No known effect, short term, long term studies are incomplete or varied plus a whole lot of misinformation is out there also. Are you in ketosis? If you are your glycogen levels will be low. Take extra protein to fight off muscle catabilism, although some say a ketogenic diet is more "muscle sparring" the effiency of protein use for energy is about 40 to 60 percent less than using carbs. Some recommend on a ketogenic diet to increase protein an additional 25% but I found that not to be a problem if you increase your fat intake. Naturally a diet in higher levels of fat, fat being the easiest for the body to breakdown and use as fuel, would also be a necessity. But use good fats, EFA, unsaturated and watch the saturated fat content. I have been seeing more "reports" than olive oil isn't all it was cracked up to be, but I still use it.
