Food and Cancer - L7

Question 1

In the world-wide exercise what did “test of reproducibility” mean ?

Answer 1

all the areas studying the effects undertook the same methodology to ensure data findings could be replicated

Question 2

Why did the WCRF do a world-wide study ?

Answer 2

because there was a huge increase in the number of papers from 1997-2007

Question 3

What is a meta-analyses?

Answer 3

looking at lots of different tides with their own risk estimates. The data is then pooled together to form an overall risk estimate

Question 4

In the stomach cancer review what different types of studies were used in the meta-analysis ?

Answer 4

11 RCTs
94 prospective studies 
197-case control studies 
10 cross sectional studies 
135 ecological studies 
7 case to case studies (genetic) 
18- case- series studies

Question 5

What is a forest plot?

Answer 5

it is plot used for meta-analysis studies

it is a typical plot for cohort or case control analysis

Question 6

What do the lines and squares on the forest plot represent ?

Answer 6

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

Question 7

What is the middle line of the plot and what does the pooled estimate show?

Answer 7

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

Question 8

What is the link between the squares and lines associated with studies ?

Answer 8

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

Question 9

What does it mean by forest plots look at heterogeneity ?

Answer 9

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

Question 10

When looking at a forest plot how can you determine whether the results are similar across the studies ?

Answer 10

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

Question 11

In the world-wide study of diet and cancer how did the experts draw conclusions from the information ?

Answer 11

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
PROBABLE
-evidence from at least 2 cohort studies or five case-control studies
-no substantial unexplained heterogeneity, measurement error or bias
-biological plausability

Question 12

What are the WCRF Uk’s recommendations for cancer prevention ?

Answer 12

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

Question 13

What are the additional WCRF’s recommendations for women ?

Answer 13

Mothers to breastfeed and children to be breastfed

- action protects both mother and child

Question 14

What is the link between red meat/processed meat and cancer ?

Answer 14

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

Question 15

Why is processed meat worse than red meat ?

Answer 15

because during the processing process chemicals are added

Question 16

What is the recommended consumption of red meat ?

Answer 16

consume less than 500g a week and very little to be processed

Question 17

Which cancers are particularly linked to red meat consumption ?

Answer 17

both red meat and processed meat consumption linked to colorectal cancer

Question 18

What was determined between colon cancer and red meat consumption in an ecological study across many different countries ?

Answer 18

indicated increased meat consumption leads to increase incidence of colon cancer
HOWEVER
ecological fallacy- dont know if individual risk in each country was true

Question 19

When a forest plot was constructed for the association between colon cancer and red meat consumption, what was shown ?

Answer 19

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

Question 20

What is the resounding evidence of red meat consumption and cancer ?

Answer 20

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

Question 21

What did a food diary study show about red meat consumption ?

Answer 21

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

Question 22

What has the WCRF stated about red meat consumption and cancer?

Answer 22

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

Question 23

What did the UK advisory committee on nutrition suggest about red meat consumption and cancer?

Answer 23

red and processed meat intake was probably associated with increased risk of CRC cancer

Question 24

What have the WCRF advised ?

Answer 24

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

Question 25

What is so bad about red and processed meat ?

Answer 25

• 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

Question 26

What effect between the high protein content of red meat and colorectal cancer and what can be concluded from this ?

Answer 26

high protein content of meat-fermentation products of excess protein didn’t cause colorectal cancer in rodents
therefore
suggested that it is the macronutrient profile of red meat that is causative

Question 27

What are HCAs and what is their link to red meat?

Answer 27

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

Question 28

Although the browning of meat and HCAs and PAH have been associated with increased colorectal cancer risk. What factor disagrees with this ?

Answer 28

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

Question 29

Why is it relevant that red meat contains a haem group ?

Answer 29

haem group

• increases colonic cytotoxicity
• epithelial proliferation
• increased oxidative stress- acts as pro-oxidant

Question 30

What does the haem in red meat do ?

Answer 30

it stimulates endogenous production of mutagenic nitroso compounds

• this compound can be found in stool samples because the colon lining cells shed in the stools and therefore the levels of damaged genetic material can be determined
• in red meat eaters there was higher damged genetic material in comparison to vegetarians and this may have been due to the higher nitroso compounds in the red meat eaters

Question 31

Although it would appear that too much red meat consumption may be bad why is it important to eat?

Answer 31

if women didn’t eat it then they could be at risk of suffering from low iron concentrations
red meats are a good source of micronutrients