REDUCED INSULIN LEVELS AND PREVENTION OF DIABETES
A high consumption of cereal fibre and
whole grain is associated with a decreased risk of diabetes. Some factors in the dietary fibre complex in
whole grain rye products seem to have favourable effects on insulin and glucose metabolism
e.g. by increasing insulin sensitivity.
The majority of nutrients are digested and absorbed in the small
intestine. Soluble fibre, such as
soluble arabinoxylan, may slow down the evacuation of stomach
contents into the small intestine by increasing the viscosity of the
food mass. This leads to the delayed hydrolysis of starch and the
absorption of nutrients, which helps to slow down the changes in
blood glucose levels (Behall and Hallfrisch 2002; Brennan and
Whole grain rye has a high content of soluble
fibre, especially soluble arabinoxylans.
Number of clinical studies support the
whole grain consumption is
assosiated with a reduced risk of type 2
(Murtaugh et al. 2003;
Venn and Mann 2004).
subjects it was found that postprandial plasma insulin responses were significantly lower
after the intake of a whole grain rye bread as compared to a white wheat bread. No significant
differences in plasma glucose levels were found (Leinonen et al.
1999; Juntunen et al. 2001, 2003). The lower
insulin response after rye bread was not explained by the amount of
fibre because low-fibre rye bread reduced the insulin
responses similar to that of
high-fibre rye bread (Juntunen et al. 2003). As compared to white wheat bread, both rye
breads decreased postprandial insulin responses. This effect might be explained by differences in the structural properties
of rye and wheat breads.
Cross-sectional results from the Botnia Dietary Study show that the energy-adjusted intake
of rye was directly related to insulin sensitivity in both sexes (Ylönen et al. 2001). The
consumption of other cereals, such as wheat, was not related to insulin sensitivity in
this group of 555 high-risk individuals for type 2 diabetes. In an eight week cross-over
study using an intravenous glucose tolerance test, insulin secretion (but not insulin
sensitivity) was improved in 20 postmenopausal women when they were given a diet
containing high-fibre rye bread compared with a diet containing white wheat bread
(Juntunen et al. 2001). In another study, wheat bran added to test meals had very little effect
on short-term glucose, insulin and lipid metabolism (Jenkins 2001).
In experiment on ileostomy subjects were given a wheat, low-fibre diet for 2
weeks, followed by a washout week, and a period of 2 weeks on a whole grain and rye bran
supplemented high-fibre period (Lundin et al. 2001a). A cross-over design was used for
meal frequency (three or seven times per day). During the seven meals per day period, the
glucose and insulin peaks had clearly reduced at the end of the day during the whole grain
rye period compared with the endosperm wheat control diet period. The daytime excretion of
C-peptide was also decreased, which supports the results of decreased insulin secretion at
the end of the day. C-peptide is a peptide, that is split off and secreted together with
insulin. This delayed effect on glucose and insulin metabolism corresponds to similar
effects on a morning meal as a result of a high fibre meal served during the previous
evening ("over-night second meal effect") observed in other studies using high
fibre diets (Björck et al. 2001; Björck and
Elmståhl 2003; Lundin
et al. 2004). It also corresponds to an increased insulin sensitivity,
which has recently been observed associated with whole grain consumption (Pereira et al.
Rye bran and rye fibre have positive effects on the prevention of diabetes in experimental
studies performed on both humans and animals. The effects of bread with a high content of
rye bran were compared with those of either low-bran bread or a patients' usual bread in
insulin-dependent diabetic patients (Nygren et al. 1984). When the bread with high rye
bran content was included in the diet the glucose profile during the day improved and the
insulin doses could be reduced.
In a study of Montonen et al (2003) an inverse
association between whole-grain intake and the risk of type 2
diabetes was found. They assumed that the reduction may also be due
to the bioactive
compounds, such as lignans,
tocotrienols, phytic acids and other antinutrients, found in
The protective effects of rye bran on the diabetic syndrome were also found in rats and
mice (Nygren et al. 1981; Lundin
et al. 2001b). The diabetic rats fed the high-fibre bread lost less
body weight, and exhibited lower blood glucose levels and lower urinary glucose excretion
than the animals fed the low-fibre bread. Rye bran lowered blood glucose levels slightly
and led to slower weight gain in normal rats and mice, and prolonged the survival of
diabetic mice (Berglund et al. 1982). Obvious effects on the small intestinal morphology
were also detected with an increased goblet cell volume and density in the ileum of
hamsters (Lundin et al. 1993), broader ileal villi, a higher density of ileal microvilli,
a thicker glycocalyx layer, and an abundance of filamentous microorganisms in the ileum of
diabetic and control mice (Lundin et al. 2001b). The morphological changes in the intestine of
the diabetic animals were associated with a favourable weight development and a
disappearance of urinary glucose excretion.
A clear association between a high intake of dietary fibre from cereal grain and a reduced
risk of diabetes has been observed in two large-scale prospective studies in females.
In one of the studies a low glycemic
index was concomitantly associated with a decreased risk (Salmeron et al. 1997) in
comparatively younger women but not in the second more recent study (Meyer et al. 2000) on
older women. Similar results were also
in the study of Qi et al.
(2005). The glycemic index is dependent on the food form and the way in which the
food has been processed. Rye bread containing whole grains had a remarkably lower glycemic
index than whole grain rye bread made of flour (Jenkins et al. 1986). The hypothesis that
there may be differences in the effects of whole grain diets and diets based on refined
grain, but with a similar total fibre concentration, has recently been tested in
postmenopausal women (Jacobs 2000). A 17% lower mortality rate was seen in women consuming
a predominantly whole grain diet. It was considered that the effect was perhaps caused by
phytochemicals in the whole grain complex. Residual confounding (other explanations are
not accurately adjusted for) is an alternative explanation. More studies are obviously
needed in order to determine the effect of diets on survival.
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