Latest scientific news 07 November 2017

Revised meta-analysis: Beneficial effects of Mediterranean diet on cancer risk

The current systematic review suggests that the strongest adherence to a Mediterranean diet was inversely associated with cancer mortality and the risk of a variety of cancer types.

Approximately, 5-10% of all tumor diseases are caused by genetic predisposition, while the remaining 90-95% can be explained by unfavorable environmental conditions or an unhealthy lifestyle. It has been suggested that 30% of cancers can be prevented by a healthy diet, however, food simultaneously can contain both ingredients that are protective and others may cause harm. Thus, rather than focusing on single nutrients, the assessment of dietary patterns might be a more adequate approach to clarify the relationship between nutrition and cancer. The Mediterranean Diet (MedD) belongs to the a priori defined dietary patterns. It is characterized by a high consumption of plant-based foods, especially whole grain products, vegetables, fruits, nuts and legumes with a regular intake of fish and seafood. Eggs, red and processed meat as well as high-fat dairy products are consumed in low amounts. In addition, moderate consumption of alcoholic beverages, preferably red wine taken with meals, is described. Fat is predominantly provided in the form of olive oil.

To gain further insights into the complex relationship between diet and cancer, German researchers carried out an update of their previous meta-analysis and examined the effects of specific food groups typical of the MedD. More than 2 million participants of 83 studies (randomized controlled trials as well as epidemiological and case-control studies) were included in this extensive review.

The results showed that the highest adherence to a MedD was inversely associated with the cancer mortality (risk was decreased by 14%) and risk of colorectal, breast, gastric, liver, head and neck, gallbladder, and biliary tract cancer.

Considering dietary patterns, instead of single nutrients or foods, are advantageous since foods are not consumed in separation and their health-related effects are additive or even synergistic. However, the authors could show significant inverse associations between specific food groups typical for a Mediterranean dietary pattern such as alcoholic beverages in moderate amounts, fruits, vegetables and whole grains.

The researchers also discussed ethanol, usually represented in the form of red wine, as a specific and controversial “ingredient” of a MedD. In their assessment, the highest rating/level of adherence could sometimes only be achieved when alcohol was consumed on a daily basis in moderate amounts. Although red wine contains a number of potential protective ingredients such as anti-oxidative polyphenols, its beneficial role regarding malignant diseases is discussed controversial. According to the authors, when assessing the effects of a MedD on health and disease, it is important to keep in mind that the different scores for this dietary pattern may include alcoholic beverages and individuals with the highest scores cannot be discriminated according to their consumption of alcoholic beverages. They conclude that at present, it is impossible to make an unequivocal statement on the effects of alcohol consumption regarding tumor pathogenesis.

The present update of their systematic review provided additional important evidence for a beneficial effect of high adherence to a MedD with respect to preventing overall cancer risk and specific types of cancer. The observed beneficial effects are mainly driven by higher intakes of fruits, vegetables and whole grains and a moderate consumption of alcoholic beverages. The authors reported for the first time a small decrease in breast cancer risk (6%).

Schwingshackl L, Schwedhelm C, Galbete C, Hoffmann G, Adherence to Mediterranean Diet and risk of cancer: An updated systematic review and meta-analysis, Nutrients 2017, 9, 1063; doi:10.3390/nu9101063

For more information about this article, read the scientific abstract here.