The Randle Cycle (Randle Effect)

The Randle Cycle is a physiological mechanism, more accurately termed the Randle Effect, in which elevated free fatty acids in the bloodstream instantaneously block the ability of cells to oxidize glucose. 2 Peat repeatedly emphasized that it is not a true cycle but a substrate competition where the presence of fat inhibits pyruvate dehydrogenase, the enzyme needed to burn glucose, while simultaneously stimulating glucagon, which in turn releases more fatty acids. 2 This process was identified by P.J. Randle in the early 1960s and, according to Peat, essentially explained the biochemical basis of type 2 diabetes and insulin resistance decades ago. 5

The effect is not uniform across all types of fats. Peat argued that the polyunsaturated fatty acids (PUFAs) are the primary drivers of the pathological Randle Effect, systematically activating stress hormones like adrenalin, ACTH, cortisol, and glucagon, which create a vicious circle of energy failure. 2 In contrast, saturated fats do not trigger this cascade; Peat noted that saturated fats like stearic acid actually block the stress reaction, and coconut oil can increase oxidative metabolism by displacing the antimetabolic PUFAs. 3 While a very high sugar diet can increase circulating triglycerides through de novo lipogenesis, these endogenously synthesized fats are saturated or monounsaturated and lower the toxic effects of free radicals, protecting tissues rather than causing the damage associated with dietary PUFAs. 5

The consequences of the Randle Effect extend far beyond simple fuel partitioning. When glucose oxidation is inhibited, respiration decreases and mitochondria retain calcium, which can accumulate until it destroys the mitochondria, leading to excitation, proteolysis, and cell death. 2 This shift away from glucose metabolism results in the overproduction of lactic acid instead of carbon dioxide, a pro-inflammatory state that fails to produce sufficient energy for normal function. 2 Peat connected this mitochondrial damage and lactic acid production to a range of degenerative diseases, including diabetes, Alzheimer's disease, and arthritis. 2 Furthermore, the excitatory amino acid glutamate is increased by dietary fat, causing cells to take up calcium and remain in an excited, proliferative state, while increasing glucose oxidation has a protective, calming effect by facilitating the extrusion of excitatory calcium and the formation of carbon dioxide. 1

Dinkov has extended this framework by detailing how the Randle Cycle drives pathology through reactive oxygen species (ROS). He explains that shifting the metabolic substrate from glucose to fat via the Randle Cycle causes a block at Electron Transport Chain Complex II due to FAD co-factor depletion, leading to reverse electron flow. 9 This reverse flow, not normal oxidative metabolism, is responsible for 98-99% of ROS generation, which causes direct structural damage and is a key driver of cancer aggressiveness and metastases. 9 Peat similarly noted that the chronic effect of a high-PUFA diet produces advanced glycation end-products (AGEs) and that the cancer field is characterized by a gradient of abnormality stemming from excitatory, inflammatory consequences of lactate overproduction. 2 The effect is initially triggered by large fat meals but is increased by stress and builds up over time, as the body's stress response itself releases free fatty acids, further inhibiting the glucose oxidation needed to overcome the stress. 2