Proof of the Prebiotic Effect: Dr. Oz’s Fat Busting Yacon Syrup

I know. It sounds like some spammy email subject line. I’d normally avoid something like this like the plague. Let me explain.

I probably spend an inordinate amount of time looking for viable sources of fermentable prebiotic fiber, preferably from whole foods. And so I stumbled upon yacon, a South American tuber related to jicama that’s slightly sweeter and exceptionally high in short-chain fructooligosaccharides (up to 70%), one of the more potent and beneficial prebiotic fibers. And then the assault began: yacon syrup everywhere. I was barraged by a ton of ad spam, claims about weight loss, and a bunch of Dr. Oz references. What on earth? So I looked into it.

It looks like it all stems from a segment on the Dr. Oz show called “The Yacon Syrup Project.”


The project seems to be based on a 2009 Argentina study that had 55 obese women with insulin resistance consume yacon syrup for 4 months. The study seems to have yielded impressive results:

Daily intake of yacon syrup produced a significant decrease in body weight, waist circumference and body mass index. Additionally, decrease in fasting serum insulin and Homeostasis Model Assessment index was observed. The consumption of yacon syrup increased defecation frequency and satiety sensation. Fasting glucose and serum lipids were not affected by syrup treatment and the only positive effect was found in serum LDL-cholesterol levels.

And it attributes the effects to the bacterial fermentation of FOS and the resulting production of short-chain fatty acids:

The major products of FOS metabolism in the intestine are short-chain fatty acids (SCFA). The data presented in this study demonstrate that yacon syrup is an excellent source of FOS with favorable health effects on pre-menopausal obese women and that these effects would be probably modulated via SCFA produced during FOS fermentation in the colon. Much has been investigated concerning SCFA production in the gut and the different metabolic significance of the individual acids. It is known that butyrate serves as fuel for the mucosa, whereas acetate and propionate enter the portal blood and may influence systemic carbohydrates and lipids’ metabolism. Therefore, the pattern of fermentation of syrup-containing FOS might be important when predicting their metabolic effects.

It’s also worth mentioning that these results were achieved with not all that much FOS — 0.14 grams per kg of body weight.

And so it looks like “America’s doctor” conducted his own experiment, asking 60 women to take one teaspoon with each meal for 4 weeks, and change nothing else about their diet or lifestyle. It, too, seems to have yielded impressive results: 73% of women lost weight, 14 of them lost five pounds or more, and the average amount of weight lost was 2.9 pounds. With nothing more than a healthy dose of short-chain fructooligosaccharides. Sadly, many who are taken in with this stuff will think yacon syrup is some special elixir with magical properties, when it’s really just an effect of prebiotic fermentable fiber.

So why am I writing about this?

Well, first I’ll say why I’m NOT writing about this: I’m not suggesting that people should go out and grab a bottle of yacon syrup. There seems to be a whole industry that’s sprouted up as a result of this segment. While the syrup is indeed a potent source of FOS, it’s pretty pricey and not all that economical. I certainly wouldn’t recommend it as a staple — maybe something to keep around for an occasional prebiotic boost and to foster some fiber diversity? Or maybe something to try if you are keen on doing a little experimentation just for the heck of it. On the upside, it seems to have a not offensive taste — similar to molasses, apparently. And most options seem to be organic and GMP-certified. But again, as a major staple, I don’t think it makes sense.

Here’s why I AM writing about this: it’s further proof of the prebiotic fiber effect. The effects line up pretty well with what people are experiencing with Resistant Starch/Potato Starch, and here we have those effects corroborated with a completely different type of prebiotic fiber. Significant reduction in body weight. Significant increase in insulin sensitivity. Improved bowel function. Lowered LDL cholesterol. Nothing about sleep improvement, but maybe if they measured it they would have found something.

And it also underlines, again, the primary reason why I think the Resistant Starch experiment has been so successful: it has found a cheap, high-dosable, and accessible source of a potent prebiotic fiber in the form of potato starch. But I don’t mean to discount the unique effects of RS — there’s just more to figure out on that front.

Anyway, it’s too bad there was no gut analysis involved in either of these experiments. Am I the only one dying to know their before and after Actinobacteria? Clostridia? SCFA production levels?

Or do I just need to get out more?

— Heisenbug


17 thoughts on “Proof of the Prebiotic Effect: Dr. Oz’s Fat Busting Yacon Syrup

  1. During your investigation on this, did you find any mention to sleep/insomnia (anecdotes or in studies).
    Just wondering if it may have similar sleep related benefits as Honey (in some people) that has been discussed recently here & on Seth’s blog.

    i seem to be a bit an outlier in regards to sleep, i have seen no improvements in the sleep department from RS (bobs red mill p.starch) or honey (various types).
    (also tried molasses, golden syrup, rice syrup, sucrose, glucose, tart cherry juice,…)

    thx for the post btw.

    • Hi Daz,

      I have not seen any references to sleep effects from yacon or FOS in general. Or for RS, for that matter. It’s all anecdotal at this point.

      I have a very speculative hypothesis right now with regard to RS non-responders — that perhaps people who are not responding do not have enough bifidobacteria to start the process. Bifido seem to be the “starter engine” for fermentation in the gut. Without them, the process might not kick into gear.

      Here is what you can do to test this out: the next time you take your PS, consider also consuming something with bifidobacteria in it during or near the time you take the RS. Yogurt works, however you have to be sure the label says it contains bifidobacteria (sometimes called “bifidus”). Or you could go with a probiotic that contains bifidobacteria. But yogurt generally contains a lot more than a pill.

      Would be interested to hear results if you do decide to try it out.

      • i guess i am a “non-responder” with regards to any sleep enhancement.
        however, the p.starch has def improved my digestion (stools). it took me a few weeks to adapt (building up the dose).
        i think 1.5 tablespoons p/d seems to be the sweet spot for me, limiting to 1 tablespoon max per dose.

        i do eat a lot of yoghurt & have eaten it with or close to PS. tho not all of them probably had the bifidus strain (would need to check).
        anyway just ate 1tbl PS with 170g greek yoghurt, which listed bifidus as the fourth strain (of five) on the label (still morning where i am).
        May try 1/2 tbl PS before bed or late evening with same yoghurt or another bifidus yoghurt.
        …Do you think timing matters for sleep benefits, ie. how long before bed should i take the Yog&PS, any suggestions?


      • I’ve been wondering about the timing question as well. I don’t have an answer yet.

        Since you do seem to in fact respond, it could be a dosage/amount issue. Most people seem to work up to 4 tbsp/day, 2 tbsp per serving.

        Also, sleep is pretty complex. Certainly beyond the scope of just one tiny gut hack.

  2. So how hard is it to find actual yacon root to add to your diet? Also, is the yacon syrup produced in such a way that it preserves the FOS? And how is it produced – high heat, chemicals, anything else bad? Reviews on Amazon indicate that people are using it as an alternative sweetener – and probably aren’t even aware of the possible benefits to the gut.

    And yes, you probably need to get out more but since we’re all here reading a blog on gut bacteria – then so do we!

    • JV,

      Apparently yacon is starting to pop up in farmer’s markets. I’ve never seen it myself.

      Most of the syrup products I looked at seem to be well-produced. Yacon syrup is made the same way as maple syrup. And yes, the syrup is high in FOS. Usually around 50%, which is a lot. The entire aim of these products is to pack in as much FOS as possible.

  3. Nativas brand makes a dried certified organic raw yacon slice product sold in a 4 oz zip-seal pouch. Nativas products are sold in natural food stores, Whole Foods, and similar quasi-natural foods stores (& maybe online), but I haven’t seen the brand stocked at conventional supermarkets. The dried yacon slices are sort of like a chewy sweet potato chip or a somewhat less sweet dried apple slice. Probably could be rehydrated. I’ve used it in smoothies or eaten from the bag, but I’ll bet it would be good rehydrated, diced, and added to dishes that call for apples (curried chicken/tuna salad comes to mind).

    Can’t remember what I paid for the bag I’m holding now, but I remember it wasn’t cheap. Would probably be more cost-effective to buy whole yacon if available locally, slice it with a mandoline, and slow-dry it in the oven or dehydrator.

  4. Hi Mr. H,
    congratulations on your blog. Great stuff! I have a couple of questions for you. What about sugar alcohols? They seem to be part of those carbs that make it to the colon and feed our tiny guests (FODMAP). Are they good, are they bad? What’s your take on them? Is there any study regarding their influence on the microbiota?
    As daz wrote on the comments, on me as well honey didn’t have an impact in terms of sleep. If anything, it appears to worsen it. A couple of weeks ago I had a Tbspof some very fancy organic german honey before going to sleep, and it was hell. It took me 3h to fall asleep (usually I fall adleep within minutes) and had generally a very bed night’s sleep. I’ve had better success with smaller doses and less fancy honey and with ripe bananas. Yesterday, after a day spent reading your blog and researching on RS, I had an unripe banana before sleep. Again, hell. It took more than 3h to fall asleep. This made me wonder. Is it possible that the more FOS or RS before sleep, the worse I sleep? I should still experiment with Potato Starch. Anyway what seems to completely knock me out are desserts. One piece of cake or some icecream before sleep and I’m gone before I even know it. Hacking sleep is not that simple afterall. Strange.

    • Some sugar alcohols are fermentable (isomalt), and others don’t seem to be fermented at all (erythritol). There isn’t a ton of research showing what their prebiotic properties actually are. As such, I wouldn’t really go out of my way to get them apart from naturally occuring ones in fruits like apples.

      It’s certainly possible that FOS/RS could interfere with sleep — improved sleep is not at all an officially documented effect. It’s purely anecdotal. Since honey/bananas are whole foods with a lot more than just fiber, they could have all sorts of effects. Experimenting with isolated fibers will probably help narrow that down.

  5. You mention jicama (also called yambean) is related to yacon. I didn’t know that.

    My family *loves* raw sturdy, crunchy, slightly juicy jicama slices for dipping homemade guacamole, hummus, and yogurt based dips, as well as just plain, or julienned/grated in salads (where the neutral taste of jicama takes on the flavors in the dressing).

    Jicama seems be overlooked, though, and under-appreciated as an inexpensive source of prebiotic soluble fiber. I didn’t know about jicama until I moved from the East Coast to So Cal in the mid-90s, where it’s pretty easy to find the homely relatively inexpensive jicama tuber just about everywhere from the bodegas to conventional supermarkets to upscale gourmet/health food stores ($1-2/lb, usually cheapest and freshest in stores that cater to Mexican-American tastes).

    Not sure how easy it is to find fresh jicama in mainstream markets throughout the US, though; ethnic grocery stores are probably the best bet. The few times I bought jicama in my hometown city in the Northeast US it wasn’t very fresh or juicy (once I bought one coated in wax, thinking it might be better than the desiccated looking specimen I passed over in a competing supermarket, but the wax only helped the jicama maintain a fresh appearance; inside it was dry, slightly bitter instead of slightly sweet, and had lost all of its crunchy appeal).

    I like to put jicama slices or sticks out on a plate while I’m preparing dinner, to keep hungry family members from raiding the fridge before the meal. I find it fastest and easiest way is to cut a jicama in half, lay the flat side down, and following the curve of the tuber, thinly slice off the thick fibrous skin from top to bottom all around with a sharp boning knife instead of peeling it with a veg peeler (my veg peeler doesn’t take nearly enough enough skin off, requiring at least two passes and removing the fibrous skin from the blade by hand). Then cut into slices or sticks as desired, or use a mandoline to cut slices, sticks, or tiny julienne strips. With even average knife skills, preparing a jicama is quite fast and easy. Peeled and cut leftover jicama stores well in an airtight container in the fridge for a few days, too.

  6. In your most recent thread, I mentioned that I had recently added yacon powder to my list of fibers, contributing to my diversity of sources. Imagine my surprise to see this later. I thought I’d share the reason in case you hadn’t seen it.

    First, I read an article about how Barnesiella can kill some antibiotic resistant pathogens. I decided to explore probiotics for Barnesiella, and found this.

    Yacon FOS seems to provide additional benefits over commercial FOS.

  7. I must need to get out more too. I’d love nothing more than to see a detailed analysis and comparison of the before and after of the various bacteria, especially beneficial ones. Ive noticed Yacon root is the Probiotic I’m currently trying.

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