We carried out the testing across five different days, leaving at least two days between the different testing days so that my teammates had time to recover from the physical performance test each time. The reason we needed five days was that we included a placebo (an artificially flavored drink with no caffeine content) alongside the four brands we tested. Our teammates didn’t know that one of the supplements was a placebo. We also gave everyone a different supplement each time, to rule out any improvement in the tests being a result of people simply getting better at those tests over time.
Skipping breakfast on a keto diet is a popular way to boost ketone levels. Despite the age-old myth that breakfast is the most important meal of the day, research shows that breakfast skipping is not only safe but beneficial. Skipping breakfast causes intermittent ketosis and also suppresses appetite [6]. Make sure your next meal of the day isn't too late in the evening as studies show that eating meals late at night causes weight gain and impairs fat metabolism [7].
The keto-esters are more appropriate for delivering higher doses of BOHB, but with repeated dosing can push the limits of taste and GI tolerance. There has been fairly extensive research on a compound 3-hydroxybutyl 3-hydroxybutyrate that is converted via hydrolysis and liver metabolism to yield 2 molecules of ketones, presumably mostly D-BOHB (Clarke 2012 and 2014). In a study involving lean athletes, an approximate 50 gram dose raised blood BOHB levels to 3 mM after 10 min and reached 6 mM by 20 min. Submaximal exercise resulted in increased ketone disposal from 2 to 3 hours and contributed significantly to whole body energy use during exercise (Cox 2016). This product has been shown to significantly reduce appetite after a single dose (Stubbs 2018) but its effect on body weight in humans over a longer period of time has not been studied, nor has its effect on blood glucose control been reported in humans with type 2 diabetes. However a single dose prior to a glucose tolerance test in healthy humans reduced blood glucose area-under-curve by 11% and non-esterified fatty acid area-under-curve by 44% (Myette-Cote 2018).

But going keto takes work. You have to overhaul your diet, restrict certain classes of foods, and pay close attention to what you eat. People prefer to avoid work if they can. They like shortcuts. Exogenous ketone supplements promise a shortcut—swallow this pill or mix this powder into your water and see your ketones skyrocket without changing the rest of your diet.
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.
Importantly, at Diet Doctor we do not think you need to spend any extra money at all in order to revolutionize your health. You can achieve radiant health just by enjoying authentic food that is naturally low in carbohydrates, getting plenty of sleep and some exercise (going for a walk is free) and reducing stress. A lot of you who answered the survey made exactly these points in your explanations of reasons for not taking the supplements. I whole-heartedly agree.
Another effect of the ketone drinks was to lower blood glucose, free fatty acids, and triglyceride levels. This sounds great. Elevated levels of all those markers are harbingers of disease, particularly if they remain chronically elevated. But think about what this means. If free fatty acids go down, that means adipose tissue isn’t being liberated for burning.
Too much cortisol tells the liver that you are in physical danger and need a lot of energy fast. The brain doesn't understand the difference between physical danger and emotional stress. When emotionally stressed, the brain thinks you're in a life-and-death situation, so the liver comes to your rescue and gives you the glucose you need to fight off your attacker.
Other ingredients: Many of the supplements contain large amounts of caffeine – the supplement we tested from Prüvit contains the same amount as a 16 oz cup of coffee! Some supplements also contain malic acid, which is “known for its ability to increase energy and tolerance to exercise”. This leaves the nagging doubt: if the experiment shows an increase in energy and physical performance, for example, how do we know it is the (expensive) BHB causing the effect and not the (inexpensive) other ingredients?
The many roles of magnesium include helping us maintain normal nerve and muscle function, as well as heart rate, supporting a healthy immune system, regulating blood glucose levels, and making energy production and protein synthesis possible[23]. Magnesium is also involved in both aerobic and anaerobic energy production. ATP synthesis (the body’s energy source) depends on enzymes that are activated by magnesium.
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.
The concentrations of blood d-βHB after KE drinks were highly repeatable whether consumed whilst fasted or fed (Figures 4F,G). The d-βHB Cmax values ranged from 1.3 to 3.5 mM when fed and 2.3 to 4.7 mM when fasted. There was no significant effect of visit order on d-βHB kinetics, with the maximal difference in d-βHB Cmax reached by one individual being 1.2 mM when fed and 1.9 mM when fasted. Approximately 61% of the variation in the data was attributable to feeding (fed vs. fasted), <1% to visit order, 16% to inter-participant variability, and the residual 24% variability due to non-specific random effects.

This was a big surprise. We were at the very least expecting that drinking a ketone supplement would cause blood ketones to rise, but an average increase of 0.33 mmol/L is very small. The supplement associated with the highest average increase in blood ketones was Prüvit’s Keto-OS Max, but it was only an increase of 0.6 mmol/L. Brianna Stubbs, the ketone researcher I consulted with, agrees that an increase of below 2.0-3.0 mmol/L is unlikely to be of much use.
Exogenous Ketones have been shown in performance studies of both humans and animals to improve metabolic efficiency, which in essence means that your body is using better fuel that burns more efficiently over longer periods of time, and decreases the amount of fuel you need while performing. Where glucose fails (glycogen depletion), ketones pick up the slack!
Your brain has a very tight barrier so not everything in the blood can get through. This is called the blood brain barrier. Because your brain uses 25% of the energy that your entire body uses throughout the day, you need to make sure it is fueled appropriately. Glucose can’t directly cross the blood brain barrier. When you eat carbs, you get swings in energy that is available to cross the blood brain barrier which leads to mental fog.
Here we investigated the effects of KE and KS consumption on blood βHB and metabolite concentrations. As we found that KE ingestion delivered a >50% higher plasma concentrations of d-βHB alone, we subsequently determined the reliability and repeatability of ketosis following KE consumption and the effects of concomitant meal ingestion on blood ketone and substrate kinetics. Finally, we determined whether nasogastric infusion could be used for KE administration, given that some patients require feeding in this manner.
Her clients have had similar success. One woman, for instance, has gone from around 170 pounds to 140 pounds since April without making any initial dietary changes. She’s started to gravitate towards more keto foods over time, but still eats her favorite high-carb treats. As for exercise? Her routine consists of a couple of walks each week, Heverly says.
The reason for testing after one hour was based on Prüvit’s “59-minute test”, which recommends testing ketones 45-60 minutes after taking the supplement (by the way, saying “59 minutes” instead of 60 minutes or 1 hour just sounds like another marketing gimmick to me). Kegenix Prime also promises “ketosis in 60 minutes” on its packaging. We carried out the testing at more or less the same time each day.
If you do the same calculations as I did above for estimating fat oxidation, you’ll see that EE in this case was approximately 13.92 kcal/min, while fat oxidation was only 67% of this, or 9.28 kcal/min, or 1.03 g/min. So, for this second effort (the test set) my body did about 5% less mechanical work, while oxidizing about 25% less of my own fat. The majority of this difference, I assume, is from the utilization of the exogenous BHB, and not glucose (again, I will address below what I think is happening with glucose levels).

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