Ketogenic Biochemistry
Expert-defined terms from the Advanced Certificate in Ketogenic Diet course at London School of Business and Administration. Free to read, free to share, paired with a professional course.
Acetyl‑CoA – central metabolic intermediate that carries two‑carbon units… #
Related terms: Coenzyme A, citrate synthase, fatty‑acid oxidation. In the liver, excess acetyl‑CoA from β‑oxidation is diverted to form ketone bodies. Practical application: Measuring hepatic acetyl‑CoA helps assess ketogenic flux. Challenge: Rapid turnover makes direct quantification difficult.
Acetoacetate (AcAc) – first ketone body produced from condensation of two… #
Related terms: Β‑hydroxybutyrate, acetone, HMG‑CoA. AcAc can be reduced to β‑hydroxybutyrate or spontaneously decarboxylate to acetone. Example: Urinary AcAc spikes during prolonged fasting. Clinical use: Urine dipsticks detect AcAc for monitoring diet adherence. Challenge: Instability in blood samples requires prompt analysis.
Acyl‑carnitine – fatty acid linked to carnitine, facilitating transport a… #
Related terms: CPT‑I, CPT‑II, carnitine shuttle. Accumulation of specific acyl‑carnitines signals incomplete β‑oxidation, useful for diagnosing fatty‑acid oxidation disorders. Practical application: Plasma acyl‑carnitine profiling guides adjustments in ketogenic diet for metabolic disorders. Challenge: Interpretation requires expertise due to overlapping chain lengths.
Adenosine triphosphate (ATP) – primary cellular energy currency generated… #
Related terms: ADP, AMP, ATP synthase. Ketogenic metabolism yields ATP efficiently from fatty‑acid oxidation, often with lower glycolytic flux. Example: Muscle ATP production during low‑intensity exercise on a ketogenic diet. Challenge: ATP demand must be balanced with NADH/NAD⁺ ratios to avoid redox imbalance.
Aldolase B – enzyme catalyzing fructose‑1‑phosphate cleavage in hepatic f… #
Related terms: Hereditary fructose intolerance, glycolysis, fructose‑1‑phosphate. In a ketogenic diet, low carbohydrate intake reduces aldolase B activity, minimizing fructose‑derived metabolites. Practical note: Patients with aldolase B deficiency tolerate ketogenic diets well. Challenge: Inadvertent fructose exposure can cause hypoglycemia and hepatic stress.
Beta‑hydroxybutyrate (β‑HB) – predominant circulating ketone body, formed… #
Related terms: AcAc, ketone body, NAD⁺/NADH. Β‑HB serves as an efficient fuel for brain and muscle, providing ~4 kcal g⁻¹. Example: Blood β‑HB concentrations of 2–5 mmol L⁻¹ indicate nutritional ketosis. Clinical use: Point‑of‑care β‑HB meters guide diet titration. Challenge: Elevated β‑HB may mask diabetic ketoacidosis if not interpreted correctly.
Beta‑oxidation – mitochondrial process that sequentially removes two‑carb… #
Related terms: Acyl‑CoA dehydrogenase, FADH₂, NADH. In ketogenic states, β‑oxidation supplies the bulk of acetyl‑CoA for ketogenesis. Practical application: Up‑regulation of β‑oxidation enzymes (e.G., CPT‑I) is a marker of successful adaptation. Challenge: Accumulation of medium‑chain acyl‑CoA intermediates can cause mitochondrial stress.
Biotin – water‑soluble vitamin acting as a cofactor for carboxylases, inc… #
Related terms: Vitamin B7, carboxylation, gluconeogenesis. Adequate biotin supports anaplerotic flux, maintaining citric‑acid cycle intermediates during low‑carbohydrate intake. Example: Biotin supplementation improves hepatic gluconeogenesis in ketogenic patients. Challenge: Deficiency is rare but can impair fatty‑acid synthesis, complicating diet planning.
Branched‑chain amino acids (BCAAs) – leucine, isoleucine, and valine, met… #
Related terms: Transamination, keto‑acid, mTOR signaling. BCAAs provide nitrogen for gluconeogenesis and can be oxidized to acetyl‑CoA or succinyl‑CoA, supporting ketosis. Practical use: Monitoring BCAA intake helps prevent excessive protein that may raise insulin and blunt ketosis. Challenge: Excess BCAAs may increase ammonia production in compromised liver function.
Carnitine – quaternary amine that forms acyl‑carnitine esters, enabling f… #
Related terms: CPT‑I, CPT‑II, carnitine deficiency. Supplemental L‑carnitine can enhance fatty‑acid transport in individuals with marginal deficiency, improving ketone production. Example: Athletes on a ketogenic diet often use carnitine to sustain performance. Challenge: High doses may cause gastrointestinal upset and are unnecessary for most healthy adults.
Carnitine palmitoyltransferase I (CPT‑I) – outer‑mitochondrial membrane e… #
Related terms: Malonyl‑CoA inhibition, fatty‑acid oxidation, CPT‑II. CPT‑I activity is a rate‑limiting step; it is up‑regulated by fasting and low insulin. Practical application: Pharmacologic CPT‑I inhibitors (e.G., Etomoxir) are used experimentally to probe ketogenesis. Challenge: Genetic CPT‑I deficiency leads to hypoketotic hypoglycemia, contraindicating a strict ketogenic diet.
Carnitine palmitoyltransferase II (CPT‑II) – inner‑mitochondrial membrane… #
Related terms: CPT‑I, acyl‑carnitine, fatty‑acid oxidation disorders. CPT‑II deficiency manifests as muscle pain and myoglobinuria during high‑fat intake. Example: Individuals with CPT‑II deficiency may require reduced fat proportion in ketogenic protocols. Challenge: Diagnosis often requires muscle biopsy and enzyme assay.
Coenzyme A (CoA) – essential thiol‑containing cofactor that activates fat… #
Related terms: Acetyl‑CoA, pantothenic acid, thioester bond. Adequate CoA levels are critical for sustained ketogenesis; pantothenic acid (vitamin B5) supplies the precursor. Practical tip: Balanced micronutrient intake ensures sufficient CoA pools. Challenge: Severe CoA deficiency is rare but can halt fatty‑acid oxidation entirely.
Cytochrome c oxidase (Complex IV) – terminal enzyme of the electron‑trans… #
Related terms: Oxidative phosphorylation, ATP synthase, mitochondrial respiration. Ketogenic metabolism increases NADH from β‑oxidation, feeding electrons into Complex I and II, ultimately driving Complex IV activity. Example: High‑fat diets can enhance mitochondrial coupling efficiency. Challenge: Excess reactive oxygen species may arise if Complex IV is overwhelmed, necessitating antioxidant support.
De Novo Lipogenesis (DNL) – synthesis of fatty acids from excess carbohyd… #
Related terms: ACC, FAS, insulin. In a ketogenic diet, DNL is markedly suppressed due to low insulin and limited carbohydrate substrate. Practical implication: Reduced hepatic fat accumulation is a therapeutic goal for NAFLD patients. Challenge: Occasional high‑glycemic “cheat” meals can reactivate DNL, compromising ketosis.
Diacylglycerol (DAG) – lipid intermediate formed during triglyceride synt… #
Related terms: Phosphatidic acid, triglyceride, lipase. Elevated DAG can activate protein kinase C, contributing to insulin resistance. Ketogenic diets lower DAG levels by limiting de novo triglyceride synthesis. Example: Muscle biopsies from keto‑adapted athletes show reduced DAG content. Challenge: Excessive dietary saturated fat may still raise DAG despite low carbohydrate intake.
Electron transport chain (ETC) – series of protein complexes (I‑IV) that… #
Related terms: Oxidative phosphorylation, mitochondrial membrane potential, ROS. Ketone oxidation yields a higher P/O ratio than glucose, improving energetic efficiency. Practical note: Measuring respiratory control ratio can assess mitochondrial adaptation to ketosis. Challenge: Chronic high‑fat intake may increase mitochondrial ROS if antioxidant defenses are insufficient.
Enolase – glycolytic enzyme converting 2‑phosphoglycerate to phosphoenolp… #
Related terms: Glycolysis, phosphoglycerate mutase, metabolic flux. In ketogenic states, enolase activity diminishes due to reduced glycolytic flux. Example: Reduced enolase expression is observed in liver tissue after 4 weeks of ketogenic feeding. Challenge: Rapid shifts from high‑carb to keto may cause transient lactic acidosis if enolase activity lags.
Fatty‑acid synthase (FAS) – multi‑enzyme complex that elongates acetyl‑Co… #
Related terms: ACC, NADPH, lipogenesis. Low insulin and carbohydrate intake down‑regulate FAS transcription, curtailing new fat synthesis. Practical outcome: Decreased endogenous triglyceride production aids weight‑loss programs. Challenge: Certain genetic polymorphisms may maintain FAS activity despite low carbs, reducing diet efficacy.
Flavin adenine dinucleotide (FAD) – redox cofactor accepting electrons du… #
Related terms: FADH₂, electron transport chain, riboflavin. Adequate riboflavin intake ensures sufficient FAD for optimal fatty‑acid oxidation. Example: Riboflavin deficiency can blunt ketone production despite high fat intake. Challenge: Diagnosing subclinical riboflavin deficiency requires specialized assays.
Glucose‑6‑phosphate (G6P) – first phosphorylated product of glucose entry… #
Related terms: Hexokinase, glycogen synthase, PPP. In ketogenic nutrition, hepatic G6P concentrations fall, limiting glycolytic flux and preserving glucose for essential tissues. Practical note: Low G6P reduces hepatic glycogen stores, promoting ketosis. Challenge: Prolonged low G6P may impair immune cell function, which relies on the pentose‑phosphate pathway.
Glutamate dehydrogenase (GDH) – mitochondrial enzyme interconverting glut… #
Related terms: Ammonia, amino‑acid catabolism, TCA cycle. GDH activity supplies anaplerotic α‑ketoglutarate during ketogenic diets, supporting TCA cycle turnover. Example: Increased GDH flux observed in keto‑adapted rodent livers. Challenge: Excessive GDH activity can raise ammonia, necessitating monitoring in patients with hepatic insufficiency.
HMG‑CoA synthase (mitochondrial) – enzyme catalyzing condensation of acet… #
Related terms: HMG‑CoA lyase, ketone body synthesis, rate‑limiting step. Up‑regulation of mitochondrial HMG‑CoA synthase is a hallmark of ketogenic adaptation. Practical application: Hepatic HMG‑CoA synthase mRNA levels serve as a biomarker for diet compliance. Challenge: Genetic deficiency leads to hypoketotic hypoglycemia, contraindicating strict ketosis.
HMG‑CoA lyase – enzyme that cleaves HMG‑CoA into AcAc and acetyl‑CoA, com… #
Related terms: HMG‑CoA synthase, AcAc, ketogenesis. Deficiency causes accumulation of HMG‑CoA and metabolic acidosis. Example: Newborn screening can detect HMG‑CoA lyase deficiency, guiding early dietary intervention. Challenge: Patients with this deficiency cannot sustain a high‑fat ketogenic diet; alternative energy sources are required.
Insulin – pancreatic hormone promoting glucose uptake, glycogen synthesis… #
Related terms: Glucagon, PI3K‑AKT pathway, malonyl‑CoA. Low insulin during ketogenic diets favors fatty‑acid mobilization and ketogenesis. Practical implication: Monitoring fasting insulin helps gauge metabolic shift. Challenge: Individuals with insulin resistance may require longer adaptation periods to achieve ketosis.
Ketone body – collective term for AcAc, β‑HB, and acetone, produced in li… #
Related terms: Ketogenesis, hepatic mitochondria, energy substrate. Ketone bodies cross the blood‑brain barrier and supply ~60 % of cerebral energy during prolonged fasting. Example: Therapeutic ketosis (β‑HB 3–5 mmol L⁻¹) is used in epilepsy management. Challenge: Uncontrolled ketone production can lead to ketoacidosis in diabetics.
Ketogenesis – hepatic metabolic pathway generating ketone bodies from ace… #
Related terms: HMG‑CoA synthase, β‑oxidation, mitochondrial matrix. Initiated when insulin:Glucagon ratio falls below ~0.1, Driving transcription of key enzymes. Practical note: Intermittent fasting can accelerate ketogenesis onset. Challenge: Hepatic mitochondrial dysfunction impairs ketone output, limiting diet effectiveness.
Ketolysis – extra‑hepatic utilization of ketone bodies, primarily in brai… #
Related terms: Β‑HB dehydrogenase, succinyl‑CoA, TCA cycle. Β‑HB is oxidized to AcAc, then to acetoacetyl‑CoA, which splits into two acetyl‑CoA molecules entering the TCA cycle. Example: Cardiac muscle oxidizes β‑HB at rates up to 60 % of total substrate during ketosis. Challenge: Impaired ketolysis (e.G., SCOT deficiency) can cause accumulation of ketones and metabolic acidosis.
Lactate dehydrogenase (LDH) – enzyme interconverting pyruvate and lactate… #
Related terms: Anaerobic glycolysis, Cori cycle, NAD⁺ regeneration. In ketogenic states, LDH activity declines as glycolytic flux wanes, reducing lactate production. Practical observation: Lower resting lactate levels are common in keto‑adapted athletes. Challenge: Acute high‑intensity bursts may still generate lactate, necessitating careful pacing.
Malonyl‑CoA – product of acetyl‑CoA carboxylase (ACC) that inhibits CPT‑I… #
Related terms: ACC, fatty‑acid synthesis, CPT‑I inhibition. Low carbohydrate intake reduces malonyl‑CoA, relieving CPT‑I inhibition and promoting β‑oxidation. Example: Hepatic malonyl‑CoA drops by >80 % after 48 h of fasting. Challenge: Certain medications (e.G., ACC inhibitors) may synergize with ketogenic diets, requiring dose adjustments.
Medium‑chain triglycerides (MCTs) – fats composed of 6–12 carbon fatty ac… #
Related terms: Caprylic acid, capric acid, ketone production. MCT oil boosts ketone generation without requiring extensive β‑oxidation, useful for individuals struggling to achieve ketosis. Practical use: 15–30 G MCT per day can raise β‑HB by 0.5–1 Mmol L⁻¹. Challenge: Gastrointestinal upset limits tolerable dose for some users.
Monocarboxylate transporter 1 (MCT1) – membrane protein facilitating tran… #
Related terms: SLC16A1, β‑HB uptake, blood‑brain barrier. Up‑regulation of MCT1 in brain endothelium enhances ketone delivery during prolonged ketosis. Example: PET studies show increased MCT1 expression after 2 weeks of ketogenic feeding. Challenge: Genetic polymorphisms reducing MCT1 function may blunt cerebral ketone utilization.
Oxaloacetate (OAA) – four‑carbon TCA cycle intermediate derived from pyru… #
Related terms: Citrate synthase, anaplerosis, gluconeogenesis. Low carbohydrate intake reduces OAA availability from glycolysis, prompting reliance on anaplerotic amino‑acid catabolism. Practical implication: Adequate protein ensures OAA supply for TCA cycle continuity. Challenge: Insufficient OAA can limit citrate formation, reducing fatty‑acid synthesis and potentially impairing energy balance.
Phosphofructokinase‑1 (PFK‑1) – key regulatory enzyme of glycolysis, conv… #
Related terms: Allosteric regulation, ATP inhibition, glycolytic flux. Ketogenic diets lower PFK‑1 activity due to reduced fructose‑6‑phosphate and elevated ATP, curtailing glycolysis. Example: Muscle biopsies demonstrate a 40 % drop in PFK‑1 Vmax after 3 weeks of keto feeding. Challenge: Abrupt transition may cause transient hypoglycemia if PFK‑1 activity does not adjust promptly.
Phosphoenolpyruvate carboxykinase (PEPCK) – gluconeogenic enzyme converti… #
Related terms: Gluconeogenesis, hepatic glucose output, cAMP. During ketosis, hepatic PEPCK expression rises to maintain basal glucose for erythrocytes and renal medulla. Practical note: Modest gluconeogenesis prevents hypoglycemic episodes. Challenge: Excessive PEPCK activity can counteract weight‑loss goals by increasing hepatic glucose production.
Pyruvate dehydrogenase complex (PDH) – multi‑enzyme complex linking glyco… #
Related terms: PDH kinase, PDH phosphatase, NAD⁺. Low insulin and high NADH/acetyl‑CoA levels inhibit PDH, diverting pyruvate toward lactate or gluconeogenesis. Example: Keto‑adapted subjects show reduced PDH activity in skeletal muscle. Challenge: In certain mitochondrial disorders, PDH dysfunction necessitates careful carbohydrate management even on a ketogenic diet.
Pyruvate carboxylase (PC) – mitochondrial enzyme that carboxylates pyruva… #
Related terms: Biotin, gluconeogenesis, TCA cycle replenishment. PC activity supports OAA supply when glycolytic flux is low, sustaining TCA cycle function during ketosis. Practical application: Biotin supplementation can enhance PC activity in marginally deficient individuals. Challenge: PC deficiency leads to lactic acidosis, making strict ketogenic diets unsafe.
Raspberry ketone – phenolic compound structurally similar to β‑HB, market… #
Related terms: Phenylpropanoid, metabolic mimicry, dietary supplement. Although termed “ketone,” it does not raise circulating β‑HB and may interfere with true ketosis if consumed in large amounts. Example: Studies show no significant effect on blood β‑HB levels. Challenge: Unregulated supplements may contain adulterants, posing health risks.
Respiratory quotient (RQ) – ratio of CO₂ produced to O₂ consumed, reflect… #
Related terms: Indirect calorimetry, metabolic flexibility, fat oxidation. In ketosis, RQ typically falls to 0.7–0.75, Indicating predominant fat oxidation. Practical use: RQ measurement helps verify metabolic shift in clinical settings. Challenge: Acute exercise or stress can transiently raise RQ, confusing interpretation.
Riboflavin (Vitamin B2) – precursor for FAD and FMN cofactors required in… #
Related terms: Flavoproteins, energy metabolism, deficiency. Adequate riboflavin intake ensures optimal fatty‑acid oxidation and ketone production. Example: Riboflavin supplementation improves mitochondrial respiration in keto‑adapted rodents. Challenge: Deficiency is uncommon but can limit ketogenesis efficiency.
SCOT (Succinyl‑CoA #
3‑Oxoacid CoA‑transferase) – mitochondrial enzyme catalyzing the first step of ketolysis, transferring CoA from succinyl‑CoA to AcAc. Related terms: Ketone utilization, extra‑hepatic tissues, metabolic acidosis. SCOT deficiency results in accumulation of ketone bodies despite normal production, causing severe ketoacidosis. Practical note: Patients with SCOT deficiency require carbohydrate supplementation even on a ketogenic diet. Challenge: Rare genetic disorder; diagnosis relies on enzymatic assay.
Sirtuin 3 (SIRT3) – mitochondrial deacetylase regulating enzymes of β‑oxi… #
Related terms: NAD⁺‑dependent deacetylase, metabolic regulation, oxidative stress. Ketogenic diets increase NAD⁺/NADH ratio, activating SIRT3 and enhancing fatty‑acid oxidation efficiency. Example: SIRT3‑knockout mice show blunted ketone production under fasting. Challenge: Age‑related decline in SIRT3 may reduce ketogenic adaptability in older adults.
Succinyl‑CoA – TCA cycle intermediate generated from α‑ketoglutarate oxid… #
Related terms: SCOT, TCA cycle, anaplerosis. In ketolysis, succinyl‑CoA donates CoA to AcAc via SCOT, linking ketone oxidation to TCA cycle replenishment. Practical observation: Elevated succinyl‑CoA levels correlate with efficient ketone utilization. Challenge: Mitochondrial disorders that limit succinyl‑CoA formation impair ketolysis.
Thyroid hormone (T₃/T₄) – regulators of basal metabolic rate influencing… #
Related terms: Deiodinase, metabolic rate, thermogenesis. Mild hyperthyroidism can increase fatty‑acid oxidation, facilitating ketosis, whereas hypothyroidism may blunt ketone production. Example: Levothyroxine dose adjustments may be required for patients on a strict ketogenic diet. Challenge: Balancing thyroid function with diet to avoid excessive catabolism.
Triacylglycerol (TAG) – main form of stored fat composed of three fatty a… #
Related terms: Lipolysis, adipose tissue, VLDL. In ketogenic diets, TAG stores are mobilized to supply fatty acids for hepatic ketogenesis. Practical indicator: A 10‑15 % reduction in body fat over 8 weeks is common among compliant individuals. Challenge: Excessive TAG mobilization can lead to transient increases in free fatty acids, potentially causing nausea.
Urea cycle – hepatic pathway converting ammonia to urea for excretion #
Related terms: Carbamoyl phosphate synthetase I, ornithine transcarbamylase, nitrogen balance. High protein intake on ketogenic diets increases amino‑acid deamination, elevating urea cycle flux. Example: Urinary urea nitrogen rises proportionally with protein consumption. Challenge: Patients with urea cycle disorders must limit protein despite ketogenic goals.
Very‑low‑density lipoprotein (VLDL) – hepatic lipoprotein transporting en… #
Related terms: ApoB‑100, hepatic secretion, lipid profile. Ketogenic diets often lower VLDL secretion due to reduced hepatic lipogenesis. Practical outcome: Fasting triglycerides decline, improving cardiovascular risk markers. Challenge: In some individuals, high saturated fat intake may sustain VLDL levels, necessitating dietary refinement.
Warburg effect – preference of cancer cells for aerobic glycolysis over o… #
Related terms: Glycolysis, lactate production, metabolic reprogramming. Ketogenic diets aim to deprive tumor cells of glucose, potentially attenuating the Warburg effect. Example: Preclinical models of glioma show slowed growth under sustained ketosis. Challenge: Tumor heterogeneity means not all cancers respond; careful patient selection is essential.
White adipose tissue (WAT) – primary energy storage depot composed of adi… #
Related terms: Lipolysis, leptin, adipokines. Ketogenic diets stimulate WAT lipolysis via reduced insulin, releasing free fatty acids for hepatic ketogenesis. Practical observation: Leptin levels drop modestly, correlating with appetite suppression. Challenge: Excessive rapid fat loss can lead to ectopic fat deposition if not monitored.
Wolff‑Parkinson‑White (WPW) syndrome – cardiac conduction disorder that m… #
Related terms: Arrhythmia, potassium balance, diet. Ketogenic diets can alter serum potassium and magnesium, potentially affecting WPW symptomatology. Practical tip: Regular electrolyte monitoring is advised for individuals with known WPW on a ketogenic regimen. Challenge: Sudden electrolyte disturbances could precipitate arrhythmias.
Xanthine oxidase – enzyme involved in purine catabolism, generating uric… #
Related terms: Uric acid, oxidative stress, allopurinol. High purine intake (e.G., From certain protein sources) combined with ketosis can elevate uric acid, increasing gout risk. Example: Keto‑adapted patients with high red‑meat consumption may show serum uric acid >7 mg/dL. Challenge: Balancing protein sources to mitigate hyperuricemia.
Y‑box binding protein 1 (YB‑1) – transcription factor implicated in stres… #
Related terms: MRNA binding, cellular stress, metabolic adaptation. Emerging data suggest YB‑1 expression rises during prolonged ketosis, influencing lipid‑handling genes. Practical implication: YB‑1 may serve as a biomarker for long‑term ketogenic adaptation. Challenge: Research is preliminary; clinical relevance remains uncertain.
Zinc alpha‑2‑glycoprotein (ZAG) – adipokine associated with lipid mobiliz… #
Related terms: Lipolysis, adipose tissue, metabolic rate. Ketogenic diets increase circulating ZAG, correlating with enhanced fat oxidation. Example: Serum ZAG levels rose by 20 % after 6 weeks of low‑carb high‑fat feeding. Challenge: Inter‑individual variability limits its use as a universal predictor of weight‑loss success.