"High-Fructose Corn Syrup Is Bad Because It's an Isomerized Sugar" — Is It True? Comparing It to Table Sugar
Published:
Written by: Shingo YoshizakiReviewed by: Tomonobu Someda
"Isomerized sugar (fructose-glucose syrup) is an industrially manufactured, unnatural sugar, so it's worse for you than regular sugar" is a claim heard especially often in Japan. We check what research actually shows about the 'it's free sugar so it's absorbed faster' reasoning and the 'it's industrially made so it's dangerous' reasoning.
Let the data settle it.
Is free sugar (HFCS) absorbed faster and does it spike blood sugar more than bound sugar (sucrose)?
What's said
異性化糖への健康不安・一部の健康情報サイト
Fructose-glucose syrup is already broken down into free glucose and fructose, so it's absorbed faster and spikes blood sugar more sharply — putting more strain on the body than regular sugar.
What research says
- Sucrose is broken down almost instantly by the enzyme sucrase at the small intestine's brush border, becoming free glucose and fructose before absorption.
- Because this breakdown step is extremely fast, the actual difference in absorption speed is minor.
- A meta-analysis pooling 767 participants found no significant difference in fasting glucose between HFCS and sucrose groups.
- The 'free sugar spikes blood sugar more' reasoning oversimplifies the digestive physiology involved.
The 'free sugar means faster absorption and bigger blood-sugar spikes' reasoning is overstated. Measured data show no significant difference in fasting glucose.
Does being an industrially manufactured sugar make it inherently riskier?
What's said
「天然=安全、人工=危険」という自然主義的な言説
Fructose-glucose syrup is an industrially manufactured, artificial sugar, so it's worse and more dangerous than natural sugar.
What research says
- Sucrose (table sugar) is also industrially refined from sugarcane or sugar beet, so the 'natural vs. artificial' framing itself is blurry.
- A meta-analysis of 767 participants found no significant difference between the two in major metabolic markers such as weight, blood glucose, or lipids.
- That said, CRP (an inflammation marker) was slightly higher in the HFCS group, so the research isn't unanimous enough to say they're 'completely identical.' Separately, a sucrose-based commercial soft drink was also shown to acutely raise plasma uric acid, indicating that uric acid effects aren't unique to HFCS.
The 'artificial therefore dangerous' simplification isn't supported. That said, some reports (like CRP) show small differences, so claiming they're 'completely identical' isn't accurate either. The core takeaway remains that managing total intake matters more than the specific type of sugar.
Related research
Sources
Published:
Written by
Shingo YoshizakiSoftware Engineer / Research Writer at BODYDATA
An engineer's job is verification. I read the source before I trust gym lore — same as code.
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Reviewed by: Tomonobu Someda
Content reviewed from the perspective of coaching practice and supplement-industry experience
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Does the Fructose-Glucose Syrup in Sports Drinks Help During Exercise?
Glucose and fructose are absorbed via separate intestinal transporters, so combining them lets the body use more carbohydrate faster than a single sugar source alone. A single carbohydrate's utilization rate (oxidation) caps at roughly 60 g/hour, while a glucose-fructose mix can push this to around 90-105 g/hour. Most of this evidence, however, comes from prolonged endurance exercise lasting over 2 hours, and doesn't necessarily transfer directly to a shorter resistance-training session.
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