Nutrients 2013, 5, 3287-3298; doi:10.3390/nu5083287
OPEN ACCESS
nutrients
ISSN 2072-6643
www.mdpi.com/journal/nutrients
Article
Linseed Dietary Fibers Reduce Apparent Digestibility of Energy
and Fat and Weight Gain in Growing Rats
Mette Kristensen 1,*, Knud Erik Bach Knudsen 2, Henry Jørgensen 2, David Oomah 3,
Susanne Bügel 1, Søren Toubro 4, Inge Tetens 5 and Arne Astrup 1
1
2
3
4
5
Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen,
1958 Frederiksberg C, Denmark; E-Mails: shb@life.ku.dk (S.B.); ast@life.ku.dk (A.A.)
Department of Animal Science—Molecular nutrition and cell biology, Aarhus University,
8830 Tjele, Denmark; E-Mails: knuderik.bachknudsen@agrsci.dk (K.E.B.K.);
henry.jorgensen@agrsci.dk (H.J.)
Pacific Agri-Food Research Centre—Summerland, Agriculture and Agrifood Canada, Summerland,
British Columbia V0H 1Z0, Canada; E-Mail: dave.oomah@agr.cg.ca
Reduce-Center, 4000 Roskilde, Denmark; E-Mail: st@reduce.dk
National Food Institute, DTU FOOD, 2860 Søborg, Denmark; E-Mail: intet@food.dtu.dk
* Author to whom correspondence should be addressed; E-Mail: mekr@life.ku.dk;
Tel.: +45-284-34070; Fax: +45-353-32483.
Received: 1 June 2013; in revised form: 1 August 2013 / Accepted: 6 August 2013 /
Published: 19 August 2013
Abstract: Dietary fibers (DF) may affect energy balance, an effect often ascribed to the
viscous nature of some water soluble DF, which affect luminal viscosity and thus multiple
physiological processes. We have tested the hypothesis that viscous linseed DF reduce
apparent nutrient digestibility, and limit weight gain, in a randomized feeding trial where
60 male, growing, Wistar rats, with an initial weight of ~200 g, were fed different diets
(n = 10 per group): low DF control (C), 5% DF from cellulose (5-CEL), CEL + 5% DF
from whole (5-WL) or ground linseed (5-GL), CEL + 5% DF from linseed DF extract
(5-LDF), and CEL + 10% DF from linseed DF extract (10-LDF). Diets were provided
ad libitum for 21 days. Feed intake and faecal output were measured during days 17–21.
Faecal fat excretion increased with increasing DF content and was highest in the 10-LDF
group. Apparent fat digestibility was highest with the C diet (94.9% ± 0.8%) and lowest
(74.3% ± 0.6%) with the 10-LDF diet, and decreased in a non-linear manner with
increasing DF (p < 0.001). Apparent fat digestibility also decreased with increased
accessibility of DF (5-WL vs. 5-GL) and when the proportion of viscous DF increased
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(5-GL vs. 5-LDF). The 10-LDF resulted in a lower final body weight (258 ± 6.2 g)
compared to C (282 ±5.9 g), 5-CEL (281 ±5.9 g), and 5-WL (285 ± 5.9 g) (p < 0.05). The
10-LDF diet reduced body fat compared to 5-CEL (p < 0.01). In conclusion, DF extracted
from linseed reduced apparent energy and fat digestibility and resulted in restriction of
body weight gain in growing rats.
Keywords: dietary fibers; linseed; fat digestibility; obesity
1. Introduction
Dietary fibers (DF) have received increasing attention for their potential role in weight regulation
because high intakes of DF have been associated with a smaller weight gain in prospective
observational studies [1–3]. Viscous soluble DFs in particular seem to play a role in short-term
appetite regulation and food intake [4], whereas the long term effects of DF on body weight are less
well documented. A meta-analysis of the effect of guar gum, a viscous DF, on body weight, concluded
that no pronounced weight loss effect was experienced [5], whereas more consistent results were found
for chitosan [6]. Chitosan interacts with intestinal fat digestion and absorption, thereby increasing
faecal fat excretion, which is thought to be the main mechanism of action [6]. This attribute is also
ascribed to viscous DF [7]. However, a recent study found that viscous fermentable guar gum did not
inhibit weight gain in high-fat fed mice, whereas insoluble oat DF did inhibit weight gain, possibly due
to differences in digestibility and energy utilisation of products deriving from gut fermentation [8].
Linseeds contain approximately 30% DF of which one third is water soluble. The majority of the
water soluble DF belongs to a group of heterogenic polysaccharides consisting of neutral
arabinoxylans and highly acidic rhamnose-containing polysaccharides present on the outside of the
seed coat (the mucilage), which form highly viscous solutions when mixed with water [9,10]. These
polysaccharides are, thus, easily extractable using only water. Alzueta and coworkers [11] investigated
the effect of whole and demucilaged linseeds on growth in broiler chickens, and found that the DF-rich
mucilage was responsible for the decreased weight gain observed in chickens fed linseed. They were also
able to correlate to decreased nutrient utilization to mucilage [12]. In line with this, we previously found
that addition of whole linseed to rye breads (18 g/day) significantly reduced the digestibility of fat and
energy in humans [13]. It was also found that a linseed DF extract incorporated into breads decreased not
only hunger, but also postprandial triacylglycerol supporting that linseed DF decrease lipid absorption [14].
However, we also found that food matrix may affect the magnitude of effect, as linseed DF in drinks were
more effective than when incorporated into breads in increasing faecal fat excretion [15].
In the present study we tested the hypothesis that a diet with linseed DF derived from the mucilage
fraction may decrease apparent energy and fat digestibility, thereby affecting body weight gain in
growing rats.
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2. Experimental Section
2.1. Animals and Study Design
The Danish Animal Experiments Inspectorate, Ministry of Justice, approved the protocol. Sixty
growing male Wistar rats (Taconic Europe, Ry, Denmark), weighing 200 ± 3 g initially, were
randomly allocated to six different dietary treatments (n = 10) and fed the experimental diets for
21 days. The cages were kept in a single room with controlled temperature (25 °C), relative humidity
(50%–60%), and 12 h light and dark cycles. Fresh water was available and un-pelleted feed was
supplied ad libitum (25 g feed supplied/day). During the last seven days of the trial the rats were
housed individually in metabolic cages made of Perspex, with stainless steel mesh floors that allowed
for quantitative collections of urine and faeces. No measurements were made on the first two days, in
order to allow the rats to become accustomed to the cages. Faeces were then collected for the
subsequent 5 days (balance period). Food and water containers were weighed before and after the
balance period. Faecal samples were collected daily during the balance period, frozen, and stored at
−20 °C. The rats were weighed to the nearest g on days 0, 4, 7, 9, 13, 16, 21 and sacrificed on day 22,
following anaesthesia in a vapour of CO2. The gastrointestinal tract (GIT) was removed and stomach,
small intestine, caecum and colon were weighed in all the animals. Stomach, small intestine, caecum
and colon were then weighed again after removal of their contents. Heart, liver and abdominal fat pads
were also removed and weighed in 5 animals in each group. In this sub-group of rats, a carcass
homogenate of the whole rats (including fur and claws, but without GIT, blood and organs) was
autoclaved with water for 1 h at 100 °C, blended into a smooth paste, freeze dried and analyzed for dry
matter (DM), ash, N and fat. Hereafter, total body fat and protein percentage was calculated.
2.2. Experimental Diets
All six diets were high fat. The macronutrient composition of all six diets was the same, with ~110 g
protein/kg DM, but they differed in DF content and source (Table 1). The DF were extracted from
linseed hulls (provided by Natunola Health Inc., Ontario, Canada) as described elsewhere [14]. DF
content of the linseed DF extract was measured according to the AOAC (No. 985.29) method [16] and
used to calculate the content of linseed DF in the 5-LDF and 10-LDF diets. A table value on DF
content in linseeds (28 g/100 g) [17] was used for calculation of DF content in the 5-WL and 5-GL
diets. Based on the nutrient composition (protein, fat, DM, ash, DF, minerals and vitamins) of each
ingredient, the feed mixtures were formulated to meet or exceed NRC recommendations for growing
and reproducing rats [18].
2.3. Feed Analyses of Major Nutritional Compounds
Content of DM and ash in the diets was determined according to an AOAC method [19]. Nitrogen
was determined by thermal conductivity after complete combustion at 1300 °C in pure oxygen (LECO
CNS-2000, Carbon, Nitrogen and Sulphur Analyser, St. Joseph, MI, USA), and protein was calculated
(N × 6.25). Gross energy was determined by bomb calorimetry using a LECO Ac 300 automated
calorimeter system 789-500 (ISO 983:1998) [20]. Total non-starch polysaccharides (NSP) and their
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constituent sugars were determined as alditol acetates by gas-liquid chromatography for neutral sugars
and by colorimetric determination for uronic acids using a modification of the Uppsala procedures as
described by Bach Knudsen [21]. Klason lignin was measured as the insoluble residue after hydrolysis
with 2 M H2SO4 and the content of total DF calculated as total NSP plus Klason lignin. Dietary fat
(hydrochloric acid-fat) was extracted according to the Bligh and Dyer method using diethyl ether [22].
Table 1. Nutritional composition of the six experimental diets.
Diet
Maize starch
Linseed oil
Animal fat (pig)
Casein + 1% methionine
Vitamin mix
Mineral mix
Linseed
Linseed mucilage
Cellulose
DM, g/kg
Ash, g/kg DM
Protein, g/kg DM
Fat, g/kg DM
Gross E, kcal/kg DM
NSP, g/kg DM
Lignin, g/kg DM
DF g/kg DM
C
CEL
5-WL
Ingredient, % (calculated)
63.7
58.7
52.7
10.00
10.00
6.45
10.00
10.00
6.45
11.80
11.80
7.00
0.81
0.81
0.81
3.70
3.70
3.70
0.00
0.00
17.9
0.00
0.00
0.00
0.00
5.00
5.00
Chemical composition (measured)
973
989
973
30.6
33.0
34.7
111
110
110
209
205
208
5280
5088
5232
14
68
76
0
3
16
14
71
92
5-GL
5-LDF
10-LDF
52.7
6.45
6.45
7.00
0.81
3.70
17.9
0.00
5.00
48.9
9.20
9.20
9.70
0.81
3.70
0.00
13.5
5.00
39.0
8.40
8.40
7.65
0.81
3.70
0.00
27.0
5.00
975
36.7
109
205
5184
76
16
92
979
39.0
107
212
5179
99
9
108
976
50.9
111
202
5139
158
31
189
C: Control; DF: Dietary fiber; DM: Dry matter; E: Energy; 5-CEL: 5% DF from cellulose; 5-WL: 5% DF
from whole linseed; 5-GL: 5% DF from ground linseeds; 5-LDF: 5% DF from linseed DF extract;
10-LDF: 10% F from linseed DF extract.
2.4. Analyses of Faecal and Tissue Samples
Faecal DM was determined by freeze drying. Faecal gross energy, fat, ash, and total carcass fat and
nitrogen, were analyzed using the methods described above for feed analyses.
2.5. Calculations and Statistical Analyses
Apparent digestibility of energy and fat was calculated on the basis of recorded quantitative feed
intake and excretion in faeces. All statistical analyses and calculations were performed using the
Statistical Analysis System software package, version 9.3 (SAS Institute Inc., Cary, NC, USA). If the
distribution of a variable was skewed it was log-transformed prior to analysis. A repeated measures
ANCOVA was applied to examine the effect of diet and time and their interaction on weight gain with
initial body weight as covariate. An ANCOVA was used to examine the effect of diet on all other
dependent variables, in which final body weight was included as covariate, as these outcomes were
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assessed at the end of the trial. All data are presented as mean ± SE unless otherwise stated and the
statistical significance level is defined as p < 0.05. The relationship between the digestibility of energy
and fat and DF was analyzed by linear regression or a second-degree polynomial.
3. Results
Overall, there was an effect of diet on feed intake and apparent fat and energy digestibility (Table 2,
Figure 1). Absolute feed intake differed between groups (p < 0.001), and was higher in the 5-CEL
group compared to all diets expect 10-LDF, which also differed from the C diet. No other differences
in feed intake were observed (Table 2). There was an effect of diet on fat (p = 0.013) and energy
intake (p < 0.001), where the rats fed the 5-CEL diet had a higher intake compared to all other
groups (p < 0.05). The largest effects were, however, observed on faecal volume (p < 0.001), where up
to 8-fold increases could be observed in the 10-LDF group, which decreased with decreasing
DF content: 10-LDF > 5-LDF> 5-GL = 5-WL > 5-CEL > C. Faecal energy excretion differed
significantly between groups and a 6-fold increase was seen in rats fed the 10-LDF compared to rats
fed the C diet (Table 2). Concomitantly, decreases in energy digestibility from 95.9% ± 0.5% in C to
76.1% ± 0.5% in 10-LDF fed rats were observed. Faecal fat excretion increased with increasing
amounts of DF and the 10-LDF fed rats excreted 5-fold more fat compared to the C fed
rats (p < 0.001), which reduced apparent fat digestibility from 94.9% ± 0.8% in the C group to only
74.3% ±0.6% in the 10-LDF group (p < 0.001) (Figure 1).
Figure 1. Apparent fat digestibility (% of intake) during the last 5 days of a 21 days
feeding trial in rats fed six different diets (C = control; 5-CEL = 5% dietary fibers (DF)
from cellulose; 5-WL = 5% DF from whole linseed; 5-GL = 5% DF from ground linseeds;
5-LDF = 5% DF from linseed DF extract; 10-LDF = 10% F from linseed DF extract)
(Mean ± SE) (n = 10). Mean values with different letters were significantly different
(p < 0.05; ANCOVA, followed by least significant difference test).
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Table 2. Nutrient digestibility, gastrointestinal tract (GIT) mass and content and body composition in rats fed diets with different source and
content of DF (Mean ±SE, n = 10).
Outcome parameter
C
5-CEL
5-WL
Mean
SE
Mean
SE
Feed intake (g/day)
Energy intake (kcal/day)
Fat intake (g/day)
Faecal volume (g/day)
Energy excretion (kcal/day)
Fat excretion (mg/day)
GIT mass and content
14.9 c
74.6 b
3.10 b
0.92 e
2.98 c
154 c
0.4
1.9
0.07
0.23
0.55
33
17.8 a
90.4 a
3.51 a
2.34 d
7.85 b
287 bc
0.3
1.9
0.07
0.23
0.55
33
Small intestine weight (g)
Small intestine content (g)
5.78 c
1.34 d
0.24
0.25
5.11 c
2.66 c
Caecum weight (g)
Caecum content (g)
Large intestine weight (g)
Large intestine content (g)
0.80 b
1.68 d
1.00 c
1.60 b
0.09
0.46
0.09
0.33
0.89 b
2.79 cd
1.08 c
1.73 b
Mean
5-GL
5-LDF
10-LDF *
SE
Mean
SE
Mean
SE
Mean
SE
15.7 bc
80.0 b
3.24 b
3.29 cd
8.67 ab
294 b
0.3
1.9
0.07
0.24
0.57
33
16.1 bc
81.5 b
3.30 b
3.33 c
9.42 ab
349 b
0.3
1.9
0.07
0.23
0.55
33
15.4 bc
78.4 b
3.27 b
4.59 b
10.27 a
306 b
0.4
1.9
0.07
0.23
0.56
33
16.5 ab
82.6 b
3.37 b
7.71 a
19.08 a
829 a
0.4
2.1
0.08
0.27
0.64
38
0.17
0.17
5.74 c
2.92 bc
0.24
0.25
6.23 b
2.54 c
0.24
0.25
6.91 b
3.66 b
0.23
0.24
9.11 a
7.57 a
0.30
0.31
0.07
0.32
0.06
0.23
0.78 b
3.45 cd
1.28 bc
2.06 b
0.09
0.46
0.09
0.33
0.78 b
3.69 bc
1.30 bc
2.21 b
0.09
0.46
0.09
0.34
1.17 b
5.47 b
1.39 b
2.65 b
0.09
0.45
0.08
0.33
2.07 a
10.82 a
1.76 a
4.88 a
0.12
0.57
0.11
0.41
5.9
5.9
1.3
0.33
0.97
29
0.16
278 ab
270 ab
14.0 b
21.5
12.6 ab
992
9.99 ab
5.9
5.9
1.3
0.28
1.0
29
0.17
279 ab
253 b
11.9 b
21.8
11.7 ab
974
9.58 bc
5.9
5.9
1.2
0.31
0.82
29
0.15
258 b
222 c
10.9 b
20.7
10.4 b
906
9.73 bc
6.2
6.6
1.6
0.66
0.82
36
0.20
Nutrient digestibility
Body composition
Final body weight (g)
Empty body weight (g)
Abdominal fat (g) †
Protein (%) †‡
Fat (%) †‡
Heart (mg) †
Liver (g) †
a
282
275 a
14.1 b
21.3
13.1 ab
949
10.56 a
5.9
5.9
1.3
0.33
0.99
29
0.17
a
281
266 ab
22.8 a
20.8
16.5 a
1028
9.34 c
5.9
5.9
0.9
0.66
1.98
20
0.11
285 a
269 ab
14.5 b
21.4
12.2 ab
984
10.11 ab
GIT: gastrointestinal tract; DF: dietary fiber; C: Control; 5-CEL: 5% DF from cellulose; 5-WL: 5% DF from whole linseed; 5-GL: 5% DF from ground linseeds;
5-LDF: 5% DF from linseed DF extract; 10-LDF: 10% DF from linseed DF extract.
a, b, c, d, e
Mean values with different superscript letters within a row were significantly different (p < 0.05; ANCOVA, followed by least significant difference test).
* n = 9 for nutrient digestibility data due to problems with sample collection; † n = 5, ‡ percentage of carcass weight.
Nutrients 2013, 5
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The intermediate diets had a less pronounced effect on energy and fat digestibility, ranging from
86% to 96%. The digestibility of energy and fat in relation to DF was therefore better described by a
second-degree polynomial than by a linear regression, and can be described as follows:
Apparent digestibility of energy = 96.95 − 0.0674x − 0.0002x2, r2 = 0.998
(1)
Apparent digestibility of fat = 94.43 + 0.0218x − 0.0007x2, r2 = 0.978
(2)
where x denotes DF.
There seemed to be an effect of linseed DF source on the digestibility of fat, with a decreased
apparent digestibility with increased accessibility of DF (5-WL vs. 5-GL) and increased proportion of
viscous DF (5-GL vs. 5-LDF) (Figure 1).
An overall effect of diet (p = 0.05) and time (p < 0.001) on body weight was observed, but no
interaction between time and diet was seen. However, only rats fed the 10-LDF had a significantly
lower body weight after 3 weeks compared to diet C (−8.6%), 5-CEL (−8.3%), and 5-WF (−9.5%)
(Figure 2, Table 2). No differences in weight gain of rats fed diets C, 5-CEL, 5-WF, 5-GF and 5-LDF
were observed. Differences in weight were more pronounced for empty body weight. Rats fed 10-LDF
had a lower empty body weight compared to rats in all other groups (p < 0.01) Rats fed 5-LDF differed
from both C and 5-CEL fed rats (p < 0.05).
Figure 2. Weight gain during the 3 weeks feeding trial in rats fed six different
diets (C = control; 5-CEL = 5% DF from cellulose; 5-WL = 5% DF from whole linseed;
5-GL = 5% DF from ground linseeds; 5-LDF = 5% DF from linseed DF extract;
10-LDF = 10% F from linseed DF extract) (Mean ± SE) (n = 10). Significant overall effect
of diet (p = 0.001) and time (p = 0.001) (repeated measures ANCOVA). Weight gain was
significantly smaller in 10-LDF group compared to all other groups (p = 0.02; repeated
measures ANCOVA followed by least significance difference).
B o d y w e ig h t g a in ( g )
100
C
5 -C E L
75
5 -W L
5 -G L
50
5 -L D F
1 0 -L D F
25
1
2
4
1
7
0
0
T im e (d a y s )
Weight of abdominal fat pads was highest in rats fed the 5-CEL diet. Total % fat of carcass weight
was lower in the rats fed the 10-LDF diet compared to the 5-CEL fed rats (p < 0.05), whereas no
differences were seen in % protein of carcass weight (p = 0.21). This means that the protein/fat ratio
was almost doubled in the 10-LDF group compared to the 5-CEL group. Furthermore, the different DF
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sources and amounts significantly affected GIT weight (Table 2). GIT weight (without content)
increased with increasing amounts of DF, and rats fed the 10-LDF diet had a larger total GIT than rats
on all other diets (p < 0.001), probably reflecting elongation of the small intestine, caecum, and large
intestine. Contents of the caecum, small and large intestine also increased, most so in the rats fed
5-LDF and 10-LDF diets (p < 0.001). As for a marker of apparent fat digestibility, both the amount of fat
found in the small and large intestine tended to increase when the linseed were ground (5-WL vs. 5-GL),
or when proportion of viscous DF was increased (5-GL vs. 5-LDF).
4. Discussion
Our hypothesis was that addition of linseed DF to animal feeds would suppress weight gain as a
consequence of decreased apparent nutrient digestibility. Rats fed the 10-LDF diet had a lower daily
weight gain compared to the rats fed the C, 5-CEL and 5-WL diets (p < 0.05), and empty body weight
was lower compared to all other rats (p < 0.01). Apparent fat and energy digestibility were decreased
by 10%–20% with the addition of a high dose of linseed DF to the feed, which could be modeled as a
second-degree polynomial relationship. The second-degree relationship is undoubtedly due to the
viscous nature of the linseed DF and its interference with the digestion and absorption of fat.
We have previously found linseed DF to be highly viscous in aqueous solution [15,23], but the
viscosity of the gut lumen content of the rats was not assessed in the present study. However, our
observations are in agreement with other studies, which have shown a reduction in weight gain with
the addition of viscous DF to high fat diets [24,25]. Contrastingly, a recent study by Isken and
colleagues (2010) suggested that soluble viscous DF was less effective for reducing body with than
insoluble DF [8]. They found that guar gum resulted in a smaller faecal volume and excretion of
energy compared to a diet with insoluble DF from oat hulls, probably due to the fermentation of the
guar gum as reflected by increased H2-exhalation, higher energy digestibility and supposedly higher
metabolisable energy content in the guar gum diet. We measured apparent energy digestibility, but not
metabolisable energy. However, as weight gain was reduced and faecal volume and energy excretion
significantly increased with the 10-LDF diet, it appears that viscosity played a larger role than
fermentation of the linseed DF in the present study. Nonetheless the significantly larger contents of
caecum of the 10-LDF fed rats suggest an increased bacterial fermentation. Our results confirm
previous findings that addition of whole linseed to the feed reduces nutrient digestibility in broiler
chickens [26] and ruminants [27]. Removal of the mucilage layer of the seeds offset the effect on
apparent energy and fat digestibility in broiler chickens [11], clearly indicating that the DF component
is responsible for the observed effects. Viscosity of the jejunal digesta of the chickens correlated with
the digestibility of nutrients [28], thus the physiological effects appear to be closely linked to the
viscous properties of the linseed DF. As in the present study, a non-linear increase in viscosity with
increased concentration of DF was found [28].
The higher feed intake in the 5-CEL group compared to the other groups did not result in increased
weight gain. The small differences in feed intake between 10-LDF and 5-LDF, 5-GL and 5-WL
suggest that the rats may have tried to compensate for the lower nutrient digestibility resulting from the
10-LDF diet. However, this was not sufficient to achieve a growth rate in the 10-LDF group similar to
that of the other groups. The high dose of DF in the 10-LDF group did not influence the protein
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digestibility to such a degree that it affected muscle mass; but the percentage of body fat decreased.
Addition of linseed DF to the feed also caused a significant increase in weight of total GIT and
different segments of the GIT. This may be due to (1) increased microvilli length and density; or (2) an
elongation of the GIT as a means of compensation for decreased nutrient utilization, although neither
length of the different segments or gut morphology were not recorded in the present study. Our
findings are in accordance with Zhao et al. [29], who found an almost two-fold increase in weight of
the GIT, with a high vs. low DF diet (257 g vs. 56 g DF/DM). DF may also affect the weight of the
liver, kidney, and heart, as observed in other animal studies [29–31], but we did not see this here.
We hypothesized that similar doses of DF provided as whole or ground linseed, or as extract, would
affect nutrient digestibility differently due to differences in botanical integrity, particle size, and DF
type. In the 5-WL and 5-GL diets the DF were a mix of soluble and insoluble DF, whereas the 5-LDF
diet contained only water-extracted soluble DF. These differences in DF type did not result in any
significant differences in body weight gain, whereas apparent fat digestibility, faecal volume and
weight of intestinal contents was larger when rats were fed extracted viscous linseed DF compared to a
mix of DF types. That fat digestibility was affected to some degree indicates that luminal viscosity
may have differed, although this was not verified in the current study. The differences in luminal
content, particularly in the caecum and large intestine, suggest that fermentation was increased with a
higher viscous DF content, as increased luminal content is believed to result from increased bacterial
mass [32]. Contrastingly, there were no detectable differences in luminal content between whole and
ground linseeds. We speculate that results might have been different if the study had been conducted in
humans, as whole linseed probably pass through the human GIT, at least to some extent, in their intact
structure. This is not the case in rats, where the seeds are chewed.
The digestive tract varies greatly between species, but previous studies have shown that the
utilization of energy, protein, fat, and NSP, are reasonably comparable in rats and humans [33–35],
although the ability to ferment cellulose differs between rats and humans. It is therefore not
appropriate to extrapolate our findings of reduced nutrient digestibility to humans. It is worth noting
that the daily dose of DF fed to the rats in the present study exceeds that of a normal DF diet in
humans, as a diet containing 10%–15% NSP of DM would correspond to a daily intake of 40–60 g of
DF in humans. Furthermore, this study was performed in growing rats, where a high proportion of
absorbed nutrients are used for growth. The results obtained on body weight gain should be interpreted
with great caution in terms of potential effects on body weight in humans, and the fact that the impact
of DF on appetite regulation may differ between rats and humans should also be taken into account.
5. Conclusions
In conclusion, a high dose of DF extracted from linseed increased faecal fat and fat excretion, and
resulted in decreased body weight gain in growing rats, whereas diets with similar DF content for the
whole or ground linseed or DF extracted from linseed did not affect body weight differently, despite
differences in apparent fat and energy digestibility. The present findings should be regarded as a proof
of concept for this new source of extracted DF. We believe that linseed DF may be a useful food
ingredient for its effect on energy balance, also in humans, although this needs to be confirmed in
long-term human intervention trials.
Nutrients 2013, 5
3296
Acknowledgements
The study was supported by a grant from Basic Research, Salt Lake City, USA, a PhD scholarship
from University of Copenhagen, Faculty of Life Sciences and LMC FOOD Research School. The
linseed hulls used for the DF extractions were kindly provided by Natunola Health Inc., Ottawa, ON,
Canada. The authors gratefully acknowledge gratitude to lab technician Kathrine Hansen Høirup for
her assistance in the practical work.
Conflict of Interest
The University of Copenhagen has a patent pending concerning the present research and A Astrup
is a consultant for Basic Research. All other authors have no conflict of interest.
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