2. Role of nutrition in prevention of cancers

• 35% of cancer cases are related to nutrition
• 30% of cancer cases are related to smoking
• 10% of cancer cases are related to infecitons
• Nutrition is the most important behavioural risk factor for cancer – more than smoking, infections

β-carotene supplementation and cancer:

• β-carotene can be either an antioxidant or a pro-oxidant, depending on these factors
  • Concentration
  • Presence of other pro-oxidant or antioxidant compounds
  • Oxygen concentration
• It was thought that β-carotene supplementation in smokers could decrease risk of lung cancer, but it actually increased the risk
  • ATBC – huge study in Finland -> daily β-carotene supplementation increased risk for lung cancer in smokers
  • CARET – huge study in USA -> daily β-carotene supplementation increased risk for lung cancer in smokers

Tea and cancer

• Green tea consumption decreased risk of oesophageal cancer
• Study: People who drank hotter tea in Iran -> increased risk for oesophageal cancer

Energy intake and cancer

• Underfeeding (energy restriction) -> decreased risk of cancer
• Overfeeding (obesity) -> increased risk of cancer
• Possible mechanisms of increased cancer risk
  • Increased insulin and IGF-1
    • These hormones stimulate cell proliferation and inhibit apoptosis
  • Increased oestrogen
  • Increased leptin
  • Increased inflammatory cytokines
  • Increased oxidative stress
  • Decreased DNA repair capacity

Fat intake and cancer

• Saturated fat, trans fat and omega-6 fats increase risk for cancer
  • Omega-6 -> increased risk for prostate cancer, breast cancer
• Monounsaturated fat and omega-3 fats decrease risk for cancer
• Possible mechanisms of increased cancer risk
  • Associated with high energy intake (see above)
  • Presence of lipid soluble carcinogens
  • Peroxidation of lipids
  • Membrane composition of cells can be influenced by diet intake
  • Prostaglandin synthesis
    • Fatty acids are precursors to prostaglandins and prostacyclins
    • Certain prostaglandins are pro-metastatic
  • Fats can have direct cytotoxic effect
  • Diacylglycerol is an intracellular second messenger -> activates protein kinase C

Other macronutrients and cancer

• Proteins probably don’t influence carcinogenesis
• Carbohydrates probably don’t directly influence carcinogenesis, but their increased intake means increased energy intake

Meat intake and cancer

• Saturated fat in red meat. Less in poultry
• Increased meat consumption -> increased colorectal carcinoma
  • Increased meat consumption -> increased presence of N-nitroso compounds in stool
• N-nitroso compounds in cured and processed meats
• Heterocyclic amines in meat prepared at high temperature (especially grilling, frying)

Secondary bile acids and cancer

• Bile acids produced by the liver are primary. When these enter the intestines, bacteria will convert them into secondary bile acids
• Secondary bile acids are a risk for colorectal cancer
• Increased consumption of red meat and saturated fat have increased levels of secondary bile acids in the intestine, perhaps these foods change the microbiome of the intestines to bacteria that produce more secondary bile acids

Fibre intake and cancer

• Decreased fibre intake -> increased colorectal carcinoma
• Suggested intake: 30 g/day
• Types of fibre
  • Water soluble (like pectin)
  • Water insoluble (like cellulose, hemicellulose)
• Cancer preventative effects of fibre
  • Takes more time to chew -> increased sense of fullness -> decreased energy intake
  • Fibre binds carcinogenic substances and secondary bile acids
  • Fibre decreases faecal transit time -> Intestines are less exposed to carcinogens
  • Fibre dilute bowel content
  • Fibre modifies the enteric bacterial flora, decreasing the production of secondary bile acids

Other dietary factors and cancer:

• Grilled, smoked, cured foods
• Hot foods and drinks
• Decreased vitamin D intake
• Inadequate fluid intake
• Contaminants
• Food additives, preservatives, artificial sweeteners
  • Nitrites
  • Nitrates

Phytochemicals and cancer

• Phytochemicals are chemical compounds of plant origin
• Mostly found in the peel or outer parts of fruits and vegetables
• Examples
  • β-carotene
  • Lycopene
  • Lutein
  • Glucosinolates
  • Flavonoids
  • Quercetin
• Mechanisms of cancer prevention
  • Antioxidant effect
  • Inhibit phase I biotransformation in liver
  • Induce phase II biotransformation in liver
  • Induction/inhibition of COX, LOX
  • Anti-inflammatory effect
  • Stimulate immune system
  • Induce apoptosis
  • Regulate intracellular signalling
  • Arrest cells in the cell cycle
  • Competitively inhibit oestrogen
  • Inhibit DNA synthesis
  • Inhibit angiogenesis
  • Changes enteric bacterial flora
  • Decrease expression of oncogenes
  • Increase DNA repair
  • Inhibit NF-κB

Alcohol consumption and cancer

• Pro: red wine contains phytochemicals (resveratrol)
• Cons:
  • Irritation
  • Fat soluble carcinogens in alcohol
  • Alcohol itself is carcinogen
  • Alcohol induces biotransformation enzymes
  • Acetaldehyde is carcinogen
• Net effect of alcohol (even red wine) consumption: increased risk for cancer!

Summary (recommendations by American institute for cancer research)

• Be as lean as possible without being underweight
• Be physically active for at least 30 minutes every day
• Avoid sugary drinks
• Limit consumption of energy-dense foods
  • Especially processed foods with much added sugar or fat
• Eat a variety of vegetables, fruits, whole grains, legumes
• Limit consumption of red meats and avoid processed meat
• Alcohol shouldn’t be consumed, or at least limited to 2 units (men) or 1 unit (women) per day
• Limit consumption of salty foods and foods processed with salt
• Don’t use supplements to protect against cancer
• Cancer survivors should follow recommendations for cancer prevention
• Mothers should exclusively breast feed for 6 months, and only after that can they add other liquids and foods