Sugars & sweeteners

Approximate figures for a quick overview. GI = glycemic index (how fast it raises blood glucose vs pure glucose = 100). “Insulin” is the direct, acute effect of the sweetener itself.

*Aspartame has 4 kcal/g but is ~200× sweeter than sugar, so the amount used adds essentially no calories.

Table sugar is sucrose: one glucose joined to one fructose. Whether it’s refined from sugar beet (most European sugar) or sugar cane, the final product is the same molecule — the body handles them identically. In the gut, sucrose is split into glucose and fructose; glucose raises blood sugar and insulin directly, while fructose is processed mainly by the liver and raises blood glucose far less acutely (which is why fructose has a low GI). The catch is that large amounts of fructose (from syrups and sweetened drinks, not from whole fruit) are what drive the metabolic concerns — not a piece of fruit. All of these are “free sugars” and count toward the limits below.

Honey, maple syrup, agave and coconut sugar are marketed as healthier, but nutritionally they are still free sugars with almost the same calories. Honey and maple carry trace antioxidants; agave is very high in fructose (low GI, but that fructose load is the downside); coconut sugar is essentially sucrose with a little fibre. Treat them as sugar with a nicer story — small amounts for flavour, not a health upgrade.

Polyols are partly-absorbed carbohydrates that taste sweet but deliver few calories and little blood-sugar rise. They’re common in “sugar-free” sweets and keto products. Two caveats: in excess they cause gas, bloating and a laxative effect (erythritol is best tolerated), and a 2023 study linked higher blood erythritol to more cardiovascular events and a pro-clotting effect on platelets — an association that needs confirmation but is worth knowing.³ (Xylitol is also toxic to dogs.)

These are intensely sweet with essentially no calories and no direct blood-sugar or insulin spike. Safety at normal intakes is broadly accepted (each has an ADI — acceptable daily intake — with a large safety margin), but two 2023 developments added nuance:

• Aspartame was classified by IARC as “possibly carcinogenic” (group 2B), while the JECFA safety committee kept the ADI unchanged (40 mg/kg/day) — meaning normal intakes are still considered safe, but very high habitual intake is the open question.⁶
• Sucralose: a breakdown product, sucralose-6-acetate, showed genotoxic (DNA-damaging) effects in vitro, at levels a single daily sucralose drink could exceed — grounds for caution and re-evaluation, not proof of harm in people.⁴

Stevia (steviol glycosides) and monk fruit are the plant-derived options, generally the best-tolerated; stevia can have a liquorice-like aftertaste. None of these is “bad” at sensible use — but see the microbiome and WHO points below.

Allulose is a “rare sugar” that occurs naturally in tiny amounts (figs, raisins, maple). It tastes and cooks like sugar but is barely metabolised — about 0.4 kcal/g and it does not meaningfully raise blood glucose or insulin (some studies even show a small lowering of post-meal glucose).

The regulatory split comes down to how each system treats new ingredients:

• United States: the FDA granted allulose GRAS (“generally recognised as safe”) status, and since 2020 excludes it from “Total” and “Added Sugars” on the label (counted at 0.4 kcal/g). So it’s widely sold in US “no added sugar” products.⁵
• European Union: allulose counts as a “novel food” (not eaten significantly in the EU before 1997), so it needs pre-market EFSA safety authorisation. As of 2025 EFSA had not been able to establish its safety from the data submitted, so it remains unauthorised for sale in the EU.⁵

So it isn’t that allulose is “banned as dangerous” in Europe — it simply hasn’t cleared the EU’s stricter novel-food approval process yet.

There is a real reflex called the cephalic-phase insulin response — the mouth and brain, sensing sweetness, can prompt a small early release of insulin before glucose arrives. But for non-sugar sweeteners the evidence is weak and inconsistent: most controlled studies show no meaningful rise in insulin or blood glucose from the sweet taste alone. So the popular claim that “diet soda spikes your insulin like sugar” is not well supported. The more plausible effects are indirect — through appetite, habit and the gut (below).

Do sweeteners trigger a sweet tooth?

The idea that sweeteners increase sugar cravings is popular but not clearly proven — trials are mixed. What’s more consistent is that keeping the diet very sweet (sugar or sweetener) helps maintain a preference for intense sweetness, which is why the WHO frames the goal as reducing overall sweetness, not just switching molecules.¹

The gut-microbiome finding

A 2022 randomised trial (Suez et al., Cell) gave healthy adults saccharin, sucralose, aspartame or stevia for two weeks. All four altered the gut and oral microbiome, and saccharin and sucralose measurably impaired glucose tolerance in a person-specific way. Transplanting the volunteers’ microbes into germ-free mice reproduced the glucose changes — showing the microbiome is a causal middle-man, not a coincidence.² This is the strongest evidence that “zero-calorie” does not mean “zero-effect” — though the effects are individual and their long-term health meaning is still being worked out.

Free sugars: the WHO recommends keeping them under 10% of daily energy, and ideally under 5% — roughly 25 g (about 6 teaspoons) a day for an average adult.⁷ A single regular soft drink can already contain that much.

Non-sugar sweeteners: each has an ADI set with a ~100× safety margin, and normal use sits well below it — e.g. you’d need many litres of diet drink a day to approach the aspartame ADI. So acute toxicity is not the practical concern; the open questions are the long-term, microbiome and habit effects above. The pragmatic middle path: use a little sweetener to help cut sugar, while gradually dialling down how sweet you need things to taste.

Regular soda & sugary drinks are the clearest problem: fast-absorbed free sugars (often as HFCS), little satiety, and a large share of many people’s sugar intake. Diet/zero drinks remove the sugar and calories; they’re a reasonable step down from sugary soda, but the WHO wouldn’t call them a health drink — water, coffee or tea are better defaults.

Protein bars and sweetened protein powders usually rely on sucralose, acesulfame-K, stevia or sugar alcohols. That keeps sugar and calories down, which is useful around training — just remember bars can still be calorie-dense, and heavy daily use means a steady sweetener (and often polyol) load, with the gut effects that can bring. Whole-food protein plus a plain powder, sweetened lightly, is the cleaner option.