Does Eating Dietary Fiber Reduce the Risk of Ovarian Cancer?

Later the Diagnosis for Ovarian Cancer, Lesser the Chances of Survival

A Diet Rich in Fiber is Good for Health Irrespective of Whether or Not it Has Impact on Cancer Risk

Ovarian cancer prevails as the leading cause of death (1,50,000 deaths annually) in gynecological cancers worldwide and is the second most common female reproductive malignant tumor (240,000 cases erupt every year). Awareness about ovarian cancer has increased tremendously during recent times but still we lack the knowledge to get it diagnosed at an early stage. This disease often remains undiagnosed until later stages by which time it has 100% chances of spreading to the abdominal cavity. We boast of scientific advancements and research in the field of ovarian cancer in the past few decades but still lack a definite prognosis that could help treat patients in their early stages of ovarian cancer despite advances in treatment options. Though the cancer generally affects women who have been through menopause (mostly above the age of 50) there are chances of it affecting younger women too. While the exact causes of ovarian cancer remain unknown, we do know that age (above 50 years), family history of breast or ovarian cancer, endometriosis and being overweight are serious risk factors. We do have data supportive of the fact that dietary factors such as glycemic load, dietary phytoestrogen, fat, fruits and vegetables do play a role in impacting ovarian cancer risk. Fruits, vegetables and whole grains are excellent sources of fiber, a nutrient that has been inversely linked to the risk of several types of cancers such as colorectal, endometrial, gastric and ovarian cancer. But the role of diet, especially fiber has been greatly conflicting providing us with inconsistent results that prevent us from either supporting or denying the role played by fiber in affecting the risk of ovarian cancer. Some studies supported the fact that intake of dietary fiber was inversely proportional to ovarian cancer risk but some others failed to prove the connection and moreover, the effects varied depending on the type and source of fiber consumed.
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Systematic Review of Ovarian Cancer Risk
The Women’s Health Initiative (WHI), a trial consisting of 48,835 postmenopausal women was the only primary prevention intervention trial that proved that eating a low-fat diet reduced the risk of ovarian cancer risk by 40%. But we do have descriptive data going as early as 1975 showing that there could be an association between dietary fat and ovarian cancer risk. There were also several results supporting that while veggies, whole grains and low-fat milk reduced ovarian cancer risk, meat intake increased the risk but still we did not get any conclusive results. To compare all the different study results and come to certain conclusions a systematic review following the recommendations of Preferred Reporting Items for Systematic Reviews & Meta-analysis Approach (PRISMA) with the help of search engines such as PubMed, MEDLINE, etc. were conducted and finally, 24 publications that met the inclusion criteria were included in the review. Many reviews supported that increased fat intake increased ovarian cancer risk while vegetables consumption decreased the risk significantly.
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A Canadian study tried looking into the perspective that fiber intake reduced the risk of ovarian cancer significantly but neither total fiber nor specific fiber types showed a significantly lower risk for ovarian cancer. The review clearly concluded that fiber did not have any impact on ovarian cancer risk in any way.

Meta-analysis of Observational Studies
Owing to inconclusive evidences in relation to the risk of ovarian cancer risk and fiber intake, two investigators searched databases such as PubMed and Web of Science using several word search criteria and inclusion criteria. They were left with 2784 publications that had a link between fiber intake and ovarian cancer risk. But it was only 17 studies that met the inclusion criteria of which four of them were cohort studies and the remaining 13 were case-controlled studies-10 of them were from United States, four from Europe and three from Asia. Results showed that:
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1. Highest intake of dietary fiber was associated with a reduced risk of ovarian cancer in comparison to the lowest intake.
2. Among case-controlled studies, six of them were population-based case-control (PCC) studies and the other seven were hospital-based case-control (HCC) studies. There was a positive association found in PCC and HCC studies where decreased risk was found in those individuals consuming highest level of fiber intake compared to those consuming lowest levels.
3. There was an inverse association between dietary insoluble fiber and vegetable fiber intake and ovarian cancer risk but no association between cereal and fruit fiber intake and ovarian cancer risk.
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A diet high in fiber is indicative of a generally healthier diet such as increased vegetables intake and lower fat intake and better lifestyle changes such as increased physical activity. There exists a previous meta-analysis that showed that high dietary fiber intake was inversely associated with colorectal cancer risk, pancreatic cancer risk, gastric cancer, breast cancer and endometrial cancer risk and the present meta-analysis too, finds its results similar to the other one.

Another meta-analysis followed the standard MOOSE and PRISMA to report the analysis and used databases such as PubMed and EMBASE to sort through the studies. Two investigators were involved here too who used specific search terms to narrow down study inclusions and finally were rewarded with 4665 articles of which 4641 were excluded as they did not meet the study criteria. Again 11 of them were excluded due to several criteria leaving the researchers with only 13 of them that contained 5,777 ovarian cancer cases and 1,42,189 participants. Of the 13 studies, 10 of them were case-controlled and 3 were cohort studies all of which measured dietary intake with the help of a food-frequency questionnaire. Results showed that:
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1. Reported relative risk (RR) for ovarian cancer per 10 g/day increase of dietary fiber intake was 0.88. There was no evidence of a non-linear association between dietary fiber intake and ovarian cancer risk.
2. Pooled RR was 0.77 for case-control studies and 0.84 for cohort studies. When the sample size was <300 the RR was 0.83 and its value was 0.77 when sample size ≥300. RR was 0.80 for vegetable fiber, 0.90 for fruit fiber, 1.24 for cereal fiber, 0.79 for soluble fiber and 0.60 for insoluble fiber. The inverse association between fiber intake and ovarian cancer risk was insignificant without adjusting for oral contraceptive use.
3. The risk of ovarian cancer reduced by 22% in the group of highest dietary fiber intake and a further 12% reduction in risk was found for per 10 g increase per day.
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We have several different theories proposed to explain how dietary fiber protects against ovarian cancer risk. The consumption of fiber has the potential to decrease circulating estrogen concentrations by changing bacterial macroflora, increasing excretion and consequently lowering serum levels and availability of estrogen that decreases availability of steroid hormones that is linked to progression of ovarian cancer. On the other hand, insulin-like growth factors are suggested risk factors for ovarian cancer. Dietary fiber is said to reduce glycemic load and improve insulin sensitivity thereby influencing these insulin-like growth factors.

Earlier identification of ovarian cancer paves way for better treatment and curing chances. But often we don’t recognize ovarian cancer until it has already spread. Even if treatment is successful there are greater chances that the cancer might recur in a few years’ time and in this case, there is no cure. It can only be controlled with the help of chemotherapy which can help in extending the patient’s life by several months or years. Hence, prevention is better than cure. While family history or age factor is not in our hands, we can do as much as we can to reduce the risk when it comes to dietary modifications and lifestyle factors. Results of fiber, vegetable and fruit intake and their association in reducing the risk of ovarian cancer might be inconclusive but we are sure that these foods are indeed good for our health and there is no harm in eating them. Consuming the right kind of foods, staying on a normal body weight and exercising regularly helps reduce the risk of ovarian cancer greatly.

References
Dietary Intake & Ovarian Cancer Risk: A Systematic Review: https://cebp.aacrjournals.org/content/23/2/255#

Association between Dietary Fiber Intake & Risk of Ovarian Cancer: A Meta-analysis of Observational Studies: https://www.researchgate.net/publication/327215865_Association_between_dietary_fiber_intake_and_risk_of_ovarian_cancer_a_meta-analysis_of_observational_studies
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Dietary Fiber Intake & Reduced Risk of Ovarian Cancer: https://nutritionj.biomedcentral.com/articles/10.1186/s12937-018-0407-1

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