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Acta Cirurgica Brasileira

Print version ISSN 0102-8650On-line version ISSN 1678-2674

Acta Cir. Bras. vol.30 no.3 São Paulo Mar. 2015 

Original Articles

Fasting does not induce gastric emptying in rats1

Marcus Vinicius Henriques Brito I  

Edson Yuzur Yasojima II  

Renan Kleber Costa Teixeira III  

Abdallah de Paula Houat IV  

Vitor Nagai Yamaki V  

Felipe Lobato da Silva Costa VI  

IPhD, Full Professor, Head, Department of Integrate Health, Medical School, University State of Para (UEPA), Brazil. Conception and design of the study, manuscript writing, critical and final revision

IIPhD, Full Professor, Department of General Surgery, UEPA, Brazil. Design of the study, critical revision

IIIMD, School of Medicine, UEPA. Brazil. Technical procedures, statistical analysis, manuscript preparation, English version

IVMD, School of Medicine, UEPA, Brazil. Technical procedures, interpretation of data, manuscript preparation

VGraduate student, School of Medicine, UEPA. Brazil.Care of animals, technical procedures, manuscript preparation

VIGraduate student, School of Medicine, UEPA. Brazil. Care of animals, manuscript preparation, English version



To evaluate the effect of fasting on gastric emptying in mice.


Twenty-eight mice were distributed into three study groups: a normal group (N=4): normal standard animals; a total fasting group (N=12): subjected to food and water deprivation and a partial fasting group (N=12): subjected to food deprivation only. The fasting groups were subdivided into three subgroups of four animals each, according to the date of euthanasia: 24, 48 and 72 hours. Was analyzed: the gastric volume, degree of the gastric wall distention and the presence of food debris in gastrointestinal tract.


The mean gastric volume was 1601 mm3in the normal group, 847 mm3in total fasting group and 997 mm3in partial fasting group. There was difference between the fasting groups in any analyzed period (p<0.05). Regarding the presence of food debris in the gastrointestinal tract and the degree of distension of the stomach, there was no difference between the groups that underwent total or partial fasting (p>0.05).


Total fasting or only-solids deprivation does not induce gastric emptying in mice.

Key words: Fasting; Gastric Emptying; Mice


The use of preoperative fasting is commonly adopted prior to the realization of several major surgeries. Such technique is instituted to ensure gastric emptying and avoid a possible aspiration during the anesthetic technique (Mendelson's syndrome)1.

However, there is evidence that small murines, such as rats and mice, do not exhibit the ability to vomit, and in case of fasting they have an eating disorder that involves the appetite perversion, demonstrated by eating non-food substances, such as soil and their bedding2 , 3. Thus, food deprivation becomes just a stress for the animal trial, and can influence in some experiments because of the changes in carbohydrate metabolism4.

The current ethical rules on animal research seek to minimize the pain and suffering of animals5 , 6, seeking mainly to avoid unnecessary procedures that would only cause stress. Thus, the practice of preoperative fasting could be a procedure eliminated in practice with small rodents if such technique is proofed to be unnecessary.

Some authors argues that the practice of preoperative fasting would decrease the amount of food debris in gastrointestinal tract7 - 9. However, there is evidence suggesting that this practice is ineffective for such purpose, because that would be no gastrointestinal emptying without water and food intake. Thus, this study aims to evaluate the effects of fasting on gastric emptying in mice.


This research was approved by the Ethics Committee in the Use of Animals of the State University of Para (UEPA).

Twenty eight adults females mice (Mus musculus) were used, weighing between 40- 42 grams, provided from the Animal Colony of the Experimental Surgery Laboratory of UEPA, kept in a controlled environment. All animals had ad libitum access to food and water except during test periods. The animals were randomized distributed into three study groups:

  • -Control Group (CG): animals with regular diet (N=4);

  • -Total Fasting Group (TFG): subjected to food and water deprivation (N=12);

  • -Partial Fasting Group (SFG): subjected to food deprivation only (N=12).

The fasting groups were subdivided into three subgroups of four animals each, according the time of elapsed until the animal euthanasia: 24, 48 or 72 hours.

The animals were weighed twice: before starting the fasting period and on the day of euthanasia, to assess animal weight loss. The animals' euthanasia was performed by overdose of intraperitoneal xylazine. The euthanasia was achieved by xylazine overdose. After the confirmation of animal death, a median laparotomy was immediately performed to assess: the stomach volume, by measuring its dimensions; presence or absent of food debris in the gastrointestinal tract and the degree of gastric wall distension.

The degree of gastric wall distension was classified as 0: collapsed walls; 1: slightly distended; 2: moderated distended; and 3: intense distended. Kruskal-Wallis test was used to compare the volume measurement and degree of distention of the gastric wall, Pearson's Linear Correlation test was used to verify the weight variation and Exact Fischer analysis for presence or absent of food debris in the gastrointestinal tract. Was adopted a significance level of 5% to reject the null hypothesis.


The analysis of animal weight curve (Figure 1) shows that there was significant weight loss during the studied period (p<0.01). However, there was no significant difference between the weight loss of the animals when the type of fasting (total or partial) was compared.

Figure 1 - Initial and final weight of the animals. TF - Total Fasting; PF - Partial Fasting 

In the analysis of the average volume of stomachs (Figure 2) was identified in the control group a volume of 1601mm3; 814 mm3 in the total fasting (899 mm3 - 24h; 796 mm3 - 48h; 747 mm3 - 72h); and was 997 mm3 in the partial fasting (1153 mm3 - 24h; 989 mm3 - 48h; 851 mm3 - 72h).A significant difference was observed between the control group and fasting groups, where the average volume was higher in the control group (p<0.01). There was a significant difference between the two fasting groups, where the partial fasting group had higher stomach volume than the total fasting group (p<0.05). In both fasting groups there was a significant decrease of the stomach volume within the analyzed time periods (p<0.001).

Figure 2 - Animals' stomach volume after fasting according to the experimental groups. TF - Total Fasting; PF - Partial Fasting 

The average stomach distension degree of the CG was 3.00; in the total fasting group the degree was 2.00 (24 hours), 1.75 (48 hours) and 2.00 (72 hours); and in the partial fasting groups was 1.75 (24 hours), 2.00 (48 hours) and 2.00 (72 hours). There was a significant difference between the CG and the other groups (p<0.05), but was not identified differences between groups that underwent partial or total fasting (p=0.96).

Table 1 shows the areas where food residues have been identified in the gastrointestinal tract of the animals. It shows that only in the control group was identified food debris in the small intestine and in all parts of the large intestine.

Table 1 - Amount of animals with presence/absence of food in the gastrointestinal tract according to the analyzed segment. 

Stomach Small intestine Caecum Ascending and descending colon
Present Absent Present Absent Present Absent Present Absent
Control 4 0 4 0 4 0 4 0
TF 24h 4 0 0 4 4 0 4 0
TF 48h 4 0 0 4 4 0 2 2
TF 72h 4 0 0 4 4 0 0 4
PF 24h 4 0 0 4 4 0 4 0
PF 48h 4 0 0 4 4 0 1 3
PF 72h 4 0 0 4 4 0 0 4

Source: Protocol search


The use of animals in experimental research is a practice that has been increasingly criticized over the past decades5 , 6 , 10. In1959, Russell and Burch11 proposed the 3 R's theory in which all the experiments involving animals should seek for the "reduction" of the number of used animals; "replacement" of animals for validated alternative techniques; and "refinement" of the research conduction, where the methods should eliminate or at least reduce the pain and suffering of the animal.

Current evidence shows that preoperative fasting in small rodents is a procedure that is just stressful to animals, since these animals have no ability to vomit2 , 3 and do not present the risk of pulmonary aspiration of gastrointestinal contents even with full load of intragastric content as evidenced in this study.

Some reasons for the inability to vomit are: 1) diaphragmatic structure relatively less muscular3 , 12; 2) esophagus length relatively longer than non-emetic species13; 3) stomach geometry with absence of a funnel shape3; 4) absent brainstem neurological component of vomit3 , 14.

The presence of intragastric contents despite the loss of weight of the animal shows that the gastric income of solid food is a stimulant factor for gastric emptying in mice, whereas in the group with only water deprivation there was no increased gastric emptying than in the group subjected to water and food deprivation. In the control group, the greater gastric volume and presence of content in distal regions of the gastrointestinal elicit that there was gastric emptying associated to grater food intake. However, the difference between the fasting groups occurred probably due to simply hydration of the gastric contents15, giving the false impression of a larger quantity of food.

Unlike humans, whom are relatively used with large fasting periods, small rodents must keep gnawing to get food and to control the steady growth of their teeth16. Hence, this constant stimulation is a major stimulus to gastric emptying17 - 20 along with many hormones, such as cholecystokinin; and neural pathways, such as parasympathetic stimuli.

Another claimed reason for conducting the preoperative fasting in small rodents would be to perform a bowel cleansing. However, this study identified that after 24 hours fasting period there is feces content in the entire large intestine and only a more prolonged fasting period (72 hours) could deliver a satisfactory colon cleansing. However, an early fasting was considered sufficient to conduct a clean surgery of the small intestine.

Preoperative (24 hours) fasting showed that was not sufficient for proper bowel preparation21, and many related substances might have better results, such as polyvinylpyrrolidone22 and retrograde flushing23. The findings from this study suggest that fasting might be substituted by other techniques for gastrointestinal cleansing.


Total fasting or only-solids deprivation does not induce gastric emptying in mice, according the methods used.


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Financial source: State University of Para

1Research performed at Experimental Surgery Laboratory, School of Medicine, State University of Para (UEPA), Belem-PA, Brazil.

Received: November 17, 2014; Revised: January 19, 2015; Accepted: February 16, 2015

Correspondence: Marcus Vinicius Henriques Brito Rua Apinagés, 630/202 66.033-170 Belém - PA Brasil Tel.: (55 91)3222-9752/8854-8895

Conflict of interest: none

Creative Commons License This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.