A couple of points: first, what Edith was getting at is that it is not necessary to move your bowel every day on a ketogenic diet. Constipation is when you need to move your bowel and can’t, or can only do so with real effort. Not needing to defecate is not constipation.
Second, be sure to stay hydrated, as that makes all things easier. You don’t—and shouldn’t, in fact—go bonkers with the liquid, but do drink to thirst. Caffeine has a diuretic effect, but it’s not enough to worry about, so you can use coffee, tea, or cola drinks to hydrate with. I don’t like the taste of tap water, so I drink Seltzer or club soda for a bit of fizz to make it interesting.
Third, constipation can be caused by too little salt in the diet, so you might want to try to get your salt intake into the range of 10-15 grams (2-3 U.S. teaspoons) a day, which includes the salt in your food. If you are already consuming salt in that range, then your constipation is caused by something else, and you might have to try other solutions. On the other hand, too much salt can cause loose, messy stools. If that occurs, back up on the salt a bit.
Fourth, MCT oil can have a laxative effect, and so can magnesium supplements. If the constipation is not caused by lack of salt, then try those. However, beware of “disaster pants!” Some of the sugar alcohols also act as laxatives, especially maltitol.