The carbohydrate molecule, fructose, is found in some of nature’s “healthiest carb” foods, including whole fruits. However, fructose is also one of two molecules that make up “table sugar,” which is anything but healthy if consumed in excess. Fructose is also a part of the notorious food additive, high fructose corn syrup (HFCS), which fills all those millions of sugar-sweetened beverages (SSBs) — the food source most blamed by scientists for the increasing incidence of obesity, type 2 diabetes, and cardiovascular morbidity and mortality in the United States. Here’s a guide to the two faces of fructose.
How does fructose fit into the carbohydrate puzzle?
As we detailed in our report, Confused About Carbohydrates?, fructose is one of the primary simple sugar molecules. It is a monosaccharide, as is glucose.
Fructose is known to many as “the fruit sugar” because it is found naturally in:
- Most fruits, including berries, raisins, dates and figs
- Root vegetables
But fructose is also one of two molecules, along with glucose, that make up the disaccharide sucrose. (See What Is Sucrose? for additional information.) As a part of sucrose, fructose is found in many complex carbs, including vegetables (such as potatoes) and grains. Sucrose, however, is also “refined” into “table sugar,” and fructose alone can also be commercially derived and added to processed foods. The three most common derivatives of fructose are:
- Crystalline Fructose
- HFCS (High Fructose Corn Syrup)
The latter, HFCS, is actually a mixture of fructose and glucose, and its use in foods and drinks has increased dramatically over the years.
How do you metabolize fructose?
Unlike glucose, naturally occurring fructose seems to cause a slightly more gradual rise in blood sugar levels than does glucose or sucrose. However, fructose is still one the “simple sugars,” so foods containing it typically provide a quick source of energy to the cells, which happens when the production of insulin is triggered.
In healthy individuals, when simple sugars are consumed in excess, they are most often converted into energy stores that can be kept and used later, either as glycogen (stored by the liver and muscles) and fat (stored in the adipose tissue, liver and muscles). However, even if individuals can successfully process large amounts of sugar without developing diabetes, they may become obese, which in and of itself is associated with a host of metabolic and cardiovascular disorders.
For those individuals who don’t have enough insulin to move glucose out of the blood, or the insulin is ineffective (aka insulin resistance), excessive fructose consumption can cause blood glucose levels to rise and stay chronically high, leading to a host of health issues — including diabetes. Learn more: The Link Between Blood Sugar and Diabetes.
New research suggests that dietary fructose, once thought to be metabolized exclusively in the liver, is also metabolized in the small intestine, with the implication that the gut-liver axis plays a key role in fructose metabolism and pathology. Interestingly, some of this new evidence emerged when scientists examined fructose intolerance, a disorder we explore in our article, What Is Fructose Intolerance?.
Is fructose bad for me?
Read on to learn more about the two faces of fructose. You will learn that the whole fruits and other natural foods that contain fructose appear to be healthy carbohydrate sources, or at least health-neutral. However, when fructose is commercially added to foods, fructose derivatives are considered a major contributor to the rapid rise in the incidence of obesity, diabetes and heart disease in the U.S.
Natural fructose foods: Healthy when consumed in moderation
Naturally-sourced fructose foods, like whole fruits, certainly should be consumed in moderation by individuals with diabetes — because any carb can and will, to one degree or another, affect glycemic control by causing a rise in blood glucose.
However, healthy individuals would really have to consume an excessive amount of fruit to experience an adverse metabolic event or long-term metabolic disorder due to fructose. Why? Because in a healthy individual, your liver or muscles can store up to 50-100 grams of sugars such as fructose, and the typical whole fruit contains only 5-7 grams of fructose.
Table 1. Free fructose in selected fruits (% fresh weight basis)
|Apples, raw, unpeeled||7.6|
|Cherries, raw, sweet||6.2|
|Cherries, raw, sour||3.3|
|Grapes, raw, American||6.9|
|Grapes, raw, European||7.6|
As it became increasingly apparent to scientists, starting over a decade ago, that “added fructose” was likely linked to rising obesity and related cardiometabolic disorders (see next section), researchers sought to study foods naturally high in fructose as well, to make sure that fructose (in and of itself, and even in smaller quantities) doesn’t have unique chemical properties that are particularly harmful. To be frank, the issue is still being debated, and well-controlled, high-quality studies (especially in people with impaired glucose tolerance and diabetes) are still lacking. One issue: Clinical outcomes attributed to fructose — obesity, high triglycerides and other features of metabolic syndrome — are not found in every experimental test and may be more reliably caused by increased total carbohydrate consumption.
As stated by authors of a 2013 Perspective, “persistence in a state of over-consumption has serious consequences and there is a clear benefit in restricting sugar, especially for children. However, suggesting that fructose is somehow a foreign substance is not consistent with the science and, therefore, should not be the basis of policy.” In essence, what these scientists were saying is that, while there are no doubt specific effects of fructose, the pathways of fructose and glucose metabolism converge at the level of the triose-phosphates and, therefore, any downstream effects also occur with glucose. In addition, a substantial part of ingested fructose is turned to glucose. So it’s hard to separate (and study) the relative effects of pure fructose vs. pure glucose.
A 2018 study concurred, stating that “research comparing pure fructose with pure glucose, although interesting from a scientific point of view, has limited application to human nutrition given that neither is consumed to an appreciable degree in isolation in the human diet.” The conclusions from their review of the research comparing fructose to sucrose and other sugars: “Whether there is a link between fructose, HFCS, or sucrose and increased risk of heart disease, metabolic syndrome, or fatty infiltration of the liver or muscle remains in dispute with different studies using different methodologies arriving at different conclusions. Further randomized clinical trials are needed to resolve many of these issues.”
A 2015 Mayo Clinic Proceedings review concluded that whole foods that contain fructose (e.g., fruits) “pose no problem for health and are likely protective against diabetes and adverse CV [cardiovascular] outcomes,” whereas “added sugars (e.g., sucrose and high-fructose corn syrup)…may pose the greatest problem for incident diabetes, diabetes-related metabolic abnormalities, and CV risk.” More recently, a 2020 JAMA meta-analysis concluded, similarly, that the adverse association of sugar-sweetened beverages (SSBs) with metabolic syndrome does not extend to other food sources of fructose-containing sugars [our emphasis], with a protective association for yogurt and fruit throughout the dose range and for 100% fruit juice and mixed fruit juices at moderate doses.
Added fructose: Unhealthy in high quantities
A 2021 meta-analysis concludes that “chronic consumption of fructose is neither more beneficial, nor more harmful than equivalent doses of sucrose or glucose for glycemic and other metabolic outcomes.” So the debate will go on, and research will continue, concerning whether fructose is more of a culprit, or just equivalent, to other added sugars in relation to obesity, cardiovascular, glycemic and other metabolic outcomes. However, understand that these authors were “not stating that consumption of sugar, especially as refined carbohydrates, is advisable or beneficial” [our emphasis].
In fact, a clear consensus has emerged among scientists that not only is excessive consumption of added sugars detrimental to health on so many levels, but the added sugars (typically high fructose corn syrup, or HFCS, as well as added sucrose) in sugar-sweetened beverages (SSBs) appear to be particularly harmful, even if that is the result in part of the very high concentrations of such added sugars in these food sources — not to mention the fact that Americans consume such large quantities of them. Most carbonated drinks and sweetened juices contain more than 50 grams of fructose, along with other complex sugars, which is in stark contrast to, say, an orange, which has less than 10 grams of total sugar (of which fructose is one type and quantity).
A 2021 perspective paper aptly refers to HFCS as “sweet death,” stating that while “the mechanistic link between these metabolic diseases and fructose remains tenuous, … the exponential increase in HFCS consumption correlates with the increased incidence of obesity and type 2 diabetes.”
The aforementioned 2020 JAMA meta-analysis also added “supporting evidence that increased SSB consumption is associated with metabolic syndrome incidence.” Most recently, a 2021 research study out of UC Davis found evidence that consumption of both sucrose- and HFCS-sweetened beverages “induced detrimental changes in hepatic lipid, insulin sensitivity, and circulating lipids, lipoproteins and uric acid in 2 weeks.” This research echoed earlier studies that concluded that SSBs made with HFCS correlate highly with greater risk of cardiovascular mortality.
There continues to be debate about the relative roles that added glucose, sucrose and fructose play in disease risks, morbidity and mortality. Large randomized controlled dietary intervention studies assessing the effects of added sugars on cardiometabolic risk factors over long periods of time are still lacking. However, the consensus among leading scientists is that the fructose found naturally in fruits and root vegetables is not associated with health risks, although those with diabetes clearly need to monitor all carbohydrates to determine which foods contribute the most (or least) to glycemic imbalance. What the majority of scientists believe is that total carbohydrate consumption should be restricted to prevent obesity and its ensuing cardiometabolic disturbances. “Added sugars” in processed foods — of which high fructose corn syrup (HFCS) is one, but not the only, major culprit — are clearly associated with the decreased production of insulin, increased liver fat, more bad cholesterol, and more visceral fat. Thus, adhering to a diet made up largely of lean proteins, healthy fats, and natural, whole carbohydrate foods (particularly fruits and vegetables and whole grains that are high in fiber) remains the surest recipe for a long and healthy life.