Benefits
Body weight, waist and BMI
In one 120-day placebo-controlled trial in 55 obese pre-menopausal women (35 finished), yacon syrup at 0.14 g FOS per kg a day was followed by lower body weight, waist size and BMI. A 2026 pooled analysis of seven yacon trials found lower body weight overall, but changes in BMI and waist size were not significant.
Fasting insulin and HOMA-IR
In the same 120-day trial, fasting insulin and HOMA-IR (an estimate of insulin resistance) fell, while fasting blood sugar did not change. A 2025 review of seven small trials reported similar insulin results, but one-meal studies gave inconsistent effects on blood sugar and insulin after eating.
LDL cholesterol
In the 120-day trial in obese pre-menopausal women, LDL cholesterol fell, while total cholesterol and triglycerides did not change significantly. The 2025 review of seven trials with 161 people in total also reported lower LDL, and its authors said more research is needed on dosing and long-term safety.
Fullness and bowel regularity
In the 120-day trial, women taking yacon syrup reported more fullness and more frequent bowel movements. In 16 healthy adults, 20 g a day for two weeks shortened gut transit time from about 60 to 38 hours. For appetite the trials give mixed results: in a one-meal test in 40 women, 40 g of syrup did not change GLP-1, ghrelin or fullness ratings.
Prebiotic fiber for gut bacteria
FOS is fermented by colon bacteria and is known to feed bifidobacteria. A 2025 review of yacon syrup trials reported that longer use was associated with shifts in gut bacteria, and that people's starting gut bacteria may have affected how their insulin responded to a single dose. Each trial involved few people.
Mechanism of action
Fructooligosaccharide (FOS) prebiotic effect
FOS is not broken down by human digestive enzymes. It reaches the colon, where bacteria ferment it into short-chain fatty acids such as acetate, propionate and butyrate. A 2025 review notes that FOS stimulates bifidobacteria and lactobacilli. Short-chain fatty acids were not measured in the 120-day yacon trial.
Gut hormones: proposed, not seen in testing
One idea is that short-chain fatty acids from fiber fermentation prompt gut cells to release appetite hormones such as GLP-1 and PYY. When this was tested with yacon syrup in a one-meal study of 40 women, GLP-1 and ghrelin did not change. Longer-term hormone effects have not been measured.
Fewer digestible calories than sugar
Because much of the syrup is FOS fiber, which is fermented in the colon rather than digested, swapping it for table sugar adds fewer digestible calories. Yacon syrup still contains real sugars and counts toward carbohydrate intake, and fasting blood sugar did not change in the 120-day trial.
Faster gut transit
Like other fermentable fibers, FOS can speed the movement of stool through the colon. In a two-week crossover trial in 16 healthy adults, 20 g a day of yacon syrup shortened transit time, while the rise in stool frequency was not statistically significant.
Clinical trials
Double-blind, placebo-controlled trial of yacon syrup at 0.29 or 0.14 g FOS per kg a day, or placebo, for 120 days, measuring body size, blood sugar, insulin, HOMA-IR, lipids and bowel habits. (Genta et al. 2009, Clin Nutr)
55 obese, slightly dyslipidemic pre-menopausal women aged 31 to 49 (35 completed).
The 0.14 g/kg dose was tolerated without digestive side effects, while the higher dose was not. Yacon syrup was followed by lower body weight, waist size, BMI, fasting insulin, HOMA-IR and LDL cholesterol, and more frequent bowel movements and fullness. Fasting glucose and other blood fats did not change. Gut hormones were not measured.
Double-blind randomized crossover trial: breakfast plus 40 g of yacon syrup (14 g FOS) or placebo, with ghrelin, GLP-1 and appetite ratings measured for 180 minutes. (Adriano et al. 2020, Food Res Int)
40 adult women, 20 with normal weight and 20 with grade I obesity.
Yacon syrup had no effect on GLP-1 or ghrelin at any time point, and no clear effect on hunger, satiety, fullness or desire to eat, in the whole group or by BMI. This was a single-meal test, not long-term use.
Placebo-controlled, double-blind crossover trial: 20 g of yacon syrup a day (6.4 g FOS) for 2 weeks per period, with transit measured by radio-opaque markers. (Geyer et al. 2008, Digestion)
16 healthy adults (8 men, 8 women).
Gut transit time fell from about 60 to 38 hours (p<0.001). Stool frequency and softness rose slightly but not significantly. Bloating was not reported more often than with placebo.
PRISMA systematic review of clinical trials of yacon syrup on blood sugar, insulin, lipids, appetite and gut bacteria, searched to October 2024. (Pereira et al. 2025, Nutrients)
7 clinical trials with 161 participants in total, aged 18 to 57.
The review reported lower fasting insulin, HOMA-IR and LDL cholesterol, and better satiety and gut transit, while one-meal studies gave inconsistent blood sugar and insulin results. Mild digestive discomfort was reported and eased with continued use. The authors called for more research on dosing and long-term safety.