Key message
– Evidence about the effects of dietary fat intake on the wellbeing of people with gallstones is uncertain.
What are gallstones?
Gallstones, also known as cholelithiasis, are deposits from digestive fluid which consist of solidified substances such as cholesterol and bile pigments that are found in bile (a fluid that breaks down fats and is made and released by the liver and stored in the gallbladder). Cholesterol (a fat-like substance) circulates in the blood and all the body's cells contain cholesterol. Too much cholesterol can cause numerous health problems. The number of people with gallstones is generally increasing because of nutritional and lifestyle changes, ageing populations, increasing levels of obesity, and improvements in diagnosis.
What did we want to find out?
We wanted to find out if changing dietary fat intake is beneficial or harmful for people with gallstones. We were interested in the effects on deaths, serious side effects, health-related quality of life (a measure of a person's satisfaction with their life and health), dissolving or reducing the size of the gallstones, or non-serious side effects.
What did we do?
We searched medical databases for clinical trials of people with gallstones who received a dietary intervention that aimed to treat gallstones.
What did we find?
We identified five trials, but only one trial with 69 participants provided some data for this review. The trial was carried out in the USA and was published in 1986. Thirty-seven (54%) people were women and all were adults. The trial randomly assigned 69 people to a modified diet including a low-cholesterol intake diet or a modified diet with additional medium-chain triglyceride (a type of fat that may be easier to absorb without bile), and compared them to a standard diet.
Key results
There was not enough evidence to state whether modifying dietary fat has beneficial, harmful, or neutral effects on outcomes of people with gallstones. The one trial that reported data did not investigate key concerns including whether modifying dietary fat influenced people's symptoms after eating, their health-related quality of life, their chance of having gallbladder inflammation, or requiring surgery to remove their gallbladder.
We found no ongoing trials.
Funding
The one trial that reported data received no funding that could bias the trial results through conflicts of interest.
What are the limitations of the evidence?
Our confidence in the evidence was very low because we were concerned about the methods used in the trial (for example, how the participants were allocated to their treatments, the trial did not report data about everything that we were interested in, there was no information about who delivered the dietary intervention). The results of further research could differ from the results of this review.
How up to date is this evidence?
The evidence is current to 17 February 2023.
The evidence about the effects of modifying dietary fat on gallstone disease versus standard diet is scant. We lack results from high-quality randomised clinical trials which investigate the effects of modification of dietary fat and other nutrient intakes with adequate follow-up. There is a need for well-designed trials that should include important clinical outcomes such as mortality, quality of life, impact on dissolution of gallstones, hospital admissions, surgical intervention, and adverse events.
The prevalence of gallstones varies between less than 1% and 64% in different populations and is thought to be increasing in response to changes in nutritional intake and increasing obesity. Some people with gallstones have no symptoms but approximately 2% to 4% develop them each year, predominantly including severe abdominal pain. People who experience symptoms have a greater risk of developing complications. The main treatment for symptomatic gallstones is cholecystectomy. Traditionally, a low-fat diet has also been advised to manage gallstone symptoms, but there is uncertainty over the evidence to support this.
To evaluate the benefits and harms of modified dietary fat intake in the treatment of gallstone disease in people of any age.
We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials in the Cochrane Library, MEDLINE ALL Ovid, Embase Ovid, and three other databases to 17 February 2023 to identify randomised clinical trials in people with gallstones. We also searched online trial registries and pharmaceutical company sources, for ongoing or unpublished trials to March 2023.
We included randomised clinical trials (irrespective of language, blinding, or status) in people with gallstones diagnosed using ultrasonography or conclusive imaging methods. We excluded participants diagnosed with another condition that may compromise dietary fat tolerance. We excluded trials where data from participants with gallstones were not reported separately from data from participants who did not have gallstones. We included trials that investigated other interventions (e.g. trials of drugs or other dietary (non-fat) components) providing that the trial groups had received the same proportion of drug or other dietary (non-fat) components in the intervention.
We intended to undertake meta-analysis and present the findings according to Cochrane recommendations. However, as we identified only five trials, with data unsuitable and insufficient for analyses, we described the data narratively.
We included five trials but only one randomised clinical trial (69 adults), published in 1986, reported outcomes of interest to the review.
The trial had four dietary intervention groups, three of which were relevant to this review. We assessed the trial at high risk of bias. The dietary fat modifications included a modified cholesterol intake and medium-chain triglyceride supplementation. The control treatment was a standard diet. The trial did not report on any of the primary outcomes in this review (i.e. all-cause mortality, serious adverse events, and health-related quality of life). The trial reported on gallstone dissolution, one of our secondary outcomes. We were unable to apply the GRADE approach to determine certainty of evidence because the included trial did not provide data that could be used to generate an estimate of the effect on this or any other outcome. The trial expressed its finding as "no significant effect of a low-cholesterol diet in the presence of ursodeoxycholic acid on gallstone dissolution." There were no serious adverse events reported.
The included trial reported that they received no funding that could bias the trial results through conflicts of interest.
We found no ongoing trials.