When carbohydrates are used by the body as an energy source, the blood sugar levels become unstable. As the energy source is not consistent it is difficult for your brain to stay focused for long periods of time. On the other hand, when you are in ketosis and the brain uses ketones as a fuel source, which has a consistent fuel source and you can focus for longer periods of time. Hence, you also tend to feel more active and alert.
Our bodies are incredibly adaptive to what you put into it – when you overload it with fats and take away carbohydrates, it will begin to burn ketones as the primary energy source. Optimal ketone levels offer many health, weight loss, physical and mental performance benefits.1There are scientifically-backed studies that show the advantage of a low-carb, ketogenic diet over a low-fat diet. One meta-analysis of low-carbohydrate diets showed a large advantage in weight loss. The New England Journal of Medicine study resulted in almost double the weight loss in a long-term study on ketone inducing diets.
Some people feel better supplementing the already active T3 (sometimes prepared from pig thyroid glands), as it can give a stronger effect than the T4 hormone, but its effect is often harder to control. Swedish healthcare rarely prescribes or offers such T3 treatment, as it often lacks advantages and may pose a risk when doses are high for an extended period of time.
Early studies reported high success rates: in one study in 1925, 60% of patients became seizure-free, and another 35% of patients had a 50% reduction in seizure frequency. These studies generally examined a cohort of patients recently treated by the physician (what is known as a retrospective study) and selected patients who had successfully maintained the dietary restrictions. However, these studies are difficult to compare to modern trials. One reason is that these older trials suffered from selection bias, as they excluded patients who were unable to start or maintain the diet and thereby selected from patients who would generate better results. In an attempt to control for this bias, modern study design prefers a prospective cohort (the patients in the study are chosen before therapy begins) in which the results are presented for all patients regardless of whether they started or completed the treatment (known as intent-to-treat analysis).[18]
The Mediterranean diet is rooted in an abundance of fresh plant-based foods including fruits, vegetables, nuts, seeds, beans, and legumes, with olive oil being the primary source of monounsaturated fat. Fish and seafood follow as a primary source of protein with moderate amounts of poultry, dairy, and eggs to follow. Red meat and sugary treats should be consumed relatively rarely and in moderate portions.
Using the Bulletproof Diet, including Brain Octane Oil every day for long periods of time, and eating carbohydrates some of the time but not always, avoiding inflammatory foods, and using Bulletproof Intermittent Fasting, I was able to recently test with perfect insulin sensitivity — I scored a one on a scale of 1 to 120 (see my numbers below). I also had above average glucose tolerance. That’s metabolic flexibility by the numbers!

Con: Results can vary depending on how much fluid you drink. By drinking more water, you dilute the concentration of ketones in the urine and thus a lower level of ketones will be detected on the strips. The strips don’t show a precise ketone level. Finally, and most importantly, as you become increasingly keto-adapted and your body reabsorbs ketones from the urine, urine strips may become unreliable, even if you’re in ketosis.