What it is
High-fructose corn syrup is made by running cornstarch through enzymes that convert some of its glucose into fructose, yielding a liquid sweetener: HFCS-55 (about 55% fructose) in sodas, HFCS-42 in baked goods and other foods. It isn't sweeter than sugar; it's just cheaper to make and easier to pump.
Why it's in your food
It exists because corn is heavily subsidized, and a pumpable liquid is cheaper to ship and measure than crystalline sugar. It blends easily into sodas, dressings, breads, sauces, and “fruit” drinks. The reasons it's used are cost and convenience, nothing more.
Why your biology objects
Your body handles fructose well only when glucose arrives alongside it, ~1:1, the way fruit and table sugar (a bonded pair) deliver it. HFCS unbonds the sugars into free form and tips the ratio fructose-heavy, so the excess spills past the gut to the liver, where fructokinase (KHK) phosphorylates it with no feedback brake, depleting ATP into uric acid and routing carbons into de novo lipogenesis (liver fat). The further a sweetener drifts from 1:1, the worse it gets.
The ancestral lens
Your biology evolved to handle fructose when it arrives alongside glucose at roughly 1:1, the way whole fruit and table sugar (a bonded pair) deliver it. Seasonal fruit and occasional wild honey were the only fructose your ancestors ate, and never as a steady daily liquid. HFCS separates the sugars and shifts the balance toward fructose, an exposure your body has no evolutionary history with.
Dose & context
The effect depends on dose: at low intake the gut clears fructose, but past a certain point the excess reaches the liver. A daily soda keeps the liver constantly processing fructose; an occasional sweet does not. As with all sugar, how much and how often is what matters.
Label tricks
Relabeled around the world and over time to dodge the name's reputation: “glucose-fructose syrup” in Europe, “isoglucose” in trade language, and a failed US industry bid to rename it “corn sugar.” Same molecule, friendlier word.
What to reach for instead
The best option is no added sweetener at all. Where that's not possible, a bonded 1:1 sugar like cane sugar at least delivers fructose alongside its glucose, and whole fruit adds fiber that slows it down. The closer to 1:1 and the more fiber, the easier it is on the liver.
Straight answers
Is high-fructose corn syrup worse than sugar?
A little. HFCS-55 runs a touch fructose-heavy and its sugars are free rather than bonded, so it drifts further from the 1:1 ratio your liver handles best. But it's in the same range as table sugar, and both are flagged on dose.
Is HFCS the same as corn syrup?
No. Plain corn syrup is nearly all glucose. High-fructose corn syrup has been enzyme-treated to convert part of that glucose into fructose.
Why is it in so many foods?
Cost and logistics: corn subsidies make it cheap, and a pumpable liquid is easier to ship and meter than crystalline sugar.
Is “glucose-fructose syrup” the same thing?
Yes. That's the standard name for HFCS in Europe and much of the world.