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Welcome to the Metabolic Classroom Podcast. I'm Ben Bickman. Thanks for letting me be your guest professor for the next few minutes. Don't worry about any pop quizzes. I'm here to simply make the science of metabolism clear, practical and engaging before we get started. Just as a reminder, you can listen to both of my podcasts ad free by becoming an insider. Just go to Ben Bickman.com or click on the link at the top of the show. Notes welcome to the Metabolic Classroom. I'm Professor Benjamin Bickman, a biomedical scientist and professor of Cell biology. Today we're examining how ketones, specifically beta hydroxybutyrate or what I will just call bhb, interact with the cardiovascular system. This topic is particularly relevant given the growing interest in not only ketogenic diets but also the fact that heart disease continues to be the number one killer. Also, the rise and adoration, for lack of a better term, for some of these medications that are generally considered anti diabetic but are increasingly used for heart health, namely SGLT2 inhibitors. What I want to show you today is that ketones are far more than just a fuel for the heart. They're metabolically active molecules that reduce cardiac workload, relax blood vessels, dampen inflammation, and modulate gene expression in Ways that promote cardiovascular resilience. We'll start with the fundamental energetics. How the heart uses ketones as fuel and what this means for oxygen efficiency. Then we'll move into hemodynamic effects, specifically how the heart uses ketones in a beneficial way to lower afterload, or how the blood vessels use ketones to reduce this load, or the resistance. And then how that then helps the heart pump out its blood, a phenomenon called cardiac output. The amount of blood coming out of the heart with every pump. From there, we'll examine the direct vascular effects, the anti inflammatory signaling pathways, and finally, the practical implications for heart health. I should note that while ketogenic diets and ketone supplementation are sometimes framed through ideological lenses, whether someone's pro carbohydrate or prolo carbohydrate, my intention in the lecture today is really just purely on the biochemistry and physiology we're examining what actually happens when ketones interact with the cardiovascular system. Let me start with a fundamental point. Your heart is a metabolic powerhouse. It has high demands for ATP, the main molecule of cellular work. And it makes a lot. It produces roughly 6 kg of ATP every single day. That means it's, it produces more mass of ATP than the heart weighs itself its own mass. This enormous demand is met almost entirely through oxidative phosphorylation. So that is to say, the mitochondria using up fats and glucose for fuel. Now, under normal conditions, fatty acids are in fact the predominant fuel, somewhere between about 40 to 70% of the amount of ATP the heart makes, followed by glucose, which is about 20 to 30%. And then all the rest of it is met with lactate and ketones, mostly because those are just at such lower levels. But here's where it gets interesting. Ketones are not the backup fuel you may think they are. They are an adaptive fuel that the heart will use as they are available, especially when the heart is under stress, as we'll get to. And the benefits go well beyond just the heart itself. All right, to get things started, let's start with the bioenergetics of it all. And we'll do so by starting with a hypothesis when it comes to the heart, called the thrifty fuel hypothesis. This is the idea that ketones are more oxygen efficient than say, fats are. And remember, that matters because fats are in fact the primary fuel for the heart. And there is some truth to this idea. There is support for this hypothesis when we look at the P O ratio, the PO ratio, that is the amount of ATP Produced per oxygen atom consumed, ketones come in at approximately 2.5 compared to 2.33 for fatty acids. That is a meaningful advantage when oxygen delivery may be compromised, as it is in heart failure. So if every unit of oxygen is precious, if you can produce more ATP for every unit of oxygen, then you have an advantage. Ketones do that. Furthermore, when we calculate ATP yield per gram of substrate, or how much ATP can you get with any given amount of ketone? In this case, 100 grams of BHB generates about 10,500 grams of ATP, whereas 100 grams of glucose yields significantly less, about 8,500 grams of ATP. So on a weight for weight basis, BHB is remarkably energy dense. It not only requires less oxygen, but over that same demand, it actually is able to produce more ATP. That's a pretty good exchange. What all of this suggests is that ketones serve the failing heart by providing an additional source of ATP. When the capacity to utilize fatty acids and glucose is impaired, and the failing heart is indeed energy impaired, it is starving. But the benefit goes beyond just oxygen efficiency, and in fact, it touches at the very heart of the bioenergetics of the of the heart itself. And so that brings us to what happens in heart failure. The pioneering work of Daniel Kelly in his group demonstrated something remarkable. The failing heart upregulates its capacity to oxidize ketones. Using a technique called quantitative mitochondrial proteomics. In a preclinical animal model, they induced heart failure through a method called pressure overload hypertrophy. So this is just an experimental model of heart failure. They found increased expression of beta hydroxybutyrate dehydrogenase 1, BDH One that matters because that is the rate limiting enzyme for ketone oxidation in the heart. And what's remarkable is that human studies confirm this. When researchers measured metabolites in failing human hearts, they found elevated levels of a marker of increased ketone oxidation. The heart is essentially reprogramming its fuel preference, shifting toward ketone utilization as its ability to rely on other fuels like fats diminishes. And work at the University of Alberta, specifically Gary Lopachuk's lab, showed that this shift is not detrimental. In a very recent paper using another model of heart failure, they demonstrated that increasing ketone supply to the failing heart increases the reliance on ketones and improved heart contractility. Now let's turn to what I consider one of the most clinically relevant aspects with namely the hemodynamic effects of ketones. So we're going a little outside the Heart now. And this is where the research really becomes fascinating. In 2019, Nielsen and colleagues published what we could call a landmark study in the journal Circulation, examining what happens when you infuse BHB into patients with heart failure, who also with the heart failure, are manifesting with something called reduced ejection fraction. So this is the amount of blood, just another marker of how much blood the heart is ejecting whenever it is pumping. What they found was remarkable. Cardiac output, or the amount of blood that the heart is pumping out every time it beats, increased by 2 liters per minute, which was about a 40% improvement. And left ventricular ejection fraction improved by 8 percentage points. The effect was dose dependent and detectable even with physiological concentration ranges. So just a normal amount of BHB was resulting in significant improvements. But to add to this, the cardiac output was accompanied by vasodilation, so reduced systemic and pulmonary vascular resistance. But that didn't mean it didn't actually lead to an overall reduction in blood pressure systemically. But what they found was that the heart was pumping more blood, not because it had to work harder, but because the afterload, or the pressure against which the heart has to pump the blood. So when the heart is pumping and it's pushing the blood out, there's a resistance to that blood coming out, that resistance went down. So it was the heart was able to more easily eject its blood. A more recent study in the Journal of the American Heart association took this further by examining the specific enantiomers of bhb. So you'll know that there's two forms of bhb, D and L. And they found that the L form of bhb, which is at generally lower levels, in fact much lower, when you're just relying on your own production, but you can of course, supplement with it. So when they increased lbhb, they found a particularly potent effect. And they found that the LBHB increased cardiac output by 2.7 liters per minute, primarily once again, through a reduced afterload. So it wasn't making the heart beat harder, it was simply reducing the pressure against which the heart has to beat, making it easier for the heart to get that blood out. What this means clinically is remarkable. Ketones make the heart's job easier. They reduce the resistance the heart pumps against, allowing it to generate more output with less strain. For a failing heart, this is exactly what you want. Improved function without improved, without increasing mechanical stress. So the heart doesn't have to work harder. You're in fact allowing it to work easier. Think enterprise software is too costly, too complex and takes too long to get up and running? Think again. Workday Go makes simplifying your small or mid sized business simple. HR and finance together on one powerful AI platform right at your fingertips. 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