Thursday, April 24, 2014
Adding fibre to your diet is one of the most commonly suggested strategies to increase satiety – however, we have long known that fibre is not fibre, as several subtypes of fibre vary widely in their different impacts on satiation.
Now, it turns out that even within distinct groups of fibre (in this case pectin), much depends on the actual physical form in which this fibre is ingested.
Thus, a randomised controlled trial by Anne Wanders and colleagues, published in Physiology and Behaviour, tested the satiety and metabolic effect of no pectin, bulking pectin (10 g), viscous pectin (10 g), or gelled pectin (10 g), whereby the latter was supplemented either as capsules (10 g) or as liquid (10 g).
Here is how the authors summarize their findings:
“Appetite was reduced after ingestion of gelled pectin compared to bulking (p < 0.0001), viscous (p = 0.005) and no pectin (p < 0.0001), without differences in subsequent energy intake (p = 0.32). Gastric emptying rate was delayed after gelled pectin (82 ± 18 min) compared to no pectin (70 ± 19 min, p = 0.015). Furthermore, gelled (p = 0.002) and viscous (p < 0.0001) pectin lowered insulin responses compared to no pectin, with minor reductions in glucose response. Regarding methods of supplementation, appetite was reduced after ingestion of the gelled test product compared to after capsules (p < 0.0001) and liquid (p < 0.0001). Energy intake was lower after ingestion of capsules compared to liquid (− 12.4%, p = 0.03).”
If you are now totally confused, so am I.
Clearly, pectin is not simply pectin – even for the same amount (10 g), much depends on exactly what form of pectin we are talking about – bulked, gelled, viscous, liquid, capsules?
They are all different!
And herein lies the problem with focussing on single nutrients – fibre is by no means alone in that the form and context in which it is consumed matters.
Along similar lines, fat is not fat, carbs are not carbs, protein is not protein, sugar is not sugar, fruit is not fruit, meat is not meat, veggies are not veggies, super foods are not super foods, and miracle supplements are not miracle supplements.
This is exactly why all dietary advice needs to be taken with a hefty pinch of salt.
Wanders AJ, Feskens EJ, Jonathan MC, Schols HA, de Graaf C, & Mars M (2014). Pectin is not pectin: A randomized trial on the effect of different physicochemical properties of dietary fiber on appetite and energy intake. Physiology & behavior, 128, 212-9 PMID: 24534170