# The Randle Cycle (Randle Effect)

Category: Metabolism

Also known as: The Randle Cycle, the randle cycle, randle effect, Randle Effect

The inhibition of the oxidation of glucose by an excess of fatty acids. This lowers metabolic efficiency. Estrogen promotes this effect.

9 passages · 2 authors · 2008–2025 · Most-cited: [Ray Peat](https://bioenergeticoracle.com/md/voices/ray-peat/index.md)

Canonical page: https://bioenergeticoracle.com/concepts/the-randle-cycle-randle-effect

## Synthesis

**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. [Source 2, 3] 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. [Source 6, 8] 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. [Source 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. [Source 6, 8] 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. [Source 6, 7, 8] 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. [Source 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. [Source 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. [Source 2, 8] Peat connected this mitochondrial damage and lactic acid production to a range of degenerative diseases, including diabetes, Alzheimer's disease, and arthritis. [Source 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. [Source 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. [Source 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. [Source 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. [Source 1, 3] 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. [Source 4, 6]

## People also ask

### How does the Randle Effect block glucose oxidation at the enzyme level?

Peat described it as a substrate competition where elevated free fatty acids inhibit pyruvate dehydrogenase, the enzyme required to burn glucose, while simultaneously stimulating glucagon to release more fatty acids.

### Why did Peat consider saturated fats safer than polyunsaturated fats in this context?

Peat argued that polyunsaturated fats drive the pathological Randle Effect by activating stress hormones, whereas saturated fats like stearic acid block that stress reaction and coconut oil can displace the damaging PUFAs.

### What role does reverse electron flow play in the damage caused by the Randle Cycle?

Dinkov explained that shifting metabolism from glucose to fat causes a block at Complex II, leading to reverse electron flow that generates the vast majority of reactive oxygen species, driving cancer aggressiveness and structural damage.

## Related concepts

- [Free fatty acid theory of insulin resistance](https://bioenergeticoracle.com/md/concepts/free-fatty-acid-theory-of-insulin-resistance/index.md)
- [Glycation](https://bioenergeticoracle.com/md/concepts/glycation/index.md)
- [Amyloid](https://bioenergeticoracle.com/md/concepts/amyloid/index.md)
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## Cited passages

Passage numbers match the `[Source N]` markers in the synthesis above.

### Source 1 — Carcinogenic Metabolism

Ray Peat · Newsletter · 2022

> Dietary fat, like free fatty acids from lipolysis, increases glutamate and lowers the oxidation of glucose (the “Randle cycle”). The excitatory amino acids, including glutamate, cause cells to take up calcium; if the calcium is retained, the cell stays in an excited state. Increasing glucose has been found to protect against glutamate excitatory damage, by increasing the cells’ ability to extrude the excitatory calcium (Nakashima, et al., 1996).
>
> This is probably another example of the Randle cycle, allowing cells to reduce fatty acid oxidation by increasing glucose oxidation, resulting in the formation of carbon dioxide and carbonic acid, which takes calcium along as it streams out of the cell. The oxidation of glucose to carbon dioxide has stabilizing effects on cells, favoring the anti-excitatory effects of GABA, and reducing the action of glutamate; CO2’s effects are generally calming. The excitatory effects of glutamate and the increased intracellular calcium generally stimulate proliferation of cells. Estrogen’s excitatory effects support those processes. The inhibitory transmitter, GABA formed by decarboxylating glutamate, tends to reduce excitation and (in many cases) proliferation, and is supported by the calming effects of progesterone.
>
> Close observation of the development of cancer of the intestine revealed that the appearance of a small area of cancer was surrounded by a larger area, in which the cells nearest the cancer center were precancerous, with a gradient of abnormality starting with merely inflamed cells at the periphery, increasing in abnormality (including mutated genes) according to their closeness to the cancer center. This has been described as the cancer field, suggesting that something emitted from a centre of inflammation has led to changes in adjoining cells. The idea of random mutations as the source of cancer simply can’t explain this concentric gradient.
>
> The idea of random mutations has been progressively discarded over the last several decades, with good experimental reason (Monroe, et al., 2022). The reductionists’ adopting of the doctrine of randomness to explain radioactive nuclear decay and genetic mutations is a natural consequence of a narrow focus on local causal interactions—“what is there besides atoms?” Any patterns that may be visible in larger contexts will be automatically excluded. When it affects medical theories and treatments, the assumption of randomness leads certainly to dead ends.

### Source 2 — Energy Structure and Carbon Dioxide A Realistic View of the Organism

Ray Peat · Newsletter · 2013

> The old idea of randomly arranged material, being ordered by the accumulation of random changes, was an idea that derived from the old concept of a watchmaker god inserting order into formless matter. In this more realistic perspective, the significant issue is what happens when disorder is introduced into the ordered cellular system. The introduction of disorder is a stimulus, a challenge to respond and to adapt. Excitation and assimilation, or excitotoxicity and degeneration, are two kinds of response to the introduction of disorder. Although the creation of order is a spontaneous tendency of the molecules, the introduction of disorder causes energetic changes that lead to the creation of a new order. The achievement of a new order builds on the old, emerges from the old, but contains the old order implicitly. The implicit presence of old structures accounts for the phenomena of memory, imprinting, transgenerational influences, and the recapitulation of phylogeny in development.
>
> In the Randle effect (it's called the Randle cycle, but there is no cycle), increasing the amount of fat in the bloodstream decreases the ability of cells to metabolize glucose; glucose tolerance decreases, as in diabetes, except that the response to fat is instantaneous.
>
> Respiration decreases, mitochondria retain calcium, which tends to accumulate until it destroys the mitochondria. The calcium, when it is released from the mitochondria, causes excitation to increase. Stimulation without efficient energy production leads to proteolysis and apoptosis or other forms of cell death. Sugars replace carbon dioxide and acetate on lysines.
>
> This process is involved in diabetes, Alzheimer's disease, arthritis, and other degenerative diseases, probably including osteoporosis. Mitochondrial damage tends to increase the production of lactic acid instead of carbon dioxide, and lactic acid can stimulate the inappropriate overgrowth of blood vessels, as occurs in the eyes in diabetes. During stress and aging, free fatty acids appear in the bloodstream in large quantities.
>
> Besides their chemical effects, which lead indirectly to chronic disruption of signalling systems, the unsaturated fats have direct and immediate effects on regulatory processes, water uptake, intercellular communication, and excitation. Cell proteins have an affinity for fats, and their hydrophobic surfaces tend to adsorb them. Unsaturated fats have a greater affinity for water than saturated fats do, and the location of the unsaturated bonds along the fat's carbon chain will affect the ways proteins interact with water.

### Source 3 — Ask the Herb Doctor: Sugar I

Ray Peat · Interview · Sep 17, 2010 · https://www.youtube.com/watch?v=pgnzAR_a2MI

> ## Diabetes, The Randle Effect, and Polyunsaturated Fats
>
> **Andrew Murray:** What is the deal with the link between diabetes and sugar?
>
> **Ray Peat:** The principle in physiology that explains it was proposed a few decades ago called the Randle effect or the Randle cycle. It refers to the fact that free fatty acids block the use of glucose by cells. This was demonstrated in hospitals when giving nutritional support to patients in the form of a soy oil emulsion. About 15 minutes after injecting this emulsified soy oil, people would get hyperglycemic. When the fatty acids involved in blocking the sugar are *polyunsaturated*, they produce long-range damage. A group led by Fu demonstrated that the glycated proteins seen in diabetic people—which are usually blamed on glucose—are actually caused more powerfully by polyunsaturated fatty acids. Spontaneously oxidized polyunsaturated fats stick to the proteins. So, the free fatty acids not only block sugar use instantaneously (Randle effect), but they produce these advanced glycation end-products (AGEs) associated with diabetes and aging. The chronic effect of a high-fat diet, if the fat is predominantly unsaturated, produces diabetes and all the things that result from glycated proteins.

### Source 4 — Diet (general)

Ray Peat · Email · 2015

> ## Thread 14
>
> **Question:** [Amount of fat eaten per meal to activate the randle cycle, even if it's saturated]
>
> **Ray Peat:** It's mostly from large fat meals, at first, but then it is increased by stress, and builds up over time.

### Source 5 — Cholesterol Is an Important Molecule KMUD 2008

Ray Peat · Interview · 2008

> **Herb Doctor:** Diabetes seems to be exploding. Can you talk a bit about diabetes? What can be done to treat it, and why is it such a prevalent diagnosis today?
>
> **Ray Peat:** The diet of Americans and Europeans has changed over these years in which diabetes has been increasing, with the greatly increased consumption of polyunsaturated vegetable oils. Even eggs now, they feed chickens so much corn and soy that even eggs have less cholesterol and more polyunsaturated fats. In 1963 or '64, a researcher named P.J. Randle observed that he could block the oxidation of glucose just by feeding an increased amount of the fatty acids. And that's now called the Randle cycle. When it became popular to feed hospitalized patients intravenously with a fat emulsion to try to keep them from losing weight, they very quickly discovered that it suppressed their immune system and caused a variety of other symptoms. But it almost immediately would cause an elevation of blood glucose. And that was exactly what P.J. Randle had noticed in his animal studies. So, diabetes was basically explained biochemically in the 1960’s, when if you eat more fat, you block the response to insulin, create insulin insensitivity or resistance. And that's now called type 2 diabetes, or syndrome X.

### Source 6 — Energy Production Diabetes Saturated Fats KMUD 2011

Ray Peat · Interview · 2011 · http://www.l-i-g-h-t.com/files/herb-doctors-energy-production,-diabetes-and-saturated-fats.mp4

> **Ray Peat:** Some people call it the Randle cycle, but there is no cycle involved; it's just a competition. When you raise your free fatty acids, you inhibit the ability to oxidize glucose. Stress increases the free fatty acids. Oxidizing glucose is what you need to overcome the stress. And so, it's sort of a counterproductive reaction. But the reason it’s counterproductive is that our systems are designed not to eat PUFA. And it's the PUFA which very systematically - it's just an amazing black-and-white almost difference- the way the PUFA turn on the very stress hormones that interfere with the energy, making it the body need more stress hormones, blocking the energy. So that if we eat more [PUFA], we are turning on the very things that cause the problem.
>
> **Herb Doctor:** Why does the body want to do that?
>
> **Ray Peat:** The body is designed, apparently from how completely systematic it is, to respond to saturated fat. Saturated fats block the stress reaction. So the properly functioning body would be logical: the stress reaction would provide energy in the absence of food, would provide the saturated fats from the storage, and at the same time it would inhibit the stress hormones and allow the cycle to be broken.

### Source 7 — Ray Peat Email Advice Depository — Post 253

Ray Peat · Email · Aug 10, 2016

> ## Thread 4
>
> **Question:** [Coconut Oil and the Randle Cycle] It's known that in the 1940s Bernardo Houssay found that coconut oil protected animals from poison-induced diabetes and in 1963 Randle described the inhibition of glucose oxidation by free fatty acids. I'm trying to reconcile the above two facts; is coconut oil exempt from becoming free fatty acids and competing with glucose in the randle cycle?
>
> **Ray Peat:** Relative to PUFA, yes. When the body contains a lot of PUFA, eating coconut oil increases oxidative metabolism, partly because of the shorter fatty acids that are more quickly oxidized, like sugar, and partly because of the antimetabolic effects of the PUFA that they displace. More recently, several investigators have found that a “deficiency of essential fatty acids” is highly protective against diabetes.

### Source 8 — Energy Production Diabetes Saturated Fats KMUD 2011

Ray Peat · Interview · 2011 · http://www.l-i-g-h-t.com/files/herb-doctors-energy-production,-diabetes-and-saturated-fats.mp4

> **Herb Doctor:** Which poisons you again, right?
>
> **Ray Peat:** Yah. The lactic acid is pro-inflammatory and doesn't produce enough energy for normal function. And the essence of diabetes was pointed out by Randle in 1963 or 1964 when he observed that if you increase the free fatty acids in the blood, you very quickly make the cells unable to use glucose.
>
> **Herb Doctor:** Did it shift their metabolism from glucose directly or?
>
> **Ray Peat:** Yah. It's now been worked out that, there are two very clear points where the free fatty acids inhibit the use of glucose: pyruvate dehydrogenase (that's the one you need to burn glucose), and then they stimulate glucagon which happens to turn on the synthesis of glucose at the expense of protein.
>
> **Herb Doctor:** Ok, they stimulate glucagon.
>
> **Ray Peat:** Yea. And glucagon, then, in turn, stimulates the release of more fatty acids. There are several points where the free fatty acids activate, for example, adrenalin, ACTH, cortisone, thyrotropic hormone (TSH) and glucagon. All of which increase the release of free fatty acids from your fat cell storage. That seems very illogical of the body to create vicious circles in which once you start having an energy failure, you turn on exactly what caused it. But it turns out that it's only the polyunsaturated fatty acids that have those terrible anti-energy effects, if you look at a comparison of stearic and linoleic acid, for example.

### Source 9 — Reactive oxygen species, derived mostly from fat oxidation, drive cancer growth/metastases

Georgi Dinkov · Article · May 17, 2025 · https://haidut.me/?p=2795

> In several of the interviews with Dr. Mercola, we touched upon the role of reactive oxygen species (ROS) in health and diseases in the context of the metabolic theory. Most doctors hold the opinion that generating massive amounts of ROS is a normal “price” to pay for high oxidative metabolism, and the higher the metabolic rate the more ROS are generated. This is one of the core arguments in favor of the so-called “rate of living theory”, which says simply that the higher the metabolism, the shorter the lifespan of an organism will be. However, unbeknownst even to most doctors, 98%-99% of ROS are generated not during normal oxidative metabolism (forward electron flow), but during so-called reverse electron flow. The latter happens whenever there is a functional or physical block at one or more of the electron transport chain (ETC) complexes, which leads to build up of electrons and thus reverse flow, which results in ROS being formed when the unpaired electrons react with molecular oxygen. Not only does reverse flow result in a dramatic shift of the redox status towards reduction, but the build-up of ROS leads to direct structural damage to various cell proteins, as well as any intracellular structure containing polyunsaturated lipids. As such, the role of ROS in many chronic conditions has already been recognized and strategies for ROS mitigation have been proposed as prevention/treatment of many diseases. What has not been widely acknowledged is that in the absence of exogenous agents capable of blocking or more of the ETC complexes (e.g rotenone, metformin, etc), reverse electron flow happens quite easily and is in fact responsible for the majority of ROS production simply as a result of shifting the metabolic substrate from glucose to fat (Randle Cycle). Namely, if the Randle Cycle (RC) shifts sufficiently in favor of fat oxidation, that results in depletion of the FAD co-factor, and thus a block at ETC Complex II. In other words, all that is needed for massive generation of ROS is to switch from oxidizing primarily glucose to oxidizing primarily fat. That sounds shocking and counter-intuitive, considering the world (and medicine) has gone crazy over low-carb diets lately, but it is well-known and undisputed biochemical fact.

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