Diet supplements don't work. Do they?
I’ve never considered taking a diet supplement; till recently I didn’t even know what they contained or how they work. (I certainly wouldn't take anything that raises metabolism–healthier to let metabolism do its own thing, I say.) Then I read in several places that some diet supplements are supposed to work the way dietary fibre works, by binding a portion of fats and reducing their absorption. This interested me, not because I'm considering diet supplements but because it's nice to know that a phenomenon I’ve been speculating about on this thread isn't unheard of in the diet world.
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One of the supplements I read about was glucomannan, which is an extract of konjac root. I even happened to have some in the house. I bought it in the early days of my low-carb diet, one of several supplements I tried in an attempt to deal with the constipation I suffered when eating about 10 grams of carbohydrate a day. The glucomannan made no difference, so I pushed it to the back of the fail cupboard and forgot about it. I now grasp that the reason it didn’t work was that it’s a soluble fibre; only insoluble fibre significantly helps with constipation. But soluble fibre does have its uses–and, as I was mentioning yesterday, one of those is its apparent ability to reduce the absorption of fats.
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When I looked into weight-loss supplements, I wasn’t surprised to find them reported by researchers as largely ineffective. (Weight-loss in a pill? As if.) In a 2004 review of dietary supplements, for example, Pittler and Ernst find little scientific evidence (in high-standard trials) that they work. But, they say (I pricked up an ear), glucomannan may be an exception. They point to an old trial from 1984, the abstract of which reads:
“An eight-week double-blind trial was conducted to test purified glucomannan fiber as a food supplement in 20 obese subjects. Glucomannan fiber (from konjac root) or placebo was given in 1-g doses (two 500 mg capsules) with 8 oz water, 1 h prior to each of three meals per d. Subjects were instructed not to change their eating or exercise patterns. Results showed a significant mean weight loss (5.5 lbs) using glucomannan over an eight-week period. Serum cholesterol and low-density lipoprotein cholesterol were significantly reduced (21.7 and 15.0 mg/dl respectively) in the glucomannan treated group. No adverse reactions to glucomannan were reported.” (Walsh et al, Effect of glucomannan on obese patients: a clinical study, 1984)
Poking further around the internet, I found the following conclusion to a review of randomised controlled trials of glucomannan:
“Glucomannan appears to beneficially affect total cholesterol, LDL cholesterol, triglycerides, body weight, and FBG, but not HDL cholesterol or BP.” (Sood et al, Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: systematic review and meta-analysis, 2008)
And an Italian paper, which concluded:
"Two groups of 25 severely obese patients underwent 3 months of hypocaloric diet therapy either alone or associated with a glucomannan-based fibrous diet supplement (approx. 4 g/die in 3 doses). The comparative analysis of the results obtained in both groups showed that the diet + glucomannan group had a more significant weight loss in relation to the fatty mass alone, an overall improvement in lipid status and carbohydrate tolerance, and a greater adherence to the diet in the absence of any relevant side effects. Due to the marked ability to satiate patients and the positive metabolic effects, glucomannan diet supplements have been found to be particularly efficacious and well tolerated even in the long-term treatment of severe obesity." (Vita et al, Chronic use of glucomannan in the dietary treatment of severe obesity, 1992)
Plus another review:
"At doses of 2-4 g per day, glucomannan was well-tolerated and resulted in significant weight loss in overweight and obese individuals. There is some evidence that glucomannan exerts its beneficial effects by promoting satiety and fecal energy loss." (Keithley and Swanson, Glucomannan and obesity: a critical review, 2005)
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Now, this still doesn't mean I'm going to start taking glucomannan. I already eat dietary fibre (in real food) that, I believe, has this very effect. But I remember the reason I tried it (on my weight-loss diet) for constipation was that I was afraid to eat traditional anti-constipatory, high-fibre foods such as prunes, oats, etc., because of their carbs. I bet a lot of low-carbers have found themselves with that conflict. So it strikes me that someone who wanted to try for a fibre-reduces-fat-absorption effect within their low-carb diet might find a use for glucomannan, a few capsules of which don’t contain that much carb.
What I particularly like about the idea of glucomannan is that it's reported to be well tolerated and safe, which is not true for something like guar gum, which can cause blockages and other frights. There have been very few reports of such blockages with glucomannan, but the risk is that a capsule taken without water might lodge in the oesophagus and swell up there. To see how much glucomannan swells, I emptied a capsule into a glass of water and stirred. It formed a very light gel, which I could easily swill in the glass, almost like normal water, even hours later–so I wouldn’t fear its gelling capacity in the body.
And glucomannan's not a test-tube product. Yes, it's processed, to the extent that the konjac root has been ground to powder–but nothing's been added to it bar what the capsule's made of, and you can tip it out of that.
So it seems there’s little downside (other than potential disappointment, but how we are used to that). I mean, the deal is: take a capsule with each meal and you might lose extra weight. Sounds like diet-miracle nonsense. But look above: it’s the scientists wot said it.
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I might give it a go, for curiosity's sake, eaten with cheese, and report my results. (Adds glucomannan to list of five thousand planned experiments.)
Last edited by Plinge : Wed, Jun-27-12 at 14:29.
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