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.
I began by simply playing all of the games over and over again (each game many dozens of times over the period of a week) to remove any “learning effect.” I then selected two games from each category (for a total of 10 games) and for a period of five days prior to “ketone-day” played each game five times each day. My “before ketones” baseline scores put me in the top 4% of all Lumosity users, so I was already in a good place. But could I improve even more, just one hour after consuming the ketones?

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 mU.ml−1 after both the meal and the dextrose drink, but also increased to 13 ± 2 mU.ml−1 when KE was consumed whilst fasted owing to the 15 g of glucose in the flavored drink used as a diluent (Figure ​(Figure5D5D).


If you have been reading the science behind the ketogenic diet, you know there can be a lot of benefits associated with choosing this way of eating. There is usually a transition period from when someone chooses to go on a ketogenic diet and implements the changes to their menu to when they actually get into ketosis and are able to produce and burn ketones for fuel.
Effects of ketone supplementation on blood glucose. a, b Blood glucose levels at times 0, 0.5, 1, 4, 8, and 12 h (for 10 dose) post intragastric gavage for ketone supplements tested. a Ketone supplements BMS + MCT and MCT significantly reduced blood glucose levels compared to controls for the duration of the 4-week study. BMS significantly lowered blood glucose only at 8 h/week 1 and 12 h/week 3 (b) KE, maintained at 5 g/kg, significantly reduced blood glucose compared to controls from week 1–4. BD did not significantly affect blood glucose levels at any time point during the 4-week study. Two-Way ANOVA with Tukey’s post hoc test, results considered significant if p < 0.05. Error bars represent mean (SD)

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.


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.
When the results for the supplement and the placebo were within 0.2 (either % or mmol/L) of each other, we classed the supplement as neither “better” nor “worse” than the placebo. We gave a “winning brand” sticker to the brand that scored highest against the placebo for each marker, but not for physical performance, since none of the supplements performed better than the placebo for that marker.
We designed a test for each of the chosen benefit claims and enlisted the help of four of our Diet Doctor teammates to try out the supplements and go through the testing. They were Jonatan and Giorgos from the video team, Emőke from the recipe team and Erik from the IT team. We had a mix of people who were naturally in endogenous ketosis during testing, and people who were not.

After a few days of fasting, or of drastically reduced carbohydrate consumption (below 50 g/day), glucose reserves become insufficient both for normal fat oxidation via the supply of oxaloacetate in the Krebs cycle (which gave origin to the phrase ‘fat burns in the flame of carbohydrate') and for the supply of glucose to the central nervous system (CNS).4


If you have been reading the science behind the ketogenic diet, you know there can be a lot of benefits associated with choosing this way of eating. There is usually a transition period from when someone chooses to go on a ketogenic diet and implements the changes to their menu to when they actually get into ketosis and are able to produce and burn ketones for fuel.
The CNS cannot use fat as an energy source; hence, it normally utilizes glucose. After 3–4 days without carbohydrate consumption the CNS is ‘forced' to find alternative energy sources, and as demonstrated by the classic experiments of Cahill and colleagues4 this alternative energy source is derived from the overproduction of acetyl coenzyme A (CoA). This condition seen in prolonged fasting, type 1 diabetes and high-fat/low-carbohydrate diets leads to the production of higher-than-normal levels of so-called ketone bodies (KBs), that is, acetoacetate, β-hydroxybutyric acid and acetone—a process called ketogenesis and which occurs principally in the mitochondrial matrix in the liver.6

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).
I’m getting an increasing number of questions about exogenous ketones. Are they good? Do they work for performance? Is there a dose-response curve? If I’m fasting, can I consume them without “breaking” the fast? Am I in ketosis if my liver isn’t producing ketones, but my BOHB is 1.5 mmol/L after ingesting ketones? Can they “ramp-up” ketogenesis? Are they a “smart drug?” What happens if someone has high levels of both glucose and ketones? Are some products better than others? Salts vs esters? BHB vs AcAc? Can taking exogenous ketones reduce endogenous production on a ketogenic diet? What’s the difference between racemic mixtures, D-form, and L-form? What’s your experience with MCTs and C8?

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