjusted the amount of food to prevent weight change), that difference would produce substantial weight loss — about 20 pounds after a few years. If a low-carbohydrate diet also curbs hunger and food intake (as other studies suggest it can), the effect could be even greater.

Strategic fasting improves race times

In this particular study, both groups actually consumed the same amount of carbohydrates, but the sleep-low group ate all of theirs between their morning and afternoon sessions while the control group also had carbs after their second workout. Both groups completed a test triathlon to assess their fitness and then a second one three weeks later to determine the effectiveness of the training method. The sleep-low group had improved their running times on the 10-km segment by an average of 75 seconds while the control group showed no improvement. The sleep low athletes also lost about 3 pounds of body fat while the control group stayed the same.