In ketogenesis, two acetyl-CoA molecules instead condense to form acetoacetyl-CoA via thiolase. Acetoacetyl-CoA momentarily combines with another acetyl-CoA via HMG-CoA synthase to form hydroxy-β-methylglutaryl-CoA. Hydroxy-β-methylglutaryl-CoA form the ketone body acetoacetate via HMG-CoA lyase. Acetoacetate can then reversibly convert to another ketone body—D-β-hydroxybutyrate—via D-β-hydroxybutyrate dehydrogenase. Alternatively, acetoacetate can spontaneously degrade to a third ketone body (acetone) and carbon dioxide, although the process generates much greater concentrations of acetoacetate and D-β-hydroxybutyrate. When blood glucose levels are low, ketone bodies can be exported from the liver to supply crucial energy to the brain.
Physical or mental fatigue during workouts (or while you’re sitting at your office) is caused by the low blood glucose that occurs as your carbohydrate fuel tank approaches empty (also known as the infamous “bonk”, which is awesomely demonstrated in this funniest running cartoon I’ve ever seen). Because it is generally (and sadly) accepted as orthodox knowledge that the human body can’t burn fat as a reliable fuel source – especially when you’re exercising for long periods of time or at high intensities – nearly every shred of nutrition science is simply looking for ways to somehow increase the size of your carbohydrate fuel tank and hack the body to allow it to store more carbs or absorb carbs more quickly.
One downside to a ketogenic diet for weight loss is the difficulty maintaining it. “Studies show that weight loss results from being on a low-carb diet for more than 12 months tend to be the same as being on a normal, healthy diet,” says Mattinson. While you may be eating more satiating fats (like peanut butter, regular butter, or avocado), you’re also way more limited in what’s allowed on the diet, which can make everyday situations, like eating dinner with family or going out with friends, far more difficult. Because people often find it tough to sustain, it’s easy to rely on it as a short-term diet rather than a long-term lifestyle.
1. If a set number ketones in the blood is an indicator that my body has transitioned to ketosis and not necessarily the cause (the cause being limited access to glycogen because of limited carb intake) then how does using exogenous ketones put me in ketosis as opposed to mimic being in ketosis (because when measuring blood ketones suddenly there are more because I put them there, I didn’t create them)?
People on the diet report being significantly more full and satisfied. Even though you may be ingesting LESS calories on the diet, your hunger doesn't increased. One possible explanation is greater consumption of satiating foods, primarily protein and fat. However, multiple studies indicate that the state of ketosis itself (apart from effects from food) plays a role as well.10
It usually takes three to four days for your body to go into ketosis because you have to use up your body's stores of glucose, i.e., sugar first, Keatley says. Any major diet change can give you some, uh, issues, and Keatley says he often sees patients who complain of IBS-like symptoms and feeling wiped out at the beginning of the diet. (The tiredness happens because you have less access to carbs, which give you quick energy, he explains.)