The benefits of a "Mediterranean diet" (MD) are well-known when it comes to colorectal protection, but it's hard to know specifically what elements of the diet are the healthiest.

Now a new study, presented today at the ESMO 19th World Congress on Gastrointestinal Cancer suggests loading up on fish and fruit, and cutting back on soft drinks are the three most important things.

"We found that each one of these three choices was associated with a little more than 30% reduced odds of a person having an advanced, pre-cancerous colorectal lesion, compared to people who did not eat any of the MD components. Among people who made all three healthy choices the benefit was compounded to almost 86% reduced odds," said Naomi Fliss Isakov, PhD fromTel-Aviv Medical Center, in Tel Aviv, Israel.

Colorectal cancer (CRC) develops from intestinal polyps and has been linked to a low-fibre diet heavy on red meat, alcohol and high-calorie foods, said Fliss Isakov.

And while the Mediterranean diet has been associated with lower rates of colorectal cancer, the definition of what elements in the diet are the most beneficial, has not always been clear.

Using dietary questionnaires from 808 people who were undergoing screening or diagnostic colonoscopies, the research team was able to dig down to look at the fine details of their daily meals.

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All subjects were between 40 and 70 years old, without high risk of CRC, and answered a food frequency questionnaire.

Adherence to the MD components was defined as consumption levels above the group median for fruits, vegetables and legumes, nuts and seeds, whole grains, fish and poultry and a high ratio of monounsaturated to saturated fatty acids, as well consumption below the median of red meat, alcohol, and soft drinks.

The investigators found that compared to subjects with clear colonoscopies, those who had advanced polyps reported fewer components of the Mediterranean diet (a mean of 1.9 versus 4.5 components). Yet even consumption of two to three components of the diet, compared to none, was associated with half the odds of advanced polyps.

Odds were reduced in a dose response manner with additional MD components -- meaning that the more MD components people adhered, the lower their odds of having advanced colorectal polyps.

After adjusting to account for other CRC risk factors, including other dietary components, the researchers narrowed in on high fish and fruit and low soft drinks as the best combo for reduced odds of advanced colorectal polyps.

The next step will be to see whether the MD is linked to lower risk of CRC in higher risk groups, she concluded.

Commenting on the study, ESMO spokesperson Dirk Arnold, MD, PhD, from Instituto CUF de Oncologia in Lisbon, Portugal, said "this large population-based cohort-control study impressively confirms the hypothesis of an association of colorectal polyps with diets and other life-style factors. This stands in line with other very recent findings on nutritive effects, such as the potential protective effects of nut consumption and Vitamin D supplementation which have been shown earlier this year. However, it remains to be seen whether these results are associated with reduced mortality, and it is also unclear if, and when a dietary change would be beneficial. Despite this lack of information, it makes sense to consider this diet for other health-related reasons also."