First, a little background: Eric Westman, MD, director of the Duke Lifestyle Medical Clinic, explained to Health in a previous interview that in order to successfully follow the keto diet, you need to eat moderate amounts of protein, reduce your carb intake, and increase fats. When you reduce your carb consumption, your body turns to stored fat as its new fuel source—a process called ketosis. To stay in ketosis, followers of the keto diet must limit their carbs to 50 grams a day, Dr. Westman says.

Neville, C., Henwood, T., Beattie, E., & Fielding, E. (2013, July 3). Exploring the effect of aquatic exercise on behaviour and psychological well‐being in people with moderate to severe dementia: A pilot study of the Watermemories Swimming Club [Abstract]. Australasian Journal On Ageing, 33(2), 124–127. Retrieved from
Basically, carbohydrates are the primary source of energy production in body tissues. When the body is deprived of carbohydrates due to reducing intake to less than 50g per day, insulin secretion is significantly reduced and the body enters a catabolic state. Glycogen stores deplete, forcing the body to go through certain metabolic changes. Two metabolic processes come into action when there is low carbohydrate availability in body tissues: gluconeogenesis and ketogenesis.[4][5]

On a ketogenic diet, you’re generally eating a diet that’s high in fat (roughly 70 percent of your total calories come from fat), moderate in protein (about 20 percent of your calories), and low in carbohydrate (about 5 percent of calories). By limiting carbohydrates (to usually less than 45 grams for the average person), your body lacks the glucose (from carbs) that it normally uses for energy, so it eventually switches over to burning fat as its primary fuel source instead; through a metabolic process called ketosis, the liver converts the fat into fragments of fatty acids called ketones, which power the brain and other organs and tissues.
This workout is definitely for those who are familiar with an intermediate to advanced Pilates routine. The cardio portions fit well into the mat/Pilates routine, although working on one's hands to do the vigorous cardio portion on segment two of the workout can cause quite a bit of wrist and shoulder tendinitis strain. Also, it seems that many of the movements are quite rushed, as Pilates was meant to be done in a more focused, concentrated, and refined manner. Sometimes it feels as if Kristin is rather rushing through some of the Pilates exercises without really breaking down the important elements of the movement (this is where an instructional book might be better, as it describes the finer points about a specific exercise for best execution and allows one to achieve the perfect form at one's own pace). Of course, this is meant to be a cardio workout, so it the pace must be maintained to keep the heart rate up, and so technique suffers slightly in the end. However, once I become much more adept at some of the intermediate to advanced Pilates moves on my own, I'm sure this workout will become more pleasant to run through without feeling like I'm being left behind. Kristin is energetic and strong, but just a tad bit too much on the anorexic side, which appears a somewhat concerning if one is trying to convey an image of good health and a reasonable body image of someone who works out regularly. However, this may just be her body type/disposition.
It’s not always about how much you eat, but the nutritional balance of carbohydrates, fats, and protein in what you’re eating. Endurance athletes need extra carbs to fuel their rides, fat to feel satiated, and protein to repair your muscles post-workout. It usually isn’t necessary to make radical adjustments to achieve this balance—small changes work best. For instance, don’t eat a whole bowl of chili with meat. Instead, fill half the bowl with brown rice, then ladle a small amount of chili on top. You can also try substituting fat-free yogurt for sour cream and fruit for sweets.