Every sweetener, rated: from aspartame to allulose

In short

• Sweeteners fall into four families: synthetic (aspartame, sucralose, acesulfame K, saccharin, cyclamate), plant extracts (stevia, monk fruit, thaumatin), sugar alcohols (erythritol, xylitol, sorbitol, maltitol) and rare sugars (allulose, tagatose).
• None of them rots teeth or spikes blood sugar the way sugar does (maltitol is the partial exception). That part is settled.
• What is not settled: effects on gut bacteria, appetite, and — newest — blood clotting with erythritol and xylitol. Several old "safe" verdicts have been reopened since 2023.
• In 2023 the WHO advised against using non-sugar sweeteners to control weight, because long-term studies show no lasting benefit.
• Our overall view: the best option is to need less sweetness. When you do sweeten, stevia or monk fruit in small amounts are the strongest choices; the synthetic ones are better kept occasional.

How a sweetener tricks the tongue

Sweetness is detected by one receptor on the tongue, a pair of proteins called T1R2/T1R3. Sugar fits it loosely, which is why we need a lot of it. Many sweeteners fit it far more tightly, so a tiny amount gives the same signal — aspartame is about 200 times sweeter than sugar, sucralose 600 times, advantame 20,000 times.

The same receptor exists in the gut and the pancreas, which is one reason researchers question whether sweeteners are as "silent" in the body as once thought.

How we rate

• Traffic light: green = good choice in normal amounts, amber = fine occasionally, watch the dose or the open questions, red = we would avoid it.
• Origin: plant (extracted from a plant, purified), fermented (made by microbes or enzymes), synthetic (built in a chemical plant).
• Frogwise score (out of 10): health, environment and transparency, averaged into an overall score, following The Frogwise Standard. Scores are our editorial judgement based on the sources below and will be updated as research moves.

The overview table

Sweetener	E-number	Origin	Sweetness vs sugar	Calories	Salute	Environment	Trasparenza	Overall	Rating
Stevia (steviol glycosides)	E960	Plant	200–400×	0	8	8	7	7.7	Green
Monk fruit (mogrosides)	—	Plant	150–250×	0	8	6	6	6.7	Green
Thaumatin	E957	Plant protein	2,000×	~0	8	6	6	6.7	Green
Allulose	—	Rare sugar, enzymatic	0.7×	0.4 kcal/g	7	6	6	6.3	Green / amber
Tagatose	—	Rare sugar, enzymatic	0.9×	1.5 kcal/g	7	6	6	6.3	Amber
Erythritol	E968	Fermented	0.7×	0	5	6	7	6.0	Amber
Xylitol	E967	Plant / fermented	1×	2.4 kcal/g	6	5	7	6.0	Amber
Sorbitol	E420	From glucose	0.6×	2.6 kcal/g	5	5	6	5.3	Amber
Maltitol	E965	From starch	0.9×	2.1 kcal/g	4	5	5	4.7	Amber / red
Isomalt, mannitol, lactitol	E953, E421, E966	From sugar	0.4–0.6×	~2 kcal/g	5	5	6	5.3	Amber
Aspartame	E951	Synthetic	200×	~0	4	5	6	5.0	Amber / red
Acesulfame K	E950	Synthetic	200×	0	4	4	6	4.7	Amber / red
Sucralose	E955	Synthetic (chlorinated sugar)	600×	0	3	3	5	3.7	Red
Saccharin	E954	Synthetic	300–500×	0	4	4	6	4.7	Amber / red
Cyclamate	E952	Synthetic	30–50×	0	3	4	5	4.0	Red
Neotame, advantame	E961, E969	Synthetic	8,000–20,000×	0	5	5	5	5.0	Amber

Plant sweeteners

Stevia — green

The leaves of Stevia rebaudiana, a shrub from Paraguay, contain steviol glycosides (rebaudioside A, M, D and stevioside). In the gut, bacteria cut off the sugar parts; the remaining steviol is absorbed, processed by the liver and leaves in urine. It does not raise blood sugar or insulin.

• Good: decades of use, no credible cancer or heart signal, low land and water use per unit of sweetness.
• Watch: the bitter, liquorice aftertaste of cheaper extracts (mostly Reb A). Newer Reb M tastes cleaner but is increasingly made by fermentation or enzymes. Many "stevia" powders are 95% erythritol or maltodextrin — read the label.
• Acceptable daily intake: 4 mg/kg body weight (as steviol).

Monk fruit (luo han guo) — green

A gourd from southern China, dried and extracted for mogrosides, especially mogroside V. Like stevia, gut bacteria break the mogrosides down and they bring no calories. It has a long history in Chinese medicine and very few safety concerns.

• Watch: monk fruit extract is permitted in the US (GRAS) but in the EU its use as a sweetener is still under assessment, so most EU "monk fruit" products are blends based on erythritol. Long shipping distances and limited supply affect its environmental score.

Thaumatin — green

A protein from the katemfe fruit of West Africa. Your body digests it like any protein. Very sweet, with a lingering, liquorice-like tail, so it is used mainly as a flavour enhancer in tiny amounts.

Rare sugars

Allulose (psicose) — green / amber

A mirror image of fructose found in small amounts in figs, raisins and maple syrup, now made from fructose with enzymes. About 70% of the body absorbs it, but it is not metabolised: it leaves in urine. It does not raise blood sugar and early studies even suggest it slightly blunts the rise from other sugars.

• For makers: it behaves like sugar — it browns (fast), softens ice cream and adds body.
• Watch: large doses cause bloating. It is approved in the US, Canada and Japan; in the EU it is not yet authorised as a food ingredient.

Tagatose — amber

A rare sugar made from lactose. Partly absorbed, about 1.5 kcal/g, mild on blood sugar, prebiotic in the colon. Gut discomfort at higher doses; limited availability.

Sugar alcohols (polyols)

Polyols are sugars whose chemical "head" has been reduced to an alcohol group. Bacteria in the mouth cannot ferment them, so they do not cause cavities. Most are only partly absorbed: the rest reaches the colon, draws in water and ferments — which is why EU labels must warn that excessive consumption may produce laxative effects.

Erythritol — amber

Made by fermenting glucose with yeasts. About 90% is absorbed and leaves unchanged in urine, so it is the gentlest polyol for the gut and has no calories.

• New concern: a 2023 study in Nature Medicine (Witkowski et al.) found people with high blood erythritol had more heart attacks and strokes, and that 30 g of erythritol raised blood levels a thousandfold for days and made platelets clot more easily in the lab. The body also makes some erythritol itself, so cause and effect are not proven. Until that is clearer, we treat large daily doses — a sweetened drink every day, keto baking — with care.

Xylitol — amber

Found in birch bark and corn cobs. Best evidence of any sweetener for teeth: xylitol gum after meals reduces cavity-causing bacteria. In 2024 the same research group reported a similar platelet signal for xylitol in the European Heart Journal. Fine in gum and mints; we would not bake with it by the cupful. Deadly to dogs even in small amounts.

Sorbitol, mannitol, isomalt, lactitol — amber

Common in sugar-free sweets. Strong laxative effect (sorbitol from about 10–20 g). Sorbitol is also high in FODMAPs, a problem for people with IBS.

Maltitol — amber / red

The most sugar-like in taste and texture, which is why it fills "sugar-free" chocolate. But it is partly digested to glucose, so it raises blood sugar (GI about 35–50), carries about half the calories of sugar and causes the most gut trouble per gram.

Synthetic sweeteners

Aspartame — amber / red

Two amino acids (phenylalanine and aspartic acid) joined with a methyl group. In the gut it splits into those amino acids and a small amount of methanol — less than in a glass of tomato juice.

• 2023: the WHO cancer agency (IARC) classed aspartame as possibly carcinogenic to humans (group 2B, the same group as aloe vera extract), based on limited evidence for liver cancer. The WHO food additive committee (JECFA) kept the acceptable daily intake at 40 mg/kg.
• Must avoid: people with phenylketonuria (PKU); labels must say contains a source of phenylalanine.
• Breaks down with heat, so it is not used for baking.

Sucralose — red

Sucrose in which three hydroxyl groups are replaced with chlorine atoms. Most passes through unabsorbed.

• A 2023 study found that sucralose-6-acetate, an impurity and gut breakdown product, damaged DNA in human cells in the lab.
• Heated above about 120 °C, especially with fat, sucralose can form chlorinated compounds such as chloropropanols. Germany's risk assessment institute (BfR) advises against baking with it.
• It passes through sewage treatment almost untouched and is now found in rivers and groundwater worldwide — the reason for its low environmental score.
• Several studies suggest it changes gut bacteria and glucose responses in some people.

Acesulfame K — amber / red

A synthetic compound, absorbed and excreted unchanged. Usually blended with aspartame or sucralose to mask bitterness. Like sucralose, it persists in waterways. Animal studies hint at gut microbiome effects; human data are thin.

Saccharin — amber / red

The oldest sweetener (1879). The bladder-cancer scare from rats in the 1970s did not apply to humans, and it was cleared in 2000. Metallic aftertaste; one 2014 study in Nature linked it to glucose intolerance via gut bacteria in some people.

Cyclamate — red

Banned in the US since 1969, allowed in the EU with a low daily limit. Some people's gut bacteria convert it into cyclohexylamine, which is toxic to the testes in animals. Little reason to choose it.

Neotame and advantame — amber

Aspartame relatives, thousands of times sweeter, used in microscopic amounts. Less studied, so we keep them amber.

What the big picture says

• Weight: short trials show swapping sugar for sweeteners cuts calories and weight a little. Long observational studies link high sweetener intake with ulteriore weight gain, type 2 diabetes and heart disease — partly because people who are already at risk use more of them. The WHO 2023 guideline concluded sweeteners should not be used for weight control.
• Taste: regular intense sweetness keeps the palate expecting it. Many people find that cutting all sweeteners resets their taste within two to four weeks.
• Children and pregnancy: most health services advise keeping sweetened drinks away from young children, and evidence in pregnancy is too limited to be reassuring.

Our recommendations

1. Best: reduce sweetness, or use whole foods (see part 4 on dates, fruit and spices).
2. When you need a zero-sugar sweetener: stevia or monk fruit, preferably without fillers.
3. For texture in baking: allulose where it is legal; otherwise a little real sugar is often the honest choice.
4. For teeth: xylitol gum after meals.
5. Keep occasional: aspartame, acesulfame K, saccharin, erythritol in large amounts.
6. Avoid: sucralose (especially heated) and cyclamate.

Continue with part 3, on inulin and the fibres sold as sweeteners.