Cori Cycle

The Cori cycle is a metabolic loop in which lactate, produced by tissues engaged in aerobic glycolysis, is transported to the liver and reconverted into glucose. 2 Peat framed this cycle not as a benign shuttle but as a pathological drain, noting that when lactate is carried to the liver, its conversion to glucose adds to the energy drain on the organism. 4 Dinkov has described the subjective experience of this cycle as a systemic "downing effect," where the constant interconversion of pyruvate and lactate creates a vicious cycle of inefficient energy production that leaves a person feeling heavy and lethargic. 2

The cycle is driven by a respiratory defect in which cells fail to oxidize glucose completely to carbon dioxide, even in the presence of oxygen. 1 Peat argued that the relevant therapeutic intervention is the prevention of lactate formation—or the stimulation of its oxidation—to prevent its entry into the Cori cycle for gluconeogenesis. 1 He identified thyroid hormone, magnesium, and progesterone as key factors that make respiration efficient, producing sufficient ATP to trigger the Pasteur effect and shut down glycolysis, thereby stopping the flow of substrate into the cycle. 1 The carbon dioxide produced by efficient oxidation is itself a crucial antagonist, as Peat explained the "lactate paradox" of high altitude by noting that retained CO2 takes care of the lactic acid, creating a greased pathway for electrons that prevents the reductive stress that forms lactate. 2

Peat treated the Cori cycle as a central mechanism of systemic degeneration because the lactate that fuels it is not merely a marker of stress but a direct contributor to tissue damage. 2 He documented that lactate increases blood viscosity, mimics stress, causes inflammation, and promotes the growth of new blood vessels, thereby supporting tumor expansion. 2 In the brain, lactate accumulation causes nerve cell loss by increasing the release of excitotoxic glutamate, and a panic reaction produced by sodium lactate reduces protective neurosteroids, making the brain more susceptible to damage. 3 Roddy has connected this to a hormonal cascade in which injected lactate increases prolactin, which in turn suppresses thyroid function, locking the organism into a self-reinforcing loop of stress and inefficient energy production. 11

The cycle also intersects with the Randle cycle, where the oxidation of fatty acids suppresses glucose oxidation, reducing CO2 and shunting pyruvate toward lactate. 2 Peat observed that cancer cells exploit this dynamic, turning glucose into lactate or fat and then oxidizing the fat, a process that does not produce as much carbon dioxide and leads the cell down a path of reduced function. 7 The healthy brain, in contrast, uses a localized version of this cycle adaptively; astrocytes can absorb lactate from excited neurons and convert it back to glucose via gluconeogenesis, storing it as glycogen during rest. 8 However, Peat warned that lactate revisionists who concentrate on this utility distract attention from the effects of increasing lactate in the systemic circulation on brain metabolism. 8