Food and Cancer- L8 Flashcards
What is the median body mass index for adults ?
between 21 and 23
What is the link between being overweight and cancer?
convincing evidence that being overweight/obese increases the risk of many cancers including bowel and breast cancer
What are the recommendations about body fatness?
ensure that throughout childhood and adolescent that your BMI is towards the lower end of normal
maintain BMI within the average range throughout adulthood
try to avoid weight gain and increased waist circumference during adulthood
Which cancers have convincing links with body fatness?
- oesophageal
- pancreas
- colorectal
- breast
- endometrium
- kidney
What cancers have convincing links with abdominal fatness?
colorectal
What are the BMI scores?
40= grade 3 overweight- morbidly obese
What are the limitations of BMI ?
- doesn’t directly measure body fat
- limitations based on differences in sex, age, ethnicity and atheletic experience
- women tend to have higher fat content than men
- BMI overestimates body fat in persons who are very muscular
- BMI can underestimate body fat in persons who have lost muscle mass e.g. elderly
What are the different methods of assessing the percentage of fat and lean mass ?
- water or air displacement
- dual energy x-ray absorptiometry
- bioelectrical impedance
- skinfold thickness measures
What was the link in men between body fatness and oesophageal carcinoma ?
from 5 different studies large increase in risk associated with a higher BMI
- each increase in 5 BMI units increases the risk of cancer by 52%
What is the link between lung cancer and oesophageal squamous cancer and BMI?
strangely it demonstrated that increased BMI reduced risk of these cancers
Which female cancer is most strongly linked to BMI?
cancer of the endometrium - there is very little variation - barely any confidence intervals
What happens with BMI and breast cancer risk ?
premenopause- increased BMI reduces risk of breast cancer
postmenopause- increasing BMI increases risk of breast cancer
researches think there are 2 different aetiologies driving breast cancer before and after menopause
What type of breast cancer is most common ?
postmenopausal breast cancer is most common - strong links with estrogen status which is associated with fatness
What is a major worrying aspect about the link between BMI and cancer ?
Although the increase in risk per 5Kg/m2 increments are modest, the numbers of incident cases attributable to excess BMI might be substantial as the prevalence of overweight and obesity is icnreasing in many countries
What has happened between 1993 and 2009 in relation to fatness?
in both men and women there has been an increase in obesity
What is abdominal fatness and what increased risks does it cause ?
it is associated with health risks such as CVD
the waist circumference can be measured and used as an estimate for abdominal or visceral fat
could be a better indicator of health risks than BMI alone
How is waist circumference measured ?
measuring waist circumference is midway between the uppermost border of the iliac crest and the lower border of the costal margin
What has happened to waist cicrumference of men and women between 1993-2009?
it has increased in both, however more substantially in women
What did a study looking at waist circumference and mortality demonstrate ?
Low WC but obese= doesn’t increase risk of mortality
High WC but not obese= increased risk of mortality
High WC and obese= Increased risk of mortality but only slight more than high WC and not obese
therefore having a high WC and not being obese is very detrimental
What different results were shown in colon cancer when different measurements of fat were used?
ABDOMINAL OBESITY
- increased risk factor for colon cancer in both men and women
BODY WEIGHT and BMI
- increased risk factor for colon cancer seen in men but not in women
Why is it not necessarily a good idea to do self-reported data for looking into association between weight and cancer risk ?
people will lie about their weight and therefore when self-reported dat and measured data results are compared there are differences
What does BMI reflect ?
reflects both lean and fat mass
What has recently bean indicated as an equivalent or stronger predictor of cancer risk in adults in comparison to BMI?
weight gain - it largely reflects increase in body fat independent of BMI
What is the link between height and cancer?
the taller a woman is the greater risk they have in developing post menopausal cancer - could be linked to growth rates during childhood
Why is weight very important in postmenopausal women ?
data suggests that advising women to lose/maintain weight after menopause may reduce breast cancer risk
- women who lost weight after menopause had a reduced risk of breast cancer - 40% reduction
- gaining weight after menopause is very detrimental, increases breast cancer risk
What happens when weight is lost after menopause?
weight loss lowers circulating oestrogens
- these hormones are directly related to the risk of breast cancer so weight loss is suspected to decrease risk - not consistently shown
What potentially can intentional weight loss in obese cause ?
might protect against malignancy but the evidence is limited
- swedish obese subjects
- 2010 obese patients - had bariatric surgery
- 2037 match obese controls had dietary controls
those that had surgery had lost about 19+ Kg whereas other group slightly gained weight
the surgery was linked to reduced risk of in cancer for women but not for men
What are the 3 candidate systems in which obesity increases cancer risk ?
- insulin and insulin-like growth factor-1 axis
- sex steroids
- inflammation
What is the insulin cancer hypothesis ?
excess body weight leads to increased insulin production and leads to hyperinsulinaemia and insulin resistance
- the increased IGF proteins leads to increased IGF1 which increases tumour development
What is the link between sex steroids and cancer risk ?
- adiposity influences synthesis and bioavailability of endogenous sex steroid
- relationship between obesity and breast cancer risk post menopausally may be largely explained by increased levels of oestrogens particularly bioavailable estradiol from adipose tissue
What happens to the levels of estradiol throughout a women life?
levels are maintained high throughout the reproductive lifehood of a female but after menopause levels drop to very low due to ovarian function declining therefore any increased levels will be due to adipose tissue
How is increased endogenous hormones linked to breast cancer ?
higher circulating levels of oestrogen is associated with increased risk of breast cancer
What is suggested as the causative factor of breast cancer?
increased levels of estradiol- these levels will be increased in women with a higher BMI due to greater fatness
What is obesity characterised as ?
it is a low grade chronic inflammatory state
What inflammatory factor is increased in obese people?
increased circulating levels of tumour necrosis factor alpha, interleukin-6 and c-reactive proteins in comparison to lean people
- such chronic inflammation may contribute to the development of cancer- favours tumour development/progression
What are examples of cancer specific factors which increase risk ?
oesophagus (adenocarcinomas) and gastric cardia
- these cancers are difficult to differentiate between
- obesity causes reflux, barretts oesophagus and inflammation - more closely linked to abdominal obesity
- the contents of the stomach can be regurgitated up the oesophagus damaging the lining of the oesophagus - if this happens often then pre tumour state can occur when
Why is important to limit consumption of energy dense foods ?
because they increase obesity which increases risk of cancer
what are the public health goals associated with energy dense foods?
average energy density of diets to be lowered towards 125kcal per 100g
population average recommended consumption of sugary drinks to be halved every 10 years
What factor shows good evidence for protecting against cancer?
physical activity
- e.g. breast cancer and bowel cancer
What are the personal recommendations for levels of physical activity?
be moderately active every day(brisk walking) for at least 30 minutes
as fitness improves aim for 60 mins moderate exercise every day or 30 mins intense
dont be sedentary for most of the time
How does physical activity reduce the risk of cancers ?
by reducing fatness
endogenous steroid hormone metabolism
potentially strengthen immune system
reduce circulating levels of oestrogen and androgens
Although there is an association between many different factors and cancer what is the most substantial ?
the link between smoking and lung cancer is far more substantial than any other factor
