Fructose Impact on Glycation: Comparing Meat, Fruits, and Juices

# Meat, Fruits, and Fruit Juices: A New Study Reveals Fructose’s Impact on Protein Glycation

**by Laurent Glatz – for Athletic Carnivore**

Is eating only meat the same for our body as eating meat accompanied by fruits? And what happens if we replace whole fruits with fruit juices?

These questions are especially relevant today, as some so-called *animal-based* diets regularly combine red meat, eggs, fruits, and sometimes large amounts of honey or fruit juices.

A scientific study published on October 5, 2026, in the *American Journal of Clinical Nutrition* offers an intriguing answer.

Researchers from Maastricht University in the Netherlands demonstrated that a significant reduction in dietary fructose markedly decreased the blood concentration of a specific glycation product called glucoselysine.

In their intervention, this reduction reached about **20% within six weeks**.

This result does not prove that eating fruits with meat is harmful. However, it shows that dietary fructose can directly influence a biochemical process highly relevant to metabolic health: protein glycation.

This discovery helps clarify what distinguishes a strict carnivore diet from one that regularly includes fruits or fruit juices.

Glycation: When a Sugar Alters a Protein

Our bodies contain thousands of proteins essential for vital functions.

Some build muscles. Others transport substances in the blood, form tissues, enable cell communication, or participate in chemical reactions necessary for life.

To function properly, these proteins must maintain specific structural characteristics.

Sugars can spontaneously react with them.

This phenomenon is called **non-enzymatic glycation**.

Imagine a protein as a perfectly crafted lock. When a sugar molecule reacts with part of this protein, it’s like a small element altering the lock.

The protein doesn’t necessarily become unusable, but some modifications can change its properties.

Subsequent chemical reactions can transform initial glycation products into more complex compounds, notably advanced glycation end products, or AGEs.

Some AGEs are involved in tissue aging mechanisms, protein stiffening, or inflammatory signaling.

But beware: not all glycation-derived molecules have the same biological activity, and their mere presence doesn’t prove they cause disease.

What matters is understanding which molecule formed, from which sugar, and under what conditions.

Glucose Is Not the Only Sugar That Can Participate in Glycation

When we talk about glycation, we usually think of glycated hemoglobin, or HbA1c.

This test measures a particular modification of hemoglobin, mainly linked to glucose exposure.

It provides information about average blood sugar levels over the previous two to three months.

But glucose isn’t the only sugar that can react with proteins.

Fructose can also participate in these reactions.

It naturally occurs in fruits and honey. It is also part of sucrose, table sugar, which combines one glucose and one fructose unit per molecule.

Chemically, fructose is particularly interesting because it can react with certain protein functions via pathways different from glucose.

Under some experimental conditions, it can exhibit significant glycation reactivity.

However, this doesn’t automatically mean it causes more glycation in humans: local concentrations, metabolism speed, and tissue exposure must also be considered.

This is precisely why Maastricht researchers undertook their study—to better understand fructose’s effects in humans.

A Dutch Study Published on October 5, 2026

The research was conducted by Michelle A. J. van Oeteren, Nynke Simons, Marjo P. H. van de Waarenburg, Alfons J. H. M. Houben, Casper G. Schalkwijk, Martijn C. G. J. Brouwers, and Jean L. J. M. Scheijen.

These scientists work primarily at Maastricht University Medical Center and the Cardiovascular Research Institute Maastricht.

Their publication focuses on glucoselysine, a protein modification specifically linked to fructose.

The researchers first developed an analytical method to precisely measure this molecule in human serum.

They used a technique called ultra-performance liquid chromatography coupled with tandem mass spectrometry, or UPLC-MS/MS.

Simply put, this method allows detecting a particular molecule among all those present in the blood and measuring its concentration.

They then analyzed samples from two human studies.

The first compared 15 patients with hereditary fructose intolerance, who follow a fructose-restricted diet, to control subjects.

The second was a randomized, double-blind trial involving 35 overweight adults with excessive liver fat accumulation.

For six weeks, participants in the second study followed a fructose-restricted diet. One group received a glucose supplement, while the other received fructose.

This protocol allowed comparing two different fructose exposures in a controlled experimental setting.

The Result: Fructose Restriction Lowers Blood Glucoselysine

The first observation concerned people with hereditary fructose intolerance.

Their blood glucoselysine concentration was significantly lower than controls: 35.1 versus 45.8 nmol/L.

However, this was a group comparison and insufficient to establish direct causality.

The randomized trial provided more convincing evidence.

In the glucose-supplemented group on a low-fructose diet, total fructose intake was about 1.4 grams per day.

In the fructose-supplemented group, intake reached approximately 49.1 grams per day.

After six weeks, glucoselysine concentrations significantly decreased in the highly fructose-restricted group—from 38.8 to 31.2 nmol/L.

This represents an observed reduction of about **19.6%**.

Conversely, in the fructose-supplemented group, glucoselysine levels did not change significantly.

Researchers also found a statistically significant difference between the two groups’ changes.

**The key takeaway: a substantial reduction in dietary fructose can lead to a measurable decrease in a glycation product specifically linked to this sugar.**

But this research did not measure a 20% reduction in cardiovascular disease, aging, or tissue damage.

It measured a decrease in blood glucoselysine.

This distinction is crucial for correctly interpreting the results.

First Scenario: Eating Only Meat

Let’s consider someone following a strict carnivore diet.

Their diet consists of meat, fish, eggs, and possibly some animal fats.

Unprocessed meat naturally contains very little fructose.

A serving of beef, lamb, or game provides virtually no fructose, unlike fruits or sweetened products.

From a dietary exposure standpoint, a diet mainly composed of meat and animal fats naturally limits fructose intake.

This difference could have an interesting metabolic consequence.

Since the Maastricht study shows that dietary fructose quantity influences blood glucoselysine, it is biologically plausible that a carnivore diet very low in fructose limits this particular glycation source.

However, there is an important nuance.

**The human body can produce fructose from glucose itself.**

This occurs notably through a series of reactions called the polyol pathway.

Glucose can be converted into sorbitol, then into fructose by specific enzymes.

That’s why glucoselysine remains detectable even in people consuming very little fructose.

Eliminating dietary fructose does not necessarily remove all fructose-related glycation.

The study also does not provide glucoselysine concentrations in people following a carnivore diet for several years.

No carnivore group was directly studied.

The reasonable conclusion is: a strict carnivore diet greatly reduces dietary fructose exposure, which could limit glucoselysine formation, but does not guarantee its complete elimination.

Second Scenario: Eating Meat with Fruits

Now imagine a meal consisting of red meat and several fruits.

Meat provides proteins, lipids, and many nutrients.

Fruits provide water, fiber, micronutrients, and carbohydrates, including variable amounts of fructose, glucose, and sucrose.

Simply adding fruits changes the meal’s nutritional composition.

Unlike a strict carnivore diet, this meal supplies dietary fructose.

After digestion, sugars are absorbed, and a significant portion of fructose reaches the liver via the portal circulation.

Fructose can then enter various metabolic pathways.

Some is converted into glucose, lactate, or other metabolites. Another part may participate in reactions leading to glycation products.

This last aspect is precisely what the new study explores.

At the dietary level, **the higher the fructose exposure, the more relevant it becomes to consider its possible influence on glucoselysine formation**.

But beware of overinterpreting this observation.

Researchers did not compare meals of meat alone to meals combining meat and fruits.

They also did not study apples, oranges, bananas, or berries separately.

Therefore, it’s impossible from their results to determine how much additional glucoselysine forms after a specific fruit quantity.

The answer likely depends on total fructose intake, other foods consumed, and individual metabolic characteristics.

Moreover, a whole fruit is more than just its fructose content.

Its structure, water content, fiber, and other components influence digestion and the effects of consumption.

This explains why identifying a sugar in a food is insufficient to predict all its health effects.

The study thus provides an argument to consider fructose quantity but does not prove that adding fruits to meat necessarily causes metabolic harm.

Third Scenario: Eating Meat with Fruit Juices

The third scenario is particularly interesting.

Consider someone who regularly eats meat but accompanies meals with large glasses of fruit juice.

Compared to whole fruits, juices generally have a different food structure.

Pressing or extraction removes some fiber and alters the fruit’s natural matrix.

More importantly, it becomes easy to quickly consume the sugar from several fruits in liquid form.

A glass of juice can represent a sugar amount that would be consumed more slowly by eating whole fruits.

At usual volume or portion, the exposure difference depends on the fruit type, juice concentration, and actual quantity consumed.

This is important: juice is not chemically different because its fructose is more “aggressive.”

**The fructose molecule remains the same. What mainly changes are the quantities, food matrix, and consumption conditions.**

Biologically, a higher fructose intake could logically influence the reactions measured in the Maastricht study.

However, researchers did not directly compare whole fruits and fruit juices regarding glucoselysine formation.

It would be incorrect to attribute a specific demonstration about juices to them.

Other research, however, provides interesting data.

A 2019 meta-analysis of prospective cohorts published in *BMJ Open*, involving 154,289 participants, found an association between high fruit juice consumption and increased gout risk.

No statistically significant association was found for whole fruits.

Authors noted that data on fruits and juices remained limited and of low certainty.

Also, some studies grouped pure juices and fruit drinks, complicating interpretation.

These observations do not directly concern glucoselysine but illustrate an important principle: the form in which sugar is consumed can influence metabolic consequences and observed disease associations.

Why Fructose Also Interests Researchers Studying Gout

Fructose has another particularity.

In the liver, its metabolism by fructokinase rapidly consumes ATP, a molecule essential for cellular energy transfer.

With high intake, this consumption can temporarily promote degradation of adenine nucleotides, contributing to uric acid production.

Uric acid is the final product of purine metabolism in humans.

When its concentration remains chronically elevated, it can promote urate crystal formation responsible for gout.

There is thus a biologically plausible link between high fructose consumption, uric acid production, and gout risk.

However, two mechanisms must be distinguished.

Glucoselysine formation corresponds to a glycation reaction.

Possible uric acid increase results from fructose’s energy metabolism.

These phenomena may share a common origin but are not interchangeable.

The new Maastricht study did not show that glucoselysine causes gout.

Nor did it demonstrate that fructose elimination alone prevents gout attacks.

For someone on a carnivore diet, reducing fructose may represent a relevant metabolic difference without eliminating other factors affecting uric acid metabolism, including purines, kidney function, and energy status.

The Real Difference Between Strict Carnivore and Animal-Based Diets Enriched with Fruits

This publication ultimately offers a new way to compare two dietary models sometimes presented as very similar.

In a strict carnivore diet, dietary fructose intake is generally negligible.

Adding whole fruits increases this intake, in variable amounts depending on fruit types and quantities consumed.

Regularly adding fruit juices can increase exposure further, mainly because sugars are easier to consume quickly and in large amounts.

These three scenarios thus do not necessarily present the same dietary fructose exposure.

The October 2026 study shows that a significant reduction in fructose intake can significantly lower blood glucoselysine.

This is a concrete result worth integrating into our understanding of nutrition.

But it does not yet allow ranking these three diets by their actual ability to prevent metabolic, cardiovascular, or inflammatory diseases.

To establish such a hierarchy, trials directly comparing these dietary models, measuring glucoselysine, and tracking long-term clinical outcomes would be needed.

The presence or absence of fructose is a real biological difference. The exact medical significance of this difference remains to be determined.

What We Should Take Away from This Study

The value of this research is not in creating a new ideological divide between animal and plant foods.

It mainly shows that a specific dietary factor—fructose—can influence a measurable glycation product in human blood.

The Maastricht team observed about a 20% decrease in glucoselysine after six weeks of significant fructose restriction, while fructose supplementation prevented this decrease in the comparison group.

This demonstrates that fructose intake plays a role in this biochemical mechanism.

For Athletic Carnivore, this publication adds another argument to examine differences between an exclusively animal diet and one combining meat and fruits.

But the most interesting question is not just whether a food contains fructose.

It is understanding how much is consumed, how the body metabolizes it, and whether observed biochemical changes truly impact health.

A person can have perfectly normal blood sugar without this measurement directly reflecting their glucoselysine concentration.

This does not mean they have a hidden disease. It simply means biological markers measure different phenomena.

And this is where individual reflection becomes essential.

If your goal is to reduce dietary fructose exposure, the three models we examined do not necessarily offer the same conditions.

But if your goal is to improve a specific metabolic issue, fructose quantity is only one parameter among many.

Before adding or removing foods simply because a study identified a biological difference, it remains crucial to understand the real significance of that difference.

**Understand your nutritional terrain — [Athletic Carnivore](https://athleticcarnivore.fr)**

**What if the real challenge isn’t just whether you eat meat, but also what you add to that meat and how your body responds?**

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Scientific References

**1. van Oeteren M. A. J. et al. (2026).**

*Circulating levels of glucoselysine, a fructose-specific glycation product, are modulated by dietary fructose; post-hoc analysis of a case-control study and a randomized controlled trial.*

The American Journal of Clinical Nutrition, article 101571. Online publication: October 5, 2026.

DOI: https://doi.org/10.1016/j.ajcnut.2026.101571

PubMed: https://pubmed.ncbi.nlm.nih.gov/42833446/

**2. Ayoub-Charette S. et al. (2019).**

*Important food sources of fructose-containing sugars and incident gout: a systematic review and meta-analysis of prospective cohort studies.*

BMJ Open, 9, e024171.

DOI: https://doi.org/10.1136/bmjopen-2018-024171

**3. Jamnik J. et al. (2016).**

*Fructose intake and risk of gout and hyperuricemia: a systematic review and meta-analysis of prospective cohort studies.*

BMJ Open, 6, e013191.

DOI: https://doi.org/10.1136/bmjopen-2016-013191

**4. Semchyshyn H. M. (2017).**

*Formation of Fructose-Mediated Advanced Glycation End Products and Their Roles in Metabolic and Inflammatory Diseases.*

Nutrients, 9(2), 120.

DOI: https://doi.org/10.3390/nu9020120

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