Yacon (Smallanthus sonchifolius) is a tuber, whose syrup contains a large amount of fructooligosaccharides (FOS), which are carbohydrates that are partially absorbed and prebiotic in nature. Yacon may have benefits for intestinal health and may reduce appetite, but studies on it are limited.
Sources and Composition
Yacon refers to the plant Smallanthus sonchifolius (of the family Asteraceae) which is also synonymous with polymnia edulis and polymnia sonchifolius. It is native to South America, and is cultivated in countries such as Colombia and Ecuador for both nutritive and medicinal uses. It is sometimes paired alongside Maca due to their similar places of origin and both being tuber vegetables used as dietary supplements.
Yacon is a plant which has usage as a nutritive functional food (mostly due to its syrup) and the name 'Yacon' is thought to originate from yakku (tasteless) and unu (water) from the Quechua Indian language. Other names for this plant include 'Yacon strawberry' (US), 'Yacon Potato' or 'Diet Potato' (Brazil), or the names of aricoma and jicama (Ecuador and Peru, no botanical relation to the mexican tuber pachyrhizus erosus which is more commonly called Jicama) and despite the aforementioned 'tasteless' origin of its name the syrup derived from Yacon is said to have physical and sensorial characteristics are similar to those of honey or sugar cane syrup.
It is sought after as a dietary supplement due to its fructooligosaccharide (FOS) content, mainly because it has a low production cost and high yield per hectare whereas other supplemental sources of FOS (Jerusalem artichoke, Chicory) tend to be more expensive to produce.
Yacon is a nutritive vegetable (a tuber vegetable resembling a Jerusalem artichoke or variant of potato) grown mostly in South America, and is used as a functional food for general health and weight loss. It is also a common dietary staple
It appears that the leaves are also used medicinally at times, as an infusion of the leaves of Yacon are traditionally used for the treatment of diabetes and disorders related to glucose metabolism as well as kidney impairments.
Yacon (as a whole plant product, water weight inclusive) tends to contain:
- 85-90% moisture content
- Carbohydrates (9-13g/100g) and dietary fiber (3.1–4.1mg/100g) of which 6.4 to 70% of the root's dry mass is said to consist of fructooligosaccharides (FOS) while 15-40% of the dry mass is simple sugars
- Proteins (2.7–4.9g/100g
With lesser noncaloric components of (tubers unless otherwise specified):
- Diterpenes Smallanthaditerpenic acids A and C (leaves) and acyclic diterpenes smaditerpenic acid E and F
- A sesquiterpene lactone known as enhydrin (leaves at 0.97% dry weight) as well as sonchifolin, uvedalin, and uvedalin (Melampolides)
- Phenolic compounds (203mg/100g) based off of caffeic acid, most notably chlorogenic acid (48.5+/-12.9μg/g) and caffeic esters of octulosonic acid (a carboxylated sugar)
- Ferulic acid
- Potassium (1.80-2.95mcg/g)
- Calcium (0.56–1.31mcg/g)
- Phosphorus (1.82–3.09mcg/g
- Iron (3mcg/g)
- Zinc (6.74mcg/g)
- Vitamin C (13110mcg/g)
The total antioxidant capacity due to the aforementioned phenolics is moderate to low, but comparable with other tuber vegetables grown in the same region (Olluco, Oca, Mashua) and potato as well as being similar to another FOS rich tuber known as Chicuru.
The short chain fructooligosaccharides appear to be the bioactive component of yacon, since there does not appear to be much else in this plant's tubers (the commercial product from where the syrup is derived). There are some phenolic compounds in yacon based off of caffeic acid, but they appear in low levels
The fructooliogosaccharides (FOS) in yacon are predominantly short chain FOS between 2-10 fructose molecules, in contrast to the 60+ fructose molecules in an inulin molecules chain which are referred to fructopolysaccharides (Yacon is sometimes thought to be a major source of inulin due to its similarities to Jerusalem Artichoke, a major inulin bearing plant); regardless, FOS from yacon is structured in a similar manner as inulin, having the fructose being configured as β(2→1)fructofuranosylsaccharose molecules and is similarly indigestible in humans, as humans cannot digest the β(2→1) bond between sugars due to a lack of enzymes in the small intestines.
Due to the lack of human digestion yet microbial ingestion in the colon, FOS from yacon are classified as prebiotics particularly for Bifidobacterium and Lactobacillus species.
The short chain FOS in yacon are structurally different from inulin in regards to their size (inulin being much larger), but the bonds between the fructose molecules are quite similar and they appear to work in a similar way
When processed into a syrup, the overall composition of the syrup is approximately:
- 67.04-75% carbohydrate, of which 40-60% is fructooligosaccharides (FOS)
- 2.16% protein
- 0.14% lipids
- Potassium (936mg/100g)
- Sodium (84mg/100g)
When breaking the fructooligosaccharides into chain length via degrees of polymerization (DPs; a way of explaining how many sugar molecules are in a chain) the FOS in yacon syrup tend to be:
- 3 DPs at 7.4% total carbohydrates
- 4 DPs at 11.2% total carbohydrates
- 5 DPs at 10.2% total carbohydrates
- 6 DPs at 8.1% total carbohydrates
- 7 DPs at 5.9% total carbohydrates
- 8 DPs at 4.9% total carbohydrates
- 9-12 DPs at 10.7% total carbohydrates
- Inulin (60+ DPs) at 13.5+/-0.4mg/g (1.3%) dry weight
FOS that are lower than 12 fructose molecules in length predominate almost exclusively in yacon, they are relatively balanced, meaning a 4 fructose chain is not favored over an 8 fructose chain, and so on
Yacon appears to have a high heat tolerability (up to 140°C; anything further breaks down the FOS into free fructose and greatly enhances sweetness) and stability in solutions with a pH greater than 3, with the only limiting factor for production being a short shelf-life due to the high water content of yacon; this is circumvented a bit with production of yacon syrup which reduces the 85-90% water content and promotes shelf-life and which is stable at room temperature and standard conditions for up to a year.
Yacon syrup has a slightly acidic pH (5.4) and a Brix of around 73° when standardized for 40-50% FOS.
Yacon tends to have high heat tolerance until the FOS breaks down, which suggests that the tubers and the syrup derived from it can be used in cooking. The only limiting factor of its short shelf life is the high water content of the tuber itself. Water content is reduced with the syrup however, thus extending shelf life
In rats, when ingestion of Yacon syrup (340mg/kg or 6,800mg/kg) alongside fatty acids was compared to fatty-acid only controls, serum triglycerides were reduced 39.6-41.6% with no apparent dose-dependence; dietary cholesterol absorption was unaffected.
One study has noted a reduced overall exposure (absorption) of triglycerides when yacon was consumed alongside dietary fatty acids. The mechanisms underlying this are not known at this time
In obese and slightly dyslipidemic adults given 140mg/kg FOS (via Yacon syrup) daily for 120 days, there was a reduction in LDL cholesterol (although this was confounded with weight loss) and no significant alteration in total cholesterol nor HDL cholesterol.
The lone study assessing cholesterol levels in humans noted a reduction in LDL cholesterol that occurred alongside weight loss. It is not known if yacon has an inherent influence on cholesterol levels in humans
Fructooligosaccharides (FOS) in general are thought to have hypolipidemic (triglyceride reducing) properties secondary to producing GLP-1 in the colon (prebiotic effect) and to produce short chain fatty acids (SCFAs) such as propionate; both of which have hypolipidemic (triglyceride reducing) properties.
This hypolipidemic property, in rats, appears to be secondary to suppressing triglyceride synthesis in the liver resulting in less production and efflux of vLDL cholesterol (known to mediate efflux of triglycerides from the liver to serum) as most lipogenic enzymes in the liver have been noted to be suppressed with rat diets consisting of up to 10% dietary FOS. Despite reducing efflux of triglycerides from the liver, dietary FOS appears to reduce liver fat buildup from excesses of dietary fructose in rats.
Propionate is known to be increased in the liver following ingestion of fermentable carbohydrates and is a known inhibitor of fatty acid synthase (FAS, a highly nutrient responsive enzyme that produces fatty acids), although this enzyme is significantly less responsive to propionate in humans relative to rats.
Dietary fructooligosaccharides (FOS) are known to have triglyceride-reducing properties in rats, secondary to the suppression of triglyceride synthesis in the liver. Triglyceride synthesis pathways in rats are more sensitive to inhibition than in humans however, so it is not currently known if these effects extend to humans
In obese adults with minor dyslipidemia (high blood triglycerides), consumption of yacon syrup providing 140mg/kg FOS daily (10g per 70kg bodyweight) failed to significantly alter fasting triglycerides.
The one study in humans to assess triglycerides failed to find any benefit with yacon syrup, despite weight loss
Interactions with Glucose Metabolism
Although a large number of studies have investigated the effects of yacon on diabetes, most of these studies use yacon leaf extracts as that is a traditional medicine for diabetes probably due to the 0.97% enhydrin content which is bioactive on its own. The roots and tubers (from which the syrup is derived) are not commonly utilized for this purpose.
Yacon leaves are known to have hypoglycemic (glucose reducing) properties, but this may not apply to the tubers/roots of the plant, nor the syrup derived from the tubers. These properties may also be accompanied by deleterious effects on the kidneys (see kidney section for more detail)
In rats fed an acute dose of either 340mg/kg or 6,800mg/kg fructooligosaccharides (FOS) from yacon flour, there was a minor reduction in the spike of blood glucose following an oral glucose tolerance test at 60-120 minutes yet not prior to the test. This efect only occurred with the low dose, and ingestion of yacon flour did not modify the overall exposure (AUC) of glucose after a meal.
When not consumed in the presence of a tolerance test, yacon itself showed a similar increase in blood glucose as glucose itself when measured at 60-120 minutes, but the spike seen at 20 minutes (with glucose) was not present.
In rats, consumption of yacon tuber/syrup FOS alongside dietary sugars does not appear to significantly prevent an increase in glucose levels in the blood from the sugars. Consumption of yacon alone will cause an increase in blood sugar, but without the spike seen with pure sugar
In a study of Zucker rats fed 6.5% yacon for five weeks, compared to an isocaloric control diet, yacon significantly reduced fasting glucose. Euglycemic-hyperinsulinemic clamp showed an improvement in insulin sensitivity in the rats fed yacon, and comparable glucose disposal rate in yacon and control groups paired with tracer data indicating stabilized hepatic glucose output suggests that yacon improves hepatic insulin sensitivity but does not affect skeletal muscle insulin resistance. One study with diabetic Wistar rats fed aqueous extract of yacon root (at 60 mg/kg body weight) for seven days showed a significant reduction in blood glucose levels, which may have been mediated by a reduction in food intake and increase in water intake (causing loss of glucose via urine).
Fat Mass and Obesity
When obese and dyslipidemic consumed two divided doses of Yacon an hour prior to both the morning and evening meal (conferring 140mg/kg yacon FOS daily, or 10g per 70kg) over the course of 120 days, there were increases in self-reported satiety and weight loss relative to placebo. This study did not track caloric intake, but a reduction in food intake secondary to satiety can be inferred from weight loss. While a doubling of the dose (280mg/kg FOS) was also effective, it was associated with adverse intestinal side-effects such as bloating and flatulence.
One study has noted weight loss in obese women given yacon syrup, and although calories were not tracked in the study, a reduction of food intake can be inferred due to an increase in satiety and weight loss occuring. This suggess yacon is an appetite suppressant when taken with meals
Bone and Joint Health
Fructooligosaccharides (FOS) in general are known to promote absorption of minerals from the colon into serum, which is thought to preserve bone mass via providing more exposure to dietary minerals involved in regulating bone mass (calcium, magnesium, and phosphorus mostly).
This increased absorption is due to bacterial production of short chain fatty acid (SCFA) binding to minerals and facilitating their absorption and may promote increased expression of proteins regulating calcium uptake in the colon; while this effect is primarily seen in the distal colon, it may not extend to the proximal colon or the small intestines, as bacteria are not present in high levels in the small intestine.
Fructooligosaccharides are known to promote calcium/magnesium/phosphorus reuptake from the colon,secondary to producing SCFAs. This increased mineral uptake is thought to promote bone health
In otherwise normal Wistar rats, yacon flour (from the tubers) at 15.6% of the diet by weight for four weeks failed to significantly increase the mineral content of the tibia relative to control; in the same study, rats given Bifidobacterium longum culture (probiotic at 0.1mL, 109 CFU/mL) noted a significant improvement whereas the combination of treatments was similar in potency to culture alone and no group experienced an increase in femur thickness nor fracture resistance. In another study, a lower dose of yacon (conferring 5-7.5% total FOS in the diet) in growing Wistar rats was associated with increased mineral status of bones as well as increased femur stiffness and peak load capacity.
There is mixed evidence as to the efficacy of yacon FOS promoting bone health in rats. Although it has a possible role in promoting bone growth in immature rats, there are no studies conducted in osteoporotic rats
Inflammation and Immunology
Interferons and Immunoglobulins
Consumption of yacon-derived fructooligosaccharides (FOS) in rats has failed to alter serum immunoglobulin concentrations (IgA, IgM, IgG) although an increase in IgA fecal elimination was noted relative to control, suggesting localized effects in the colon. This increase in intestinal IgA is thought to underlie prevention of intestinal infections by the Salmonella enteritidis serovar Typhimurium bacteria in mice fed these pathogens with a diet containing yacon-derived FOS.
Yacon FOS are thought to promote immune defenses in the intestines, but this may not be associated with any systemic increase in immune parameters
Interactions with Hormones
Oral ingestion of 200mg/kg of a yacon tuber extract (50% ethanolic; 73.1% yield) for six weeks in otherwise normal rats appears to increase circulating testosterone approximately three-fold (5.09+/-2.53ng/mL) relative to control (1.66+/-1.08ng/mL); while 50-100mg/kg were also tested, their influence on testosterone was not stated. This is thought to be due to yacon extract (40-60mg/mL in vitro) suppressing the degradation of testosterone, possibly related to a concentration-dependent reduction in testosterone degradation by chlorogenic acid at 4-10mg/mL.
Limited evidence suggests a relative increase in testosterone, secondary to a reduction in degradation. While definite effects on testosterone degradation were noted, the specific enzyme responsible for this was not identified
Peripheral Organ Systems
Yacon fructooligosaccharides (FOS) are not digestible in the upper (small) intestines, resulting in them being partially metabolized in the colon and conferring prebiotic properties. There may be a small caloric content associated with these carbohydrates due to short chain fatty acid (SCFA) production, a normal occurrence with fermentable fibers. Up to 55% of ingested carbon from FOS may be converted to SCFAs (being detected as exhaled carbon dioxide 48 hours after ingestion) of which 90% is used within 24 hours, suggesting about 2kcal energy per gram of FOS ingested.
Yacon FOS have been noted to be preferentially fermented by the bacterial strains of bifidobacteria and lactobacilli when tested in vitro and these prebiotic properties have been confirmed in a rodent trial where yacon promoted the proliferation of these bacterial species with a potency comparable to inulin. The production of SCFAs was noted to be nonsignificantly greater with Yacon FOS than inulin in regards to acetate (51% vs. 21%), propionate (41% vs. 33%), and butyrate (1,293% vs. 1,090%) as well as total SCFAs (78.5% vs. 40%) when the oral doses were similar.
FOS are fermentable in the colon. Due to this fermentation, FOS can exert prebiotic effects on certain bacterial strains. The bacteria that respond to FOS are those that are generally seen as beneficial. This prebiotic effect has been confirmed in rats (with yacon) with a potency comparable to inulin and is known to occur in humans with FOS in general
Fructooligosaccharides in general are able to produce GLP-1 locally in colonic tissue which may underlie the hypertrophy seen with very high doses (6,400mg/kg FOS in rats) in this tissue with yacon syrup and FOS in general. This enhancement of colonic tissue size is associated with an increase in absorptive area and bifurcated crypts, and is thought to contribute to increased feed efficiency in rats and improved mineral absorption from the colon into serum.
A local increase in GLP-1 in the colon is known to promote colonic tissue hypertrophy, which is thought to contribute to increased colonic nutrient reuptake. This includes dietary minerals (calcium and magnesium) as well as short chain fatty acids
Yacon syrup at the dose of 20g (6.4g Fructooligosaccharides) in otherwise healthy adults was able to reduce colonic transit time to 64% of baseline (from 59.7+/-4.3 hours down to 38.4+/-4.2 hours) associated with a mild increase in stool frequency and moisture content but without any notable bloating.
A water leaf extract of yacon has failed to show acute toxicity to the kidneys when fed to diabetic rats but one study using an oral water extract (9% yield) oral ingestion for 90 days noted that the lower two doses (10 and 50mg/kg) were not associated with any toxic signs but 100mg/kg was associated with renal toxicity (inflammation and loss of glomeruli); it should be noted that the petroleum ether extract also tested in this study (lacking any sequesterpene compounds) was fully nontoxic and a sequesterpene rich leaf-rinse extract also tested was highly toxic.
Yacon leaf extract in water, which is commonly consumed as tea, is potentially toxic to the kidneys. The toxicity appears to be associated with the sequesterpene content. This is not thought to extend to the tubers (where syrup is derived from) due to a lack of sequesterpenes in this part of the plant
Sexuality and Pregnancy
Supplementation of Yacon leaves (ethanolic extract of 7.8% yield; 5mg/mL in the water) appears to preserve seminal parameters such as seminal count and daily sperm production in diabetic rats, with a potency comparable to maca (same dose of 5mg/mL) and mixtures of them either in even amounts of in a 9:1 ratio all performing statistically comparable to one another. This spermatogenic property has been noted elsewhere with the leaves and this was replicated by Yacon tubers (50% ethanolic extract giving a 73.1% yield, ingested at 50-200mg/kg for six weeks) as well as the isolated molecules ferulic acid (5mg/kg) and chlorogenic acid (5mg/kg).
Limited and nonreplicated evidence in diabetic mice suggests an increase in spermatogenesis associated with yacon tuber ingestion, although the mechanism is currently not known or replicated
Fructooligosaccharides tend to have differential influences on mineral absorption, as some direct binding to minerals in the small intestine may reduce absorption (this is usually mediated by a phytic acid content) while any increase in colonic pH may be met with increased mineral uptake from the colon into serum, usually demonstrated with calcium and magnesium.
Absorption of calcium, magnesium, and phosphorus from the colon into the blood is enhanced when fructooligosaccharides (FOS) from any source are ingested, and this also applies to yacon
The relative bioavailability of iron (as ferric pyrophosphate at 12mg/kg) appears to be reduced when coingested with a diet containing 7.5% fructooligosaccharides from yacon, with the bioavailability being 63.1% less than iron control without FOS.
Iron, which is one of the minerals not easily taken up by colonic tissue, may have its bioavailability reduced when ingested alongside yacon
Fructooligosaccharides have been implicated in promoting the overall absorption of soy isoflavones as circulating isoflavones are dependent on colonic metabolism, since Yacon may slow intestinal transportation it may allow more time for this metabolic process to occur.
Bioavailability of soy isoflavones, which depend on colonic exposure, may be increased when rats are also given yacon FOS alongside the isoflavones
Safety and Toxicology
In rats fed Yacon flour (up to 6,800mg/kg fructooligosaccharides daily) for four months, there was an increase in cecal hypertrophy seen that did not occur at lower tested doses (340mg/kg; human equivalent of 55mg/kg) and no alterations in other biomarkers of toxicity were noted at either dose.
Yacon syrup up to 140mg/g fructooligosaccharides (FOS) which is around 10g per 70kg bodyweight appears to be well tolerated, although double this dose (20g FOS per a 70kg human) is associated with intestinal pain and diarrhea over the course of 120 days.
Limited studies in humans have found no adverse effects with moderate usage of yacon, although taking higher than normal doses results in intestinal side-effects, likely related to excessive fermentation of the FOS in the colon, producing gas and loose stool
As mentioned more in depth in the kidney section, the leaves of yacon contain sequesterpene compounds which may be harmful to renal tissue.
The leaves of yacon may be harmful to the kidneys based on preliminary evidence, and should be avoided for the time being
There has been one reported case study of anaphylaxis following consumption of Yacon root, of which an allergic reaction was confirmed with a skin prick test. This woman reported numbness of the oral cavity and chest tightness following the tolerance test with an oral dose of yacon root.
One case study suggests that it is possible to be allergic to yacon, although due to the prominent usage of yacon as a food product and limited reported cases of allergies, this condition is inferred to be quite rare