The real problem: insulin, not fructan
Over the last two decades, our understanding of laminitis has changed significantly. The question does fructan cause laminitis in horses is still asked because the majority of cases seen in everyday practice are now recognised as endocrinopathic laminitis.
This is a form of the disease driven by hormonal dysfunction, specifically hyperinsulinemia (chronically elevated insulin levels) [1].
This shift in understanding is crucial because it changes how we should think about horse diets and the question ‘Does fructan cause laminitis?’.
Laminitis in these horses is not caused simply by “too much carbohydrate” in a general sense. Instead, it is triggered by excessive insulin responses following the consumption of certain types of carbohydrate.
When blood insulin rises to abnormal levels, it can directly disrupt the structures within the hoof, leading to laminitis.
This means that the central dietary question is not whether a forage contains carbohydrate, but whether it contains carbohydrates that raise insulin.
Once that distinction is made, the role of fructan becomes much clearer and much less concerning.
Does fructan cause laminitis? Quick answer
No. Fructan does not cause laminitis in the way it is commonly claimed.
Fructan produces little to no insulin response compared to sugars and starch in most feeding scenarios., which is the primary driver of endocrinopathic laminitis. The carbohydrate fractions that matter are simple sugars (ESC) and starch, not fructan.
What fructan actually is in grass and hay
Fructan is a naturally occurring carbohydrate found in many temperate grasses eaten by horses.
It functions as a storage molecule, allowing plants to retain energy in a form that can be mobilised when needed, particularly during periods of growth or environmental stress [2].
Chemically, fructan is made up of chains of fructose molecules linked together into polymers. These chains can vary in length and structure depending on the plant species and growing conditions.
This variability is important because it means that “fructan” is not a single uniform substance, but a broad category of related compounds.
Although fructan is often grouped under “sugars” in forage reports, this is chemically misleading. Fructan is a polysaccharide, meaning it is a chain of fructose molecules, not a simple sugar. In this respect, it is no more a “sugar” than starch or even cellulose (fibre).
This distinction matters because polysaccharides differ significantly in how they are digested and how they affect metabolism.
Unlike simple sugars, fructan is not enzymatically broken down in the small intestine and does not contribute to blood glucose or insulin responses.
In forage analysis, fructan is not measured as a standalone value in most standard tests. Instead, it is typically included within water-soluble carbohydrates (WSC). This category also includes simple sugars such as glucose, fructose, and sucrose.
At first glance, this grouping appears logical; all of these carbohydrates dissolve in water. However, from a nutritional and metabolic perspective, this grouping is misleading and can lead to incorrect feeding decisions.
It encourages the assumption that all “sugars” behave in the same way in the horse’s body. They do not.
Why fructan does not directly spike insulin
To understand why fructan is not a driver of laminitis, it is essential to understand how horses digest different types of carbohydrate.
When a horse consumes forage, digestion begins in the small intestine. This is where hydrolysable carbohydrates, primarily simple sugars and starch are broken down by enzymes and absorbed into the bloodstream as glucose. This process leads to a rise in blood glucose, followed by a rise in insulin.
Fructan does not follow this pathway.
Unlike simple sugars and starch, fructan cannot be broken down by the horse’s own digestive enzymes in the small intestine. Instead, it passes through to the hindgut, where it is fermented by microbes in a process similar to the digestion of fibre.
This difference in digestive pathway has a critical consequence:
“Fructan does not produce the rapid rise in blood glucose or the hyperinsulinemic response associated with endocrinopathic laminitis”
This is not just theoretical. It has been demonstrated experimentally.
In a controlled study, ponies were fed different carbohydrate sources, including glucose, fructose, and inulin (a type of fructan). Glucose and fructose produced clear increases in blood glucose and insulin. In contrast, inulin resulted in minimal changes in both [3].
A separate study examining the effects of fructooligosaccharides and inulin supplementation found no increase in post-prandial insulin or glucose responses when compared to control feeding [4].
Taken together, these findings support a simple conclusion: Fructan does not behave like a carbohydrate that drives insulin.
What carbohydrates actually matter for laminitis
If fructan is not responsible for insulin spikes, then attention must shift to the carbohydrates that are.
These are the carbohydrates that are:
- digested in the small intestine
- absorbed as glucose
- directly stimulate insulin release
In practical terms, this means:
simple sugars (measured as ESC) and starch
These are often grouped together as hydrolysable carbohydrates (HC), because they are hydrolysed (broken down) and absorbed before reaching the hindgut.
This framework is central to the recommendations of Dr. Eleanor Kellon and the ECIR Group, who focus specifically on ESC + starch when assessing forage suitability for hyperinsulinemic horses [5].
This is not an arbitrary preference. It is a direct reflection of equine physiology. If insulin is the problem, then the diet must be evaluated based on the nutrients that influence insulin. Fructan is not one of them.
How fructan became linked to laminitis
Given the evidence, it is reasonable to ask why fructan has been so strongly associated with laminitis in horses and ponies for so long.
The answer lies in the history of laminitis research.
In order to study laminitis, researchers needed a reliable way to induce the condition under controlled conditions. One method that proved effective was the administration of large quantities of purified fructan (oligofructose) directly into the horse’s stomach.
Important Context
These doses were extremely high. In many cases, they ranged from 7.5 to 12.5 grams per kilogram of body weight. For a 500 kg horse, this equates to several kilograms (3.5 – 5kg) of fructan delivered in a single bolus [6].
This protocol consistently induced laminitis, making it useful as an experimental model. However, this is where the misunderstanding began.
Why the hindgut overload model has been misapplied
The fructan overload model was never intended to represent normal feeding conditions. Its purpose was to create a pathological state, not to mimic everyday grazing or hay consumption.
There are several fundamental differences between this model and real-world horse feeding.
In experimental settings, fructan is administered as a large, rapid bolus of purified compound. In contrast, horses consuming pasture or hay ingest carbohydrates gradually over time, within a complex plant matrix that includes fibre, water, and other nutrients.
The sheer scale of the difference is difficult to overstate. Delivering several kilograms of purified fructan in one dose bears little resemblance to natural intake patterns when horses and ponies are grazing.
Importantly, the mechanism by which laminitis is induced in these studies is not related to insulin. Instead, it involves rapid fermentation in the hindgut, leading to a drop in pH, disruption of microbial populations, and downstream inflammatory effects.
Even within the scientific literature, this model is described as representing a disease pathway, not a direct analogue of pasture-associated laminitis [7].
Despite this, the association between fructan and laminitis became widely accepted, often without recognising the limitations of the model and putting it into a real world horse environment context.
Why is fructan still blamed for laminitis?
If the science is clear that fructan does not spike insulin, it is reasonable to ask why it is still so widely associated with laminitis. The answer lies in how feeding advice develops over time.
Much of the concern around fructan comes from earlier research and how those findings were interpreted in practical horse feeding recommendations. Once a concept becomes widely accepted, it is often repeated for many years, even as scientific understanding evolves.
This is not unique to fructan. The same pattern has been seen in other areas of equine nutrition, including the historical inclusion of iron in feeds and long-duration hay soaking practices.
In all of these cases, advice was originally based on the best available evidence, but has gradually been refined as more horse feeding data became available.
It is also important to recognise the human element in this process. When a particular approach has been widely taught, followed, and trusted over many years, it can be inherently difficult to change that perspective.
This is especially true for those who have given advice based on earlier understanding, where updating that position may involve revisiting long-held beliefs and previously shared guidance.
In practice, this can create a strong resistance to change, as equestrian individuals naturally seek to protect and maintain confidence in their knowledge and professional judgement. This is entirely understandable.
However, it also means that updates in equine scientific understanding are not always reflected immediately in real-world horse advice, even when the underlying evidence has evolved.
Understanding this process helps explain why fructan is still often treated as a risk factor, even though established current evidence shows that the primary dietary drivers of laminitis in metabolic horses are simple sugars (ESC) and starch, not fructan.
The key distinction most people miss
One of the most important developments in equine science has been the recognition that laminitis is not a single disease with a single cause.
There are different forms of laminitis, with different underlying mechanisms.
The hindgut overload model represents one pathway, associated with extreme dietary disruption and inflammatory processes. However, the form of laminitis most commonly seen in practice today is different.
Endocrinopathic laminitis is driven by hyperinsulinaemia, not hindgut acidosis. In these cases, insulin itself appears to play a direct role in the development of lamellar damage [1].
This distinction is not academic, it has direct implications for feeding. If a horse is at risk of endocrinopathic laminitis, then dietary management must focus on controlling insulin response.
Fructan does not fit into that pathway.
Why NSC and total sugar can mislead
In practical horse feeding situations, many horse owners rely on forage analysis values such as NSC (non-structural carbohydrates), WSC, or total sugar to assess risk.
The problem is that these values do not consistently reflect the carbohydrates that matter for insulin.
WSC includes fructan as well as simple sugars. NSC may be calculated differently depending on the laboratory, sometimes including fructan and sometimes not [8].
As a result, these values can overestimate the risk posed by forage, particularly in relation to equine insulin response.
This can lead to unintended consequences. Owners may reject hay that is perfectly suitable for a metabolic horse, simply because the NSC value appears too high. In doing so, they may end up feeding more mature, lower-quality forage with reduced nutritional value.
Lower quality forage will always have a poorer protein profile, and as protein is a key component of metabolic health in horses and ponies is often a poor feed choice.
Data from the ECIR Group highlights this issue clearly. In one dataset, the vast majority of hay samples met recommended thresholds when assessed using ESC and starch, but far fewer met the same thresholds when NSC was used [5].
From a purely practical point of view, it helps horse and pony owners enormously if they have a wider choice of suitable hay to choose from. The reluctance to understand the science clearly illustrates how the choice of metric can dramatically influence feeding decisions.
What this means for owners feeding horses
For horses with hyperinsulinemia (chronically elevated insulin levels), the goal is not to eliminate all carbohydrates from the diet. Horses are naturally adapted to consume forage, and carbohydrates play an important role in their overall nutrition.
The goal is to manage the types of carbohydrate that influence the insulin baseline level in horses and ponies.
In practical terms, this means focusing on:
and not on:
This approach allows for more accurate, more effective feeding decisions.
It also helps to avoid unnecessary interventions, such as prolonged hay soaking, which can reduce nutritional value without providing meaningful benefit if the underlying carbohydrate profile is already suitable.
Test the horse forage, don’t guess
The only reliable way to assess the hay or haylage horses are eating is through testing. Visual assessment is not sufficient. Neither is relying on assumptions based on grass species or the time of cut during the hay and haylage making season.
There are many varying factors which will affect hydrolysable carbohydrate levels in cured forage. Weather temperature, rainfall, cutting time of day and amount of fertilisation are just some factors affecting levels.
It is also worth understanding that levels of hydrolysable carbohydrates in spring and early summer grass (UK) can be extremely high. Horses with above normal baseline insulin are best removed from pasture at this time of year because turning out on grass can be a gamble that is not worth taking.
Testing for sugar levels in grass is not feasible due to the fluctuation of levels over the day in response to sunlight and the weather. Some horses with a difficult-to-control baseline insulin may need to be removed from grass all year round.
However, testing hay and haylage is worth doing because analysis provides the information needed to:
- Measure ESC and starch directly
- Assess insulin-related risk
- Make informed feeding decisions
Without this information, management becomes guesswork. With it, horse feeding management can be tailored precisely to the needs of the individual horse.
Conclusion
Fructan has been widely blamed for laminitis due to a combination of historical research models, confusing terminology, and the misinterpretation of forage analysis data.
However, the evidence is clear.
Fructan does not behave like a hydrolysable carbohydrate and does not produce the insulin response that drives endocrinopathic laminitis.
Instead, the primary dietary drivers of laminitis risk in metabolic horses are simple sugars (ESC) and starch.
Understanding this distinction allows for more accurate forage assessment, more targeted nutritional management, and more effective prevention of laminitis.
As our understanding of equine nutrition continues to evolve, the focus must remain on measuring what matters, rather than relying on assumptions.
References
- [1] Durham, A. E. et al. (2019). ECEIM consensus statement on equine metabolic syndrome. Journal of Veterinary Internal Medicine.
- [2] Abeynayake, S. W. et al. (2015). Fructan metabolism in perennial ryegrass. Frontiers in Plant Science.
- [3] Borer, K. E. et al. (2012). Effect of feeding glucose, fructose, and inulin on insulin and glucose. Journal of Animal Science.
- [4] Glatter, M. et al. (2017). Glycaemic and insulinaemic responses to Jerusalem artichoke meal. Journal of Animal Physiology and Animal Nutrition.
- [5] ECIR Group. Hydrolyzable Carbohydrates and the Metabolic Horse.
- [6] Harris, P. (2010). Pasture and laminitis: fructan overload models.
- [7] Crawford, C. et al. (2007). Dietary fructan and hindgut fermentation. Journal of Animal Science.
- [8] University of Minnesota Extension. Interpreting equine forage analysis.
