Yacon Syrup

What It Is

Yacon syrup is a concentrated juice from the root of the yacon plant, Smallanthus sonchifolius, an Andean root crop. It is a mixture of two things: fructooligosaccharides (FOS), the same kind of non-digestible fibre as inulin, and ordinary free sugars, mainly fructose, glucose and sucrose. It is sold as a syrup and, under dietary-supplement rules, as capsules.

The most important fact about it is that there is no such thing as “the” composition. We found no standard of identity and no labelled minimum FOS content. The proportion of fibre to sugar varies from batch to batch, and it changes in the jar.

How Much of It Is Sugar?

The International Potato Center (CIP) in Lima, which develops yacon syrup processing, measured two of its own batches:

• One batch: 47.6% FOS and 30.5% free sugars (2.6% glucose, 7.9% fructose, 20.0% sucrose), 164 kcal per 100 g.
• Another batch: 10.9% FOS and 53.1% free sugars (15.5% glucose, 25.4% fructose, 12.2% sucrose), 265 kcal per 100 g.

The syrup in the best-known weight-loss trial was 41.39% FOS and 25.65% free sugars. The syrup in most later trials was 22% FOS. So a quarter to over half of yacon syrup is free sugar, and its energy runs from about 1.6 to 2.7 kcal per gram, depending on the batch. That is a reduced-calorie syrup, not a calorie-free one. On a US label, the FOS would take the 2 kcal/g used for soluble non-digestible carbohydrates and the free sugars the usual 4.

The FOS also turn into sugars over time. CIP reports that in syrup about 25% of the FOS convert to simple sugars over six months at pH 4, and 45% at pH 3, which is why it keeps syrup at pH 4 or above. The syrup used in the Brazilian trials was made at pH 3.7. Syrup bottled at pH 5 changed very little over twelve months. We found no data on how much FOS survives home baking. The jar you buy may hold more sugar than its tested batch did.

Net Carbs and the Label

This site counts yacon syrup’s grams in full. Only the FOS part is non-digestible, and it varies from about 11% to 48%, while a quarter to over half is sugar. At most, subtract the dietary fibre that a specific jar’s own label declares.

On a US label, all of it is in Total Carbohydrate, and the free sugars count under Total Sugars: on the batches above, roughly 25 to 55 g of sugar per 100 g. Sugars from syrups are added sugars. A jar sold as a pure single-ingredient syrup may instead follow FDA’s treatment of honey, maple syrup and “other pure sugars and syrups”: no “Includes Xg Added Sugars” line, but the percent Daily Value for added sugars still shown. Yacon is not named in that guidance, so applying it here is our inference. Used as an ingredient in another food, its free sugars are added sugars in that food. Any “sugar-free” impression in its marketing is wrong for the syrup.

Blood Glucose

Two small trials, both from the Embrapa group in Brazil that made the syrup it tested:

• With breakfast (40 women, crossover): adding 40 g of yacon syrup, 14 g of it FOS, lowered glucose at 30 minutes and insulin at 15, 30 and 45 minutes compared with placebo. That is syrup added to a meal, not syrup used in place of sugar. We read the abstract, which does not say what the placebo was.
• Over two weeks (40 g a day against placebo, 30 people completing): “Yacon syrup did not affect blood lipid, glucose or metabolic endotoxemia”.

We found no glycaemic index measured to a standard method on a characterised syrup.

The Weight-Loss Claim

Yacon syrup’s reputation for weight loss and insulin sensitivity rests on one trial, Genta 2009. It enrolled obese, constipated women, and the problems are in its own text:

• “Thirty-five out of a total of 55 women completed this study.”
• A higher-dose group had flatulence they “considered severe and unacceptable”, and that group “was excluded from the present study”.
• Reported weight fell from 91.2 to 76.2 kg over 120 days on yacon, and went from 90.7 to 92.3 kg on placebo. But the only test reported compares each group with its own starting point. The trial never tests yacon against placebo directly.
• It was funded in part by CIP, which made the syrup and employs one of the authors. The paper declares no conflict of interest.

It has not been replicated. Later trials found no change in fasting glucose over two weeks, and no effect on the appetite hormones GLP-1 and ghrelin. Large changes reported in one unreplicated trial that compared each group only with itself are not evidence that yacon syrup causes weight loss.

Tolerance

In Genta’s trial, about 0.14 g of FOS per kg a day (about 10 g for a 70 kg adult) was taken for 120 days “with no difficulties”, while 20 g of FOS a day caused diarrhoea, severe bloating, flatulence and nausea, with no adaptation over time. How much syrup that is depends on its FOS content: 10 g of FOS is about 24 g of Genta’s 41% syrup, or about 45 g of a 22% syrup. A shorter trial found 20 g of syrup a day, 6.4 g of FOS, “well tolerated”; one of its authors is CIP staff.

We found no direct measurement of yacon syrup’s FODMAP content. By composition it is high-FODMAP: it carries fructans, and high-sugar batches carry more free fructose than glucose. In people with irritable bowel syndrome, fructans left symptoms uncontrolled in 77% of those given them, against 14% given glucose.

Regulatory Status

• US: sold as a food, and as capsules under dietary-supplement rules. FDA’s GRAS notice inventory returns no records for “yacon” or “Smallanthus” (searched 27 October 2026). A traditional food does not need one, and we found no FDA statement on yacon; calling it a conventional food is our characterisation.
• EU: not a novel food since the start of 2014, according to the Finnish Food Authority, because “A history of significant food use of yacón roots or Smallanthus sonchifolius in the EU before 1997 has been demonstrated”. That is a national authority’s summary, and it speaks of the roots; the syrup is not named. The European Commission’s own catalogue entry could not be opened.

Comparison Note

Against inulin: the same kind of fibre, but an inulin ingredient is mostly fibre, while yacon syrup arrives mixed with a quarter to over half free sugar. Against sugar and honey: fewer calories per gram, but still a source of sugar, and this site counts it as one. Against high-intensity sweeteners used in milligram amounts, such as stevia or monk fruit: not in the same category at all.

What would change this page: an assayed FOS and free-sugar content on retail labels; a glycaemic index measured to a standard method on a characterised syrup; or an independent repeat of Genta 2009 that compares yacon with placebo directly.