Dr. Neal Barnard:

The available research is limited, but very encouraging. The study by Susana Genta and colleagues used a yacon extract in a group of overweight women and found a 33-pound (16 kg) average weight loss in four months, which is about two pounds per week. LDL (“bad”) cholesterol also fell significantly. These are impressive changes.

There were no negative effects. Given that yacon is high in soluble fiber (as are oats and beans), I would have expected some gassiness, but the participants did not report that problem at the 10 mg dosage level used in the study (higher doses did cause some nausea and cramps). Many participants had had constipation prior to the study, and that seemed to be relieved by the yacon, but there did not appear to be adverse digestive effects.

The limitation is that there have not been many studies. A PubMed search revealed only three human studies. The absence of additional human studies makes one wonder if the results have not panned out well in subsequent experience. Although there have been some animal experiments, I would not judge them to be useful indicators of either safety or efficacy.

Based on what I have seen, yes. It appears to be safe, it is widely available, and may help with weight loss as well as cholesterol control. It should be used in modest quantities, as high levels can cause diarrhea and cramping.

Also, it is the yacon root and root extracts that are to be used, not the leaves, which may be potentially toxic.

If a person was not keen on the idea of taking a yacon extract, fructooligosaccharides are also found in onions, garlic, asparagus, bananas, artichokes and chicory.

The results are noteworthy in that the rate of weight loss [of the women on the show] – not quite a pound per week – is about what we see with calorie-restricted diets. Yacon was well-tolerated and did not require calorie-counting or going hungry.

The thing we don’t know is whether the weight change that occurred is due to the yacon or due to a placebo effect. It is entirely possible that the participants expected to lose weight and were more attentive to their diets overall. So the next step would be to do a placebo-controlled test.

Dr. Mike Roizen:

Other than the issues below the Genta et al study from 2009 appears to be ok.

Defects to study:
1. Failure to list the number of subjects whose data was available for analysis in Table 2.
2. Appropriate statistical treatment, though it would probably would still be statistically significant.
3. No definition of how good blinding was.
4. 100% compliance with a peculiar time to take the active and the placebo

Benefits to study:
1. Remarkable weight loss after 120 days
2. Cure of constipation in some subjects

3. Improvement in other markers of the metabolic syndrome that would decrease with weight loss, like LDl decreases and HDL increases.

Overall, the Genta et al research in 2009 would benefit from some improvements in study design, but the results are impressive enough that they merit further large studies.

A 2.9 pound and 1.9 inch waist reduction is exactly what one wants in a 3.5 week period. Pretty darn good! Nothing works for everyone, but that this worked for two thirds is probably great. The data in the one prior study in humans had about twice the rate of loss for a sustained period – so this may be able to help these women do so as well.

But such a small loss when you are trying to lose for a television show may reflect the television show effect. I would like to see what happens over a longer period.

The only negative side effect (and some will consider it a benefit) is the increased frequency of bowel movements. It is unclear from the comments if this was problematic for more than 5%.

Based on available data, YES it is worth trying; but keep exercising, avoiding the five food felons, and managing stress.  But yes it is worth a try if you are on a plateau.

Dr. Garth Davis:

I need to really research even more but I am very familiar with FOS which are the primary active ingredients in the yacon.

The study was actually very well put together. They utilized a placebo control randomized trial which is about as statistically valid as can be done. I would have liked to have seen a crossover. I would also like to have seen another source of FOS used to see if it is the FOS or if this was secondary to something unique to the yacon itself. We know from studies of isolated vitamins that they don't work unless part of the plant.

The study had some pretty impressive result although the improvement in insulin sensitivity and drop in LDL are likely just secondary to the weight loss. However, the study was just four months. I have seen all kinds of diets work for four months then fail. We see this over and over. They don't go into enough detail about what diet they utilized. I also would like to know if the yacon group felt nauseated. We see several medicines that cause weight loss mainly because people get sick.

What we do know of FOS is that they serve as a prebiotic, meaning the become food to sustain a healthy bowel flora, and emerging research has shown that the type of gut bacteria we have may affect our weight.

My concern with the promotion of a "product" is pretty soon it no longer is the juice of a yacon. Remember, this stuff grows in the Andes. I am sure it would become expensive. Companies may just use a bit of it to make a product and then add preservatives to help it survive the flight to New York City so people can buy it. The FDA does not monitor nutraceuticals so the public really doesn't know what they are getting. Next thing you know you have the next acai berry craze. And the crazy thing is that people shell out tons of money for the acai berry juice, loaded with preservatives, when a handful of blueberries is just as good for you.

What I take away from this research is what I take away from much of the research I do on a day to day basis: Fruits and vegetables are good for you. You can get FOS from all kinds of natural fruits and vegetables. FOS are certainly a good part of the diet but you don't need an Andean tuber to get it.

Leslie Bonci

I think the weight loss was modest, and could have been achieved just by people paying more attention to diet, BUT the fact that most participants lost two inches around their waist is meaningful. As we do get concerned about visceral fat, so losing that weight can also help to lower risk of diseases.

So that being said, at the end of the day, any changes that people make need to be sustainable. Many of the participants said they found this fairly easy to use, whereas others, not so much.

So it seems that if people find a way to use yacon, either stand-alone, added to tea, or perhaps to bake with, and find it palatable, AND still lose weight, then it certainly could be part of one's weight loss tool kit.

Dr. Caroline Apovian

Yacon is a tuber which is consumed as a fruit in the Andes. Yacon stores its carbs in the form of fructoligosaccharides which resist digestion in the upper part of the gut in humans. Therefore this type of sugar has a low caloric value and may be studied as a weight loss aid.

Studies so far using Yacon syrup have not been controlled trials and so it is hard to determine whether or not Yacon syrup can help people lose weight.

A study by Genta S et al in 2009 showed that yacon syrup given to patients trying to lose weight showed that a high intake compared to a low intake of Yacon did cause some notable side effects such as severe flatulence which was considered unacceptable – therefore it is hard to discern from this study whether or not Yacon syrup had a weight loss effect over and above a diet and exercise program compared to placebo because so many people dropped out of the study.

However, I think that more studies should be conducted on Yacon syrup as an alternative to other sugars for patients with obesity and type 2 diabetes to help them with weight loss.

Dr. Lou Aronne:

The study is small, preliminary and pilot, and given the incidence of adverse events that you've seen, I agree with Dr. Caroline Apovian that I would not be enthusiastic about the general public being told that it is the next thing to try.

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