PHAT FIBRE Development

Written by Tommy Wood MD, PhD

Feb. 16, 2017

If you’ve been following the NBT podcast and website for a while, you’ll probably know that we dreamed up a product a while back: PHAT FIBRE.*

The product is a simple 50:50 combination of two ingredients – MCT oil and a digestion-resistant maltodextrin (a “Bionic Fibre”). Note, this is not the normal maltodextrin used to create Type 2 Diabetes in endurance athletes. It’s heat-treated to make it more like a resistant starch (i.e. RS3).

There were a number of reasons for putting this together:

  1. We like to use MCT oil in various guises, especially during endurance events, but travelling with the oil to races is a pain.

  2. A powder is easier add to cooking or beverages.

  3. Pure MCT oil often causes GI distress.

  4. Most MCT oil powders on the market contain a lot of additives, including high-GI carbohydrates (i.e. maltodextrin or highly-branched cyclic dextrin) and dairy-based powders (i.e. sodium caseinate), which a lot of our athletes can’t tolerate.

PHAT FIBRE (PF) was designed to overcome these issues. We chose the digestive-resistant maltodextrin as it is relatively inert, can promote certain beneficial gut bacteria, and allowed us to avoid other additives that people with food allergies have to avoid.

This was basically an attempt to create something that we wanted ourselves but wasn’t available on the market. Many of our clients tried PF, and we sent some to our friends. Most of these guys are nutrition geeks, scientists, low carb or keto-adapted, and/or elite athletes. The feedback was overwhelmingly positive:

Just wanted to let you know that I received PHAT FIBRE. It's awesome, especially in a shake. I love these two ingredients together, too. I've only tried it a few times, but I was full for hours more than I expected.

It's an ideal creamer for me. Much better consistency than hand blending Br*in Oct*ne… Not the rocket fuel that straight liquid C8 is but minus the GI discomfort I'll take this any day.

I like your product, PHAT FIBRE. I’ve been playing around with that. I think it’s pretty cool.

Importantly, a number of people with gut issues have tried it with no negative effects. Chris used it as his main energy source during the multi-stage BC Bike Race, where he beat a number of professional mountain bikers to come 29th. A number of cyclists and marathon runners have also told us they use it during races and it works really well for them.

In terms of a sports supplement, the closest thing available elsewhere is probably UCAN Superstarch, a hydrothermally-treated corn starch initially used in people with glycogen storage disease and then adapted to low carb endurance athletes. They’ve published a paper on the glucose and insulin responses to UCAN vs maltodextrin,1 and Peter Attia has made a video about it. Chris and I also talked about UCAN and this study on a previous podcast.

The next step of the story was obviously for us to find out what PF actually does. Had we just created a nice big placebo effect in 1lb bags? To answer this question, the PHAT FIRBE study was born.

The PHAT FIBRE study

We sent some PF, ketone meters, and Meridian Valley Kraft assays to 12 people – a mixture of NBT people, clients, pro athletes, and ketone buffs. The idea was to track blood glucose, blood ketone (beta-hydroxybutyrate, BHB), and insulin levels for 4 hours after taking 25g (two heaped tablespoons) of PF on an empty stomach. In all the graphs below, PF is taken after the reading at time = 0.

The first thing that comes out is a reminder of how difficult it is to produce and understand data from studies in humans. They’re all so different that the data immediately looks like a bit of a mess. But that shouldn’t deter us! This is what the glucose looked like in the first hour after PF in our subjects (lines connect data from individual people):

I’ve given the data as the change from baseline (in mg/dl) because the absolute values were taken from the Meridian test that measured glucose from a bloodspot on filter paper. We’ve started to see that this always comes out low, probably because the red blood cells continue to metabolise glucose while the filter paper goes to the lab. The glucose on the paper can also degrade over time. However, we’ve done some internal calibrations and we’re pretty confident that the relative changes over time are reasonably accurate. The first thing you’ll notice is that most people see a glucose bump of 10-20 mg/dl in the first 30 minutes, which then begins to decrease. On average, the increase in blood glucose we saw was about half that seen in the UCAN study after 1mg/kg of UCAN Superstarch. But we also gave about half the weight of powder, so they’re potentially comparable.

Three immediate thoughts come out of this:

  1. The “digestion-resistant” maltodextrin we sourced clearly isn’t completely digestion resistant!

  2. If you’re using MCT-based products to support a therapeutic ketogenic diet for cancer (or similar), this version of PF probably isn’t for you.

  3. If you’re a fat-adapted athlete, this glucose delivery could actually be beneficial if provided during a race or during training.

We actually expected we might see something like this, because giving resistant starch to people with some aspects of gut dysbiosis can often cause negative effects (bloating or gas etc), but nobody reported any gastrointestinal side-effects. Therefore it was likely that some of the fibre was being digested.

The next interesting thing to look at is the insulin response:

If we wanted to plot the aggregated data over 4 hours, this is what it would look like in a typical sports science study (such as the UCAN study):

This graph depicts the mean insulin (in µU/ml) with error bars showing the standard error of the mean (SEM) after ingesting 25g of PF at time 0 (baseline). You’ll notice that by averaging everything out, this looks a lot cleaner than all the individual insulin curves! Most studies give the mean with SEM because it makes a nice-looking graph. However, you lose all the individual variability. Any time I see a plot of mean+SEM, I always wonder what the authors are hiding…

If we try to provide more of the data on the graph, it could look like this:

The axes are the same, but this time each line is at the median (which we should use instead of the mean because this data does not follow a normal distribution), and the shapes show all the individual data points. Here you can actually see how much variability there is. It’s also worth noting that a lot of our guys had very low insulin levels that came back below the detection limit of the test (<2 µU/ml). I assigned them an insulin value of 1µU/ml if that was the case.

What you’ll see is that there appears to be an average increase in insulin of almost 5µU/ml (median 2.1µU/ml at baseline to 6.7µU/ml) in the first 30 minutes, which rapidly comes down. For all but one of our participants, the insulin value stayed under 10µU/ml, which is thought to be around the point at which insulin significantly suppresses lipolysis.2,3 Crucially, however, if you took PF during exercise, the insulin and glucose peaks would probably be much smaller. Even if you take high-GI maltodextrin, your insulin and glucose levels drop as soon as you start exercising.1 Also, the occasional spike in insulin signalling is not necessarily a bad thing!4

At this point, based on the insulin and glucose measurements, you might wonder why our fat-adapted athletes like PF. But if you look at the recent data on utilising ketones during exercise, giving a small supply of glucose provides some substrate for anapleurosis (i.e. regenerating oxaloacetate) to allow you to use the Acetyl-CoA coming from ketones or beta-oxidation of fats. I think this is one major reason why UCAN has received so many supporters: it gives a slow drip of glucose to allow fat-adapted athletes to maintain anapleurosis during extended endurance efforts, without having to rapidly drain muscle glycogen (or cannabilise muscle) to do so.

In the work by Professor Kieran Clarke’s research group at Oxford giving a ketone ester (KE) to boost performance in athletes,5 they have found that providing glucose alongside the KE increases performance compared to KE alone, as you need anapleurosis to utilise the extra “energy” coming from the ester. This is why Chris perhaps didn’t see as many benefits as he’d have liked when he tried their KE, and why both Chris and Ben Greenfield have been told by Prof. Clarke to take the KE with glucose during their future experiments with it. More on that soon.

Back to the PF study. You’re probably wondering what happened to ketones. The individual curves in the first 60 minutes look like this:

In this graph I’ve done some statistics excluding those with high fasting BHB (i.e. >1.0mmol/L). In those with a fasting BHB of 0.5mmol/L or below, PF significantly increases BHB within 30 minutes.

This is the aggregated data over time:

As with both insulin and glucose, some people had higher ketones that came down a bit, and others had lower ketones that increased. On average, it looks like there’s both an early bump at 30 minutes from the MCT oil, and then a general increase over the next 2-4 hours. This may be because people remained fasted, or because MCTs cause bimodal ketone production,6 with peaks of absorption after around 15 and 75-90 minutes.7 All-in-all, it’s not a huge change, but considering that it was only 12.5g of MCT in 25g of powder, a BHB increase of 0.2-0.3mM is what we’d expect:

Maximal plasma BHB in response to ingesting increasing doses of MCT. Figure from Cunnane et al., 2016.8

So while PF does look like a good product for the fat-adapted endurance athlete as a small supply of ketones and glucose, we thought we could do better…

Enter PHAT FIBRE version 2.0 (PFv2)

By playing with the components of PF we developed a second iteration that we’ve just had in for “beta-testing” (i.e. Chris takes it and sends me his data).

In PFv2 we replaced the MCT oil (a mixture of C8:0 and C10:0 triglycerides) with pure C8:0 (caprylic acid). Compared to the mixed MCT oil, C8:0 is more likely to drive ketogenesis in the liver. Secondly, we managed to get 70% oil loading in the final powder. Therefore, PFv2 now has 40% more MCTs and 40% less of the “digestion-resistant” maltodextrin. We’re still including a small glucose source, which should be beneficial during exercise, but the idea is to minimise the overt glucose excursions.

Using a hand-held glucose meter after 25g of PFv2, this is how blood glucose looks compared to PFv1:

So far so good! WIth PFv2, glucose started at 88mg/dl and never went above that. What about ketones?

We’re pretty happy with this! With PFv2, BHB increased by 0.5mmol/L within half an hour, and remained elevated for at least 4 hours. As we discover more about “total energy load” (i.e. glucose plus available ketones), it seems increasingly likely that we probably don’t want to push too hard with exogenous ketone sources unnecessarily. In addition to more novel ketone supplements, I think we could find a sweet spot where we can give something like PFv2 over a race to support both ketogenesis and anapleurosis to maximise substrate utilisation without overloading the system.

The data above has been accepted for publication in a peer-reviewed journal (The Journal of Insulin Resistance) and is currently in press awaiting publication.

We’ll be doing some more testing, and Chris will be doing some more racing taking PFv2, and we’ll report back. If you have any thoughts, comments, or questions, please let us know below!

* Yes, that’s the way we like to spell fibre :-)


1.    Roberts MD, Lockwood C, Dalbo VJ, Volek J, Kerksick CM. Ingestion of a high-molecular-weight hydrothermally modified waxy maize starch alters metabolic responses to prolonged exercise in trained cyclists. Nutrition (Burbank, Los Angeles County, Calif) 2011;27:659-65.

2.    Jensen MD, Caruso M, Heiling V, Miles JM. Insulin regulation of lipolysis in nondiabetic and IDDM subjects. Diabetes 1989;38:1595-601.

3.    Sonksen P, Sonksen J. Insulin: understanding its action in health and disease. British journal of anaesthesia 2000;85:69-79.

4.    Bravi MC, Armiento A, Laurenti O, et al. Insulin decreases intracellular oxidative stress in patients with type 2 diabetes mellitus. Metabolism: clinical and experimental 2006;55:691-5.

5.    Cox PJ, Kirk T, Ashmore T, et al. Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell metabolism 2016;24:256-68.

6.    Courchesne-Loyer A, Fortier M, Tremblay-Mercier J, et al. Stimulation of mild, sustained ketonemia by medium-chain triacylglycerols in healthy humans: estimated potential contribution to brain energy metabolism. Nutrition 2013;29:635-40.

7.    Guillot E, Vaugelade P, Lemarchal P, Rerat A. Intestinal absorption and liver uptake of medium-chain fatty acids in non-anaesthetized pigs. The British journal of nutrition 1993;69:431-42.

8.    Cunnane SC, Courchesne-Loyer A, Vandenberghe C, et al. Can Ketones Help Rescue Brain Fuel Supply in Later Life? Implications for Cognitive Health during Aging and the Treatment of Alzheimer's Disease. Frontiers in molecular neuroscience 2016;9:53.

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