Great question. So if you are already in nutritional ketosis from your diet, exogenous ketones would still help raise ketone (energy) levels when you want that (maybe for focus at work or energy at the gym. They also help get you back into ketosis after cheat meals and skip the “keto flu” which is the period when your body is using up stored glycogen.
In a nutshell… WOW! The chart above shows each of the games/categories I played, showing my prior 5-day averages compared to the day I took the ketone esters. Compared to my baselines, my scores increased across the board, with the biggest improvements in spatial orientation (+32.2%), working memory (+23.7%), quantitative reasoning (21.5%), task switching (+14.9%), and information processing (+14.9%). Below are more detailed comparisons:

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.

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).
Next, BHB salts are the only supplement that elevates BHB levels while muscle glycogen remains at capacity (low muscle glycogen can drastically impede long-duration athletic performance). In short, athletes who consume carb-based diets, and those on low-carb diets, stand to benefit from exogenous ketone supplements taken prior to training/exercise.

Meanwhile Brinkworth, et al., in their 2009 paper "Long-term Effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive Function" looked at the effects on ketogenic diet on cognitive function and mood. The study participants ate a ketogenic diet for a year and the researchers found that mood levels decreased when compared to a group eating a high carb/low fat diet. They go on to remark “there was no evidence that the dietary macronutrient composition of LC and LF diets affected cognitive functioning over the long term, as changes in cognitive function were similar for both diets”.
For all studies, the area under the curve (AUC) of blood [βHB] was calculated using the trapezium rule. In Study 3, for each of the three drinks, the initial rate of d-βHB appearance was estimated using d-βHB concentrations at baseline and 30 min post-drink, and d-βHB elimination was estimated using the AUC between the post-drink peak (60 min) and trough (180 min) d-βHB concentrations, with a baseline correction to the value at 180 min.
Interestingly, poly-BOHB has recently been reported to have important roles in mammalian mitochondrial membranes, cell membrane calcium channels, and in exotic functions like protein folding (Dedkova 2014). It exists in a variety of chain lengths, ranging from short to very long. It is not clear if humans can digest and use poly-BOHB consumed in the diet, but in animals, poly-BOHB appears to have probiotic and bowel protective functions. This is a rapidly evolving topic that we will be watching closely.
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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