Latest / Common Sense Health / Why Low Ketones Don't Mean You're Not Burning Fat
Transcript
- Stephen Thomas BSc. Hons: Hello A subject that came up a lot in my most recent fasting cohort was ketone levels. Now participants would ask if I have low ketones, does that mean I'm not using fat for fuel? Now this is a really common question, especially for people eating a ketogenic or carnivore diet. Someone checks their blood ketones, sees a reading of 0.2 or 0.3 and thinks no, I'm not in ketosis, I must not be burning fat. But that Is not necessarily true. Blood ketones are not a direct measurement of how much fat you are burning. They are a measurement of how many ketones are circulating in the blood at that moment. And that is an important distinction. You could be making fewer ketones, you could be using ketones very efficiently, or you could simply be testing at the wrong time of the day. So let's walk through this really simply. First, let's talk about the carbohydrate pathway. Carbohydrates. So when you eat carbohydrate, it's broken down into glucose, and that glucose can then be converted into pyruvate. Pyruvate can then become acetyl CoA, and acetyl CoA enters the Krebs cycle, also called the citric acid cycle, where we make energy. So just to reiterate, the simple flow is carbohydrate becomes glucose, glucose becomes pyruvate, pyruvate pyruvate becomes acetyl CoA, acetyl CoA enters the Krebs cycle. The Krebs cycle helps produce ATP, which is cellular energy. But pyruvate can also do something else that is very important. Pyruvate can help make oxaloacetate. And oxaloacetate matters because acetylco A needs oxaloacetate to enter the Krebs cycle efficiently. So with carbohydrate, you are not just providing fuel, you're also providing some of the machinery that allows that fuel to move through the Krebs cycle. Now let's talk about the fat pathway. When you burn fat, either from your body fat or your dietary fat, fatty acids are broken down through a process called beta oxidation. This produces acetyl CoA. So the simple flow is fat becomes fatty acids, fatty acids become acetyl CoA. Acetyl CoA can enter the Krebs cycle. The Krebs cycle then helps produce energy. But here is the crucial point. Fat provides lots of acetyl-CoA, but fat does not meaningfully replenish oxaloacetate. So fat provides the fuel, but it does not directly provide much of the energy entry partner that acetyl-CoA needs to go into the Krebs cycle. So the simple way to picture this is this: acetyl-CoA plus oxaloacetate goes into the Krebs cycle, the Krebs cycle produces energy. But if there is a lot of acetyl CoA but not enough oxaloacetate, then some of that acetyl CoA may be diverted into ketone production. That is one reason ketones can rise during fasting or very low calorie dieting. You are mobilizing lots of fat, creating lots of acetyl-CoA, but oxaloacetate may be pulled towards glucose production. So more acetyl-CoA gets diverted into making ketones. Next, let's talk about the protein pathway because this is where it becomes particularly interesting for people eating carnivore or higher protein ketogenic diets, especially. Now when you eat protein, it is broken down into amino acids, and those amino acids are used for repair, for muscle, for enzymes, immune function, and all the usual protein jobs. But some amino acids can also be used to support glucose production or to replenish glucose. Krebs cycle intermediates, including pathways connected to oxaloacetate. So the simple flow is protein becomes amino acids, some amino acids support glucose production, some amino acids support Krebs cycle intermediates. This can help replenish oxaloacetate. That oxaloacetate then helps acetyl-CoA from fat enter the Krebs cycle more efficiently. So on a high-protein carnivore diet, You might have very low carbohydrate intake, but you still are supplying amino acids that can support the Krebs cycle. That means you may be burning plenty of fat, producing plenty of acetyl CoA, but instead of that acetyl CoA being diverted into lots of ketones, more of it may be going straight into the Krebs cycle to make energy. So the simple version is high protein carnivore diet, amino acids help replenish oxaloacetate. Oxaloacetate helps acetyl CoA enter the Krebs cycle. Acetyl CoA from fat is being used more efficiently, fewer ketones may be left circulating in the blood. So low ketones do not automatically mean poor fat burning. In some people, especially on the high protein carnivore diet, low ketones may simply mean the body is using fat dry fuel efficiently. Now, someone might ask can we prove this with a serum oxaloacetate blood test? Well, not really. At least not in the practical everyday sense. It is in research, but not for the everyday person. Because what oxaloacetate is, is basically in the cells, in the mitochondria. It is not a standard routine blood marker. And even if you could measure it in the serum, it would not necessarily tell you what is happening inside the liver and muscle cells where the real metabolic action is happening. So instead of trying to measure serum oxaloacetate directly, we could look at the overall pattern. Yeah, I'm boring. I'm always talking about patterns, but it helps. So we could look at blood ketones and glucose and fasted insulin and C peptide and triglycerides and liver markers and the wider clinical picture. And of course, interpreting blood in the context of a carnivoro ketogenic way of eating is crucial. A low ketone reading with high glucose, high insulin, and high triglycerides is very different from a low ketone reading with normal glucose, low insulin and low triglycerides. Now the first Pattern may suggest carbohydrate intolerance or poor metabolic health. The second pattern may suggest someone is metabolically adapted and simply not leaving lots of ketones floating around in the blood. If we are discussing longer term glucose control, HBA1C can be useful, but I would always consider a fructosamine assay because it reflects roughly the previous two to three weeks and can sometimes give a clearer picture of recent dietary changes. Now that is One possible explanation for low ketones, protein may be helping replenish the Krebs cycle intermediates, allowing acetyl CoA from fat to be used more directly for energy. But there are other simple explanations too, and one is timing. You may just be testing at the wrong time of the day. When I experimented with a continuous ketone meter, I was surprised to see readings around zero point two millimoles per litre at nine AM in the morning, but then around one point three millimoles at three AM in the middle of the night. And this was something that was repeated quite often, I would at least see like 0.9 in the middle of the night. So if you only test once in the morning, you may not be seeing the full picture. Now another simple explanation is that ketone use may be matching ketone production. In other words, you might be producing ketones, but your tissues are using them efficiently so they are not building up in the blood. The blood reading is what is left circulating, remember, not necessarily the total amount produced or used. So the big takeaway is this. Low blood ketones do not automatically mean you are not using fat for fuel. It could mean insulin is suppressing ketone production, especially if glucose, insulin and triglycerides are high. But it could also mean you are using fat-derived acetyl-CoA efficiently through the KREP cycle. It could mean your ketones are higher at another time of the day, or it could mean your body is using ketones at a similar rate to how it is producing them. So rather than obsessing over one finger prick ketone number, look at the bigger picture. What is your glucose doing? What is your insulin doing? What are your triglycerides doing? What's your energy like? What is your body composition doing? What is your health actually doing, basically? Because a ketometer can be useful, but it is not a divine oracle. It is a little plastic gadget that occasionally makes people question their entire existence before breakfast. The main point is simple. Low ketones do not necessarily mean low fat burning. In the right context, especially on a well formulated higher protein carnivore ketogenic diet, low ketones may simply mean you are using the fuel efficiently. 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