Sucralose: How Chlorinated Sugar Became Splenda

In 1976, a graduate student at Queen Elizabeth College in London was working with modified sugar molecules when he apparently misunderstood an instruction to “test” a compound and tasted it instead. He found it intensely sweet.

That compound became sucralose. It took another 22 years to reach the US market as Splenda, but the accidental origin story fits: sucralose is table sugar rearranged just enough to fool your taste receptors while your digestive enzymes can’t recognize it.

What Sucralose Actually Is

Sucralose is made from table sugar (sucrose) by replacing three of its hydroxyl (OH) groups with chlorine atoms. The resulting molecule is about 600 times sweeter than sugar.

Because of those chlorine substitutions, your digestive enzymes can’t break sucralose down the way they break down ordinary sugars. Most of it passes through the gut unchanged. What little is absorbed gets excreted in urine, also largely unchanged. This is why sucralose provides essentially no calories.

The chlorine connection alarms some people. It shouldn’t. The chlorine in sucralose is covalently bonded to carbon atoms — the same type of bond found in many organochlorine compounds that occur naturally in plants, seaweed, and soil microorganisms. It’s not free chlorine. It’s not the chlorine in bleach. The same carbon-chlorine bond structure is found in compounds like chlorophyll derivatives and amino acids that have never attracted safety concerns.

What makes sucralose useful beyond sweetness: it’s heat-stable. Aspartame breaks down above about 150°C. Sucralose stays intact through baking temperatures. This makes it genuinely versatile in a way aspartame isn’t.

How Splenda Works (and What’s in the Bag)

Pure sucralose is so intensely sweet that you’d need a fraction of a gram to sweeten a cup of coffee. That’s too small to measure or use practically.

So Splenda granular adds maltodextrin and dextrose as bulking agents — they give the product the same volume as an equivalent amount of sugar so you can use a 1:1 substitution. Those bulking agents add a small caloric contribution (about 12 calories per packet or tablespoon) and a small glycemic load that pure sucralose doesn’t have.

If you’re using Splenda specifically to avoid glycemic impact, liquid sucralose is the cleaner option. The packets and pourable versions contain the bulking agents.

Regulatory Status Across Major Agencies

The FDA approved sucralose in 1998. Health Canada, EFSA, JECFA, Food Standards Australia New Zealand, and most other major regulatory bodies have also reviewed and approved it.

EFSA’s 2017 re-evaluation set an acceptable daily intake (ADI) of 15 mg per kg of body weight per day. A 70 kg adult could consume 1,050 mg of pure sucralose per day before reaching that limit. A typical diet soda contains about 70 mg. That’s roughly a 15-to-1 margin for an average adult drinking one diet soda a day.

The Gut Microbiome Question

The most scientifically active area of sucralose research right now is its effect on gut bacteria.

A 2008 study by Abou-Donia et al. found that rats fed sucralose showed reductions in beneficial gut bacteria (Lactobacillus, Bifidobacterium) and increases in intestinal p-glycoprotein expression. The study was widely cited by critics of sucralose.

It was also widely criticized for methodological problems: the doses were high, the sample sizes were small, and some results were inconsistent.

More recent human data is more concerning. A 2023 study found gut microbiome changes in participants consuming higher doses of sucralose over two weeks. The changes were modest and their clinical significance isn’t clear. But unlike earlier rodent studies, this involved actual humans.

The FDA’s ADI of 5 mg/kg/day provides a margin, but the science is still developing. This is a legitimate area to watch rather than dismiss.

The 2023 IARC Classification

In 2023, IARC evaluated sucralose as part of a broader sweetener review and placed it in Group 2B: “possibly carcinogenic to humans.”

The same caveats that apply to aspartame’s 2B classification apply here. Group 2B means limited evidence — not that cancer causation has been demonstrated. The classification was based primarily on one positive animal study at very high doses. Multiple human studies have not found consistent associations.

Regulatory bodies including EFSA and the FDA have maintained their current safety assessments without change.

Blood Sugar and the Cephalic Phase

Sucralose doesn’t raise blood glucose — the molecule isn’t metabolized to glucose and triggers no direct insulin response.

The more subtle question is whether sucralose (or any sweet taste) might trigger a cephalic phase insulin response: an anticipatory release of insulin based on the sensation of sweetness, before any glucose actually enters the bloodstream.

Some studies show this effect. Others don’t. The discrepancy may depend on the individual, whether the sweet taste is accompanied by glucose, and how the test is run. The clinical significance of a small anticipatory insulin release isn’t established.

Where Sucralose Stands

Sucralose is safe at dietary levels. The regulatory consensus across three major agencies is consistent on this. The gut microbiome research is the most scientifically interesting open question, and it deserves further study — but it hasn’t changed the risk assessment.

If you’re using sucralose occasionally, the evidence doesn’t give you a reason to stop. If you’re consuming large amounts daily, the emerging microbiome research is a reasonable argument for diversifying your sweetener use or reducing overall intake of highly processed foods that tend to contain multiple additives.

The strongest thing the evidence supports is monitoring, not panic.