Published 8th May 2025
High fructose corn syrup and metabolic health: The science
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You’ve likely heard of high fructose corn syrup (HFCS) and seen it printed on food labels. You may have also heard that it’s not great for your health.
Over the years, HFCS has been in and out of the news. Most recently, RFK Jr. promised to ban its use in food.
But why does HFCS have such a bad reputation? Is it really making people obese? And how does it differ from other sugars?
In this article, we’ll explain what it is, how it’s made, and whether you should worry about it.
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What is high fructose corn syrup?
HFCS, as the name suggests, is derived from corn starch, which consists of long chains of glucose molecules bonded together.
To create HFCS, manufacturers break the starch down into individual glucose molecules.
Then, they use enzymes that convert some of the glucose into another sugar, called fructose — the sugar that naturally occurs in fruits.
HFCS comes in different formulations depending on the amount of fructose in the mix. Two of the most common forms are:
HFCS 42: Contains 42% fructose
HFCS 55: Contains 55% fructose
The remaining percentage consists of glucose and water.
Why do manufacturers use HFCS?
HFCS is used by food manufacturers as a replacement for sucrose (table sugar) because it’s similarly sweet, cheaper thanks to widespread corn subsidies, and it helps improve a food’s stability.
It’s also more soluble than sucrose and produces a desirable brown color on baked goods.
Lastly, because it's more acidic than sucrose, when HFCS is added to products, the manufacturers don’t need to use as much preservatives, so they make another cost saving.
How does sucrose differ from HFCS?
Sucrose is chemically very similar to HFCS. Sucrose is 50% glucose and 50% fructose, while HFCS, as we’ve seen, is usually 42% or 55% fructose.
The main difference is that in sucrose, each glucose molecule is bound to a fructose molecule. But in HCFS, some of the fructose is “free,” meaning that it isn’t bonded to anything.
Also, while these ratios of fructose to glucose are considered safe, there’s evidence that food manufacturers have been using much higher levels, with several major brands using 65% fructose.
This is where some of the concerns lie: Fructose, although similar in taste, is metabolized differently to glucose. Normally, we only consume fructose in plants, where it comes alongside bioactive compounds and fibre that are very good for our health, rather than in its free form.
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Fructose and metabolic health
Scientists have conducted a wide range of animal studies investigating how fructose metabolism — compared with glucose metabolism — may impact health.
These studies have shown that high fructose intake can increase the risk of obesity, dyslipidemia (unhealthy levels of blood fats), a fatty liver, high blood pressure, insulin resistance, and diabetes.
However, we have to be cautious when interpreting animal research, and in many of these studies, the animals were fed amounts of fructose well above those that humans would ingest.
Scientists have conducted some human studies, too. For instance, a 10-week study compared the effects of glucose-sweetened drinks with fructose-sweetened drinks on people with obesity or overweight.
They found that both groups gained a similar amount of weight, but those consuming fructose put on significantly more abdominal, or visceral fat.
This is important, as increased visceral fat is linked to poorer metabolic health and increased inflammation.
The fructose group also had higher blood sugar levels and decreased insulin sensitivity. Again, though, this study used levels of fructose that are above what the average American consumes.
Another study tested drinks using various levels of fructose, some of which were similar to real-life exposures.
Again, the scientists found that, compared with an artificially sweetened drink (the placebo), all of the fructose beverages increased levels of blood fat linked to cardiovascular disease risk, such as triglycerides and LDL (“bad”) cholesterol.
And these changes were measurable in just 2 weeks.
In line with these studies, a systematic review and meta-analysis of 15 studies concluded that:
“Fructose consumption from industrialized foods has significant effects on most components of metabolic syndrome.”
These components include higher blood sugar, triglycerides, and blood pressure.
We should also mention that not all scientists have reached the same conclusions. One review from 2022, for instance, concluded that, compared with sucrose, HFCS has similar metabolic effects, although it was linked to increased levels of a marker of inflammation.
Overall, we need more research, but evidence is mounting that HFCS, and high intakes of fructose consumed in processed foods may interfere with metabolism in a number of ways.
Important note: When fructose is consumed in its natural form — in fruit and veg — it poses no health risks. These foods are hugely important for good health.
Does HFCS cause obesity?
You may have heard that HFCS contributes to obesity. But does it contribute more to obesity than excessive intakes of sucrose? If it’s chemically so similar to sucrose, is it really any worse?
One of the theories is to do with how fructose and glucose are metabolised. Hold onto your hat, here’s some science:
Glucose causes a rise in insulin, which helps glucose move out of your blood and into your cells. Insulin also triggers the release of leptin, a hormone that makes you feel full. Fructose, on the other hand, doesn’t trigger the release of insulin, and therefore, leptin levels don’t rise.
This, the theory goes, means that you are more likely to overeat if you’re consuming food rich in fructose, compared with a food rich in glucose.
And as we’ve seen, HFCS often has more fructose than glucose.
As an energy-dense compound, when consumed in large amounts over long periods, HCFS can cause weight gain. However, whether HFCS influences weight gain more than sucrose or other similar carbohydrates is still an open question.
A report on HCFS produced by the European Commission summarizes it well:
“Further research needs to be conducted before the health consequences of HFCS consumption can be determined with accuracy. This also leads to the overall conclusion that unless new evidence appears, efforts should be targeted at decreasing total (added) sugar/sweetener consumption rather than specific types of sugar.”
What should you do?
Rather than worry about cutting HFCS from your diet entirely — which would be challenging to do; it’s everywhere — try to limit your intake of added sugars overall.
The free ZOE app can help you do that, with the in-app risk scale there to help you choose products that have less HFCS.
Sadly, food manufacturers make spotting added sugars challenging. They know that many people try to limit their sugar intake, so they use a wide range of confusing names to hide sugar on their labels.
Our app knows all these tricks and cuts through the confusion, giving you a clear indication of the healthfulness of the food.
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These are just some of the alternative names for added sugars:
agave nectar
agave syrup
barley malt
blackstrap molasses
brown rice syrup
buttered syrup
coconut blossom nectar
For a full list of alternative terms for sugar and some tips on reducing your intake of added sugars, try this guide.
Aside from cutting down on your intake of added sugars, where possible, opt for whole foods, lots of whole fruit and veg, fermented foods, legumes, and nuts and seeds.
Filling your plate up with plants will leave less space for products that contain HFCS.
While scientists unravel the metabolic differences between fructose, glucose, and HFCS, following this advice will certainly support your health.
Most importantly, try to limit your intake of soda.
The evidence that these drinks are linked to poorer health is now watertight — whether it’s due to the HFCS or not. This article has some great, healthy alternatives to soda that will still hit the spot.
And if you'd like to learn more about the chemicals added to food, try this extensive guide to more than 100 common food additives.
