Endogenous fructose refers to fructose that your body creates internally, rather than consumes from food. Most people associate fructose with table sugar or high-fructose corn syrup, but your body can actually convert glucose—or other sugars—into fructose through a biochemical pathway known as the polyol pathway. This process happens deep within your cells, and it's often triggered in times of stress, dehydration, or excess nutrient intake, including salt, refined carbohydrates, or alcohol.

The key transformation goes like this: glucose → sorbitol → fructose. This is catalyzed by the enzymes aldose reductase and sorbitol dehydrogenase, and once fructose is formed, it's rapidly metabolized by fructokinase in the liver. This metabolism depletes cellular energy (ATP), increases uric acid, and promotes fat storage, all without requiring a single gram of sugar to be eaten.

Endogenous fructose is part of an evolutionary ""survival switch""—a mechanism that was once helpful during times of drought or famine, allowing the body to store fat, retain water, and reduce energy usage. However, in today’s environment, where we face chronic stress, processed food, and overnutrition, this same switch becomes a liability. It gets flipped too easily and too often.

Common triggers for endogenous fructose production include:
- High salt intake – elevates blood osmolality, stimulating the polyol pathway
- Alcohol – metabolized in a way that mimics fructose and can enhance its production
- Refined carbohydrates – elevate blood glucose, feeding into the pathway
- Dehydration – signals the body to conserve resources by activating this pathway
- Chronic stress – can raise cortisol and oxidative stress, indirectly triggering the switch

Even if your diet is sugar-free, these triggers can keep fructose metabolism active behind the scenes.

People often wonder why they still feel inflamed, tired, or metabolically stuck despite giving up sugar. The answer may lie in endogenous fructose. It's like having a hidden sugar faucet turned on inside your body—converting fuel into fat, creating uric acid, and stressing your mitochondria with each spin of the cycle.

Endogenous fructose has been linked to the pathogenesis of:
- Obesity
- Fatty liver (NAFLD & NASH)
- Type 2 diabetes
- Gout
- Hypertension
- Alzheimer’s disease
- Certain cancers

This makes it a key, yet often overlooked, contributor to metabolic dysfunction.

Since the internal production of fructose is a cellular response, not a dietary choice, it requires a cellular-level solution. That’s where the concept of modulating fructose metabolism comes into play.

Compounds like luteolin, a natural flavonoid, have been studied for their ability to reduce the activity of fructokinase, the enzyme that kicks off fructose breakdown. Additionally, tart cherry extract may help lower uric acid, one of the harmful byproducts of fructose metabolism. These two ingredients together support a system-wide defense against both dietary and endogenous fructose.

Understanding endogenous fructose changes the game. It means that avoiding sugar isn’t enough. If you want to address the root of stubborn metabolic issues, you have to look at the mechanisms inside your body, not just what’s on your plate.

Whether you're trying to lose weight, reduce inflammation, stabilize energy, or improve long-term metabolic health, addressing endogenous fructose may be one of the most powerful and underappreciated strategies available today.