Not all sugar behaves the same way inside the body. Glucose is burned for energy by cells throughout the entire body.
Fructose, the sweet half of table sugar and the dominant sugar in high-fructose corn syrup, travels almost directly to the liver.
A review of dietary sugars in fatty liver disease published in the journal Nutrients reports that patients with non-alcoholic fatty liver disease consume two to three times more fructose than matched controls.
Another analysis of the same evidence put average intake in patients at 52 grams a day, compared with 42 grams in people without the disease.
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Non-alcoholic fatty liver disease, now often renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a build-up of fat in liver cells that is not caused by alcohol.
A 2025 study in Hepatology Communications estimated that about 42 percent of US adults had hepatic steatosis before the pandemic, and that roughly 50 million US adults met the criteria for MASLD.
Estimates of how common the condition is vary, and fatty liver disease may affect around one in three adults depending on the population studied.
How fructose reshapes the liver
The reason fructose acts differently sits in a single enzyme. The Nutrients review describes how liver cells break fructose down using ketohexokinase, better known as fructokinase, into a compound called fructose-1-phosphate.
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That reaction rapidly depletes intrahepatic adenosine triphosphate, the cell's energy currency, and pushes up adenosine monophosphate, which the liver then converts into uric acid.
The fragments left over feed into de novo lipogenesis, the liver's own fat-making pathway.
They also activate two master regulators called ChREBP and SREBP-1c, which switch on the genes that build new triglycerides.
When intake outpaces what the liver can send back out into the bloodstream, the excess is stored inside liver cells.
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A 2017 review of fructose-induced fatty liver in Nutrients identified four pathological processes that follow chronic overload: increased fat synthesis, mitochondrial dysfunction, inflammation and insulin resistance, meaning the body's cells respond less effectively to insulin.
Fructose enters liver cells with little regulation, unlike glucose, whose uptake is tightly gated.
That is what makes it, in the authors' description, a highly efficient inducer of lipogenesis.
Fruit is not the concern
The fructose in whole fruit reaches the liver slowly. Fiber, water and other nutrients blunt absorption, and the amounts are modest.
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The concern lies with added sugars in processed foods and drinks, where fructose arrives in a fast, concentrated dose.
According to the Harvard T.H. Chan School of Public Health, the average American adult, teenager and child consumes about 17 teaspoons of added sugar a day, or roughly 270 calories.
A single 20-ounce bottle of sugar-sweetened soda, lemonade or iced tea contains about 65 grams of added sugar, often from high-fructose corn syrup.
Sugar-sweetened beverages are the single largest source of added sugars in the US diet.
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Fatty liver rarely announces itself in the early stages, so anyone with obesity, type 2 diabetes or elevated liver enzymes on routine bloodwork should ask their doctor whether liver imaging is warranted.
This article is made and published by Mie Hermansen, who may have used AI in the preparation.