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Fibre Supplement Can Decrease Glycemic Index

Yesterday, I blogged about the results of the DIOGENES study showing that a moderately high-protein diet, that also has a relatively low glycemic index, may be better for sustaining weight loss.

This post prompted a number of questions regarding the glycemic index (GI) – which most readers may recall refers to the relative speed with which carbohydrates in a given food can be digested and enter the blood stream as glucose.

Thus, high-glycemic index foods (e.g. baked potatoes, white bread, polished rice, corn flakes, sugar-sweetened beverages, etc.) result in a rapid rise in blood glucose levels whereas low-glycemic index foods (e.g.most fruits and vegetables, legumes/pulses, whole grains, meat, eggs, milk, nuts, etc.) take longer to digest and therefore result in a more gradual rise in blood sugar levels.

Clearly, based on yesterday’s post (and several previous studies on the benefits of low-GI diets), reducing the glycemic index of a meal may be beneficial for maintaining weight loss, a strategy that is of course best adopted by choosing low-glycemic-index foods in your diet.

However, we also know that choosing the right foods may not always be possible or practical.

This is where readers may be interested in new data showing that you can also substantially modify the glycemic index of foods (or a meal) by simply adding or taking a fibre supplement.

Thus, a paper by Brand-Miller and colleagues from the University of Sydney, Australia, published last month in the European Journal of Clinical Nutrition, now shows that adding a viscous fibre supplement (PolyGlycopleX (PGX) – which was co-developed by researchers in Toronto, Canada), can delay the glycemic response after a meal.

This paper reports the findings from three separate trials, each in 10 normal weight subjects.

Study 1: Granular PGX supplement was tested at four doses (0, 2.5, 5.0 and 7.5 g) with a mixed breakfast

Study 2: Granular and capsule forms of PGX were given in a single dose (5 g for granules and 4.5 g in capsules) at -60, -45, -30, -15 and 0 before, and +15 min after a bread meal.

Study 3: PGX capsules at increasing doses (1.5, 3, 4.5 and 6 g) were consumed with the evening meal to determine effects on glucose tolerance at breakfast.

In Study 1, doses of 2.5, 5 and 7.5 g PGX at breakfast reduced the incremental area under the glucose curve by up to 50% in a linear dose-response fashion.

In Study 2, the granular PGX (5 g), but not the capsules, reduced glycaemia by up to 28% when consumed from -45 before to +15 min after the bread.

In Study 3, capsules containing 3, 4.5 and 6 g PGX consumed with the evening meal reduced glycaemia at breakfast by up to 28%.

Thus, this study nicely documents that adding PGX to meals or even taking this fibre as a capsule well before a meal (even the night before) can markedly reduce the glycemic index of a meal in a dose-related fashion.

Obviously, simply sprinkling PGX over your food or taking PGX capsules is very unlikely to have all of the benefits of actually eating low-glycemic-index foods (which tend to be healthier for many reasons other than just their glycemic index).

But, when food choices are limited, PGX may well provide a practical solution to dropping the glycemic index of a meal.

Whether or not using PGX to reduce the glycemic-index of foods would have the same weight maintenance benefits as observed in the DIOGENES study in people who actually ate low-glycemic index foods is of course not clear – however, this may well be a hypothesis worth testing.

This be as it may, it is certainly refreshing to see a “supplement” company investing in serious clinical research to support their claims (something that cannot be said for all players in this industry where science-defying claims and “results-not-typical-style” testimonials rule).

Toronto, Ontario

Disclaimer: I have received consulting honoraria from Natural Factors the makers of PGX.

Brand-Miller JC, Atkinson FS, Gahler RJ, Kacinik V, Lyon MR, & Wood S (2010). Effects of PGX, a novel functional fibre, on acute and delayed postprandial glycaemia. European journal of clinical nutrition PMID: 20924393


  1. Question- Does PGX also make you feel fuller on less food?

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  2. I found this product pretty interesting as well (and the paper in NEJM) – one thing that gives me a bit of caution though is it is a very small trial, only 10 people. Interestingly the same group published a few days ago in Nutrition Journal something very similar ( – I wonder if they would have been better off with just the one, more detailed paper, maybe a bit of salami slicing going on!

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  3. For the past few years in the States, fiber has been added to lots of processed foods, as a way to create satiety. Fiber has been seen as a holy grail of sorts for weight loss. We have lots of advertising assuring us that fiber is a weight-reduction bonus that will help us all remove those excess pounds. The reduction of GI seems somewhat intuitive with fiber. However, with all the fiber-rich foods available (both processed and natural), weight gain is on the rise. So I don’t think it will be ‘the solution’. I do appreciate your comment that adding fiber when healthy choices are not available is a strategy for readers. 5 servings of fuits and veggies gets me my fiber daily.

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  4. Could a person get a similar benefit by eating a couple of apples a day?

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  5. I tried PGX. It helps with the keeping me more regular on a low carb diet. Any low carb is low fiber, hence the issue. A tablespoon of psyllium fiber, flax meal or sometimes oat bran does as much, along with a couple of glasses of cold water. It is also cheaper. I could not feel any “fuller” effects.

    No sugar, no grains, no manufactured oils, slow carbs (low caloric density) and a little animal products (fats and proteins) leads to no hunger, which is a proven N=1 method.

    Canada good food guide is all about nutrition, which is not anything to do this weight loss.

    Keep up the good work

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