# Fructose

Category: Foods & Substances

Also known as: fruit sugar

Fructose is a monosaccharide that Ray Peat identified as a uniquely protective sugar, primarily because it catalytically increases the overall metabolic rate of the organism, with experiments showing up to a 50% increase in whole-body metabolism. Unlike glucose from starch…

9 passages · 2 authors · 1997–2025 · Most-cited: [Ray Peat](https://bioenergeticoracle.com/md/voices/ray-peat/index.md)

Canonical page: https://bioenergeticoracle.com/concepts/fructose

## Synthesis

**Fructose** is a monosaccharide that Ray Peat identified as a uniquely protective sugar, primarily because it *catalytically increases the overall metabolic rate* of the organism, with experiments showing up to a 50% increase in whole-body metabolism. [Source 1] Unlike glucose from starch, fructose does not provoke a sharp insulin spike; instead, it is absorbed more slowly from the intestine, which buffers the rapid rise in blood glucose that triggers a cascade of insulin and cortisol. [Source 1, 3] Peat argued that fructose enters cells easily and is converted in a way that **promotes glycogen storage**, thereby steadying blood sugar over time and acting as an *anti-stress* and *anti-insulin* agent. [Source 5]

Mechanistically, Peat explained that fructose and the **pyruvic acid** it turns into stimulate the enzymes that oxidize pyruvic acid, an action indistinguishable from insulin’s effect on the same enzyme, allowing fructose to fulfill insulin’s role in the relative absence of the hormone. [Source 3] This means fructose accelerates the uptake of glucose by tissues including the brain, kidney, and heart, bypassing the need for insulin secretion and sparing the pancreas. [Source 3, 5] Furthermore, the high **potassium** content naturally accompanying fructose in fruit exerts its own insulin-like activity, helping cells absorb glucose without requiring insulin, which makes fruit a particularly safe sugar source for diabetics. [Source 4, 5] Peat also noted that fructose supports liver function by promoting **cholesterol production**, which, when thyroid function is adequate, provides the substrate for protective hormones like pregnenolone and progesterone. [Source 2]

Peat directly challenged the narrative that fructose causes fatty liver disease, attributing such findings to experimental designs that used diets high in **polyunsaturated fats** (typically 5% corn oil), excessive total calories, and sometimes magnesium-deficient chow, creating a setup biased to produce fatty acid poisoning of the liver rather than isolating a toxic effect of fructose itself. [Source 7, 9] He cited historical clinical evidence from 19th-century physicians who cured terminal diabetic patients by adding large amounts of sugar to a diet of milk, meat, and fruit, observing that the patients stopped wasting away, ceased excreting glucose in their urine, and rapidly rebuilt muscle. [Source 4] In wild monkeys, a diet high in fruit correlates with low cortisol, and human studies show that sucrose consumption lowers **ACTH**, the primary pituitary stress hormone, suggesting that the body perceives a need for sugar under stress. [Source 9]

Danny Roddy has defended Peat’s view against the "paleosphere" critique that fructose causes insulin resistance and gut permeability, countering that those who consume the most fructose, such as raw fruitarians, exhibit none of the alleged pathology in real life. [Source 6] Peat acknowledged that manufactured fructose can provoke allergic-type reactions in some people, but emphasized that fructose consumed in whole fruits is buffered by minerals and does not present this problem. [Source 4] He also noted that while many doctors claim the brain and heart cannot use fructose, evidence shows these tissues do possess the transporter for it, and that fructose enters glycolysis at nearly the same point as glucose to be oxidized for energy. [Source 8]

## People also ask

### How does fructose increase metabolic rate without spiking insulin?

Peat argued that fructose catalytically boosts whole-body metabolism by up to 50% while being absorbed slowly from the intestine, which avoids a sharp insulin and cortisol cascade. It also stimulates enzymes that oxidize pyruvic acid, mimicking insulin’s effect and allowing tissues to take up glucose without requiring much insulin.

### Why did Peat believe fruit sugar does not cause fatty liver disease?

Peat attributed fatty liver findings to experimental diets high in polyunsaturated fats, excess calories, and magnesium deficiency, which poison the liver rather than isolate fructose’s effect. He also cited historical cases where adding large amounts of sugar to a nutrient-dense diet reversed diabetic wasting and glucose excretion.

### Can the brain and heart actually use fructose for energy?

The corpus notes that despite common medical claims to the contrary, evidence shows the brain and heart possess the transporter for fructose, and fructose enters glycolysis at nearly the same point as glucose to be oxidized for energy.

## Related concepts

- [Orange juice](https://bioenergeticoracle.com/md/concepts/orange-juice/index.md)
- [Fish Oil](https://bioenergeticoracle.com/md/concepts/fish-oil/index.md)
- [Fruit](https://bioenergeticoracle.com/md/concepts/fruit/index.md)
- [Glucose](https://bioenergeticoracle.com/md/concepts/glucose/index.md)
- [Honey](https://bioenergeticoracle.com/md/concepts/honey/index.md)
- [Sugar (sucrose)](https://bioenergeticoracle.com/md/concepts/sugar-sucrose/index.md)

## Cited passages

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

### Source 1 — Sugar Myths Part 2

Ray Peat · Interview · 2011

> **Ray Peat:** Yeah, they referred to that as a catalytic property of fructose. It doesn't just increase the metabolism and uptake of glucose, but it increases the whole metabolism of the animal. In several types of experiments, they've seen a 50 % increase in the whole metabolic rate and that's basically why I am so interested in the effects of fructose, because the research I did at university had to do with aging and oxidative metabolism, and the perversion of oxidative energy production with aging and with various toxins (hormones and unsaturated fats and so on) and the thyroid hormone is what basically distinguishes humans from fungus and bacteria and such; the higher development of the brain goes, the more oxidative energy production is needed. And the development of a baby's brain prenatally is very closely tied to the amount of glucose it metabolizes. You restrict the glucose to the baby, and the brain is smaller; you feed it extra glucose and the brain is bigger.
>
> **Herb Doctor:** Sorry to interrupt you there Dr Peat but, for our listeners, just go over a little bit of sugar science here. Everybody's familiar with white sugar and that’s sucrose, which is half fructose, cause you’ve mentioned fructose now and also half glucose, and then all fruits contain approximately the same ratio of fructose and glucose as white sugar: that's half fructose, half glucose. And then other sources of carbohydrates like grains, beans, starches, any other carbohydrate-like food - bread, pasta, potatoes, root vegetables - they are almost all glucose, so they’re devoid of the fructose. That's easy to remember fructose because it sounds kind of like fruit.

### Source 2 — Your Own Health And Fitness: Nutrition And The Endocrine System

Ray Peat · Interview · Feb 11, 1997 · http://l-i-g-h-t.com/files/your-own-health-and-fitness-nutrition-and-the-endocrine-system.mp4

> **Ray Peat:** The fruit comes with many of the minerals which work in place of insulin and have a slightly suppressive effect on the insulin and the fruit has a strange side effect that it happens to promote cholesterol production and that's one of the reasons I emphasize having plenty of fruit sugar because the fructose while it doesn't cause obesity, it does help your liver to produce more cholesterol which is then available if your thyroid is functioning to turn into the protective hormones, pregnenolone and progesterone.

### Source 3 — Ray Peat: Sugar vs PUFA — The Truth About Diabetes, Fructose, and Metabolic Healing

Ray Peat · Interview · Jun 18, 2025 · https://www.youtube.com/watch?v=R2VrKacRr5Y

> **Sarah Murray:** And that's why it's a safer sugar for diabetics, fructose or white sugar or fruits.
>
> **Ray Peat:** Yeah, and so the glucose from the fructose gets absorbed and then the smaller amount of fructose coming in accelerates the absorption of the glucose by the various tissues, not just the liver, but brain, kidney, heart, everything. And so it's fulfilling some of insulin's responsibility without having to call on the insulin. But it actually, under some circumstances, can inhibit the release of insulin so that it prevents the spiking of insulin. takes care of insulin's work in relative absence of insulin.
>
> **Sarah Murray:** So because, again, to explain to our listeners, a diabetic's problem is that they have high sugar, a lot of sugar in their blood, and they need their cells to pick that up. And when the fructose is combined with the glucose, the fructose is actually helping the cells pick up the glucose as well as the fructose. Is that what you're explaining, Dr. Peat?
>
> **Ray Peat:** Yeah. stimulates the cells to take up glucose very much the way insulin does. And in fact, you can't distinguish the effects on some of the crucial enzymes that handle the absorption and use of glucose. Fructose and the pyruvic acid that it turns into stimulate the enzymes that oxidize pyruvic acid just the same way insulin stimulates that same enzyme. So one replaces the other perfectly.

### Source 4 — Ray Peat Interview with Tucker Goodrich, David Gornoski on PUFAs, Seed Oils, Benefits of Sugar, Milk

Ray Peat · Interview · Apr 8, 2022 · https://www.youtube.com/watch?v=PR5OqIPNZo0

> **Tucker Goodrich:** Right, and of course, for just that, it's advocated as a better sweetener for diabetics for a while.
>
> **Ray Peat:** Yeah, but it has to be, unless you extract it from... ripe Jerusalem artichokes, which take a lot of care in storage and so on. It's generally manufactured chemically. And so it turns out that quite a few people have an allergic type reaction to the manufactured form of fructose. But if you eat fruits, for example, You not only get the fructose component of the sucrose, but the high potassium content of the fruit has an insulin-like activity that also restrains your body's production of insulin. So the fruit goes in with a slightly insulin-moderating fructose content. and also the simultaneous leads of potassium which takes care of absorbing the glucose without needing to secrete insulin. And so it has these surprising ways of bypassing the insulin problem or what's related to diabetes. I ran across two 19th century doctors, one in Paris and one following up in England. The one in Paris was the first to observe that a high sugar diet cured his terminal diabetic patients, originally diabetes, because you couldn't assimilate glucose, you turned your protein of your tissues into glucose to survive. And so the diabetic wasted away, lost their muscles, and finally died in essentially a starvation condition. The doctor in France gave his terminal diabetic patients who were wasting away the amount of sugar they craved and found that they stopped wasting away and very quickly started building muscle when they were eating a regular diet, milk, beef, fruits and vegetables and so on, but along with a sugar supplement. So the doctor in England did exactly the same thing and described, of course, of people who were dying, wasting away, putting out tremendous amounts of sugar in their urine, even though they weren't eating any. They were restricted because they called diabetes the sugar disease. So they were torturing their patients by not letting them have any of the sugar that they craved.

### Source 5 — Dr. Ray Peat, Day Two: Full Interview from On the Back of a Tiger

Ray Peat · Interview · Feb 18, 2021 · https://www.youtube.com/watch?v=Z3yVUELD2ZA

> **Ray Peat:** The nutritionists in the 1970s started talking about the glycemic index in connection with the idea that sugar is the cause of diabetes and so on. And in looking, they were saying that it's good to eat foods that don't have such a high glycemic index on the idea that glycemia is what is harmful, causing diabetes. But the actual figures show that a pure starch is much more glycemic than a pure sucrose. Pure glucose and pure starch have the absolute perfection of raising your blood sugar. Sucrose is much lower, and when you test the components, the glucose half of the molecule It is just like starch, and the fructose part of the molecule can actually lower the insulin because it goes into your cells so easily and is converted. It promotes the production of glycogen when it's taken in ordinary physiological amounts. It raises your glycogen, helps to steady your blood sugar over time because the glycogen is available as soon as your blood sugar falls to oxidize. So the glycogen, the fructose part of the sucrose molecule that you find in most fruits is anti-stress, anti-insulin stimulating. and anti-obesity because it prefers to increase your glycogen stores and steady your blood sugar rather than stimulating insulin insulin stimulating fat synthesis as well as glycogen synthesis so it's a little steadier to have a sugar diet rather than a starch diet And besides, the fruits come with a high concentration of certain minerals, pretty much the balance of minerals that we have in our cells. a high potassium concentration, for example. You hear about bananas and orange juice as rich sources of potassium, but that's typical of any fruit or any cellular material. And so it's compatible with supplying the nutrients that we need. Potassium itself has an insulin-like action, helps the cells to take up and use carbohydrates, bypassing the need to secrete insulin so it's easy on the pancreas.

### Source 6 — Reader Comment Q&A — Reader Mail: Criticisms, Credibility & Dr. Ray Peat - Weblog - Nutrition For Hair & Health

Danny Roddy · Forum Q&A · Dec 22, 2011 · http://www.dannyroddy.com:80/main/2011/12/22/reader-mail-criticisms-credibility-dr-ray-peat.html

> **Ryan:** It is startling how much conflicting research there is on fructose. As far as my research has gone, fructose has great short term/small dosage benefits, but in the long-term/high dosage it is extremely detrimental. First off, in the short term fructose does not create a significant insulin response, at least not when compared to straight glucose. This has been shown to be beneficial for hypoglycemics. The problem is that over the long-term fructose causes insulin resistance. Glucose tends to create a large insulin spike initially but allows insulin to bring sugars back down fairly quickly. (Sometimes too quickly) Fructose is also much worse if you are already obese/overweight. Here are just a few studies showing fructose causing insulin resistance. There are quite a few more out there. [references] Fructose also fails to suppress your appetite causing you to eat more then you normally would. http://jcem.endojournals.org/content/89/6/2963.short And lastly, fructose causes the most gastrointestinal distress when compared to glucose and even sucrose. Fructose increases endotoxins in the blood by increasing gut permeability, which in turn causes some problems with the liver. So in my opinion I would think that eating refined carbohydrates (which Ray Peat himself says gets digested almost as quickly as the sugar he loves) is a better bet then fruit juice/sucrose. Root vegetables being preferable to cereal grains. Whole grains on the other hand I think are a scam/fad that needs to go away. The only issue with refined carbohydrate would be the lack of nutrition which needs to be made up for. (veggies) [references] I'm actually a big Ray Peat fan. His stuff on the thyroid and certain hormones is fascinating and intriguing. Unfortunately some of his other information is very dated and misleading.
>
> **Danny Roddy:** @Thanks for commenting Ryan, You did a good job encapsulating the paleosphere's view on fructose. I mean this in the most "unflip" way possible, but none of it is true. In REAL LIFE, as Cliff has stated, those who consume the most fructose (raw fruitarians) have none of the pathology you are describing.

### Source 7 — One Radio Network — Peat Ray (July 2021)

Ray Peat · Interview · Jul 19, 2021

> **Patrick Timpone:** Here's a question for you, Robert, in California. Why does or doesn't fructose from juice or fruit cause fatty liver since it can only exclusively be metabolized in the liver? Jason Fung and others seem concerned about damage from fructose.
>
> **Ray Peat:** Yeah. If you look at some of the, well, all of the high fructose liver damage studies I've seen, contained 5% corn oil, an excessive amount of polyunsaturated fats, and then a total caloric excess, meaning that you're going to store a high proportion of the excess of fatty acids in the diet. So the setup is biased to create fatty acid poisoning of your liver essentially from an excess of calories and where they're using it to supposedly to incriminate the sugars having a toxic effect on the liver. But even worse than that, some of these studies used a particular stock animal food diet that was deficient in magnesium for doing their studies with fructose. I haven't seen the explanation how they explained it away, but it was formulated with less magnesium than normal, making it an especially liver-toxic, PUFA-rich diet. So basically, I think it's a setup to sell fatty acids and incriminate the use of sugar in causing heart disease and liver disease and so on.

### Source 8 — One Radio Network: Health & Diet

Ray Peat · Interview · Dec 4, 2013 · http://l-i-g-h-t.com/files/one-radio-network-patrick-timpone-dr-peat-answers-questions-regarding-health-diet-and-nutrition-part-1.mp4

> **Ray Peat:** the body can exchange them. The Fructose enters the glycolysis process almost the same place as glucose, and is oxidized almost the same way that glucose is. And a lot of Doctors are saying that the brain and muscle and heart and scuh can’t use Fructose, but there is evidence to say that they do have the transporter so that the brain and heart can use fructose. Ketones are good if you get them fom fruit and vegetables, but if you have to produce Ketones, they are only produced under stress in the body, so they are good if you can get them but hard to make them yourself.
>
> **Caller:** Why does the Budwig diet against cancer have so much use when they use Omega 3 oils, when Ray Peat has concluded the PUFAs are not good for us?

### Source 9 — Glucose and sucrose for diabetes.

Ray Peat · Article · 2012 · https://raypeat.com/articles/articles/sugar-issues.shtml

> Much of the current concern about the dangers of fructose is focussed on the cornstarch-derived high fructose corn syrup, HFCS. Many studies assume that its composition is nearly all fructose and glucose. However, Wahjudi, et al. (2010) analyzed samples of it before and after hydrolyzing it in acid, to break down other carbohydrates present in it. They found that the carbohydrate content was several times higher than the listed values. "The underestimation of carbohydrate content in beverages may be a contributing factor in the development of obesity in children," and it's especially interesting that so much of it is present in the form of starch-like materials.
>
> Many people are claiming that fructose consumption has increased greatly in the last 30 or 40 years, and that this is responsible for the epidemic of obesity and diabetes. According to the USDA Economic Research Service, the 2007 calorie consumption as flour and cereal products increased 3% from 1970, while added sugar calories decreased 1%. Calories from meats, eggs, and nuts decreased 4%, from dairy foods decreased 3%, and calories from added fats increased 7%. The percentage of calories from fruits and vegetables stayed the same. The average person consumed 603 calories per day more in 2007 than in 1970. If changes in the national diet are responsible for the increase of obesity, diabetes, and the diseases associated with them, then it would seem that the increased consumption of fat and starch is responsible, and that would be consistent with the known effects of starches and polyunsaturated fats.
>
> In monkeys living in the wild, when their diet is mainly fruit, their cortisol is low, and it rises when they eat a diet with less sugar (Behie, et al., 2010). Sucrose consumption lowers ACTH, the main pituitary stress hormone (Klement, et al., 2009; Ulrich-Lai, et al., 2007), and stress promotes increased sugar and fat consumption (Pecoraro, et al., 2004). If animals' adrenal glands are removed, so that they lack the adrenal steroids, they choose to consume more sucrose (Laugero, et al., 2001). Stress seems to be perceived as a need for sugar. In the absence of sucrose, satisfying this need with starch and fat is more likely to lead to obesity.

_Generated 2026-07-20 from the Bioenergetic Oracle corpus._