Flashcards in Food and Cancer - L7 Deck (31)
In the world-wide exercise what did "test of reproducibility" mean ?
all the areas studying the effects undertook the same methodology to ensure data findings could be replicated
Why did the WCRF do a world-wide study ?
because there was a huge increase in the number of papers from 1997-2007
What is a meta-analyses?
looking at lots of different tides with their own risk estimates. The data is then pooled together to form an overall risk estimate
In the stomach cancer review what different types of studies were used in the meta-analysis ?
94 prospective studies
197-case control studies
10 cross sectional studies
135 ecological studies
7 case to case studies (genetic)
18- case- series studies
What is a forest plot?
it is plot used for meta-analysis studies
it is a typical plot for cohort or case control analysis
What do the lines and squares on the forest plot represent ?
each of the lines and squares represents a separate study -the size of the square indicates the population size of each study
estimate and confidence interval of each study is highlighted
What is the middle line of the plot and what does the pooled estimate show?
the middle line is the line of no effect - if an estimate lies on this line then there is no increase or decreased risk of that study
if the pooled estimate went across the line of no effect then it would not be statistically significant
the pooled estimate indicates the level of risk depending on which side on the line it lies
What is the link between the squares and lines associated with studies ?
even if the square of a study is indicating an increased or decreased risk, if the confidence interval crosses the line of no effect then it may not be statistically sginifcant due to lots of variation between studies
What does it mean by forest plots look at heterogeneity ?
they look at how variable the outcome are from different studies
- if very different studies had been pooled together then it would be meaningless and this would be shown in the meta-analysis plot
When looking at a forest plot how can you determine whether the results are similar across the studies ?
1) Eyeball test: do they look similar
2) Test o "null hypothesis" of no variation (p-value)
3) proportion of variation not due to chance (I>2)- important to check because it may have been manipulated . The higher it is= less confidence of pooling data appropriately
In the world-wide study of diet and cancer how did the experts draw conclusions from the information ?
CONVINCING- indicates component of diet was causal
-evidence from more than 1 study type and at least 2 cohort studies
-no substantial unexplained heterogeneity, measurement error or confounding factors
-confirmatory experimental evidence
-evidence from at least 2 cohort studies or five case-control studies
-no substantial unexplained heterogeneity, measurement error or bias
What are the WCRF Uk's recommendations for cancer prevention ?
1) be as lean as possible without being underweight
2) be physically active for at least 30 minutes everyday
3) limit consumption of energy dense foods
4) eat more of a variety of plant foods
5) limit consumption of red meats and avoid processed meats
6) limit alcoholic drinks to 2 for men and 1 for women per day
7) limit consumptions of salty foods
8) dont use supplements to protect against cancer
What are the additional WCRF's recommendations for women ?
Mothers to breastfeed and children to be breastfed
- action protects both mother and child
What is the link between red meat/processed meat and cancer ?
strong evidence that red and processed meat are causes of bowel cancer and that no amount of processed meat can be confidently shown not to increase risk
Why is processed meat worse than red meat ?
because during the processing process chemicals are added
What is the recommended consumption of red meat ?
consume less than 500g a week and very little to be processed
Which cancers are particularly linked to red meat consumption ?
both red meat and processed meat consumption linked to colorectal cancer
What was determined between colon cancer and red meat consumption in an ecological study across many different countries ?
indicated increased meat consumption leads to increase incidence of colon cancer
ecological fallacy- dont know if individual risk in each country was true
When a forest plot was constructed for the association between colon cancer and red meat consumption, what was shown ?
the pooled estimate was 43% therefore there is a 43% increased risk of colorectal cancer for every extra red meat eating occasion per week - it was statistically significant
What is the resounding evidence of red meat consumption and cancer ?
from at least 4 meta-analyses studies:
- 17-30% increased risk of bowel cancer in relation to 100-120g/day of red meat
- 9-50% increased risk of bowel cancer in relation to 25-50g/day of processed meat= there is a large variation for processes meat, this may be due to different classifications of what processes meat is
What did a food diary study show about red meat consumption ?
it found no effect of 50g/day red or processed meat
however the number of participants was small and the amount they consumed was relatively low
What has the WCRF stated about red meat consumption and cancer?
substantial amounts of evidence from cohort studies have demonstrated a dose-response relationship supported by evidence for plausible mechanism between red meat consumption and cancer and therefore there is sufficient evidence that red and processed meat consumption increases CRC risk
What did the UK advisory committee on nutrition suggest about red meat consumption and cancer?
red and processed meat intake was probably associated with increased risk of CRC cancer
What have the WCRF advised ?
limit to 70g/day of red and processed meat
which is approximately
- steak size of a pack of cards
-3 rashes of bacon
-2 average sized beef burgers
-1 quarter pound beef burger
-3 average slices of ham
What is so bad about red and processed meat ?
- energy rich - obesity linked to colorectal cancer- meat eaters tend to have a higher BMI which is linked to increased risk of colorectal cancer
- total and saturated fat content of meat - sat fat affects cholesterol production, precursor of oestrogens
What effect between the high protein content of red meat and colorectal cancer and what can be concluded from this ?
high protein content of meat-fermentation products of excess protein didn't cause colorectal cancer in rodents
suggested that it is the macronutrient profile of red meat that is causative
What are HCAs and what is their link to red meat?
heterocyclic amines and polycyclic hydrocarbons (PAH) formed during browning of meat
- these are potent carcinogens in animal models at high doses
-several epidemiological studies have shown an increased risk of colorectal cancer in people eating browned red meats
Although the browning of meat and HCAs and PAH have been associated with increased colorectal cancer risk. What factor disagrees with this ?
the fact that chicken is also rich in HCAs and PAH but there is no link to colorectal cancer - could be due to different HCAs and PAHs having different potencies
Why is it relevant that red meat contains a haem group ?
- increases colonic cytotoxicity
- epithelial proliferation
-increased oxidative stress- acts as pro-oxidant