Research shows that diets high in fiber reduce the risk of colorectal cancer. Now, a major analysis of the literature that included almost one million women suggests that dietary fiber may also protect against breast cancer.
The research was funded by the World Cancer Research Fund as part of AICR/WCRF's Continuous Update Project (CUP), an ongoing review of cancer prevention research. It builds on a 2007 and 2009 AICR/WCRF review of the literature, which concluded the evidence linking dietary fiber and breast cancer prevention was too limited or inconsistent to draw a conclusion.
Here, lead author Dagfinn Aune, a nutritional epidemiologist at Imperial College London who is part of the CUP team, talks about the findings.
Q: Your analysis looked at 16 studies on fiber and breast cancer risk. What were the main findings?
A: We found that there was a 5 percent reduction in risk of breast cancer for each 10 grams per day of dietary fiber women eat. Our analyses suggest that increasing dietary fiber intake may be a promising approach to reduce breast cancer risk. Although the association is weak, breast cancer is such a common cancer and everybody eats, so increasing fiber intake could still result in many breast cancer cases being prevented.
"We found that there was a 5 percent reduction in risk of breast cancer for each 10 grams per day of dietary fiber women eat."
Q: And you looked at prospective studies, which follow a population over time?
A: Yes. We only included prospective studies to avoid potential biases that can affect retrospective case-control studies, such as recall and selection biases.
Q: Did the results surprise you, given that the WCRF/AICR 2007 report and its updates found the evidence was inconclusive.
A: We were not very surprised by the findings. Updating the evidence is the role of the CUP and with more published studies, we are able to detect associations now that could not be detected in 2007, when the number of published studies was lower.
Because we included all the available prospective studies we had more statistical power to detect a significant association than each individual study had on its own and that is probably one of the reasons we found an association in contrast to the previously inconsistent results from individual studies. Also, the hypothesis has been supported by results from experimental studies.
Q: Can you talk about how the CUP systematic process works in general?
A: There is a protocol that we follow which specifies how the searches are done, how the analyses are conducted etc. We search in the PubMed database and all the searches are then screened for relevant studies. We then extract the relevant data from the studies into a database. Much of the work we do goes into conducting the searches, screening studies, extracting data and cleaning up datasets before analyses can be conducted and reports be written. We have double-checking procedures of article selection and data extraction.
Q: You looked at many types of fibers independently, from vegetables to grains; can you talk about what you found?
A: Yes, we looked at fruit fiber, vegetable fiber and cereal fiber in relation to breast cancer risk. We did not find a significant association for any of these, but this may have been due to limited statistical power because of the limited number of studies that reported on fiber types. There was some suggestion of an inverse association for fruit and cereal fiber, but not vegetable fiber, but neither of these results was significant. However, we did find a significant association for soluble fibers, but not insoluble fibers.
Q: What are some possible mechanisms why dietary fiber may protect against breast cancer?
A: Experimental studies both in humans and animals have shown that higher intake of dietary fiber can reduce estrogen levels in blood. Fiber may bind estrogens in the colon and increase the fecal excretion of estrogens. In addition, high fiber intake can reduce hyperinsulinemia and may also reduce the risk of overweight and obesity, which are established risk factors for postmenopausal breast cancer. In our analysis the association appeared to be independent of body fatness, thus, it appears that the latter explanation is not the main mechanism.
A: I have a passion for preventive medicine. The many indefinite answers in the field of nutritional epidemiology make it even more exciting to work in this area by trying to come up with clearer answers through systematic reviews and meta-analyses of the overall evidence. We have shown in several meta-analyses now that even though individual studies by themselves may not provide clear answers with regard to specific diet-cancer relationships, meta-analyses of the evidence can bring more definitive answers. Being part of the Continuous Update Project is great because the work we do will result in recommendations that can help reduce the world cancer burden.
Stepping in place while watching TV commercials adds up to near the minimum recommended amount of daily physical activity, according to a new study released in the early online edition of Medicine & Science in Sports & Exercise.
In the study, researchers measured how many calories TV watchers burned while doing different types of activity – or non-activity. During the commercials in one hour of TV, the 23 participants either, sat, stood, stepped in place, or walked at 3 mph on a treadmill. Participants were healthy adults, ranging from a normal weight to obese.
Stepping in place during the ads led to 25 minutes of physical activity and taking 2,111 steps. On average, participants burned 258 calories from stepping in place and 304 calories from walking on the treadmill; they burned about 80 calories by sitting down for the whole hour of TV.
Source: Steeves, Jeremy A. et al. "Energy Cost of Stepping in Place while Watching Television Commercials." Medicine & Science in Sports & Exercise: February 2012 - Volume 44 - Issue 2 - p 330335
With approximately one-third of adults and close to one-fifth of youth overweight, the obesity rates have slowed then leveled off over the past decade, according to a Centers for Disease Control and Prevention (CDC) report released last week.
The new CDC findings, drawn from 2009-2010 data, estimated that more than 35 percent of adults and 17 percent of youths were obese. That translates into almost 78 million adults and 12 million youths. The prevalence of obesity was essentially the same among men and women, whereas for youths, it was higher among boys than girls.
From 1999-2000, the prevalence of obesity among men and youths crept upwards until 2007-2008, and then it plateaued. Women stayed essentially the same throughout the entire decade.
Overweight and obesity increase the risk of seven types of cancers, along with type 2 diabetes and other chronic diseases.
Sources: Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of obesity in the United States, 2009-2010. NCHS data brief, no 82. Hyattsville, MD: National Center for Health Statistics. Number 82, January 2012.
Insulin-like growth factors (IGFs) are proteins needed for cell growth but, at high levels, research has linked certain IGFs to increased colon cancer risk. A new cell study has found that a phytochemical found in thyme, celery, sweet peppers and other plant foods reduces the growth-stimulating effects of IGFs in colon cancer cells.
The study was published this week in the journal BMC Gastroenterology.
The scientists studied the phytochemical luteolin, a flavonoid found to show anti-inflammatory and cancer protective properties in lab studies. When the scientists treated colon cancer cells with luteolin, the cells had lower levels of one type of IGF – IGF-II – and blocked the ability for IGF communication, when compared to cells not treated with the phytochemical.
Earlier studies by this same team of Korean scientists found that luteolin reduced colon cancer cell growth. Disrupting IGFs actions may possibly explain this, the scientists conclude.
Source: Do Young Lim, Han Jin Cho, Jongdai Kim, Chu Won Nho, Ki Won Lee and Jung Han Yoon Park. "Luteolin decreases IGF-II production and downregulates insulin-like growth factor-I receptor signaling in HT-29 human colon cancer cells." BMC Gastroenterology 2012, 12:9. 23 January 2012
Next time a tantalizing picture of food makes you hungry, a new study may help explain why. The small study, published in the journal Obesity, found that looking at savory images of meals was followed by an increase in the hormone ghrelin, known to stimulate our appetite.
In the study, researchers showed eight healthy men 50 photographs of non-food items, such as a bicycle or piano one week; then 50 photographs of desirable meals the following week, including chocolate cake, pizza, and ice cream. (A distinct set of volunteers had previously rated the picture as tasty.) The men saw each set of photos between breakfast and lunch for a total of 15 minutes, looking at each image six seconds apiece multiple times. Blood samples were collected every 10- or 15-minutes from before breakfast until after lunch.
The study found, as the researchers expected, that ghrelin levels increased before each meal regardless of the picture contents. But in the half-hour after seeing both sets of images, the men had significantly higher ghrelin levels after seeing food pictures compared to the non-food images.
Source: Schüssler P, Kluge M, Yassouridis A, Dresler M, Uhr M, Steiger A."Ghrelin levels increase after pictures showing food." Obesity (Silver Spring). 12 January 2012, doi: 10.1038/oby.2011.385. [Epub ahead of print]