The Effects of Dietary Dilution on Food Intake


In modern society, it is advisable to add indigestible food to the diet. The benefits of these indigestible foods have been emphasised for a long time. Consequently, they are now widely accepted as part of dietary goals.

All food has energy albeit in various forms. Some components of the diet contain energy, which is not available for body metabolism. This component of diet is never digested and can be regarded as junk because the energy it consists of is passed out unutilised (Elsenhans & Caspary 2000). Only a small portion of food ingested is converted into useful energy. Therefore, if the portion of digestible energy is very small, the animal consuming the food must take large amounts of the food in order to reach the energy requirements of the body (Shock 1978).

Digestion takes place in the gastrointestinal system. During the normal functioning of the gastrointestinal system, many changes occur. Its ability to adapt to various kinds of diet makes it a highly versatile system. Diet containing high proportion of indigestible component leads to morphological changes in the gastrointestinal system (Siebrits, Martinez & Buttery 1985).

This experiment is designed to illustrate the effects of indigestible material on the gastrointestinal structure and function.

Materials and Methods

18 female Wistar rats (153 ± 4.5 g body weight) were housed in wire mesh metabolism cage, which allowed separate urine and faeces collection. The animals were fed their experimental diet for 1 week prior to the experiment. The experimental diets consisted of a control ration (ground commercial rat cubes), the control ration diluted 1:2 with cellulose powder and the control diet diluted 1:2 with bentonite (clay). Six rats were assigned to each diet.

The rats were weighed and the weight of the experimental ration eaten over a three- day period monitored. The faeces produced for this period was also collected, oven dried at 100°C for 3 days and weighed. After grinding and mixing, the energy content of both the food and faeces was determined using a bomb calorimeter (Ser 330: Gallenkamp. Sussex). From this data, the apparent digestibility of both dry matter and energy was calculated.

The rats were then maintained on their experimental diets for a further 5 weeks, prior to being weighed and slaughtered. Following dissection, the lengths of the small intestine and colon and the weights of the stomach, small intestine, caecum and colon and of some individual faecal pellets were measured.


Dry Matter Digestibility

No Control Bentonite Cellulose
1 0.818182 0.289116 0.387218
2 0.923567 0.488127 0.420863
3 0.734043 0.359862 0.405325
4 0.795276 0.58284 0.36
5 0.740113 0.523179 0.3125
6 0.769784 0.161157 0.539683

Table 1: Dry matter digestibility.

Energy digestibility

No Control Bentonite Cellulose
1 0.930579 0.618707 0.468922
2 0.957962 0.762677 0.498082
3 0.783607 0.668292 0.357185
4 0.856693 0.635933 0.512381
5 0.808629 0.761589 0.404167
6 0.870242 0.611082 0.587906

Table 2: Energy digestibility.

Effects of dietary dilution

Parameter Control
(Mean ± SE)
(Mean ± SE)
(Mean ± SE)
Initial Body weight (g) 165.17 ± 6.253a 145.67 ± 5.702a 150.00 ± 7.429a
Final Body weight (g) 200.50 ± 7.233a 182.67 ± 12.690a 189.67 ± 10.585a
Food Eaten g/24h 16.617 ± 1.263a 30.733 ± 1.905b 29.483 ± 1.145b
Feacal output g/24h 3.40 ± 0.568a 17.933 ± 1.212b 17.483± 0.885b
Feacal energy KJ/g 13.733 ± 1.403a 6.150 ± 0.702b 18.683 ± 0.895c
Length of SI (cm) 88.250 ± 8.402a 101.917 ± 5.124ab 109.33 ± 2.404b
Weight of stomach (g) 1.950 ± 0.283a 2.50 ± 0.198ab 2.933 ± 0.338b
Length of LI (cm) 16.017 ± 0.7213a 18.650 ± 0.832ab 21.667± 1.108b
Weight of SI (g) 8.401 ± 0.722a 13.950 ± 0.827b 12.083 ± 0.684b
Weight of LI (g) 3.250 ± 0.254a 5.717 ± 0.605b 6.433 ± 0.956b
Weight of Caecum (g) 4.583 ± 0.591a 10.400 ± 1.142b 7.383 ± 0.515b
Weight of feacal pellet (g) 0.180 ± 0.007a 0.183 ± 0.021a 0.170 ± 0.016a
Length of feacal pellet (cm) 1.283 ± 0.101a 1.367 ± 0.049a 2.050 ± 0.123b
Food energy (KJ/g) 22.00 11.00 21.00
digestibility of dry matter 0.796 ± 0.028a 0.401 ± 0.065b 0.404 ± 0.031b
digestibility of energy 0.375 ± 0.063a 0.441 ± 0.063a 0.110 ± 0.043b

Table 3: Effects of dietary dilution on food intake, digestibility of energy and the ability of the gastrointestinal system to adapt.

The experiment revealed that on average there was high intake of food after dietary dilution. The statistics show that there was increased intake by approximately 85% and 77% when the rats were fed on control diet diluted with bentonite and cellulose respectively (see table).

During the experiment, it was observed that digestibility of food ingested was reduced by half in rats fed on diet diluted with bentonite and cellulose. The average digestibility reduction was almost the same in both cases of bentonite and cellulose (0.400713 and 0.404265 respectively). See table.

It was found out that dilution of diet led to elongation of both the small and large intestines. The weight of the small and large intestines also increased in rats fed on both bentonite and cellulose-diluted food. The small intestine length increased 15% and 24% in bentonite and cellulose respectively while the large intestines were elongated 16% bentonite and 35% cellulose with respect to the control.

The intestinal weight was observed to have increased incredibly with the large intestines registering more growth than the small intestines. The large intestines grew 76% (bentonite) and 98% (cellulose) with relation to the intestines of rats fed on control diet. The small intestines on the other hand grew 66% and 44% on bentonite and cellulose-diluted food respectively. Thus, the small intestines appear to have grown in weigh least on cellulose-diluted food. However, the combined average of large intestines stood at 71% increase, which is same as that of the small intestines. This means that there was a marked intestinal growth in rats fed on both bentonite and cellulose diluted food.

In addition, the weight of caecum was determined. All the rats on bentonite-diluted diet registered very high growth in caecum (average of 127%) which was twice that of rats on cellulose-diluted diet (61%).


The Effects of Dietary Dilution on Food Intake

Dietary dilution reduces the amount of energy in food. Therefore, the animal has to consume more in order to achieve its energy requirements. This explains the increase in consumption of food by the rats fed on bentonite and cellulose- diluted food. The difference in the level of feeding between rats fed on control diet diluted with bentonite and cellulose lies in individual energy properties of the dietary diluting matter (Ebihara, Shiraishi & Okuma 1998). Perhaps the rats on cellulose are able to derive minimal energy from cellulose. On the contrary, bentonite is just clay and may not add any energy value to the rat.

The Effects of Dietary Dilution on Digestion of Food and Energy Digestibility

The digestion of food in both the stomach and the intestines is shown to be greatly hampered by dilution of diet. The experiment shows that the type of diet diluting matter does not significantly differ from one another. The digestion is nonetheless, is reduced by half as opposed to when the diet is not diluted.

The energy digestibility in rats is also reduced when they are served with diluted diet. In particular, cellulose reduces energy digestibility more than bentonite.

The Effects of Dietary Dilution on the Gastrointestinal System

Dietary dilution leads to less food available for digestion and absorption. Furthermore, the indigestible food components such as cellulose make penetration of digestive enzymes to take a long time. Consequently, the animal must adapt to the new diet. This, as observed in the experiment prompts morphological changes in the gastrointestinal system to allow efficient digestion of diluted diet. The adaptation is two-fold; firstly, the intestines become larger and heavier and secondly, they become elongated. Bentonite and cellulose are certainly heavy and the intestines must accordingly enlarge in order to handle the load. In order to maximise the reduced energy content in diluted diet, the intestinal walls enlarge due to increased activity. In addition, the intestines are elongated to maximally, absorb the nutrients from luminal contents (Ramirez 1991).

Whereas the difference between average intestinal weight increase in both bentonite and cellulose-fed rats is minimal, the difference in intestinal lengths is significant. Both the large and small intestines are longer in rats fed on cellulose. This is because diet diluted with cellulose requires longer time to allow digestion and absorption of nutrients to take place (Naya 2008). The major explanation to the enlargement and elongation of the small intestines is that the luminal contents from less digestible diet e.g., cellulose, are more viscous than those from digestible food.

Another notable change was the enlargement of caecum along with the intestines. The fermentation of dietary fibre takes place in the caecum and its enlargement could be because of natural progression of fibre into the organ. The increased microbial activity may lead to general enlargement of the caecum (Cripps & Williams 2006).

Feeding rats on less digestible or diluted diet hampers their growth as demonstrated in this experiment and other studies conducted elsewhere as well. In this experiment, the weight of rats fed on control diet diluted with bentonite and cellulose dropped marginally in relation with those fed on the control diet. The marginal variation in body weight is due to the compensation through increased feeding (Ramirez 1991).

This experiment demonstrates the role of dietary fibre in the intake, digestion, and energy implications. Inclusion of dietary fibre into the diet has various effects, which include reduced digestion of food ingested and energy requirements. Inclusion of dietary fibre in diet can contribute to weight loss, thereby helping people avoid weight related problems (Naya 2008).


Dietary dilution has significant impact significant on intake of food, digestibility of energy, and the morphology of gastrointestinal system. Diluted diet can enhance energy digestibility but decrease digestibility of dry matter. High levels of dietary cellulose could decrease energy and dry matter digestibility. Diluting diet with indigestible material could stimulate the development of alimentary tract.

Reference List

Cripps, AW & Williams, VJ 2006,” The effect of pregnancy and lactation on food intake, gastrointestinal anatomy and the absorptive capacity of the small intestine in the albino rat,” Journal of General Nutrition, Vol. 3, no. 2, pp.1-18.

Ebrihara, K, Shiraishi, R & Okuma, K 1998,” Hydroxypropyl-Modified Potato Starch Increases Fecal Bile Acid Excretion in Rats,” The Journal of Nutrition, Vol. 128, No. 5, pp. 848-854.

Elsenhans, B &Caspary, WF 2000,” Food viscosity as determinant for adaptive growth responses in rat intestine: long-term feeding of different hydroxyethyl celluloses,” British Journal of Nutrition, Vol. 84, no. 1, pp. 39–48.

Naya, DE 2008,” Gut size flexibility in rodents: what we know, and don’t know, after a] century of research,” Revista Chilena de Historia Natural, Vol. 2,no.1, pp. 599- 912.

Ramirez, I 1991, “High-fat diets stimulate transient hyperphagia whereas wet diets stimulate prolonged hyperphagia in Fischer rats,” Physiology & Behavior, Vol. 49, no. 6, pp. 1223-1228.

Shock, NW 1978, “Current Publications in Gerontology and Geriatrics,” The Gerontological Society of America, Vol. 34, no. 2, pp. 1-8.

Siebrits, F, Martinez, JA &Buttery, PJ 1985,” The effect of lactation on the fractional synthetic rate of protein in the liver and muscle of rats,” International Journal of Biochemistry, Vol. 17, no. 6, pp. 731-732.

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