TL;DR : Low numbers are completely normal! The most likely culprits for low ketone readings are too many carbs, too much protein, and too much stored glycogen.
You started your keto plan, and, as far as you know, you’ve eliminated all carbs.
But why the heck are your ketone readings so low? To understand ketosis, you’ll first have to understand your body a little better.
The human body is truly amazing. The reason you can survive in even the most extreme circumstances is because your body is built for the job and the job description hasn’t changed in millions of years. Your body’s goal is to keep you in a state of normalcy (i.e. homeostasis), and it will try to do so using whatever you feed it. But since the body’s preferred fuel source is glucose, when you deprive it by cutting carbs, it will do whatever it can to find and manufacture more. The body will only start burning fat for fuel once it has run out of options for glucose.
The first thing it will do is seek out any remaining droplet of glucose in your blood. That means, if you’ve gone carb free but are still providing even small amounts detectable to the body, it will take it. You might be thinking about the obvious foods to forgo. A candy bar, a piece of bread, etc. But the body will take any carbohydrate, healthy or not – and run with it. Even eating a whole container of cashews will fit the bill since those carbs can add up. Also, carbs may come from unexpected sources like salad dressings and sauces.
Once your body has used up all the glucose from your food, the next thing it will do is start to tap your glycogen, or your stored glucose. Your glycogen stores get filled up whenever you consume more glucose than you need, and your body returns to use these stores once you stop eating carbs and sugar. Amazingly, your body stores about a pound and a half of glycogen! This is probably the most important factor to remember when scratching your head about your low ketone readings. If you’ve cut your carbs but are still seeing low numbers, you have probably not yet burned through that pound and a half of glycogen.
Lastly, if you are consuming a high amount of protein, your liver can actually take that protein and convert it into glucose (remember that the body will do what it can to find and make more glucose!). This process is called gluconeogenesis. Once this newly created glucose is released into the blood, your body will use it. Because of this, excessive protein can prevent your body from having to tap its fat stores.
So here is how the scenario may play out. You started your keto plan on Monday, but for a year prior to that Monday you loaded up with carbs of all kinds, all day, every day. You’ve got a lot of stored fuel to burn through! If you stick to your plan, by Thursday or Friday, you’re starting to think that you’ve depleted these stores. The liver could step in there and start using byproducts of protein. Oh no – the numbers on my monitor are still low. You can try moderating your protein and starting to count carbs so you can keep better track. A few days later, your body may have no choice than to look for alternative sources. Now there is only one source left: fat. That’s when the magic happens!
When the body has finally accepted that there is no more glucose to be had, it starts burning fat and your ketone readings go up. Exactly when this happens varies based on what you did before your lifestyle change (which determines your glycogen storage) and on your current carb and protein consumption. Remember that your body is basically a petulant toddler who wants to get her way. Just like that toddler, it will find the candy in the house if it exists.Ketone levels vary throughout the day and many things can impact your numbers. The benefit of diligent tracking is that it helps to identify trends related to diet and other lifestyle choices. Remember that low numbers are completely normal, especially when you first start cutting carbs or fasting. Try not to get discouraged, keep experimenting, and most of all, give yourself a pat on the back for your efforts!