Biology Reference
In-Depth Information
found similar results when they related grains at various levels of processing
to satiety. Satiety was inversely related to the area under the insulin response
curve for various meals, with increased processing of grains increasing
glucose and insulin responses and decreasing satiety ratings.
Another mechanism responsible for satiety effects of low-GI foods may
be reduction in gastric emptying. Many low-GI foods are high in fiber,
which prolongs distension of the gastrointestinal tract, causing increased
and prolonged secretion of the gut peptides cholecystokinin, ghrelin,
glucagon, glucagon-like-peptide-1, and glucose-dependent insulinotropic
polypeptide, all of which have been suggested as potential satiety factors
of the short-term feeding studies that have investigated the effects of low-
GI meals on subsequent satiety, hunger, and energy intake have used meals
that differ in aspects other than GI, thereby resulting in inconsistent results.
A meta-analysis of crossover studies investigating the effects of low- and
high-GI preloads by
Roberts (2000)
has found a significant increase in
energy intake following high-GI meals when compared with low-GI meals.
Another review by
Raben (2002)
comparing studies using low-GI and high-
GI preloads found that low-GI meals decrease hunger or increase satiety in
half of the studies compared. The effect of low-GI meals on lowering energy
intake at a later meal was also evident in 6 of the 12 studies compared. Both
the above-mentioned reports are reliable as the studies dealt with diets mat-
ched in energy, macronutrient, and fiber contents. However, these studies
did not result in weight loss in any group. In a study in which a low-GI diet
was compared with a standard hypoenergetic reduced-fat diet for 4 months
in 107 obese, but otherwise healthy, children (
Spieth et al., 2000
)
, reduc-
tions in weight and BMI were achieved with the low-GI diet, but not with
the standard treatment. The study was limited by the fact that there could
have been selection bias resulting from no randomization of subjects.
A limitation of diets that match energy content is that they reduce the
possibility of effects via satiety mechanisms. Only a few studies have inves-
tigated effects of ad libitum low-GI diets on weight, which include
a 10-week parallel trial in 45 overweight women (
Sloth et al., 2004
)
subjects who were instructed to incorporate low- or high-GI versions of
carbohydrate-rich foods into their diets, to replace 75% of the carbohydrate
intake along with the rest of their ad libitum habitual diets. A reduction in GI
by 24 units did not result in any significant weight loss, energy intake, or fat
mass between the groups. Contradictory results were obtained in another
study using 20 normal weight women who consumed ad libitum high-starch
