Last Updated on August 8, 2026 by Staff
The heart never gets a break. Every beat requires energy, and heart muscle cells must constantly turn nutrients into fuel to keep blood moving around the body.
Diabetes can disrupt this process long before a person notices anything unusual. Changes in how heart cells use and store nutrients may begin while the heart still appears to pump normally.
Scientists have spent decades studying glucose because high blood glucose sits at the center of diabetes. But another sugar may also deserve attention.
Fructose can build up inside the diabetic heart, and new research suggests that this rise may begin before doctors can detect clear changes in heart function.
Researchers at the University of Auckland in New Zealand investigated how heart tissue processes fructose and when the sugar begins to accumulate during diabetes.
Their results reveal an unusual metabolic pathway that separates fructose from glucose and may help scientists better understand the earliest stages of diabetic heart disease.
Diabetes alters heart metabolism
The heart uses several fuels to meet its constant energy demands. These include glucose, fatty acids, and other nutrients circulating through the blood.
Inside heart cells, those nutrients enter a network of chemical reactions that eventually help produce the energy required for contraction and relaxation.
Diabetes can disturb that balance.
Over time, abnormal fuel use may contribute to diabetic cardiomyopathy, a condition in which diabetes damages the heart muscle even when other major causes of heart disease are absent.
Researchers have already found that fat and glycogen, the stored form of glucose, can accumulate inside heart cells during early diabetes.
Those changes can appear before the heart shows obvious functional problems.
The new study suggests fructose may join that list.
Fructose also reaches hearts
Fructose occurs naturally in foods such as fruit, but it is also part of several sweeteners used in processed foods and drinks.
The body can also produce fructose through its own metabolic pathways.
Previous research has shown that fructose levels can rise during diabetes. Scientists have also linked greater fructose exposure with metabolic problems.
Yet researchers still lacked a clear picture of what heart muscle actually does when fructose reaches it.
Can the heart burn fructose for energy? Does it process fructose like glucose? And when diabetes develops, does fructose accumulate before or after the heart starts losing function?
The Auckland team designed experiments to address these questions.
Beating hearts reveal answers
The researchers first studied hearts taken from healthy mice.
They placed each heart in a system that allowed it to continue beating outside the body. This approach gave the team tight control over the nutrients supplied to the heart while allowing them to measure its performance.
The researchers initially reduced the available sugar supply. This created mild metabolic stress and allowed them to see whether adding fructose could help the heart.
Fructose did provide some support.
When the researchers added it, heart pumping pressure increased slightly. The hearts also relaxed more quickly between contractions.
However, glucose produced a stronger response.
The results showed that heart muscle can use fructose, but fructose does not appear to support cardiac performance as effectively as glucose.
Scientists track fructose carbon
The team then wanted to know what happened to fructose after heart cells absorbed it.
They supplied the hearts with a labeled form of fructose that allowed them to follow its carbon atoms through different metabolic reactions.
This technique gave the scientists a way to see which molecules formed as the heart processed the sugar.
The results revealed a major difference between fructose and glucose.
Fructose did not simply enter the same energy pathway and produce similar metabolic products.
Instead, much of it moved in another direction.
Fructose follows a detour
Heart cells normally break glucose down through several reactions that eventually produce pyruvate.
Pyruvate can then move into mitochondria, structures that generate much of the energy used by cells.
Fructose behaved differently.
About 32 percent of the fructose consumed by the hearts became glycerate. Another 22 percent became glyceraldehyde.
Only around 8 percent became pyruvate.
Even less fructose reached mitochondrial pathways in a form that could contribute directly to energy production.
The metabolic profile of the heart tissue reflected this difference.
Hearts given fructose contained more glycerate than hearts supplied with glucose. They also contained lower levels of lactate, pyruvate, and citrate, compounds closely connected with cellular energy metabolism.
One enzyme shapes processing
The researchers found another clue when they examined possible products of fructose metabolism.
They detected no conversion of fructose into glycerol.
Instead, the results pointed toward a metabolic route involving ketohexokinase, an enzyme that helps cells process fructose.
This pathway may explain why fructose provided less support for the beating heart than glucose.
The heart could consume fructose, but much of the sugar became other metabolic compounds instead of moving efficiently toward energy production.
The researchers next asked whether the same sugar behaves differently once diabetes develops.
Diabetes drives fructose higher
For this part of the research, the scientists studied male rats.
They induced diabetes using a compound that destroys insulin producing cells in the pancreas. This causes blood glucose to rise sharply and produces a condition that resembles type 1 diabetes.
The team then examined the animals’ hearts at different stages.
Cardiac fructose increased dramatically.
Four weeks after diabetes began, fructose levels inside the heart were around 11 times higher than normal.
By eight weeks, they had climbed to around 17 times normal levels.
The scale of the increase caught attention, but the timing proved especially important.
Fructose rises unusually early
Several other metabolic changes did not appear at the same time.
Sorbitol, another compound connected with sugar metabolism, increased later. Proteins involved in fructose transport and breakdown also showed increases later in the disease process.
Fructose itself rose first.
That sequence suggests that fructose accumulation may represent an early metabolic change in the diabetic heart instead of appearing only after substantial heart damage has developed.
Still, the timing cannot prove that fructose causes heart damage.
A biological change can appear before another event without causing it. Researchers will need additional experiments to determine whether fructose contributes directly to later cardiac problems.
Heart function remains normal
The scientists also examined how well the rats’ hearts worked.
They used echocardiography, an ultrasound method that allows researchers and doctors to measure heart structure, contraction, and relaxation.
After four weeks of diabetes, the animals already had much more fructose inside their hearts.
Yet their hearts continued to contract and relax normally.
This finding created a clear gap between the metabolic change and the appearance of measurable heart problems.
At this stage, fructose had already accumulated even though standard measurements of cardiac function showed no major decline.
Heart problems appear later
The situation changed by eight weeks.
At that point, the researchers detected significant problems with both systolic and diastolic function.
Systolic function describes the heart’s ability to contract and push blood forward. Diastolic function describes its ability to relax and fill with blood between beats.
Both had deteriorated.
The timeline therefore showed two distinct stages.
First, fructose accumulated inside the heart while cardiac function still looked normal.
Later, measurable problems with contraction and relaxation appeared.
This makes fructose an interesting candidate for further research into the early metabolic stages of diabetic heart disease.
The study has limits
The findings do not show that fructose directly damages the heart.
The experiments with beating mouse hearts lasted only 15 to 30 minutes. That is useful for watching metabolism in real time, but diabetic heart disease develops over much longer periods.
The animal diabetes experiments also included only male rats.
Researchers still need to determine whether female hearts show the same metabolic changes and whether similar fructose accumulation occurs in people with diabetes.
The team also measured relative changes rather than precise absolute fructose concentrations.
Without those absolute values, scientists cannot easily compare the amount of fructose inside diabetic hearts with the much larger amount of glucose present in the same tissue.
Glycerate raises new questions
One finding may offer another direction for future research.
A large share of the fructose used by heart tissue became glycerate.
Scientists have proposed that glycerate could contribute to chemical pathways connected with advanced glycation end products, commonly called AGEs.
AGEs form when sugars or related molecules react with proteins and other biological structures.
When these compounds accumulate, they can interfere with normal protein activity and contribute to tissue damage.
However, the current experiments cannot show whether fructose metabolism causes AGE formation in the heart.
The isolated heart experiments lasted far too little time for researchers to study processes that develop over much longer periods.
Early timing could matter
The study’s most notable finding may therefore be less about how much fructose accumulated and more about when it happened.
Fructose levels had already risen sharply while the heart still appeared to function normally.
Problems with contraction and relaxation emerged later.
That pattern gives scientists a new metabolic event to study during an important window in diabetes, after blood sugar becomes abnormal but before obvious heart dysfunction appears.
If future research shows that fructose contributes to cardiac injury rather than simply accompanying it, scientists may eventually find new ways to identify harmful metabolic changes earlier.
They may also discover whether targeting fructose production, transport, or metabolism could alter the progression of diabetic heart disease.
Those possibilities remain unproven.
Fructose changes the picture
Glucose remains one of the most important markers in diabetes, and controlling blood glucose remains central to disease management.
But diabetes changes much more than the concentration of one sugar in the bloodstream.
It can reshape the way individual organs process nutrients, store fuels, and produce energy.
This study shows that the heart can metabolize fructose, although it handles the sugar very differently from glucose. Large amounts of fructose become glycerate and glyceraldehyde, while relatively little reaches pathways linked directly with mitochondrial energy production.
During experimental diabetes, fructose also accumulates inside the heart well before measurable cardiac dysfunction develops.
Researchers now need to determine what that buildup means.
Fructose may simply mark metabolic disruption that is already underway. Or it may play a more active role in the chain of events that eventually weakens the diabetic heart.
Finding the answer could reveal more about a stage of heart disease that begins long before patients feel its effects.
The study was published in the Journal of Molecular and Cellular Cardiology.
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