Saturday, October 16, 2010

Evidence Summary: Dietary fiber supplements and obesity

Evidence Summary: Dietary fiber supplements and obesity

Dietary fiber supplements and obesity


Evidence Summary

Fiber supplements were defined, for the purposes of this project, as fibers which have been isolated from the original source. The fiber may be incorporated into foods and beverages or taken as a pill or powder.

Body Weight

11 studies: Three positive-rated randomized controlled trials (Birketvedt et al, 2005; Rossner et al, 1987; Ryttig et al, 1989), five neutral-rated randomized controlled trials (Birketvedt et al, 2000; Hylander et al, 1983; Pasman, Westerterp-Plantenga et al, 1997; Rigaud et al, 1990; Solum et al, 1987) and three positive-rated randomized controlled trials with crossover (Kovacs et al, 2001; Meada et al, 2005; Vuksan et al, 1999), examined the impact of fiber supplements on body weight in overweight and obese individuals.

Increased Weight Loss

Seven studies found increased weight loss with fiber supplement intake of 0.8g to 20g for five weeks to 14 months (Birketvedt, 2000; Birketvedt, 2005; Pasman and Westerterp-Plantenga, 1997; Rigaud, 1990; Rossner, 1987; Ryttig, 1989; Solum, 1987).

* Increased weight loss
o Birketvedt, 2000, 24 weeks: 1,200-kcal diet (15g per day dietary fiber) plus fiber supplement (grain and citrus fiber; 85% insoluble) or control; Weeks One to Eight, six grams per day; Weeks Nine to 24, four grams per day
o Birketvedt, 2005, five weeks: 1,200-kcal diet plus fiber supplement or control; Glucosahl, 6.1g (4.32g glucomannan, 0.9g guar, 0.9g alginat); Chrombalance, 1.24g (1.24g glucomannan) or Appe-Trim, 0.84g (0.42g glucomannan, 0.42g guar)
o Pasman and Westerterp-Plantenga, 1997, 14 months: 16g to 20g guar gum, 10g to 15g guar gum or control
o Rigaud, 1990, six months: Seven grams per day insoluble fiber supplement (beet, barley, citrus; 90% insoluble) or placebo
o Rossner, 1987, three months: 1,400-kcal diet with five grams per day fiber supplement (grain and citrus fiber) or placebo; two months AND 1,600-kcal diet with seven grams per day fiber supplement (vegetable, grain and citrus fiber) or placebo
o Ryttig, 1989: 1,200-kcal diet with seven grams per day fiber supplement or placebo for 11 weeks, then 1,600-kcal diet with six grams per day fiber supplement or placebo for 16 weeks, then ad lib diet with six grams per day fiber supplement for 25 weeks
o Solum, 1987, 12 weeks: 1,200-kcal diet (25g per day dietary fiber) with six grams per day fiber supplement (grain and citrus fiber) or control.

No Increase in Weight Loss

Four studies found no increase in weight loss with 4.5g to 6.6g fiber supplementation for two to 12 weeks (Hylander, 1983; Kovacs, 2001; Meada, 2005; Vuksan, 1999).

* No difference in weight loss
o Hylander, 1983, three weeks: 6.6g ispaghula, 6.6g bran or control
o Kovacs, 2001, two weeks each diet: Breakfast replaced with solid meal or semi-solid meal with or without fiber supplement; 6.6g per day guar gum
o Meada, 2005, 12 weeks: Reduced calorie diet (Output, 400kcal) plus fiber supplement; 4.5g agar
o Vuksan, 1999, three weeks: Two grams per 100kcal konjac mannan fiber or two grams per 100kcal wheat bran fiber.

Energy Intake

Six studies: One positive-rated randomized controlled trial (Rossner et al, 1987), two neutral-rated randomized controlled trials (Pasman and Westerterp-Plantenga et al, 1997; Rigaud et al, 1990), one negative-rated randomized controlled trial (Dudani et al, 1986), one positive-rated randomized controlled trial with crossover (Kovacs et al, 2001) and one neutral-rated randomized controlled trial with crossover (Pasman et al, 1997), investigated the impact of fiber supplements on energy intake in obese individuals.

Decreased Energy Intake

Two studies (Pasman, 1997; Rossner, 1987) found decreased energy intake with five grams to 40g fiber per day for one week to three months.

* Decreased energy intake
o Pasman, 1997, one week each (crossover): 40g per day guar gum; one week AND four mJ with 20g guar gum or control or six mJ with 20g guar gum or control
o Rossner, 1987, three months: 1,400-kcal diet with five grams per day fiber supplement (grain and citrus fiber) or placebo; two months AND 1,600-kcal diet with seven grams per day fiber supplement (vegetable, grain and citrus fiber) or placebo.

No Difference in Energy Intake

Three studies (Kovacs, 2001; Pasman and Westerterp-Plantenga, 1997; Rigaud, 1990) found no difference in energy intake in individuals that consumed 6.6g to 20g fiber supplements for two weeks to 14 months.

* No difference in energy intake
o Kovacs, 2001, two weeks each diet: Breakfast replaced with solid meal or semi-solid meal with or without fiber supplement; 6.6g per day guar gum
o Pasman and Westerterp-Plantenga, 1997, 14 months: 16g to 20g guar gum, 10g to 15g guar gum or control
o Rigaud, 1990, six months: Seven grams per day insoluble fiber supplement (beet, barley, citrus; 90% insoluble) or placebo.

Satiety and Hunger

Eight studies: Two positive-rated randomized controlled trials (Rossner et al, 1987; Ryttig et al, 1989), three neutral-rated randomized controlled trials (Hylander et al, 1983; Pasman and Westerterp-Plantenga et al, 1997; Rigaud et al, 1990) and two positive-rated randomized controlled trials with crossover (Adam et al, 2005; Kovacs et al, 2001) and one neutral-rated randomized controlled trial with crossover (Pasman et al, 1997), explored the impact of fiber supplements on hunger in obese individuals.

Less Hunger

Five studies (Hylander, 1983; Kovacs, 2001; Pasman and Westerterp-Plantenga, 1997; Rigaud, 1990; Ryttig, 1989) found significantly less hunger or increased satiety, following consumption of fiber supplements providing six grams to 20g fiber for two weeks to 14 months.

* Less hunger or greater satiety with fiber supplements
o Hylander, 1983, three weeks: 6.6g ispaghula, 6.6g bran or control
o Kovacs, 2001, two weeks each diet: Breakfast replaced with solid meal or semi-solid meal with or without fiber supplement; 6.6g per day guar gum
o Pasman and Westerterp-Plantenga, 1997, 14 months: 16g to 20g guar gum, 10g to 15g guar gum or control
o Rigaud, 1990, six months: Seven grams per day insoluble fiber supplement (beet, barley, citrus; 90% insoluble) or placebo
o Ryttig, 1989: 1,200-kcal diet with seven grams per day fiber supplement or placebo for 11 weeks, then 1,600-kcal diet with six grams per day fiber supplement or placebo for 16 weeks, then ad lib diet with six grams per day fiber supplement for 25 weeks.

No Impact on Hunger

Three studies (Adam, 2005; Pasman, 1997; Rossner, 1987) found that fiber supplements providing five grams to 40g fiber for one meal to three months had no impact on satiety or hunger in obese individuals.

* No change between groups in hunger or satiety with fiber supplements
o Adam, 2005, one meal: 50g galactose with 2.5g guar gum or control at breakfast
o Pasman, 1997, one week each (crossover): 40g per day guar gum; one week AND four mJ with 20g guar gum or control or six mJ with 20g guar gum or control
o Rossner, 1987, three months: 1,400-kcal diet with five grams per day fiber supplement (grain and citrus fiber) or placebo; two months AND 1,600-kcal diet with seven grams per day fiber supplement (vegetable, grain and citrus fiber) or placebo.

Adam also explored the impact of fiber supplements on Glucagon-like peptide 1 (GLP-1), a gastrointestinal peptide believed to signal satiety via gastric and small bowel nerves. GLP-1 was found to be elevated with administration of 50g galactose and 2.5g guar gum, however the increase in GLP-1 was not related to ratings of satiety in obese individuals, as was seen in normal-weight individuals.

Serum Lipids

Five studies: Three neutral-rated randomized controlled trials (Birketvedt et al, 2000; Pasman and Westerterp-Plantenga et al, 1997; Solum et al, 1987) and two positive-rated randomized controlled trials with crossover (Meada et al, 2005; Vuksan et al, 1999), examined the impact of fiber supplements on serum lipids in overweight and obese individuals.

No Difference in Change in Serum Lipids

The majority of studies (Birketvedt, 2000; Pasman and Westerterp-Plantenga, 1997; Solum, 1987; Vuksan, 1999) found no difference in the change in serum lipids from control with fiber supplementation on primarily hypocaloric diets.

Improved Total Cholesterol

One study found greater improvement in total cholesterol in the group which consumed 4.5g fiber from agar for 12 weeks.

* Decreased serum lipids with fiber supplements
o Meada, 2005, 12 weeks: Reduced calorie diet (Output -400kcal) plus fiber supplement; 4.5g agar.
* No change between groups in serum lipids with fiber supplements
o Birketvedt, 2000, 24 weeks: 1,200-kcal diet (15g per day dietary fiber) plus fiber supplement (grain and citrus fiber; 85% insoluble) or control; Weeks One to Eight, six grams per day; Weeks Nine to 24, four grams per day
o Pasman and Westerterp-Plantenga, 1997, 14 months: 16g to 20g guar gum, 10g to 15g guar gum or control
o Solum, 1987, 12 weeks: 1,200-kcal diet (25g per day dietary fiber) with six grams per day fiber supplement (grain and citrus fiber) or control
o Vuksan, 1999, three weeks: Two grams per 100kcal konjac mannan fiber or two grams per 100kcal wheat bran fiber.

Blood Pressure

Seven studies: Two positive-rated randomized controlled trials (Rossner et al, 1987; Ryttig et al, 1989), two neutral-rated randomized controlled trials (Rigaud et al, 1990; Solum et al, 1987) and three positive-rated randomized controlled trials with crossover (Kovacs et al, 2001; Meada et al, 2005; Vuksan et al, 1999), examined and explored the impact of fiber supplements on blood pressure in overweight and obese individuals.

Decrease in Diastolic Blood Pressure

Two studies (Rossner, 1987, Ryttig, 1989) found a decrease in diastolic blood pressure (DBP) with seven to 26g dietary fiber for three to 12 months. Solum (1987) and Vuksan, 1999, found a decrease in blood pressure with six to 14g fiber for three to 12 weeks.

* Decreased blood pressure with fiber supplements
o Rossner, 1987, three months: 1,400-kcal diet with five grams per day fiber supplement (grain and citrus fiber) or placebo; two months AND 1,600-kcal diet with seven grams per day fiber supplement (vegetable, grain and citrus fiber) or placebo
o Ryttig, 1989: 1,200-kcal diet with seven grams per day fiber supplement or placebo for 11 weeks, then 1,600-kcal diet with six grams per day fiber supplement or placebo for 16 weeks, then ad lib diet with six grams per day fiber supplement for 25 weeks
o Solum, 1987, 12 weeks: 1,200-kcal diet (25g per day dietary fiber) with six grams per day fiber supplement (grain and citrus fiber) or control
o Vuksan, 1999, three weeks: Two grams per 100kcal konjac mannan fiber or two grams per 100kcal wheat bran fiber.

No Difference

Three studies (Kovacs, 2001; Maeda, 2005; Rigaud, 1990) found 4.5 to seven grams dietary supplements, for two to 30 weeks, led to no difference in the change in blood pressure from control.

* No change between groups in blood pressure with fiber supplements
o Vuksan, 1999, two weeks each diet: Breakfast replaced with solid meal or semi-solid meal with or without fiber supplement; 6.6g per day guar gum
o Meada, 2005, 12 weeks: Reduced-calorie diet (Output -400kcal) plus fiber supplement; 4.5g agar
o Rigaud, 1990, six months: Seven grams per day insoluble fiber supplement (beet, barley, citrus; 90% insoluble) or placebo.

Serum Glucose:

Six studies: One neutral-rated randomized controlled trial (Pasman and Westerterp-Plantenga et al, 1997) and five positive-rated randomized controlled trials with crossover (Adam et al, 2005; Behall et al, 2005; Kovacs et al, 2001; Meada et al, 2005; Vuksan et al, 1999), examined the effect of fiber supplements on glucose levels in obese and overweight individuals. All studies found no difference in change in glucose from control with fiber supplementation on primarily hypocaloric diets.

* No change in serum glucose with fiber supplement
o Adam, 2005, one meal: 50g galactose with 2.5g guar gum or control at breakfast Behall, 2005, one meal (crossover): 3.23g B-glucan (oats), 12.1g B-glucan (barley) at breakfast Kovacs, 2001, two weeks each diet: Breakfast replaced with solid meal or semi-solid meal with or without fiber supplement; 6.6g per day guar gum Meada, 2005, 12 weeks: Reduced calorie diet (Output - 400kcal) plus fiber supplement; 4.5g agar Pasman and Westerterp-Plantenga, 1997, 14 months: 16g to 20g guar gum, 10g to 15g guar gum or control Vuksan, 1999, three weeks: Two grams per 100kcal konjac mannan fiber or two grams per 100kcal wheat bran fiber.

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