Some think so because higher ketone levels imply increased fuel for the brain and heart (that prefer ketones), and increased protection against inflammation and oxidation. But are the health benefits coming from the ketones themselves, or are they coming from the state you have to put your body in to actually produce them? And if you're kicking yourself out of ketosis by ingesting ketones would you still get the same benefits?
Ketone Bodies are then used by tissues as a source of energy3 through a pathway that leads to formation from β-hydroxybutyrate of two molecules of acetyl CoA, which are used finally in the Krebs cycle. It is interesting to note that the KBs are able to produce more energy compared with glucose because of the metabolic effects of ketosis—the high chemical potential of 3-β-hydroxybutyrate leads to an increase in the ΔG0 of ATP hydrolysis.3 
If you read about ketosis in magazine or heard about it in a podcast and wanted to jump on the bandwagon, then I think you should avoid it. Remember, it is a strict diet, and the potential health downsides may not be worth the upsides, unless you are working with a medical professional and or you are tracking your labs to see what’s going on with your health (thyroid).
Exogenous ketones (also known as ketone supplements) and well-formulated ketogenic diets share at least one thing in common. They both result in increased circulating concentrations of beta-hydroxybutyrate (BOHB), but ultimately are associated with very different patterns of ketosis, as well as differing metabolic and physiologic outcomes. In short, they should not be assumed to have equivalent effects simply because they achieve similar BOHB blood levels. Having said that, there are many reasons we should continue to study the various forms and potential applications of ketone supplements.
After a minimal amount of internet "research," I decided to try my first exogenous ketones. I have used the ketogenic diet off and on for at 15 years and my body is pretty efficient at fat adapting. (Usually by the end of 2 strict days, I am in ketosis, but not without symptoms and intense cravings.) I can consistently fast from carbs for 20 - 24 hours and do this consistently. However, around hour 20, my mind begins to negotiate that intermittent fasting is advantageous too and that I can afford to have some carbs once a day. Hence the yo-yo effect.
You may find a tiny amount here and there is ok (i.e., 2g of sugar with a meal full of fat may be ok).  But if you are starting out I would recommend cutting all sugar from your diet, and most importantly avoiding any sugar consumption on an empty stomach. For best results track your ketone levels before and after meals to see the impact the food has on your ketone levels.
When your body transitions from using energy from carbohydrates to ketones, there can be a lot of nasty and unwanted side effects. These include low energy, bloating, irritability, headaches and fatigue. This is because your body is “in between” burning carbs and burning ketones and hasn’t become efficient at burning ketones and producing them from your fat stores yet.
Athletic performance benefits: The use of exogenous ketone supplements for bettering physical/athletic performance is promising for several reasons. Firstly, taking exogenous ketones (particularly BHB salts) induces acute nutritional ketosis for upwards of eight hours, mimicking fasting physiology (e.g. increases fat burning, insulin sensitivity, etc.).[3]
Zhou Nutrition’s MCT Powder is another great quality MCT powder to try out. Taking a note from Perfect Keto, Zhou uses only Acacia Fiber during its manufacturing process and avoids all use of the common additives and fillers you see in most MCT powders. Zhou’s MCT Powder is made with the patented “goMCT” MCTs. While you don’t get the delicious flavors Perfect Keto have perfected, Zhou’s MCT Powder is a proven product pushing a 4 digit tally in positive reviews. Hundreds have attested to its true lack of flavor and positive ketone results.
77. Volek JS, Sharman MJ, Gomez AL, Scheett TP, Kraemer WJ. An isoenergetic very low carbohydrate diet improves serum HDL cholesterol and triacylglycerol concentrations, the total cholesterol to HDL cholesterol ratio and postprandial pipemic responses compared with a low fat diet in normal weight, normolipidemic women. J Nutr. 2003;133(9):2756–61. [PubMed]
Divided attention involves processing multiple streams of information. The game involves observing a pond full of koi fish swimming around, and tapping each fish only once to feed it a pellet without feeding any fish previously fed. Each level adds more fish with increasing speed and redirection. It’s similar to pretending to be an air-traffic controller who must keep track of every plane on their radar.

Participants refrained from alcohol and caffeine for 24 h prior to each visit AND were asked to consume a similar meal the night before each visit. All studies were carried out at the University of Oxford Human Physiology Laboratories and started at 0800 h following an overnight (>8 h) fast, with a minimum of 72 h between visits. Visit order was randomized prior to commencement by an administrative investigator using a pseudo-random number generator to produce a list of combinations of visit order, which were then allocated based on order of enrolment by a different investigator.
Intense exercise -- more than just fidgeting or pacing -- uses ketones, when glucose is in short supply, which means the body has to create more ketones to replace what you use. This is great for those who are used to a moderate to intense activity level, but intensity is a fine dance between encouraging ketone production and elevating cortisol for the rest of us.

Ketone supplementation did not affect the size of the brain, lungs, kidneys or heart of rats. As previously mentioned, the rats were still growing during the experimental time frame; therefore, organ weights were normalized to body weight to determine if organ weight changed independently to growth. There could be several reasons why ketones influenced liver and spleen weight. The ratio of liver to body weight was significantly higher in the MCT supplemented animals (Fig. 5). MCTs are readily absorbed in the intestinal lumen and transported directly to the liver via hepatic portal circulation. When given a large bolus, such as in this study, the amount of MCTs in the liver will likely exceed the β-oxidation rate, causing the MCTs to be deposited in the liver as fat droplets [94]. The accumulated MCT droplets in the liver could explain the higher liver weight to body weight percentage observed with MCT supplemented rats. Future toxicology and histological studies will be needed to determine the cause of the observed hepatomegaly. It should be emphasized that the dose in this study is not optimized in humans. We speculate that an optimized human dose would be lower and may not cause hepatomegaly or potential fat accumulation. Nutritional ketosis achieved with the KD has been shown to decrease inflammatory markers such as TNF-α, IL-6, IL-8, MCP-1, E-selectin, I-CAM, and PAI-1 [8, 46], which may account for the observed decrease in spleen weight. As previously mentioned, Veech and colleagues demonstrated that exogenous supplementation of 5 mM βHB resulted in a 28 % increase in hydraulic work in the working perfused rat heart and a significant decrease in oxygen consumption [28, 41, 42]. Ketone bodies have been shown to increase cerebral blood flow and perfusion [95]. Also, ketone bodies have been shown to increase ATP synthesis and enhance the efficiency of ATP production [14, 28, 40]. It is possible that sustained ketosis results in enhanced cardiac efficiency and O2 consumption. Even though the size of the heart did not change for any of the ketone supplements, further analysis of tissues harvested from the ketone-supplemented rats will be needed to determine any morphological changes and to understand changes in organ size. It should be noted that the Harlan standard rodent chow 2018 is nutritionally complete and formulated with high-quality ingredients to optimize gestation, lactation, growth, and overall health of the animals. The same cannot be said for the standard American diet (SAD). Therefore, we plan to investigate the effects of ketone supplements administered with the SAD to determine if similar effects will be seen when the micronutrient deficiencies and macronutrient profile mimics what most Americans consume.
Possible GI distress (flatulence) at exceptionally high doses –  In the studies referenced in this article, exogenous ketones taken in large doses occasionally resulted in GI distress, especially flatulence. However, the cause of this is hypothesized to be due to the fact that ketones were mixed in a milky fluid that wasn’t very palatable. If you’re taking a nominal dose of exogenous ketones the likelihood of GI distress is rather low. Moreover, if some GI distress is prevalent, it should improve as you become accustomed to taking ketones.
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.
77. Volek JS, Sharman MJ, Gomez AL, Scheett TP, Kraemer WJ. An isoenergetic very low carbohydrate diet improves serum HDL cholesterol and triacylglycerol concentrations, the total cholesterol to HDL cholesterol ratio and postprandial pipemic responses compared with a low fat diet in normal weight, normolipidemic women. J Nutr. 2003;133(9):2756–61. [PubMed]
As repeated KE consumption would be required to maintain nutritional ketosis, we investigated the kinetics of drinks in series and of continuous intra-gastric infusion. During starvation, the accumulation of ketones (>4 mM) reportedly inhibited ketone clearance from the blood, however the underlying mechanism is unknown (Hall et al., 1984; Wastney et al., 1984; Balasse and Fery, 1989). In Study 3, βHB uptake and elimination were identical for the second and third KE drinks, suggesting that βHB may have reached a pseudo-steady state should further identical boluses have been given at similar intervals. Furthermore, when the KE was given at a constant rate via a NG tube, blood ketone concentrations remained ~3 mM. Therefore, repeated KE drinks effectively maintain ketosis at the intervals and doses studied here.
Human's ability to produce and oxidize ketone bodies arguably evolved to enhance survival during starvation by providing an energy source for the brain and slowing the breakdown of carbohydrate and protein stores (Owen et al., 1967; Sato et al., 1995; Marshall, 2010). The brain is normally reliant on carbohydrate as a substrate, being less able to metabolize lipids, despite adipose tissue representing a far larger energy store than muscle and liver glycogen. Therefore, during starvation, lipids are used for hepatic ketogenesis and, via ketone bodies, lipids sustain the brain. Endogenous production of the ketone bodies, d-β-hydroxybutyrate (βHB) and acetoacetate (AcAc), increases slowly, driven by interactions between macronutrient availability (i.e., low glucose and high free fatty acids) and hormonal signaling (i.e., low insulin, high glucagon and cortisol). Produced continuously under physiological conditions, blood ketone concentrations increase during starvation (Cahill, 1970), when consuming a “ketogenic” (low carbohydrate, high-fat) diet (Gilbert et al., 2000) or following prolonged exercise (Koeslag et al., 1980).
EK use can be compared to the nootropics that have been developed for optimizing focus, memory creation, and faster cognitive performance. While you may not notice this effect on a minute to minute basis if you keep a journal of “forgetful moments” you’ll find that you have fewer of them as time goes on. You’ll also find that you’re able to come up with better ideas, and your workflow is more efficient through the day (10, 11).
Personally, I think it is wise to include a regular carb meal in your diet if you are going to follow a ketogenic diet. Long term ketogenic diets do seem to downregulate your thyroid and metabolism, and a weekly carb meal (or carb day) can help avoid this. The Carb Nite diet by J. Kiefer is a good example of this. And BJJCaveman posted his labs showing how a weekly carb meal helped his thyroid HERE.
Sometimes waiting for your body to make the switch from carbohydrate metabolism to beta hydroxybutyrate metabolism (aka ketosis) can be an uncomfortable and lengthy process. Another way to get beta hydroxybutyrate into your system so your body is using “clean” energy is by taking it supplementally or through nutrition. A betahydroxybutyrate supplement is what can be used in this scenario. This is an exogenous ketone. Exogenous means you get it from outside of your body. Think EX = exit = outside.

But there have also been studies done showing that the Inuit Eskimo’s do not actually reach a state of ketosis. This is due to numerous factors. One being that the diet the eskimo’s eat ‘would not be expected to cause ketosis, because the calculated anti-ketogenic effect of the large protein ingestion was somewhat more than enough to offset the ketogenic effect of fat plus protein.” 

Consuming exogenous ketones isn't the same as following a ketogenic diet–the ketones in the blood haven't been naturally produced by the breakdown of fat stores. However, scientists believe many of the health benefits of the keto diet and fasting (aside from weight loss) are triggered by ketones. Therefore, raising ketone levels through either endogenous or exogenous ketosis could help to improve health and performance by:
Yes — you read that correctly — 24 hours of intermittent fasting without any resistance training and these subjects were able to preserve more muscle mass than the subjects that ate fewer calories every day without fasting at all. This finding contradicts our common sense, but when we dig deeper into autophagy we can find the mechanism behind this result.
1 – If you’re not looking to spend a ton of money up front while testing the ketogenic lifestyle – no problem! For starters, you need to try nutritional ketosis before ever worrying about exogenous supplementation. If you don’t like the diet, it’s not going to matter how many supplements you by. However, if you want to get an idea if exogenous ketones are for you, we would suggest a simple MCT Oil, or a great beginner exo keto like Keto CaNa.
Beta-Hydroxybutyrate (BHB) is naturally ketone body that is produced when free fatty acids are broken down in the liver. The other two types of Ketone bodies are acetoacetate (AcAc) and acetone. Ketones provide pure energy to fuel the human brain and other tissues. The elevation in ketones in your blood have been a rapidly emerging area of research and studies are continuing to show improvements in performance, brown adipose tissue, and several other possible applications.
Intense exercise -- more than just fidgeting or pacing -- uses ketones, when glucose is in short supply, which means the body has to create more ketones to replace what you use. This is great for those who are used to a moderate to intense activity level, but intensity is a fine dance between encouraging ketone production and elevating cortisol for the rest of us.
KE consumption decreased FFA from 0.6 to 0.2 mM, TG from 1.0 to 0.8 mM, and glucose from 5.5 to 4.7 mM by the end of the study (4 h). The effect was not altered by a meal (Figures 5A–C). Dextrose drinks also lowered FFA from 0.6 to 0.2 mM and TG from 1.0 to 0.7 mM (Figures 5A, B). This was likely mediated by the transient increase in glucose, which rose from 4.6 to 6.5 mM following the dextrose drink (Figure ​(Figure5C).5C). The anti-lypoytic effect of dextrose drinks was shorter than that of KE drinks as d-βHB concentrations were elevated for longer after KE drinks than glucose after dextrose drinks. Insulin increased to ~ 35−1 after both the meal and the dextrose drink, but also increased to 13 ± 2−1 when KE was consumed whilst fasted owing to the 15 g of glucose in the flavored drink used as a diluent (Figure ​(Figure5D5D).
Dusty you assume only everyone wants fat burning. I think this is silly. The brain and heart will prefer ketones over carbohydrates when both are present in the blood stream. Look at the research and mechanism. I don’t want fat loss, I want better brain function. I also regularly eat carbs myself. This is one of the reasons I myself use exogenous ketones. No this isn’t a magic fat loss powder, but don’t sit here and quote T-nation trying to rebuttal this article acting like that is a credible source.
The ‘carb-sparing’ effect from BHB suppresses the break down of muscle glycogen. This leads to lower lactate levels. When increasing exercise intensity, fat oxidation (burning) reaches a limit. At that point the muscle burns carbohydrates as fuel. But when consuming Ketone esters, the body does not make this switch. This suggests Ketones are being used instead. 11

Caveat emptor: the following post doesn’t come close to answering most of these questions. I only document my experience with BHB salts (and a non-commercial version at that), but say little to nothing about my experience with BHB esters or AcAc esters. But it will provide you will some context and understanding about what exogenous ketones are, and what they might do for athletic performance. We’ll likely podcast about the questions and topics above and cover other aspects of exogenous ketones in more detail.

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