Your body produces three different types of ketones; acetone, acetoacetate and beta- Hydroxybutyrate. Of these, urine strips only measure one kind: acetoacetate. Acetoacetate are excess ketones your body has produced and excreted via urine. These ketones are basically wasted calories.
Drinking large amounts of water as you should be while on a keto diet (or any diet for that matter), especially if that is a change in your normal levels of hydration, may dilute the concentration of these ketones in your urine and will cause lower readings of acetoacetate ketones.
Additionally, as your body becomes keto-adapted over the course of 3-4 weeks when you begin your keto diet, your body is better able to use the ketones it creates, and you will therefore excrete less ketones as waste via urine.
Finally, blood glucose and some hormones in your body that negatively impact your body’s production of ketones are generally higher in the morning when you first wake up, during & after exercise, and just after eating; even while on a strict ketogenic diet.
For the best possible results from urine strips, make sure you wait to measure until 1-2 hours after you wake up, eat, or exercise. Also, make sure you haven’t consumed a lot of water 1-2 hours before measuring to avoid dilution.
So, just because the urine strips don’t show you the results you’re expecting, that doesn’t mean that you aren’t in ketosis. You should focus on the bigger picture. How do you feel? Are you more awake? Do you have more mental clarity? Are you losing weight? Do you feel healthier?
If you are really keen on knowing what your ketones are as proof, you can check out this article to learn more about different testing methods and what might work best for you: