LC Tip of the Day #207 Revisited
Thursday, July 07, 2016
I wanted to revisit this tip: Soluble fiber in particular helps with weight loss.
Specifically, it's VISCOUS soluble fiber -- which is found exclusively in plant foods. A recent review of 44 studies found that while 39% of fiber treatments increased satiety, only 22% actually reduced food intake. It seems that the more viscous a fiber is, the better it is at reducing appetite and food intake. Fibers with low viscosity appear to have no influence.
Put simply, the viscosity of a substance refers to its resistance to stress -- as in, the "thickness" of a liquid. For example, honey is much more viscous than water. Viscous soluble fibers such as pectins, psyllium, glucomannan and guar gum all thicken in water, forming a gel-like substance that "sits" in the gut. This gel slows down the emptying of the stomach and increases the time it takes to digest and absorb nutrients. The end result is a prolonged feeling of fullness and a significantly reduced appetite.
There is some evidence that the weight loss effects of fiber target the belly fat specifically, which is the harmful fat in the abdominal cavity that is strongly associated with metabolic disease.
A very large review study found that psyllium and guar gum (both soluble, viscous fibers) are ineffective as weight loss supplements. HOWEVER, one notable exception is glucomannan, a fiber extracted from the konjac root. This is one of the most viscous dietary fibers known, and has been shown to cause modest weight loss when used as a supplement (2-4 g, 3x daily, taken 30 minutes before each meal). Or, eat your Miracle Noodles!
But in the real world, it's the synergy of all the nutrients in foods that provides the most benefits; consuming isolated nutrients will never have the same effects. For this reason, getting your fiber from whole plant foods is best. Rich sources include beans (legumes), flax seeds, asparagus, brussels sprouts and oats, to name a few.
If you're planning to switch to a high-fiber diet, remember to do it gradually to give your body time to adjust. Abdominal discomfort, cramps and even diarrhea are common side effects if you ramp up your fiber intake too quickly.