A study by the National Cancer Institute, presented this week at the Experimental Biology 2002 meeting in New Orleans, shows that even moderate caloric restriction reduced by 60 per cent the number of precancerous intestinal polyps in mice at high risk of gastrointestinal cancers (mice with the same genetic mutation seen in some humans who develop these cancers).
It also found that quantity had a less important role in cancer risk than nutritional quality : animals eating as much as they wanted of a diet high in olive oil, fruits and vegetables had a third fewer polyps than control mice.
Dr Volker Mai , who presented the study, highlighted the importance of these findings as this moderate caloric restriction and/or the use of a diet in which fat came from olive oil are more likely to be followed by humans and have been shown to have broad health benefits even beyond an effect on gastrointestinal cancer risk.
However, Mai added that when the continuing trend of high caloric food intake in most developed nations was taken into account, the findings proved worrying.
To determine the safe levels of calorie intake, the researchers used a well-proven mouse model of intestinal cancer, and allowed some mice to eat as much food as they wanted. As mice will, they ate almost all the time, gaining weight as a result.
The researchers measured the mice's food intake and then limited similar mice to only 60 per cent of the amount, satisfying their nutritional requirements while providing a reasonable amount of food to eat as well. In this case the number of the precancerous polyps went down by 60 per cent compared to the mice eating as much as they wanted.
Previous mouse studies, like epidemiological studies of humans, have shown that the type of food eaten also has an effect on colorectal cancers. Mai and his colleagues compared the number of polyps in mice on a high-fat diet, mice on a "healthy" diet with olive oil and fruit and vegetable extract, and mice on the standard laboratory mouse diet. Mice consuming a diet high on fruits and vegetables had 33 per cent fewer polyps than the control mice, whereas the mice on the high-fat diet had slightly elevated polyp numbers.
The researchers also looked at exercise. A moderate amount of exercise did lower the number of polyps but the difference was not statistically significant.
The research team, headed by Dr Steve Hursting, is now planning to look at different combinations of caloric intake, fat, and exercise in an effort to determine effective intervention combinations that have the potential to be tested in humans.