Some common short-term effects that some people experience in the early stages of the process are excessive thirst, fatigue and keto constipation. These minor side-effects occur due to a sudden change to a persons diet, but as I said, once your body starts to adjust to the process, you will start to feel normal again, if not better than before you started. We understand that constipation isn't exactly fun, but it's a small price to pay to experience the long-term health benefits. 
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.

Nutritional ketosis induced with the KD has proven effective for the metabolic management of seizures and potentially other disorders [1–26]. Here we present evidence that chronic administration of ketone supplements can induce a state of nutritional ketosis without the need for dietary carbohydrate restriction and with little or no effect on lipid biomarkers. The notion that we can produce the therapeutic effects of the KD with exogenous ketone supplementation is supported by our previous study which demonstrated that acutely administered KE supplementation delays central nervous system (CNS) oxygen toxicity seizures without the need for dietary restriction [29]. We propose that exogenous ketone supplementation could provide an alternative method of attaining the therapeutic benefits of nutritional ketosis, and as a means to further augment the therapeutic potential of the KD.
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.
It’s sometimes the case that a person has been attempting to transition to a state of ketosis, but in spite of their best efforts, they seem stuck in a kind of limbo where they’re eating hardly any carbs, but they don’t seem to be losing weight or experiencing the other benefits of the keto diet. But the science is the science, which means if you’re doing everything right you should be in ketosis. If you’re not, or you seem to be drifting in and out of a keto state, it’s not your body’s fault, it’s your diet.
For anyone who wants to get a bit more technical, research by Stubbs and colleagues shows that BHB shuts off lipolysis (fat breakdown). With endogenous ketosis there are many other factors that stimulate lipolysis meaning that a kind of balance is reached and lipolysis stays constant. But with exogenous ketosis those factors stimulating ketosis are not present, so the overall effect of the ingested BHB is to decrease lipolysis.
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.
There’s debate raging about which dietary tactic is the god particle for making you leaner, faster and healthier. How the ketogenic diet option squares off against the low carb route is vital for understanding the ways in which exogenous ketone supplements work. To get into ketosis the natural way, you need to keep your carb intake low enough for long enough for your body to begin using use fat as fuel. Your liver then converts a portion of that fat into energy molecules called ketones. These work together with glucose as a fuel source, but can actually kick in faster, allowing your body to operate more economically during lengthy, high-energy exercise efforts.

Over the 28-day experiment, ketone supplements administered daily significantly elevated blood ketone levels without dietary restriction (Fig. 2a, b). Naturally derived ketogenic supplements including MCT (5 g/kg) elicited a significant rapid elevation in blood βHB within 30–60 min that was sustained for 8 h. BMS + MCT (5 g/kg) elicited a significant elevation in blood βHB at 4 h, which was no longer significant at 8 h. BMS (5 g/kg) did not elicit a significant elevation in blood βHB at any time point. For days 14–28, BMS + MCT (10 g/kg) and MCT (10 g/kg) elevated blood βHB levels within 30 min and remained significantly elevated for up to 12 h. We observed a delay in the peak elevation of blood βHB: BMS + MCT peaked at 8 h instead of at 4 h and MCT at 4 h instead of at 1 h. Blood βHB levels in the BMS group did not show significant elevation at any time point, even after dose escalation (Fig. 2a). Synthetically derived ketogenic supplements including KE and BD supplementation rapidly elevated blood βHB within 30 min and was sustained for 8 h. For the rats receiving ketone supplementation in the form of BD or the KE, dosage was kept at 5 g/kg to prevent adverse effects associated with hyperketonemia. The Precision Xtra™ ketone monitoring system measures βHB only; therefore, total blood ketone levels (βHB + AcAc) would be higher than measured. For each of these groups, the blood βHB profile remained consistent following daily ketone supplementation administration over the 4-week duration. (Fig. 2b).

My two cents: I wouldn’t take ketone supps if not on some sort of low(ish) carb diet because the idea of high levels of BOTH fuels (ie, ketones AND glucose) doesn’t seem physiologically appropriate… more like a recipe for disaster, and by “disaster,” I mean “out-of-control production of Reactive Oxygen Species” — this might not matter if you’re an athlete looking for a quick performance boost, because the fuels are going to be cleared rather quickly… not so much if you’re a desk jockey.
Instead of being bound to a mineral (like ketone salts), the ketone molecule (BHB or AcAc) is bound to a ketone precursor (e.g. butanediol or glycerol) via an ester bond. While there aren't as many esters on the market as salts, there is still some variance–especially when looking at the ketone molecule in these products. Before selecting the best one for you, it's important to gather all the necessary information to make your decision.

As I mentioned before, this was by no means a scientific experiment carried out under lab conditions, and this means we can only draw tentative conclusions from any of the data. Nonetheless, carrying out the testing in the way described above should give most people a good idea of how well the ketone supplements show the noticeable benefits they are marketed to have and provide a clear enough basis for a decision on whether or not to buy them.

I wrote this post at about the same time Germany won the World Cup in Rio de Janeiro in 2014. There’s been a lot of moving and shaking in the world of exogenous ketones since then, not to mention soccer. Looking back on my post, I still consider it relevant in terms of what exogenous ketones possibly can (and cannot) do for performance. In this case, to see if exogenous ketone esters provide me a “boost” by allowing me to do the same amount of work while expending less energy (and work at a relatively lower VO2) compared to no supplementation.

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