Yacon (Smallanthus sonchifolius) is a plant grown for its root. Its syrup is rich in fructooligosaccharides (FOS), a fiber that gut bacteria ferment, and is sold as a sweetener and weight-loss supplement.
Also known as: yacon syrup, Smallanthus sonchifolius, yacon root.
A 120-day trial used syrup giving 0.14 or 0.29 g of FOS per kg of body weight a day (Genta 2009). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
What studies show: a 2025 meta-analysis of 7 trials (239 people) found no significant effect on fasting blood sugar, insulin, insulin resistance or cholesterol overall; some subgroups using it for more than 8 weeks showed lower fasting sugar and LDL (Nilghaz 2025). In an earlier 120-day trial in obese premenopausal women, yacon syrup lowered body weight, waist size, fasting insulin and LDL, and increased bowel movements and fullness; fasting sugar and other blood fats did not change (Genta 2009).
Safety: the higher amount in the 2009 trial caused gut side effects; the authors reported 0.14 g of FOS per kg a day as the amount without unwanted digestive effects (Genta 2009). The sources here do not describe drug interactions.
Yacon's main ingredient, FOS, is a fiber fermented by gut bacteria rather than absorbed into the blood, so a half-life or time to peak does not apply.
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