No one doubts that fruit is healthy, but is there a limit to how much fructose we can handle? Has the increased intake of added fructose (fruit sugar) as a sweetener changed the rules for our liver, the only organ in the body capable of absorbing, converting, and breaking down fructose? Research shows that the long-term health effects of excessive fructose intake are negative.
Fructose
Fruit, fruit juice, and berries contain the monosaccharide fructose in varying amounts. A rough estimate suggests that for a large part of human evolution, we consumed approximately 15–40 grams of fructose per day, mostly from whole, fresh fruits. Today, the amount in a Western diet is around 85–100 grams of fructose per day. Fructose is metabolised (absorbed, converted, broken down, and utilised) in the liver, which means it does not cause blood sugar levels to rise in the same way as glucose, which directly increases blood sugar. Consequently, fructose has a relatively low glycaemic index (GI), which is why it was previously believed that fructose from sources like HFCS was a good substitute for glucose as a sweetener. However, growing research suggests that the daily doses of fructose we consume with today’s diet have significantly greater impacts on the body, particularly the liver, than previously thought.
Metabolic Syndrome
A single high dose of fructose does not cause acute problems, but chronically high fructose exposure from added fruit sugar (often in the form of HFCS – High Fructose Corn Syrup) has been shown to be harmful to health. It leads to stimulation of fatty acid production and triglyceride (fat) accumulation, reduced insulin sensitivity, and increased insulin resistance in the liver. Chronically high fructose doses also increase the amount of uric acid in the body, which in turn reduces nitric oxide, increases a peptide protein called angiotensin that constricts blood vessels, raises blood pressure, and can strain the kidneys. Increased uric acid levels can also lead to chronic low-grade inflammation in blood vessels and other tissues.
Furthermore, high fructose intake from sources other than fruit can disrupt the body’s appetite-regulating system by failing to stimulate insulin production. This, in turn, means that the hunger-stimulating hormone ghrelin is not reduced, and the satiety hormone leptin is not activated. The result is increased appetite, weight gain, and over time, a heightened risk of developing insulin resistance and other metabolic syndromes. In this case, the issue is not caused by excessive glucose exposure, which normally leads to insulin resistance, but by other mechanisms in the body.
Differences in Fructose Content in Fruits and Vegetables
A total daily fructose intake of 15–40 grams from fresh fruit, berries, and honey has positive effects, as it can improve the body’s glucose tolerance. Fruits, berries, and vegetables contain both pure fructose and fructose in the form of sucrose, a disaccharide (a type of carbohydrate) made up of one glucose molecule and one fructose molecule. The following examples consider both the content of pure fructose and the fructose molecule present in sucrose:
- 250 grams of banana contains approximately 14.8 grams of fructose (a medium-sized banana weighs about 120 grams),
- 250 grams of apple contains approximately 13.8 grams of fructose (a medium-sized apple weighs about 180 grams),
- 250 grams of blueberries contain approximately 7.9 grams of fructose,
- 250 grams of carrot contains approximately 6.8 grams of fructose.
Fruit is Not Unhealthy
Fruit in moderation is not unhealthy. On the contrary, it contains plenty of beneficial vitamins, minerals, phenols, carotenoids, and other phytochemicals that have positive effects on the body. What is harmful, however, are the large amounts of fructose we consume from added fructose or HFCS.
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