Topic 5 - Diet & Cancer (PART A) Flashcards
What are the top 3 causes of cancer, according to the WHO Global Status Report on Non-Communicable Diseases?
1) tobacco
2) alcohol consumption
2) little physical activity
3) diet
What is the main diet-affected cancer?
colon & rectum
chemical components in food come into direct contact with colon
Most common type of cancer?
lung & bronchus
Most common cancers diagnosed by life stage are:
1) leukaemia (0-24)
2) breast cancer for women, melanoma for men (25-49)
3) prostate cancer for men, breast cancer for women (50-64)
4) colorectal cancer for all people (65+)
What are some features of cancer in comparison to other NCDs?
- cancer is more heterogeneous than other NCDs
- needs a nuanced & geographically-specific understanding, rather than a generalized one focusing on a narrow set of shared personal + behavioural risk factors across the world
What are some types of carcinogens?
- tobacco
- UV radiation
- asbestos
- oncogenic infections
Most of the cancer does NOT arise from inherited genes
1 in ___ cancers, and 1 in ___ cancer deaths, are due to smoking
9
5
About ___% of cancers are related to alcohol consumption
3
Example of oncogenic infections and associated cancers
oncogenic infection: human papilloma virus (HPV)
associated cancers: cervical and penile cancers
Outline how occupational exposure can lead to cancer.
- cancer related to occupation represents about 2-20% of all cases
- every year, ~ 200,000 people die worldwide from cancer related to workplace
- most cancer deaths caused by occupational risk factors occur in the DEVELOPED world
What kinds of cancers can develop as a result of occupational exposure?
lung cancer
mesothelioma (From inhaling asbestos fibres & tobacco smoke)
leukemia (from exposure to benzene / other chemicals)
The percentage contribution of work place exposures to national cancer rates is ____, as not many of the population are exposed, but the percentage of workers exposed who get cancers is _____
low
high
How is cancer a genetic disease?
it is caused by change to genes that control the way our cells function, especially how they grow and divide
Cancer-causing genetic changes can also be acquired during our lifetime. How?
- as a result of random errors that occur as cells divide
- due to exposure to substances (chemicals, tobacco, UV radiation) that damage DNA
Cancer cells have more genetic changes than normal cells, but each person’s cancer has a _____ combination of genetic alterations
unique
even within the same tumour, cancer cells may have different genetic changes
What are the 4 basic stages of cancer development?
1) Mutation inactivates tumour suppressor gene
cell proliferate
2) Mutation inactivates DNA repair gene
3) Mutation of proto-oncogene creates an oncogene
4) mutation inactivates several more tumour suppressor genes
What is an oncogene?
a gene that has the potential to cause cancer
in tumour cells, they are often mutated and/or expressed at high levels
most normal cells will undergo a programmed form of APOPTOSIS when critical functions are altered and malfunctioning
activated oncogenes can cause those cells designated for apoptosis to survive and proliferate instead
What is angiogenesis?
when the cancerous cells (malignant or invasive cancer) stimulates the development of blood vessels to supply blood to the growing tumour
How does cancer spread?
- cancer that metastisizes (cancer cells break away from the tumour and they enter the lymph vessels or blood vessels & locate themselves in other organs of the body)
Distinguish b/w benign and malignant tumours.
- benign (NOT CANCER) tumour cells: grow only locally and cannot spread by invasion / metastisis
- malignant (CANCER) cells: invade neighbouring tissues, enter blood vessels, and metastisize to different sites
What can cause breast cancer?
BRCA1 genes can be inherited from parents; they increase the risk of breast, ovarian, & colon cancer in women; & prostate, breast, and colon cancer in men
2 defective BRCA1 genes = high risk
1 defective BRCA1 gene = some increased risk of cancer
Normal BRCA gene = no risk
Why is it so difficult to detect developing cancer?
because there are no similar types of biomarkers to indicate a cancer may be developing
RCTs (random trial controlled studies) on cancer almost impossible
Most our data on cancer comes from. . .
epidemiological cohort studies
cannot give us cause-and-effect
very rough guide that give us an idea of what is happening; usually have to follow it up with animal studies
What is the most reliable source of emerging info about diet and cancer?
research published in peer-reviewed journals
Excess BODY WEIGHT is associated with. . .
the development of MANY TYPES of cancer and is a factor in 14-20% of all cancer deaths
How does physical inactivity contribute to cancer risk?
through negative effects on immune system and endocrine system
More than half of the effect from diet is due to . . .
OVER-NUTRITION –> overweight
rather than from eating insufficient healthy foods or any specific dangerous foods
diets HIGH in processed food / red meat are linked with cancers (the exact mechanisms are not understood)
Why does obesity lead to cancer?
Adipocytes (fat cells) are not just storage vessels for fat
they are actually ENDOCRINE type cells which means they are producing chemical compounds (hormone-like) that spread to different parts of the body and control diff functions
these “cytokines” can actually stimulate different cancers
A high-salt diet is linked to . . .
GASTRIC cancer
Aflatoxin B1, a frequent food contaminant, has been linked with . . .
liver cancer
Betel nut chewing is linked with oral cancer
Why are diets rich in plant foods good for cancer?
They contain protective factors
these plant foods include whole grains, veggies, fruits, beans and can reduce risk for some types of cancer like colorectal, oral, & oesophageal
Some studies have linked a diet high in animal products such as processed meat with. . .
a SMALL increase in cancers of the COLON & PROSTATE
(biological relevance vs statistically significant)
Which foods may have (quite) small cancer protective properties?
1) High-fibre foods - e.g. fruits, veg, beans, legumes, grains (reduce colorectal cancer)
2) Cruciferous veggies - cabbage, broccoli, brussel sprouts all contain bioflavinoids (chemicals associated lower risk of colorectal cancer)
3) Foods with antioxidants (carotenoids, vit C, vit E, selenium) reduce damage to tissues from oxygen free radicals (which can impair DNA)
4) Foods containing phytoestrogens - these substances (high in soy products) help reduce risk of HORMONE-DEPENDENT cancers like breast / uterine cancers
Foods no longer on the hit list as cancer causing . . .
- coffee
- food additives (BHA & BHT)
- fluorides
- artificial sweeteners
To reduce risk of cancer, restrict fat to . . .
<30% of total calories
What did animal studies on omega 6 PUFA suggest?
showed that omega-6- PUFA may increase tumour growth, no relationship has been found b/w omega-6 PUFA and cancer in HUMANS
omega-3 PUFA in animals suppress cancer formation (no evidence for humans)
Trans fats and cancer
no evidence for a relationship b/w the 2
Why is insulin a risk factor for cancer?
it has been shown to stimulate cell division, supporting the growth and spread of cancer cells and making them harder to eliminate
it can also cause inflammation in the body; in the long term, this can lead to the growth of abnormal cells
Processed foods that are high in SUGAR, low in FIBRE and nutrients have been linked to . . .
a higher cancer risk
a diet that causes blood glucose levels to spike is associated with an increased risk of several cancers, including stomach, breast, and colorectal cancers
Why might people with diabetes have an increased risk of cancer?
due to high insulin and blood glucose levels
e.g. risk of colorectal cancer is 22% higher if you have diabetes
Why might a moderate consumption of high-quality dairy products have a protective effect?
contain beneficial fatty acids, conjugated linoleic acid (natural trans) and fat-soluble vitamins
How are the findings on dairy and cancer mixed?
high levels of dairy could increase risk of prostate cancer
different effects on diff people
theories suggest that negative effects are due to INCREASED intake of calcium, insulin-like growth factor 1 (IGF-1) or estrogen hormones from pregnant cows - all linked to prostate cancer
Vegetarians & vegans may have a ___ and ____ lower risk of cancer
8%
15%
but based on observational studies, so hard to identify possible reasons
vegetarians also eat other healthy foods (and less likely to eat processed + overcooked foods)
How effective certain foods are at fighting cancer depends on?
- how they’re cultivated
- how they’re processed
- how they’re stored
- how they’re cooked
How might certain foods fight cancer?
by blocking the blood vessels that feed cancer in a process called anti-angiogenesis
What are some key anti-cancer food groups?
- vegetables
- fruit
- flaxseeds
- spices
- beans and legumes
- nuts
- olive oil
- garlic
- fish
- dairy
Which compound is found in processed / smoked meat and fish that may cause colon cancer?
nitrosamines or nitrosamine precursor compounds such as nitrites and nitrates are a moderate risk for colon cancer
they are important in making sure microorganisms don’t grow
Meat & starchy food cooked at high temps as in frying may also produce other compounds with carcinogenic properties –
- polycyclic aromatic hydrocarbons (PAHs)
- hetrocyclic amines (HCAs)
- acrylamides
Why is Vitamin C sometimes added to processed meat?
they can act as anti-oxidants and inhibit formation of nitrosamines from nitrate/nitrite preserving agents
What are the 2 conditions needed for formation of nitrosamines?
- strongly acidic conditions such as that of the human stomach
- high temperatures processing, also enhances the formation of nitrosamines
What are some features of polycyclic aromatic hydrocarbons?
- organic compounds containing only carbon and hydrogen (that are composed of multiple aromatic rings)
- toxicity of PAHs is structure-dependent
- carcinogenic, mutagenic, tetratogenic
- can be found at moderate levels in cooked foods, such as in meat cooked at high temps or over open flames
What are some features of heterocyclic amines?
- found in cooked & especially burnt meat
- known from the cooking of muscle meats such as beef, pork, fowl, fish
- HCAs form when amino acids & creatine (a chemical found in muscles) react at high temps –> pose cancer risk
People who eat medium-well or well-done beef were more than ____ likely to suffer stomach cancer as those who ate rare or medium-rate beef
3 times more likely
What is creatine?
a chemical found in muscles
reacts with amino acids and glucose to produce heterocyclic amines (HCAs)
Which foods is acrylamide usually found in?
coffee
potato chips
bread and toast
cakes and biscuits
How is acrylamide produced in food?
acrylamide is a chemical produced naturally as a result of cooking starch-rich food at high temps, such as when baking or frying
- also likely to be produced by grilling and roasting food
How was acrylamide discovered?
- accidentally discovered in foods in 2002 by scientists in Sweden when they found the chemical in starchy foods which had been heated higher than 120 degrees C
- temp-dependent
- not found in foods that had been boiled or that were not heated
it is still not clear whether dietary acrylamide consumption affects people’s risk of developing cancer
What is a common mistake made with relative risk ratios (RR)?
they assume any value about (>1.00) indicates that the factor causes cancer in EVERYONE at ANY level of consumption
In epidemiological cohort study, to determine if a variable has an effect on a health outcome, the population studies are divided into groups (usually 4 or 5 levels) of exposure to the variable. Provide an example.
- testing rates of colon caner and processed meat intake
- we could have those that do not eat processed meats, low consumers, moderate consumers, and high consumers
- then compare their frequency (in this case as a %) of colon cancer over the same time period
- this data is then plotted and a RR ratio determined
So how might you calculate a risk ratio?
e.g. if risk of highest meat consumers getting cancer is 4% and risk of lowest meat consumers is 2%,
RR = 4/2 = 2.0
moderate RR (only a small increased chance of colon cancer)
There is usually a ______ time between smoking and lung cancer
20-year
What did the EPIC study findings suggest in regards to fruit and veg?
people should eat at least 5 portions of fruits and vegetables a day to achieve optimum health & have a lowered risk of colon cancer
EPIC study results
- fruit, veg, fibre reduce cancer of colon & rectum
- preserved meats like salami bacon, cured ham, hot dogs increase risk of colorectal cancer
- decreased chance of developing colon cancer in people eating lots of fish
People who smoke a packet of cigarettes a day and drink more than a bottle of wine are ________ more likely to suffer from throat cancers
50 times
Where are chloropropanols found?
found in fermented soy products
high levels of potentially cancer causing chemicals 3-MCDP & 1,3-DCP belong to this group of chemicals
there is a correlation b/w high intake of fermented soy product & stomach cancers
List some (additional) key findings of the EPIC study
- high dietary fibre protects against bowel cancer
- obesity increases a number of cancer risks
- high levels of sex hormones increases risk of breast cancer
- increased fat intake increases the risk of breast cancer
- regular high level consumption of processed meat moderately increases the risk of cardiovascular diseases and death from cancer
- increases in eating fruit & veg reduces the risk from all causes of an early death
List 5 simple dietary habits to reduce the risk of cancer
1) dietary habits in childhood
2) more physical activity + reduce weight gain
3) Eat 5 or more servings of a variety of veg and fruits each day
4) Whole grains > processed (refined) grains
5) Limit consumption of processed & red meats
Some chemicals in the Allium family . . .
e.g. onions, garlic, shallots, chives may be also protective
