Fruit and Vegetable consumption linked with cancer risk - L16 Flashcards
What is the consistent evidence for fruit and veg consumption and mortality ?
diets rich in fruit and veg and other plant foods are associated with moderately lower overall mortality rates and lower death rates from cardiovascular disease and some types of cancer
What consumption of fruit and veg is advised per day and why ?
5 portions of fruit and veg per day - increasing consumption by 80g per day ( 1 serving) would reduce risk of cancer by 20% the WCRF stated in 1997
Why is the consumption of fruit and veg reduction in risk not quite the same anymore?
the 20% reduction in risk associated with consumption of 5 portions of fruit per day may not strictly be true nowadays due to changes in obesity
Why do plant foods protect against cancer and heart disease?
contain nutrients - important for normal cell functioning
contain fibre- good for intestine and binds carcinogens
generally low in fat
not meat
contain protective factors
What does it mean by plant protective factors ?
these are beneficial compounds that are not nutrients
Why nowadays do we not have as good an understanding of why plants are good for us ?
thought that we would know more nowadays but we dont and it is thought that this is due to obesity problems
What % of cancers are caused by tobacco ?
30%
What % of all cancers are related to diet, exercise and weight?
30-40%
- 20%= related to low intake of fruit and veg
- 4-14% related to obesity in men
- 14-19% related to obesity in women
What is a protective factor ?
it is a food plant secondary metabolite which is NOT a nutrient but it has biological activity that may protect against disease in humans
activity may be dependent upon- dose, duration of dose, timing of dose, age, gender and health of the individual
What happens if you remove a nutrient from your diet ?
you will get unwell but once you replace it you get better
What are some examples of protective factors ?
FLAVENOIDS
- flavon-3-ol= kaempferol in tea, onions, apples, broccoli, french beans
- flaven-3-ol= tannins in tea, apples, wine, fruit
- isoflavones- daidzein in soybean, chickpeas
-glucosinolates - brassicas
- alkenyl cysteine sulfoxides
ellagitanins - pomegranetes
What are the 2 types of preventative mechanisms?
BLOCKING AGENTS= prevent the genotoxic reagent from reaching the critical target sites e.g. inhibit metabolic activation reactions, activation/induction of detoxifying reactions and trapping genetoxic species
SUPPRESSING AGENTS= prevent the evolution of the neoplastic process in cells previously exposed to doses of carcinogenic agents that would otherwise cause cancer
Where can protective factors act?
There are plenty of different places where protective factors can act
- reduce activation of phase 1 enzymes to reduce production of ultimate carcinogens
- enhance phase 2 enzymes to increase metabolic detoxification
- act to enhance DNA repair
- enhance replication and cell cycle control, help induce apoptosis when necessary
What experiments are needed to prove that protective factors are beneficial ?
- epidemiology/in vitro/animal studies
- knowledge of food composition- what are the levels of compounds within food
- understanding of the absorption and metabolism of the compound
- human studies
- hypothesis of mechanism
- dose-response curves
What are the alternatives to the direct antioxidant action ?
The low molecular weight compounds in fruit and veg may…
- induce protective enzymes - phase 2 enzymes
- inhibit phase 1 enzymes
- induce apoptosis
altogether leading to protection of cellular DNA, proteins and lipids against toxins and free radical oxygen species
What are cruciferous vegetables ?
family of plants that include various familiar members of the species brassica oleracea
e.g. broccoli, cabbage, cauliflower, kale, brussel sprouts, oriental cabbage, arugula, watercress and radish etc
brassicas are part of cruciferae veg and there are any different types
What are glucosinolates?
secondary metabolites produced in plants, containing a sugar and phosphate group
many different types: sinigrin, gluconapin, progoitrin, glucobrassicin- they dont have the same activites and their levels vary in foods
How many glucosinolates have been identified?
at least 120, majority from crucifers, but other plant families also contain them
What are the functions of glucosinolates in plants ?
they are the precursors of isothiocyantes (mustard oils)
play a protective and evolutionarily important role in plants
- ALLELOPATHY= suppression of growth of neighbouring plants, more nutrients, space and light
- SPECIFIC POSITIVE AND NEGATIVE FEEDING CUES= for some insects
- BROAD ANTIBIOTIC PROPERTIES= including nematodes, anti-microbial, anti-fungal, anti-protozoal and insecticidal activities
Why do the levels of glucosinolates vary ?
levels vary according to genetics and growing condition
composition of individual glucosinolates varies from variety to variety
processing/cooking will affect their levels
consumption of different types will vary in different countries
What happens when food is prepared or chewed ?
the enzyme tyrosinase is released an it hydrolyses glucosinolates to isothiocyanates
What happens when food is cooked?
the tyrosinase is inactivated and therefore not present
we have the ability to convert glusinolates efficiently to isothiocyanates through the action of microflora in the GIT
What does the enzyme myrosinase do to glucosinolates?
it removes the sugar and phosphate group to produce isothiocyanates
What is sulforaphane ?
it is an isothiocyanate isolated from SAGA broccoli as the principal and very potent phase 2 enzyme inducer
- stimulates the biosynthesis of enzymes that will help remove toxic compounds more quickly
What have sulforaphanes been able to do in animal models ?
inhibit tumour development when administered with or after carcinogens or both and is effective against a variety of carcinogens
What has been shown between glucosinolates and bladder cancer ?
there was no significant association found between total fruit and veg consumption, fruits only or veg only for reduced risk of bladder cancer
BUT
the multivariate risk reduction ratio for cruciferous veg was highly significant- associated with a statistically significant 51% decrease in bladder cancer
What has been shown between glucosinolates and prostate cancer?
high fruit consumption didn’t reduce risk in >65 year old men but high veg consumption in particular cruciferous veg consumption did demonstrate protective effects
3 or more servings of cruciferous veg a week, compared to 1 serving reduces the risk of prostate cancer by 41%
What is the link between cruciferous veg consumption and breast cancer?
increased consumption reduces risk with the highest quartile having only 50% of the risk of the lowest intake group
What was shown about cruciferous veg consumption and non-hodgkin lymphoma?
nurses’ health study showed that a high intake (5 or more servings a week) vs less than 2 was associated with a 33% lower risk of non-hodgkins lymphoma
