Venous blood samples (2 ml) were obtained during all visits using a 22 G catheter inserted percutaneously into an antecubital vein. The catheter was kept patent using a saline flush following each sample collection. Additionally, during Study 1, arterialized blood from a catheter inserted into a heated hand (Forster et al., 1972) was collected into heparinized blood gas syringes (PICO 100, Radiometer, Copenhagen) from a subset of participants (n = 7) and immediately analyzed for pH and electrolytes using a clinical blood gas analyser (ABL, Radiometer, Copenhagen).
I bought this because I didn't want to be sucked into an autoshipment for a ketone supplement like KetoOS, which is HOT right now. I did the comparison on the ingredient list between this product and KetoOS and they are quite similar. I think one of the big differences is that KetoOS has the option of caffeinated or non-caffeinated powders. For the cost and the free shipping (I'm a Prime member), it's something I could easily fit into my budget, rather than the $114 canister you'd get with KetoOS.
Keep these studies in mind as your body tries to play tricks on you during your first day of fasting.  Even after three days of fasting, health complications are highly unlikely. However, it is important to know about the possible issues that can be caused by fasting. If you choose to incorporate fasting into your daily diet, you typically want to eat every day as well. Occasionally going on a longer period of fasting.

Blood, breath, and urine ketone kinetics following mole-matched ketone ester (KE) and ketone salt (KS) drinks, at two amounts, in 15 subjects at rest. Values are means ± SEM. (A) Blood d-βHB. (B) Tmax of blood d-βHB. (C) AUC of blood d-βHB. (D) Isotopic abundance (%) of d- and l-chiral centers in pure liquid KE and KS. (E) Blood d-βHB and l-βHB concentrations in subjects (n = 5) consuming 3.2 mmol.kg−1 of βHB in KS drinks. (F) d-βHB and l-βHB concentrations in urine samples from subjects (n = 10) consuming 3.2 mmol.kg−1 of βHB in KS drinks. (G) Blood d- and l-βHB after 4, 8, and 24 h in subjects (n = 5) consuming 3.2 mmol.kg−1 of βHB in KS drinks. (H) Breath acetone over 24 h in subjects (n = 5) consuming 3.2 mmol.kg−1 of βHB in KE and KS drinks (ppm = parts per million). (I) Urine d-βHB excreted over 4 h after KE and KS drinks (n = 15). (J) Urine pH 4 h after drink, dotted line indicates baseline. †p < 0.05 KE vs. equivalent amount of KS, *p < 0.05 difference between 1.6 vs. 3.2 mmol.kg−1 of βHB, §p < 0.05 difference between amounts of d- and l-βHB, p < 0.05 difference between baseline and post-drink level.


Another factor to consider is that in nutritional ketosis the liver makes a steady supply of ketones and continuously releases them into the circulation. In contrast, most ketone supplement protocols involve bolus intakes that don’t mimic the endogenous release pattern. The extent to which this impacts metabolic and signaling responses across different tissues remains unclear.
With oral ketone supplementation, we observed a significant elevation in blood βHB without dietary restriction and with little change in lipid biomarkers (Fig. 1). Over the 4 week study, MCT-supplemented rats demonstrated decreased HDL compared to controls. No significant changes were observed in any of the triglycerides or lipoproteins (HDL, LDL) with any of the remaining exogenously applied ketone supplements. It should be noted that the rats used for this study had not yet reached full adult body size [79]. Their normal growth rate and maturation was likely responsible for the changes in triglyceride and lipoprotein levels observed in the control animals over the 4 week study (baseline data not shown, no significant differences) [80, 81]. Future studies are needed to investigate the effect of ketone supplementation on fully mature and aged animals. Overall, our study suggests that oral ketone supplementation has little effect on the triglyceride or lipoprotein profile after 4 weeks. However, it is currently unknown if ketone supplementation would affect lipid biomarkers after a longer duration of consumption. Further studies are needed to determine the effects of ketone supplements on blood triglyceride and lipoproteins after chronic administration and as a means to further enhance the hyperketonemia and improve the lipid profile of the clinically implemented (4:1) KD.
When you start this process, changes in your daily food and drink intake are designed to increase the amount of healthy fats being burned by your liver, which produces and releases more of these endogenous ketones into your blood stream. When breastfeeding, the female body naturally burns more fat to produce the endogenous ketones, which is an infants resource to the nutrients they need for their young minds. As an adult, a lot of us have substituted the goodness of this compound for more sugar fueled energy. However, I'm sure there are many of you that are wondering right now, "does keto work at all and if so how long does ketosis last?" After numerous tests and studies, it has been recognized that it indeed does work and has been proven to have long lasting effects, so you can rest easy and maybe throw away those weight loss pills that claim instant results but don’t seem to do much.
A small side effect for some people is “ketosis breath”. Many people on a ketogenic diet have experienced this temporary phenomenon, and those taking exogenous ketones can experience it as well. The smell of your breath when you are early in the ketogenic diet can have a hint of acetone to it, and it might be mildly unpleasant, but it’s also harmless. Most gum is pretty low in carbohydrates and is a great option while your keto breath fades.
What is the reason for needing to keep our stress levels down? Well the body reacts to stress, whether physical or emotional, by dumping glycogen and potentially glucose in your bloodstream, thus elevating insulin levels. This in turn blocks our bodies from entering ketosis. To keep your mental and emotional stress to a minimum, it may be wise to meditate, sleep, relax, or do something that is fun and care-free.
A growing number of people are giving it a try, thanks to exogenous ketone supplements that claim to launch your body into a state of ketosis within two and a half days—even if you’ve been living on pasta and cookies instead of following a low-carb diet. How can that be, though? And can that kind of rapid transformation actually be safe? Here’s what you should know.
It’s hard to say. Achieving a natural state of ketosis (as in, by eating a ketogenic diet) is thought to be beneficial in the short-term. But experts don’t know the long-term effects, Palumbo says. And some suspect that it could lead to problems like kidney damage or an increased risk for heart disease (and day-to-day keto diet side effects are, at this point, well-documented). Assuming that ketone supplements do work identically to natural ketones, taking them long-term could have similar health effects.

If you truly want to optimize health and performance, magnesium should not be neglected. There is still more research to be done on its potential. Good sources of magnesium include whole grains, nuts, seeds, legumes, green leafy vegetables, and supplements. However, be careful about taking too much magnesium at one time, or else you might end up running to the bathroom in a hurry.
The best time to start a one day fast is in the evening (neither morning nor the night) – preferably, around 6 pm. It won’t make you lose your vital energy during the daytime workouts, nor does it let you sleep with undigested foodstuff in your stomach. Taking late meals and sleeping with undigested food doesn’t allow your body to rest. So the natural healing mechanism of your body fails during the sleep time as the entire resources are busy digesting your food.
Ketone supplements contain exogenous ketones—synthetic ketones made in a lab. Most use a type of ketone called beta-hydroxybutyrate (BHB), which is the same as the ketones the body produces naturally. “We’re literally biohacking," says Amie Heverly, who began taking a ketone supplement called Prüvit last year and now works as a promoter selling Prüvit products. "You’re not adding a foreign substance to your body, because BHB is identical to what your body would naturally produce,” she explains.
Exogenous ketones are created in a lab to accelerate both physical and mental performance. These ketone drinks were actually used in pro cycling races back in 2015, trading at prices that would make using your kidney as a bartering tool seem like a cut price deal. Fortunately, they’ve now come down in cost and are used often in between meals as a way of blackmailing your body into getting into ketosis way faster.
About the only other negative thing I have heard about the company is that if you are placing an order over the phone, they don’t answer too many questions. Instead, they refer you to their website. Their website is very informative and pretty much answers any question you might have. Ketōnd has gotten too popular, and the company had to hire an answering service like they are selling George Forman Grills or something to take calls from around the world 24-7. I know it’s popular all over Europe and Australia too. My buddies that compete in Crossfit swear that this stuff gives them the edge.

I’m often asked if it’s necessary to buy and use keto products like urine sticks. They’re small test strips that you dip in urine to see if your body is producing ketones (and therefore indicate if you’ve entered ketosis.) There's very little information on how to know that you are in ketosis other than using these ketones supplements because they are as accurate as can be in determining your current state. Outside of that, you can only guess if you are in it or not by your body's performance.


Plus, take a look at this promotional video from Prüvit. It claims that “ketones make the fat melt off your body”, which is simply not true (I’ll get back to this later). It also claims that if you wanted to reach ketosis naturally, you would either need to work out 10x harder and longer or be like one of the “extreme people” who “biohack their bodies” to get into ketosis, which “can take weeks or months”. For me, this is irresponsible. A keto diet can be simple and enjoyable, but this video makes switching to a healthy, real food, keto diet sound extreme and difficult while promoting an easy way out in the form of a drink. And that’s just bad advice.
You may wonder why we are emphasizing on using these specific oils. Well, this is because the extra virgin oil is an unprocessed form, and contains lauric acid that is antimicrobial in nature and is good for brain health. (This is the same lauric acid that is naturally found in breast milk as well.) Its antibacterial property also indirectly supports the growth of Candida that keep your gut healthy.
Ketone supplements contain exogenous ketones—synthetic ketones made in a lab. Most use a type of ketone called beta-hydroxybutyrate (BHB), which is the same as the ketones the body produces naturally. “We’re literally biohacking," says Amie Heverly, who began taking a ketone supplement called Prüvit last year and now works as a promoter selling Prüvit products. "You’re not adding a foreign substance to your body, because BHB is identical to what your body would naturally produce,” she explains.

North Americans typically live pro-inflammatory, pro-disease lives (think about your everyday: likely sitting in a flexed position for hours on end, not enough natural sunlight, not enough movement, artificial food stuffs, artificial colouring, going to bed late, blue light exposure, less in-person contact with our loved ones, late night snacks, the list goes on and on).


Great question. We can’t see any reason this can’t be a part of a successful weight loss program on the ketogenic diet. In the morning with coffee is a very popular way to raise ketone levels in the morning. See if you are on pace with your goals and perhaps try a week with a different breakfast to see what feels best. Also – new article might be helpful here too: https://perfectketo.com/exogenous-ketones-for-weight-loss/ Good luck! 🙂

Proponents like Heverly say that taking exogenous ketones can transform your body—and your life. (Her before-and-after shots below were taken just 10 days apart.) “Within 10 days, my body had this shift. My midsection wasn’t as bloated or fluffy. And I don’t have that cellulite on my legs now,” she says. Heverly also credits Prüvit with giving her a much-needed energy boost and improved mental clarity.

Currently, we lack enough evidence to change the recommendations for calcium intake. The Tolerable Upper Intake Level (UL) for adults 19-50 years old is 2500 mg. This is well over the RDA of 1000 mg for the same age group. Calcium supplements commonly contain 600-1200 mg. When assessing your own calcium intake, keep in mind that calcium from food sources and calcium from supplements may have different outcomes.
I (Kim) researched the topic and planned and ran the experiment under the guidance and supervision of Dr. Andreas Eenfeldt, who touched base with me every step of the way to check the experiment design and execution for scientific rigor (to the greatest degree possible) and who has edited this writeup for quality and trustworthiness reasons. I also consulted with other keto experts and researchers to gather feedback both on the experiment design and the results data. They are referenced in the text when this was the case.
Exogenous ketones have become a popular nutritional supplement since their introduction in 2014. Unfortunately there is a lot of inaccurate information and marketing you have to read through to find the truth about them. This article does the hard work for you. It gets right to the true benefits and drawbacks of exogenous ketones supported by research studies.
Over the years, we have seen and heard many different things about the effects and benefits of Raspberry Ketone supplements. Be it capsules or sprays, the discussion around them actually working always had opposing sides. So, we decided the best solution was to do our own research by conducting our own reviews on the most talked about products, to find out exactly how good they were as a "top-rated" ketone supplement.
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.

There is one viable explanation for consuming ketones. If you're in a calorie or carb-restricted state, then maybe during a workout it would make sense. But even then, that really only applies to endurance activities, since it has more to do with enhancing aerobic performance (where oxygen is required), than it does with enhancing high-intensity efforts (where it's not).

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.
You are probably wondering how there could possibly be a benefit to eating less frequently that goes beyond what you are already getting with a ketogenic diet. Restricting carbs and eating enough fat and protein does come with a plethora of health benefits, but when you add intermittent fasting to your lifestyle you can increase energy and reverse aging by harnessing the power of a nobel prize winning process.
Exogenous ketones don’t seem to improve high-intensity, glucose-intensive exercise, increasing fat burning during steady state exercise but dropping top-end high-intensity performance. Another study found that ketone dieters reduced 50-minute time trial performance in cyclists, though another group of researchers have criticized the methods. Even when a ketone ester didn’t improve performance in the shuttle run to exhaustion and 15 meter sprint repeats, it did reduce the drop in brain function following the exercise.
Personally, I do this on Friday night to Saturday night, so if something happens and my hunger hasn’t crashed by Sunday morning, I have another day that I can go zero carb to keep the momentum going. While the body will trigger ketosis as soon as you run out of glycogen, hunger is attached to your triglyceride and insulin levels, which might take an extra day to normalize.

Second, take a look back at table 2. Kegenix Prime scored as the “winning brand” for 4 out of the 7 markers tested: mental performance, satiety, mental clarity and energy. Compared to the other supplements, it also scored highest for physical performance, although none of the supplements were listed as a “winner” since the placebo outperformed them all for that marker.


Administration of ketone supplementation significantly reduced blood glucose over the course of the study (Fig. 3a, b). MCT (5 g/kg) decreased blood glucose compared to control within 30 min which was sustained for 8 h at baseline and at week 1. MCT (10 g/kg) likewise decreased blood glucose within 30 min and lasted through the 12 h time point during weeks 2, 3, and 4. BMS + MCT (5 g/kg) lowered blood glucose compared to control from hours 1–8 only at week 1. BMS + MCT (10 g/kg) lowered blood glucose compared to control within 30 min and remained low through the 12 h time point at weeks 2, 3, and 4. Rats supplemented with BMS had lower blood glucose compared to control at 12 h in week 4 (10) (Fig. 3a). Administration of BD did not significantly change blood glucose levels at any time point during the 4-week study. KE (5 g/kg) significantly lowered blood glucose levels at 30 min for week 1, 2, 3, and 4 and was sustained through 1 h at weeks 2–4 and sustained to 4 h at week 3. (Fig. 3b).
There is one viable explanation for consuming ketones. If you're in a calorie or carb-restricted state, then maybe during a workout it would make sense. But even then, that really only applies to endurance activities, since it has more to do with enhancing aerobic performance (where oxygen is required), than it does with enhancing high-intensity efforts (where it's not).
The ketone supplements were associated with a 5.4% decrease in physical performance while the artificially-sweetened, non-caffeinated beverage I used as a placebo was associated with a 20.3% increase: a big difference in favour of the placebo. Before you go rushing out to buy some, remember that this experiment was not performed under fully-controlled, laboratory conditions, and we were working with too small a group to prove that the placebo caused an increase in physical performance. But what we can say is that we couldn’t find any correlation between ketone supplements and an increase in physical performance in this experiment. According to Brianna Stubbs, some of the work currently being done on new kinds of ketone salts is starting to show more promise in relation to physical performance, so there may be better news on this down the line.
Ketone supplements contain exogenous ketones—synthetic ketones made in a lab. Most use a type of ketone called beta-hydroxybutyrate (BHB), which is the same as the ketones the body produces naturally. “We’re literally biohacking," says Amie Heverly, who began taking a ketone supplement called Prüvit last year and now works as a promoter selling Prüvit products. "You’re not adding a foreign substance to your body, because BHB is identical to what your body would naturally produce,” she explains.
I'm using this in conjunction with a low carb diet (40g net daily) and Adipex. Perfect Keto actually helped alleviate a lot of the keto/low carb flu symptoms I typically experience when starting a low carb diet. I can't give a full review on how this works with weight loss, because I'm just using it as a supplement (1 scoop) to help keep me in solid ketosis and have only been doing so for the past two weeks and using the low carb diet and Adipex in addition to this supplement doesn't give me a pure experience with this product. But I'm down 10 pounds in the two weeks, so I'm sure it's playing a part!
On day 29, rats were sacrificed via deep isoflurane anesthesia, exsanguination by cardiac puncture, and decapitation 4–8 h after intragastric gavage, which correlated to the time range where the most significantly elevated blood βHB levels were observed. Brain, lungs, liver, kidneys, spleen and heart were harvested, weighed (AWS-1000 1 kg portable digital scale (AWS, Charleston, SC)), and flash-frozen in liquid nitrogen or preserved in 4 % paraformaldehyde for future analysis.
Let’s briefly discuss some organic chemistry. Two molecules that are “the same” but mirror images of each other (like your hands) are known as enantiomers, a type of spatial isomer. Beta hydroxybutyrate comes in two forms, D-β-hydroxybutyrate (“right-handed”) and L-β-hydroxybutyrate (“left-handed”). D-β-hydroxybutyrate is the form that is naturally produced in the body and is most bioavailable when taken exogenously.
Effects of ketone supplementation on body weight: Rats administered ketone supplements gained less weight over the 4-week period; however, did not lose weight and maintained healthy range for age. KE supplemented rats gained significantly less weight during the entire 4-week study compared to controls. BMS + MCT, BMS, and BD supplemented rats gained significantly less weight than controls over weeks 2–4.MCT supplemented rats gained significantly less weight than controls over weeks 3–4, Two-Way ANOVA with Tukey’s post hoc test, results considered significant if p < 0.05. Error bars represent mean (SD)
Relationship between blood ketone and glucose levels: a BMS + MCT (5 g/kg) supplemented rats demonstrated a significant inverse relationship between elevated blood ketone levels and decreased blood ketone levels (r2 = 0.4314, p = 0.0203). b At week 4, BMS + MCT (10 g/kg) and MCT (10 g/kg) showed a significant correlation between blood ketone levels and blood glucose levels (r2 = 0.8619, p < 0.0001; r2 = 0.6365, p = 0.0057). Linear regression analysis, results considered significant if p < 0.05
MCT Oil is a keto supplement that helps your body make ketones. The oil contains pure medium-chain triglycerides (MCTs), which are types of fatty acids that your body prefers using for immediate energy. Unlike long-chain fatty acids, MCTs don't require enzymes and bile for digestion and they go straight to the liver where they are used for making free fatty acids or ketones. Studies on MCTs show that they promote weight loss [5].
I had the chance to interview Dr. Ryan Lowery, Ph.D. about this in person. He performs some (not peer-reviewed) research on different brands of ketone salts and is listed as one of the “specialists” on Prüvit’s website. He suggested that we had perhaps ran the tests too long after the supplements were taken, stating that blood ketones tend to peak at 30 minutes. This is, however, not what Prüvit themselves state in their article on the 59-minute test, or the promise to reach ketosis in 60 minutes on the Kegenix Prime packaging. Plus, do you really want to spend up to $390/month on a product that gives you the benefits of ketosis for half an hour?
Hybrid strategy: A hybrid strategy is to follow a low-carb/high-fat ketogenic diet to induce nutritional ketosis and use ketone supplements strategically. Supplements like Ketone salts or MCT oil can help ease the transition into ketosis, they can be an effective tool when we are knocked out of nutritional ketosis and they can help push ketone levels higher in the body for added benefit.
Bottom line: EK isn't the magic pill for instant weight loss. EK triggers ketosis which is a metabolic state where your body burns fat for fuel. EK increases satiety and feeling full, and boosts energy for exercise which helps you lose weight for the long term. You should always aim for the long term and sustainable weight loss and keep the weight off for good instead of looking for a quick fix.
Compared to our other cellular gasoline (carbs), we can store an unlimited supply of energy from ketones in our body within our fat. When you’re reliant on carbohydrates, you’re forced to keep your tank partly full as we can only store just over 2,000 calories of glycogen from carbs. An empty carb tank results in carb-withdrawal symptoms from not being able to switch into a ketone or fat burning metabolism.

Ketone supplements: are they a groundbreaking boost to a low-carb diet, or should you be wary of the broad claims that companies make about their benefits? In this article you’ll learn all about exogenous ketone supplements and, what’s more, you’ll read about the experiment we ran on the supplements at our head office in Stockholm. How did ketone supplements perform when we put them to the test? Do they work? Read on to find out our verdict!


Ketogenic diets have been successfully used to treat diseases that have an underlying metabolic component, effectively decreasing seizures in recalcitrant pediatric epilepsy (Kossoff et al., 2003), lowering blood glucose concentrations in type 2 diabetes mellitus (Feinman et al., 2015) and aiding weight-loss (Bueno et al., 2013). Emerging evidence supports several clinical uses of ketogenic diets, for example in neurodegenerative diseases (Vanitallie et al., 2005), specific genetic disorders of metabolism (Veech, 2004) and as an adjunct to cancer therapy (Nebeling et al., 1995). Ketone bodies themselves may underlie the efficacy of the ketogenic diet, either through their role as a respiratory fuel, by altering the use of carbohydrate, protein and lipids (Thompson and Wu, 1991; Cox et al., 2016), or through other extra- and intracellular signaling effects (Newman and Verdin, 2014). Furthermore, ketone metabolism may offer a strategy to improve endurance performance and recovery from exercise (Cox et al., 2016; Evans et al., 2017; Holdsworth et al., 2017; Vandoorne et al., 2017). However, achieving compliance to a ketogenic diet can be difficult for both patients and athletes and may have undesirable side effects, such as gastro-intestinal upset (Cai et al., 2017), dyslipidemia (Kwiterovich et al., 2003) or decreased exercise “efficiency” (Edwards et al., 2011; Burke et al., 2016). Hence, alternative methods to raise blood ketone concentrations have been sought to provide the benefits of a ketogenic diet with no other dietary changes.

Thank you, Mark! I am an ME/CFS patient, and I have improved quite a bit on a ketogenic diet, which I have been following for the past 3 months. I am slowly losing weight (much needed) and I wondered, does using exogenous ketones inhibit fat loss? I’m trying to balance the benefits of continuing weight loss with benefits in dealing with ME/CFS symptoms. Thank you for any info you can offer!


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.
Taking exogenous ketones not only eliminates the need to follow a strict ketogenic diet to achieve ketosis (so you can have your high carb cake and eat it too), it can also help users get there faster. “They can expedite the process of getting into ketosis and becoming fat adapted,” Davis explains. “They can also help people push past the keto flu and potentially experience more mental energy and clarity than from diet alone.”
It was like getting the benefits of a five-day fast in just 15 minutes! As my body and brain began sucking up the ketones, I felt a rush of energy and my mind became very sharp and focused in ways beyond what I attain doing an extended fast. But in this case it was the 40g of ketones I had just consumed. Even at the two-hour mark, when I took my last reading, I was still in deep ketosis.
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).
Glucose and BHB went down slightly throughout the effort and RQ fell, implying a high rate of fat oxidation. We can calculate fat oxidation from these data. Energy expenditure (EE), in kcal/min, can be derived from the VO2 and VCO2 data and the Weir equation. For this effort, EE was 14.66 kcal/min; RQ gives us a good representation of how much of the energy used during the exercise bout was derived from FFA vs. glucose—in this case about 87% FFA and 13% glucose. So fat oxidation was approximately 12.7 kcal/min or 1.41 g/min. It’s worth pointing out that “traditional” sports physiology preaches that fat oxidation peaks in a well-trained athlete at about 1 g/min. Clearly this is context limited (i.e., only true, if true at all, in athletes on high carb diets with high RQ). I’ve done several tests on myself to see how high I could push fat oxidation rate. So far my max is about 1.6 g/min. This suggests to me that very elite athletes (which I am not) who are highly fat adapted could approach 2 g/min of fat oxidation. Jeff Volek has done testing on elites and by personal communication he has recorded levels at 1.81 g/min. A very close friend of mine is contemplating a run at the 24 hour world record (cycling). I think it’s likely we’ll be able to get him to 2 g/min of fat oxidation on the correct diet.

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