Fructose is a monosaccharide that occurs naturally in fruits, honey, and some root vegetables. It is also present in table sugar (sucrose) and corn syrup. Fructose has the same chemical formula as glucose, but its molecules are arranged differently. This gives fructose different properties from glucose. For example, fructose is sweeter than glucose and is metabolized more slowly by the body.
The metabolic effects of fructose have been studied extensively over the past few decades. Some of these studies have shown that consuming large amounts of fructose can lead to weight gain, insulin resistance, and type 2 diabetes (1,2). However, it’s important to keep in mind that these studies were conducted on animals or in test tubes; they do not necessarily reflect what happens in humans (3). In addition, most of these studies used very high doses of fructose—much higher than what people typically consume (4). Therefore, it’s unclear whether the effects observed in these studies would occur in people who consume more moderate amounts of fructose-containing foods and drinks.
Nevertheless, there is evidence from observational studies to suggest that too much fructose may be harmful. For example, one large observational study found that people who consumed more than 74 grams per day of fructose (the equivalent of about 2 ½ cans of soda) had a greater risk of dying from heart disease than those who consumed less than 40 grams per day (5). Another observational study showed that people who drank sugary beverages daily had an increased risk of developing type 2 diabetes compared with those who didn’t drink them at all (6).
It’s worth noting that most observational studies cannot prove causation— meaning they cannot show definitively that too much fructose caused any health problems. Observational studies can only show associations between two things; they cannot prove that one thing caused another. So it’s possible that some other factor might explain the link between sugar consumption and poor health outcomes observed in these observational studies.
In addition to the observational evidence linking too much sugar consumption with negative health effects, there is also some experimental evidence to support this idea. For instance, when healthy people are fed large amounts of fructose-containing beverages for several weeks or months , they develop many features of metabolic syndrome—a cluster of conditions including abdominal obesity , high blood pressure , elevated fasting blood sugar levels , and abnormal cholesterol levels (7-9). These findings suggest that consuming too much sugar can lead to adverse changes in metabolism even among healthy people .
So far , most research on the potential harms associated with excessive sugar consumption has focused on fructose . However , it’s important to keep in mind that sucrose (table sugar) and high -fructose corn syrup contain both glucose and fructose . Therefore , it’s possible that both sugars might contribute to adverse health effects . Indeed , recent research suggests this may be the case ; when rats are fed diets high in either glucose or sucrose , they develop many featuresof metabolic syndrome ( 10 ) . These findings indicatethat eating large amountsof either typeof sugarcan leadto similar adverse changesin metabolism .