Foods without any simple carbs or sugars (these both are glucose in the body) that I like and eat often are seeds, nuts (& seed/nut butters), cheese, yogurt, butter, meat & fish, coconut cream & butter, as well as green veggies like celery, kale, cabbage, lettuce, broccoli, and sprouts.
Foods that are “low carb” or “low glycemic” that I like and eat often are chips & tortillas made from cauliflower or cassava, grain-free seed crackers (Mary’s Gone Crackers has certain flavors that are pure seed without rice or quinoa grains in them), cauliflower crust pizza (have to to cook it extra to get crispy crust, but it is possible!) Sweet potatoes are also a nice low-glycemic carb treat.
The main foods to avoid are refined sugars and refined grains. These are the worst for your body for many reasons, and are the scourge of ketosis.
I have been in ketosis for most of the last 4 years, and while I do intermittent fasting almost every day (I almost always skip breakfast and lunch and only eat a small dinner), I will occasionally break the diet and eat some healthy carbs or sugars, such as coconut water, dried mango, a handful of blueberries, or even a glass of dry red wine. As long as I don’t eat a meal full of refined grains and refined sugars, then I can bend the strict rules slightly and still stay in ketosis.
At the last Bulletproof conference I attended, I demo’s a ketosis breathalyzer and the guy working the booth said I had the highest ketone levels of anyone the entire conference, except for one old man (around 80) who had been in ketosis for over 30 years. So I have gotten myself so deep into ketosis over the past 3–4 years, that it would take a large helping of refined carbs and sugars -such as plateful of your typical birthday cake and ice cream- to bring me fully out of ketosis.
So I have fortunately gotten to the point where I can fast comfortably, as I have cleansed my microbiome so there isn’t an high population of sugar-eater yeast, fungus and bacteria in there, constantly screaming for cake and ice cream. Daily fasting allows my body to produce ketones from fat and continually deepen the level of ketosis that I am operating on, while avoiding the worst carbs and sugars prevents my system from reverting all the way back to full glycolysis if I decide to have a few pieces of dried mango.