Our bodies are produce three types of ketone bodies for fuel: beta-hydroxybutyrate (BHB), acetoacetate (AcAc), and acetone. Each is used by the body differently. Acetone is the least abundant, produced in much smaller amounts, and is usually exhaled through the lungs rather than being used as fuel.3 Acetoacetate is part of the metabolic pathway whereby humans make and use ketones, but it tends to be found in the blood at lower levels than BHB.
Another source of the D-BOHB isomer is an evolutionarily ancient energy source for micro-organisms. Poly-BOHB is a long chain of D-BOHB molecules strung end-to-end. It functions in many single-cell organisms as a concentrated energy source similar to glycogen in mammals, but whereas glycogen breakdown releases individual glucose molecules, poly-BOHB hydrolysis releases single D-BOHB molecules.
Most of the ketone supplements out there are either underdosed or overpriced - some don't even bother to disclose how much BHB (ie ketones) is used in their product. And why would they? BHB is EXTREMELY expensive. So by not disclosing the amount the can get away with putting in as little as they want and still claim it's a ketone supplement while keeping their costs as low as possible.
Getting into a state of ketosis normally involves eating a ketogenic diet consisting of around 80 percent fat, 15 percent protein, and 5 percent carbs. Over time, the body transitions from burning carbs for fuel to burning ketones—an alternative fuel source that the liver makes by breaking down fat, explains keto diet expert Amy Davis, RD, LDN. Since advocates say that ketosis can help you lose weight fast, think more clearly, and feel more energized, it’s tempting to try.
Given that blood βHB after identical ketone drinks can be affected by factors such as food or exercise (Cox et al., 2016), the accuracy of tools for non-invasive monitoring of ketosis should be investigated. Breath acetone and urinary ketone measurements provide methods to approximate blood ketosis without repeated blood sampling (Martin and Wick, 1943; Taboulet et al., 2007). However, breath acetone did not change as rapidly as blood βHB following KE and KS drinks. Acetone is a fat-soluble molecule, so may have been sequestered into lipids before being slowly released, resulting in the differences observed here. Similarly, significant differences in blood d-βHB between study conditions were not reflected in the urinary d-βHB elimination. As the amount of d-βHB excreted in the urine (≈0.1–0.5 g) represented ~1.5% of the total consumed (≈23.7 g), it appears that the major fate of exogenous d-βHB was oxidation in peripheral tissues. These results suggest that neither breath acetone nor urinary ketone measurements accurately reflect the rapid changes in blood ketone concentrations after ketone drinks, and that blood measurement should be the preferred method to quantitatively describe ketosis. That said, it should be noted that although commercial handheld monitors are the most practical and widely available tool for measuring blood ketones, they can overestimate blood D-βHB compared to laboratory measures (Guimont et al., 2015) and these monitors do not measure L-βHB and so may not provide accurate total blood ketone concentrations, especially if a racemic ketone salt has been consumed.
The problem? Exogenous ketone supplements work by flooding your bloodstream with ketones. But unless you’re also eating a ketogenic diet (and producing a steady stream of ketones naturally), those supplemental ketones won’t stick around forever. “The benefit of exogenous ketones is limited due to their excretion through the urine,” explains Madge Barnes, MD, family medicine specialist with Texas Health Family Care. In other words? They’ll only work for a few hours until you pee them out. As a result, you need to keep on supplementing—which can get expensive. Twenty single-serving packets of Prüvit’s Keto//OS MAX Pure Therapeutic Ketones, for example, cost $130. (The company doesn’t specify how often you should take them.)
Exogenous ketones drinks are growing in popularity as a method to elevate blood ketone concentrations and mimic a ketogenic diet without the need for dietary changes (Ari et al., 2016; Cox et al., 2016; Kesl et al., 2016; Caminhotto et al., 2017; Evans et al., 2017). The present study describes the pharmacokinetic and pharmacodynamics properties of ketone ester and salt drinks in humans at rest, and characterizes the effects of a prior meal, which is pertinent to use as a dietary supplement. The main findings were that KE drinks elevated blood d-βHB > 50% higher than KS drinks, the latter significantly increasing blood l-βHB, which was metabolized more slowly by the body. Both drinks had similar effects on FFA, TG, glucose and electrolyte concentrations, although with disparate effects on pH. A prior meal decreased total blood d-βHB appearance after a KE drink. Finally, either three KE drinks or nasogastric feeding effectively maintained nutritional ketosis over 1 mM for 9 h.

This molecule is quite essential if you are using your own fat for fuel, or taking BHB as an exogenous ketone supplement to increase energy production — essentially to be in nutritional ketosis. If you’re not certain about what ketones are or what nutritional ketosis is, you should back up a little bit and read more about that on my company site, Perfect Keto.
It's also a smart idea to start slowly with this supplement. We can thank Dave Asprey for the term “disaster pants” which has been used by those who try MCT oil at too high a dose when they first start using it. There is a chance that you can experience the same unpleasant gastrointestinal effect with exogenous ketones if you start with too high a dose, or if you maintain a higher carbohydrate diet while using this supplement. Used in appropriate doses, it gets absorbed through your stomach into your liver, then sent out to the rest of your body.
Hi. Thanks for the informative article! I have fallen down the exogenous ketone rabbit hole for the last 2 days trying to figure everything out. I am currently on a nutritional ketonic diet but after 8 months, I am finding it difficult to stay on it 100%. I would like to remain on a low-carb diet, but also have a little more flexibility in my food choices. If you take the expense out of the equation, which product would you recommend for someone who wants to use ketosis as a method of weight loss? Thank you so much.
Now onto the best ketone supplements. All of these 5 are great products with good customer experiences and reviews. The list contains 3 MCT oil powders and 2 BHB salts. Since it’s just 5 products, there’s no room for bad quality. If you see a lower rating it may be due to price/value, the taste or perhaps a lack of third-party inspection certificates.
The culprit is often restaurant meals or other meals where the nutrition facts are not available with the food itself. Such “ignorance is bliss” situations allow us to avoid dealing with daunting numbers. Many people don’t hesitate to stop and enjoy a meal at a restaurant, but they freak out when they actually see the numbers on a label.  By now, we all know that opting for fatty meat with a side of veggies cooked in butter isn’t that bad after all.  It turns out that what you thought to be the safe, “healthy,” doctor-approved choice might not always be what you think it is.
Do I still follow a ketogenic diet? Not anymore. I was strict keto for 12 weeks – enough time to experiment and learn about it. I did enjoy parts (lots of fat!) but I don’t see it as a sustainable way of eating, nor did I benefit from it health or sports performance wise (more on this in an upcoming article). But, I was following a strict keto diet – sans carbs. I think if I were to follow a ketogenic diet AND incorporate a regular carb refeed then the results may be different.
I also concluded that post by discussing the possibility of testing this (theoretical) idea in a real person, with the help of exogenous (i.e., synthetic) ketones. I have seen this effect in (unpublished) data in world class athletes not on a ketogenic diet who have supplemented with exogenous ketones (more on that, below). Case after case showed a small, but significant increase in sub-threshold performance (as an example, efforts longer than about 4 minutes all-out).

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