When you dramatically decrease the volume of the foods you eat and also cut out fiber, it is very likely that you will have less waste and will eliminate that waste less often. Every three days doesn't seem like enough. That may mean that you need to look more closely at your food selection. Nutrition isn't just about calories. You still need a variety of food to provide the right amount of fiber, vitamin, minerals, amen acids and fatty acids.
If you are on a low-carb or keto diet, increase your high-fiber veggies like celery and cauliflower even it that requires an calorie adjustment somewhere else. Also, make sure you are drinking enough water. You may find that drinking caffeinated tea or coffee will also encourage movement.