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Butyrate, carnitine and leucine are dietary ingredients that may be ketogenic but whether they are equally or more ketogenic in humans than medium-chain triacylglycerols is unclear. Our objective was to compare the ketogenic effect in healthy adult humans of l -leucine, butyrate, octanoyl-monoacylglycerol (O-MAG) and l -carnitine during a 4 h metabolic study period. Each test substance was taken with a standard breakfast: butyrate (2 or 4 g), O-MAG (5 or 10 g), l -leucine (5 g), or l -carnitine (2 g), and compared to a no treatment Control (n = 13). At the doses provided, butyrate (2 g; 4 g), O-MAG (5 g; 10 g) increased total plasma ketones AUC of 3.5, 5.0, 1.5, and 2.7-fold (P ≤ 0.05), respectively, compared to baseline. l -carnitine did not significantly stimulate ketogenesis relative to Control. Per gram tested, butyrate was the most ketogenic, and has the potential to be an ingredient in a ketogenic functional food or beverage.

The aim of the present study was to compare the effects of an α-linolenic acid-rich supplement (ALA-RS) on the ketogenic response and plasma long-chain ω-3 polyunsaturated fatty acid in healthy young adults and older individuals.Ten young (25 ± 0.9 y) and 10 older adults (73.1 ± 2.2 y) consumed a flaxseed oil supplement providing 2 g/d of ALA for 4 wk. Plasma ketones, nonesterified fatty acids (NEFA), triacylglycerols, glucose, and insulin were measured over 6 h, before and after supplementation. Total body fat mass was assessed before and after the ALA-RS.The ALA-RS did not significantly modify fasting ketones but postprandial production of β-hydroxybutyrate was increased by 26% (P = 0.037) only in the young adult group. Fasting plasma ketones were positively correlated to fasting plasma NEFA (P 0.01) in both groups. However, the relation was shifted to the right in the older group, suggesting that older adults needed higher plasma NEFA levels to achieve the same ketone amounts as young adults. At baseline, the older group had 47% higher total plasma fatty acids than the young group (P = 0.007). After the ALA-RS, plasma ALA doubled in both groups (P 0.01), an effect that was associated in the older group with a 40% higher eicosapentaenoic acid (EPA; P = 0.004), but no difference in docosahexaenoic acid. The postsupplementation increase in plasma ALA correlated positively with percent total body fat, especially in the older group (r(2) = 0.77; P = 0.0016).In young adults, ALA-RS mildly stimulated postprandial ketogenesis, whereas in the older group, it favored increased plasma ALA and EPA.

Brain glucose uptake is impaired in Alzheimer's disease (AD). A key question is whether cognitive decline can be delayed if this brain energy defect is at least partly corrected or bypassed early in the disease. The principal ketones (also called ketone bodies), β-hydroxybutyrate and acetoacetate, are the brain's main physiological alternative fuel to glucose. Three studies in mild-to-moderate AD have shown that, unlike with glucose, brain ketone uptake is not different from that in healthy age-matched controls. Published clinical trials demonstrate that increasing ketone availability to the brain via moderate nutritional ketosis has a modest beneficial effect on cognitive outcomes in mild-to-moderate AD and in mild cognitive impairment. Nutritional ketosis can be safely achieved by a high-fat ketogenic diet, by supplements providing 20-70 g/day of medium-chain triglycerides containing the eight- and ten-carbon fatty acids octanoate and decanoate, or by ketone esters. Given the acute dependence of the brain on its energy supply, it seems reasonable that the development of therapeutic strategies aimed at AD mandates consideration of how the underlying problem of deteriorating brain fuel supply can be corrected or delayed.

Brain glucose uptake declines during aging and is significantly impaired in Alzheimer’s disease. Ketones are the main alternative brain fuel to glucose so they represent a potential approach to compensate for the brain glucose reduction. Caffeine is of interest as a potential ketogenic agent owing to its actions on lipolysis and lipid oxidation but whether it is ketogenic in humans is unknown. This study aimed to evaluate the acute ketogenic effect of 2 doses of caffeine (2.5; 5.0 mg/kg) in 10 healthy adults. Caffeine given at breakfast significantly stimulated ketone production in a dose-dependent manner (+88%; +116%) and also raised plasma free fatty acids. Whether caffeine has long-term ketogenic effects or could enhance the ketogenic effect of medium chain triglycerides remains to be determined.

Brain glucose uptake is impaired in Alzheimer’s disease (AD). A key question is whether cognitive decline could be delayed if this defect were at least partly corrected or bypassed. Ketones (or ketone bodies) such as beta-hydroxybutyrate and acetoacetate are the brain’s main alternative fuels. Several studies have shown that in mild-to-moderate AD, brain ketone uptake is similar to that of healthy age-matched controls. Published clinical trials show that increasing ketone availability to the brain via nutritional ketosis has modest benefits on cognitive outcomes in mild-to-moderate AD and in mild cognitive impairment. Nutritional ketosis can be safely achieved by a high-fat ketogenic diet or supplements providing medium chain triglycerides. Given the acute dependence of the brain on its energy supply and the ineffectiveness of current therapeutic strategies for AD consideration be given to correcting the underlying problem of deteriorating brain fuel supply during aging.

Despite decades of study, it is still unclear whether regional brain glucose uptake is lower in the cognitively healthy elderly. Whether regional brain uptake of ketones (β-hydroxybutyrate and acetoacetate [AcAc]), the main alternative brain fuel to glucose, changes with age is unknown. We used a sequential, dual tracer positron emission tomography (PET) protocol to quantify brain (18)F-fluorodeoxyglucose ((18)F-FDG) and (11)C-AcAc uptake in two studies with healthy, male Sprague-Dawley rats: (i) Aged (21 months; 21M) versus young (4 months; 4M) rats, and (ii) The effect of a 14 day high-fat ketogenic diet (KD) on brain (18)F-FDG and (11)C-AcAc uptake in 24 month old rats (24M). Similar whole brain volumes assessed by magnetic resonance imaging, were observed in aged 21M versus 4M rats, but the lateral ventricles were 30% larger in the 21M rats (p=0.001). Whole brain cerebral metabolic rates of AcAc (CMR(AcAc)) and glucose (CMR(glc)) did not differ between 21M and 4M rats, but were 28% and 44% higher, respectively, in 24M-KD compared to 24M rats. The region-to-whole brain ratio of CMR(glc) was 37-41% lower in the cortex and 40-45% lower in the cerebellum compared to CMR(AcAc) in 4M and 21M rats. We conclude that a quantitative measure of uptake of the brain's two principal exogenous fuels was generally similar in healthy aged and young rats, that the % of distribution across brain regions differed between ketones and glucose, and that brain uptake of both fuels was stimulated by mild, experimental ketonemia.

Ketones (principally β-hydroxybutyrate and acetoacetate (AcAc)) are an important alternative fuel to glucose for the human brain, but their utilisation by the brain remains poorly understood. Our objective was to use positron emission tomography (PET) to assess the impact of diet-induced moderate ketosis on cerebral metabolic rate of acetoacetate (CMRa) and glucose (CMRglc) in healthy adults. Ten participants (35 ± 15 y) received a very high fat ketogenic diet (KD) (4.5:1; lipid:protein plus carbohydrates) for four days. CMRa and CMRglc were quantified by PET before and after the KD with the tracers, 11C-AcAc and 18F-fluorodeoxyglucose (18F-FDG), respectively. During the KD, plasma ketones increased 8-fold ( p = 0.005) while plasma glucose decreased by 24% ( p = 0.005). CMRa increased 6-fold ( p = 0.005), whereas CMRglc decreased by 20% ( p = 0.014) on the KD. Plasma ketones were positively correlated with CMRa (r = 0.93; p

We propose that brain energy deficit is an important pre-symptomatic feature of Alzheimer’s disease (AD) that requires closer attention in the development of AD therapeutics. Our rationale is fourfold: (i) Glucose uptake is lower in the frontal cortex of people >65 years-old despite cognitive scores that are normal for age. (ii) The regional deficit in brain glucose uptake is present in adults

Lower brain glucose metabolism is present before the onset of clinically measurable cognitive decline in two groups of people at risk of Alzheimer’s disease---carriers of apolipoprotein E4, and in those with a maternal family history of AD. Supported by emerging evidence from in vitro and animal studies, these reports suggest that brain hypometabolism may precede and therefore contribute to the neuropathologic cascade leading to cognitive decline in AD. The reason brain hypometabolism develops is unclear but may include defects in brain glucose transport, disrupted glycolysis, and/or impaired mitochondrial function. Methodologic issues presently preclude knowing with certainty whether or not aging in the absence of cognitive impairment is necessarily associated with lower brain glucose metabolism. Nevertheless, aging appears to increase the risk of deteriorating systemic control of glucose utilization, which, in turn, may increase the risk of declining brain glucose uptake, at least in some brain regions. A contributing role of deteriorating glucose availability to or metabolism by the brain in AD does not exclude the opposite effect, i.e., that neurodegenerative processes in AD further decrease brain glucose metabolism because of reduced synaptic functionality and hence reduced energy needs, thereby completing a vicious cycle. Strategies to reduce the risk of AD by breaking this cycle should aim to (1) improve insulin sensitivity by improving systemic glucose utilization, or (2) bypass deteriorating brain glucose metabolism using approaches that safely induce mild, sustainable ketonemia.

The decrease in resting energy expenditure (REE) and fat oxidation with aging is associated with an increase in fat mass (FM), and both could be prevented by exercise such as resistance training. Dairy consumption has also been shown to promote FM loss in different subpopulations and to be positively associated with fat oxidation. Therefore, we sought to determine whether resistance exercise combined with dairy supplementation could have an additive impact on FM and energy metabolism, especially in individuals with a deficit in muscle mass. Twenty-six older overweight sarcopenic men (65 ± 5 years old) were recruited for the study. They participated in 4 months of resistance exercise and were randomized into three groups for postexercise shakes (control, dairy, and nondairy isocaloric and isoprotein supplement with 375 ml and ~280 calories per shake). Body composition was measured by dual X-ray absorptiometry and REE by indirect calorimetry. Fasting glucose, insulin, leptin, inflammatory profile, and blood lipid profile were also measured. Significant decreases were observed with FM only in the dairy supplement group; no changes were observed for any other variables. To conclude, FM may decrease without changes in metabolic parameters during resistance training and dairy supplementation with no caloric restriction without having any impact on metabolic properties. More studies are warranted to explain this significant decrease in FM.

Objective The aim of this study was to evaluate the effects of long-term energy restriction (ER) on plasma, liver, and skeletal muscle metabolite profiles in aging rats fed a Western-style diet. Methods Three groups of male Sprague-Dawley rats were studied. Group 1 consisted of 2 mo old rats fed ad libitum; group 2 were 19 mo old rats also fed ad libitum; and group 3 were 19 mo old rats subjected to 40% ER for the last 11.5 mo. To imitate a Western-style diet, all rats were given a high-sucrose, very low ω-3 polyunsaturated fatty acid (PUFA) diet. High-resolution magic angle spinning- 1 H nuclear magnetic resonance spectroscopy was used for hepatic and skeletal muscle metabolite determination, and fatty acid profiles were measured by capillary gas chromatography on plasma, liver, and skeletal muscle. Results ER coupled with a Western-style diet did not prevent age-induced insulin resistance or the increase in triacylglycerol content in plasma and skeletal muscle associated with aging. However, in the liver, ER did prevent steatosis and increased the percent of saturated and monounsaturated fatty acids relative to ω-6 and ω-3 PUFA. Conclusions Although steatosis was reduced, the beneficial effects of ER on systemic insulin resistance and plasma and skeletal muscle metabolites observed elsewhere with a balanced diet seem to be compromised by high-sucrose and low ω-3 PUFA intake.

Objectives The aim of this study was to compare the ketogenic effect of the peroxisome proliferator-activated receptor-α stimulator, bezafibrate (BEZA), alone or in combination with medium-chain triacylglycerols (MCTs) in healthy adults. Methods Eighteen healthy adults completed the study: 10 were given a therapeutic dose of BEZA (400 mg/d) for 8 wk followed by a further 4 wk of BEZA (400 mg/d) plus MCT (60 g/d). Eight other participants were given MCT alone (60 g/d) for 4 wk. All participants underwent identical metabolic study days: (a) pretreatment (the control), and after (b) BEZA combined with MCT (BEZA+MCT) or (c) an equal dose of MCT only. On the metabolic study days, a standard breakfast and lunch were given and blood samples were taken hourly to measure plasma ketones, glucose, and fatty acids. Results The combination of BEZA+MCT increased ketones twofold during the metabolic study day. The addition of BEZA increased early ketogenic efficiency of MCT by 2.5-fold but did not result in higher peak or mean concentration of ketones during the metabolic study day. No other differences were seen in plasma metabolites or insulin during metabolic study days. On the final metabolic study day, MCT or BEZA+MCT had different effects on the plasma acetoacetate-to-β-hydroxybutyrate ratio compared with control. Conclusions BEZA mildly potentiated the ketogenic action of MCT but did not increase peak plasma ketone concentration or overall ketone production during the metabolic study day.

Background: Lower-brain glucose uptake is commonly present before the onset of cognitive deterioration associated with aging and may increase the risk of Alzheimer disease. Ketones are the brain's main alternative energy substrate to glucose. Medium-chain triglycerides (MCTs) are rapidly β-oxidized and are ketogenic but also have gastrointestinal side effects. We assessed whether MCT emulsification into a lactose-free skim-milk matrix [emulsified MCTs (MCT-Es)] would improve ketogenesis, reduce side effects, or both compared with the same oral dose of MCTs consumed without emulsification [nonemulsified MCTs (MCT-NEs)]. Objectives: Our aims were to show that, in healthy adults, MCT-Es will induce higher ketonemia and have fewer side effects than MCT-NEs and the effects of MCT-NEs and MCT-Es on ketogenesis and plasma medium-chain fatty acids (MCFAs) will be dose-dependent. Methods: Using a metabolic study day protocol, 10 healthy adults were each given 3 separate doses (10, 20, or 30 g) of MCT-NEs or MCT-Es with a standard breakfast or no treatment [control (CTL)]. Blood samples were taken every 30 min for 4 h to measure plasma ketones (β-hydroxybutyrate and acetoacetate), octanoate, decanoate, and other metabolites. Participants completed a side-effects questionnaire at the end of each study day. Results: Compared with CTL, MCT-NEs increased ketogenesis by 2-fold with no significant differences between doses. MCT-Es increased total plasma ketones by 2- to 4-fold in a dose-dependent manner. Compared with MCT-NEs, MCT-Es increased plasma MCFA bioavailability (F) by 2- to 3-fold and decreased the number of side effects by ∼50%. Conclusions: Emulsification increased the ketogenic effect and decreased side effects in a dose-dependent manner for single doses of MCTs ≤30 g under matching conditions. Further investigation is needed to establish whether emulsification could sustain ketogenesis and minimize side effects and therefore be used as a treatment to change brain ketone availability over a prolonged period of time. This trial was registered at clinicaltrials.gov as NCT02409927.

The extent to which the age-related decline in regional brain glucose uptake also applies to other important brain fuels is presently unknown. Ketones are the brain's major alternative fuel to glucose, so we developed a dual tracer positron emission tomography protocol to quantify and compare regional cerebral metabolic rates for glucose and the ketone, acetoacetate. Twenty healthy young adults (mean age, 26 years) and 24 healthy older adults (mean age, 74 years) were studied. In comparison with younger adults, older adults had 8 ± 6% (mean ± SD) lower cerebral metabolic rates for glucose in gray matter as a whole (p = 0.035), specifically in several frontal, temporal, and subcortical regions, as well as in the cingulate and insula (p ≤ 0.01, false discovery rate correction). The effect of age on cerebral metabolic rates for acetoacetate in gray matter did not reach significance (p = 0.11). Rate constants (min(-1)) of glucose (Kg) and acetoacetate (Ka) were significantly lower (-11 ± 6%; [p = 0.005], and -19 ± 5%; [p = 0.006], respectively) in older adults compared with younger adults. There were differential effects of age on Kg and Ka as seen by significant interaction effects in the caudate (p = 0.030) and post-central gyrus (p = 0.023). The acetoacetate index, which expresses the scaled residuals of the voxel-wise linear regression of glucose on ketone uptake, identifies regions taking up higher or lower amounts of acetoacetate relative to glucose. The acetoacetate index was higher in the caudate of young adults when compared with older adults (p ≤ 0.05 false discovery rate correction). This study provides new information about glucose and ketone metabolism in the human brain and a comparison of the extent to which their regional use changes during normal aging.

The effect of long-term calorie restriction (CR) on metabolites, fatty acid profiles and energy substrate transporter expression in the brain was assessed in aged rats. Three groups of male Sprague-Dawley rats were studied: (i) a 2 month old ad libitum-fed (2AL group), (ii) a 19 month old ad libitum-fed (19AL group), and (iii) a 19 month old group subjected to 40% CR from the age of 7.5 to 19 months (19CR group). The diet contained high sucrose and low n-3 polyunsaturated fatty acids (PUFA) so as to imitate a Western-style diet. High resolution magic angle spinning-(1)H NMR showed an effect of aging on brain cortex metabolites compared to 2AL rats, the largest differences being for myo-inositol (+251% and +181%), lactate (+203% and +188%), β-hydroxybutyrate (+176% and +618%) and choline (+148% and +120%), in 19AL and 19 CR rats, respectively. However, brain metabolites did not differ between the 19AL and 19CR groups. Cortex fatty acid profiles showed that n-3 PUFA were 35-47% lower but monounsaturated fatty acids were 40-52% higher in 19AL and 19CR rats compared to 2AL rats. Brain microvessel glucose transporter (GLUT1) was 68% higher in 19AL rats than in 2AL rats, while the monocarboxylate transporter, MCT1, was 61% lower in 19CR rats compared to 19AL rats. We conclude that on a high-sucrose, low n-3 PUFA diet, the brain of aged AL rats had higher metabolites and microvessel GLUT1 expression compared to 2AL rats. However, long-term CR in aged rats did not markedly change brain metabolite or fatty acid profile, but did reduce brain microvessel MCT1 expression.

Objective In humans consuming a normal diet, we investigated 1) the capacity of a medium-chain triacylglycerol (MCT) supplement to stimulate and sustain ketonemia, 2) 13C-β-hydroxybutyrate and 13C-trioctanoate metabolism, and 3) the theoretical contribution of the degree of ketonemia achieved to brain energy metabolism. Methods Eight healthy adults (26 ± 1 y old) were given an MCT supplement for 4 wk (4 times/d; total of 20 g/d for 1 wk followed by 30 g/d for 3 wk). Ketones, glucose, triacylglycerols, cholesterol, free fatty acids, and insulin were measured over 8 h during two separate metabolic study days before and after MCT supplementation. Using isotope ratio mass spectroscopy, 13C-D-β-hydroxybutyrate and 13C-trioctanoate β-oxidation to 13CO2 was measured over 12 h on the pre- and post-MCT metabolic study days. Results On the post-MCT metabolic study day, plasma ketones (β-hydroxybutyrate plus acetoacetate) peaked at 476 μM, with a mean value throughout the study day of 290 μM. Post-MCT, 13C-trioctanoate β-oxidation was significantly lower 1 to 8 h later but higher 10 to 12 h later. MCT supplementation did not significantly alter 13C-D-β-hydroxybutyrate oxidation. Conclusions This MCT supplementation protocol was mildly and safely ketogenic and had no side effects in healthy humans on their regular diet. This degree of ketonemia is estimated to contribute up to 8% to 9% of brain energy metabolism.

Brain energy metabolism in Alzheimer’s disease (AD) is characterized mainly by temporo-parietal glucose hypometabolism. This pattern has been widely viewed as a consequence of the disease, i.e. deteriorating neuronal function leading to lower demand for glucose. This review will address deteriorating glucose metabolism as a problem specific to glucose and one that precedes AD. Hence, ketones and medium chain fatty acids (MCFA) could be an alternative source of energy for the aging brain that could compensate for low brain glucose uptake. MCFA in the form of dietary medium chain triglycerides (MCT) have a long history in clinical nutrition and are widely regarded as safe by government regulatory agencies. The importance of ketones in meeting the high energy and anabolic requirements of the infant brain suggest they may be able to contribute in the same way in the aging brain. Clinical studies suggest that ketogenesis from MCT may be able to bypass the increasing risk of insufficient glucose uptake or metabolism in the aging brain sufficiently to have positive effects on cognition.