This chapter addresses three distinct contexts: cancer prevention, supporting health during treatment, and optimizing outcomes in survivorship.
19.1 The Biology of Cancer: Where Lifestyle Intervenes
Cancer arises from the accumulation of genetic mutations that allow cells to proliferate uncontrollably, evade immune surveillance, and invade adjacent tissue. Key lifestyle-modifiable biological mechanisms:
Insulin and IGF-1 (Insulin-like Growth Factor 1) Chronically elevated insulin (from dietary excess, insulin resistance, and obesity) stimulates IGF-1 production by the liver. IGF-1 is a potent mitogenic growth factor — it promotes cell proliferation and inhibits apoptosis (programmed cell death). This creates a permissive environment for cancer cell growth. Cancers particularly sensitive to insulin/IGF-1 signaling: colorectal, breast (especially postmenopausal), endometrial, and pancreatic.
Chronic Inflammation Sustained low-grade inflammation (driven by visceral obesity, poor diet quality, sedentary behavior, and gut dysbiosis) produces pro-inflammatory cytokines (IL-6, TNF-α) and reactive oxygen species (ROS) that cause DNA damage and promote tumor-supporting microenvironments.
Obesity and Adipose Tissue Adipose tissue is not metabolically inert — it is an active endocrine organ. Visceral fat produces estrogens (via aromatase enzyme), pro-inflammatory adipokines, and contributes to hyperinsulinemia. This explains the elevated risk of estrogen-sensitive cancers (breast, endometrial, ovarian) in postmenopausal women with excess body fat.
Immune Surveillance Capacity A well-functioning immune system continuously identifies and destroys nascent cancer cells (immunosurveillance). Chronic stress, poor sleep, nutrient deficiencies, and sedentary behavior all impair NK (natural killer) cell activity, T-cell function, and inflammatory resolution — reducing the immune system's cancer-clearing capacity.
19.2 Dietary Protocol for Cancer Prevention
The Anti-Cancer Dietary Framework
No single food causes or cures cancer. The pattern of dietary intake over years and decades is the meaningful variable. The most evidence-supported cancer-preventive dietary pattern shares most characteristics with the Mediterranean diet:
Core principles:
| Principle | Practical application | Cancer risk reduction |
|---|---|---|
| Abundant plant foods | ≥5–7 servings vegetables/day | Colorectal, stomach, esophageal, lung |
| Cruciferous vegetables daily | Broccoli, Brussels sprouts, cauliflower, kale, cabbage | Breast, prostate, colorectal (via sulforaphane, indole-3-carbinol) |
| Legumes regularly | Lentils, beans, chickpeas (3–4×/week) | Colorectal; high fiber, resistant starch |
| Limit red meat | ≤ 350–500g cooked red meat/week | Colorectal cancer risk increases 17% per 100g/day (WCRF) |
| Eliminate processed meat | No regular consumption of bacon, sausage, salami, hot dogs | IARC Group 1 carcinogen; 18% increased colorectal cancer risk per 50g/day |
| Minimize alcohol | Ideally none; maximum 1 drink/day | Alcohol is IARC Group 1 carcinogen for 7 cancer sites |
| Limit added sugar and refined carbs | Reduce hyperinsulinemia and IGF-1 | Colorectal, breast, endometrial |
| Maintain healthy weight | BMI 18.5–24.9; waist < 90cm men / < 80cm women | Strongest modifiable cancer risk factor after smoking |
Key Phytonutrients with Anti-Cancer Evidence
| Compound | Food source | Mechanism |
|---|---|---|
| Sulforaphane | Broccoli sprouts, cruciferous vegetables | Induces phase II detoxification enzymes; inhibits histone deacetylase (epigenetic cancer suppression) |
| Lycopene | Cooked tomatoes, watermelon | Antioxidant; reduces prostate cancer risk in epidemiological studies |
| Curcumin | Turmeric (with black pepper for bioavailability) | Inhibits NF-κB (pro-inflammatory signaling); pro-apoptotic in cancer cells in vitro |
| EGCG | Green tea | Inhibits cancer cell proliferation; reduces angiogenesis |
| Resveratrol | Red grapes, berries, peanuts | Activates sirtuins; anti-inflammatory and anti-proliferative |
| Allicin / Diallyl disulfide | Garlic, onions | Inhibits carcinogen activation; promotes apoptosis |
| Omega-3 (EPA/DHA) | Fatty fish, algae oil | Anti-inflammatory; inhibits pro-tumorigenic eicosanoids |
| Fiber | Legumes, whole grains, vegetables | Dilutes carcinogens in colon; reduces transit time; gut microbiome production of butyrate (anti-cancer SCFAs) |
Sugar, Insulin, and Cancer: The IGF-1 Connection
Elevated circulating insulin and IGF-1 do not cause cancer directly — but they provide a permissive metabolic environment in which existing cancer cells grow more aggressively and resist apoptosis.
Strategies to reduce insulin/IGF-1 tone:
- Reduce dietary refined carbohydrates and added sugars
- Maintain healthy body weight (obesity is the dominant driver of chronic hyperinsulinemia)
- Increase physical activity (exercise lowers both insulin and IGF-1)
- Consider time-restricted eating (reduces total insulin secretion)
- Higher protein diets (>1.8g/kg) may modestly increase IGF-1 — context-dependent; muscle-building benefits likely outweigh this in active individuals
19.3 Exercise for Cancer Prevention
Physical inactivity is an independent cancer risk factor. The evidence is now sufficiently robust that the WCRF, ACS, and WHO all include physical activity recommendations in their cancer prevention guidelines.
Cancer risk reduction by exercise (meta-analytic estimates):
| Cancer site | Risk reduction with regular exercise |
|---|---|
| Colorectal | 19–24% |
| Breast (postmenopausal) | 20–25% |
| Endometrial | 20–30% |
| Gastric | 19% |
| Esophageal | 21% |
| Kidney | 12% |
| Bladder | 15% |
| Lung | 20–30% (independent of smoking history) |
Mechanisms of exercise-mediated cancer protection:
- Reduced adiposity: Lowers estrogen, insulin, IGF-1, and pro-inflammatory adipokines
- Improved insulin sensitivity: Reduces the hyperinsulinemia-IGF-1 growth signaling axis
- Enhanced immune surveillance: Exercise acutely mobilizes NK cells, cytotoxic T-lymphocytes, and macrophages — cells that identify and destroy aberrant cells
- Reduced inflammatory mediators: Chronic exercise lowers IL-6 (paradoxically, acute exercise-induced IL-6 acts as an anti-cancer myokine)
- Reduced intestinal transit time (aerobic exercise): Decreases duration of carcinogen contact with colon wall
Prevention exercise protocol:
- Aerobic: 150–300 min/week moderate-intensity or 75–150 min/week vigorous-intensity
- Resistance training: 2–3×/week (additional independent cancer risk reduction)
- Minimize prolonged sitting: Break sedentary time every 60–90 minutes; sedentary time is a cancer risk factor independent of total exercise volume
19.4 Diet and Exercise During Cancer Treatment
This section addresses patients actively receiving chemotherapy, radiation, immunotherapy, or surgical treatment. The goals shift from prevention to: maintaining lean mass, supporting immune function, managing treatment side effects, and preserving quality of life.
All dietary and exercise modifications during active treatment must be approved and coordinated with the oncology team.
Nutritional Priorities During Treatment
1. Protein — Non-Negotiable
Cancer and its treatments (particularly chemotherapy and radiation) are profoundly catabolic. Lean mass loss during treatment is associated with worse outcomes, greater treatment toxicity, and reduced survival.
Target: 1.5–2.0g protein/kg of ideal body weight per day — significantly higher than general population recommendations.
Practical challenge: Chemotherapy commonly causes nausea, mucositis (mouth sores), taste alterations, and appetite suppression. Strategies:
- Small, frequent protein-rich meals (every 2–3 hours)
- Cold or room-temperature foods (often better tolerated than hot meals)
- Protein shakes or smoothies when solid food is poorly tolerated
- Bland, easily digestible proteins (eggs, fish, yogurt, tofu) during nausea
2. Caloric Adequacy
Unintentional weight loss during cancer treatment worsens prognosis. Priority shifts to preventing malnutrition — some previously "unhealthy" calorie-dense foods become appropriate when the alternative is significant weight loss.
3. Antioxidant Supplementation: Caution Required
High-dose antioxidant supplements (vitamins C, E, beta-carotene) during chemotherapy and radiation are generally contraindicated — chemotherapy works partly through oxidative damage to cancer cells, and antioxidants may reduce treatment efficacy. Obtain antioxidants from whole foods rather than supplements during active treatment, unless specifically approved by the oncologist.
4. Managing Treatment-Specific Side Effects
| Side effect | Dietary strategy |
|---|---|
| Nausea | Ginger tea, small frequent meals, cold foods, avoid strong odors |
| Mucositis | Soft foods, cold/cool foods, avoid acidic or spicy foods; blend meals |
| Diarrhea | BRAT diet (banana, rice, applesauce, toast); low-fiber temporarily; probiotics with physician approval |
| Constipation | Increase fluid and gentle fiber (oats, cooked vegetables); prunes |
| Taste changes | Experiment with cold foods, marinades, herbs; use plastic utensils if metal taste is problematic |
| Appetite suppression | High-calorie, high-protein small portions; liquid nutrition if needed |
Exercise During Cancer Treatment
The long-standing advice to "rest" during chemotherapy has been largely overturned by robust evidence. Exercise during treatment is now recommended by the American College of Sports Medicine (ACSM) as safe and beneficial for most cancer patients.
Benefits of exercise during treatment (meta-analyses):
- Reduced cancer-related fatigue (the most common treatment complaint) — counterintuitively, exercise reduces fatigue more effectively than rest
- Improved chemotherapy completion rates
- Reduced depression and anxiety
- Preservation of lean mass and functional capacity
- Enhanced immune function and NK cell activity
Exercise guidelines during treatment:
| Phase | Recommendation |
|---|---|
| Low-energy/high-fatigue days | 10–20 minute gentle walks; light stretching; yoga |
| Moderate-energy days | 20–30 min moderate walking; light resistance bands |
| Good-energy days | 30–45 min moderate aerobic; supervised resistance training |
| Neutropenic periods (low white blood cell counts) | Avoid public gyms; exercise at home or outdoors away from crowds |
Start low, progress slowly. The goal during treatment is maintenance and immune support, not performance enhancement.
19.5 Cancer Survivorship: Optimizing Long-Term Outcomes
Cancer survivorship — life after active treatment — is now the reality for over 50% of cancer patients in high-income countries. Diet and exercise in survivorship serve to: reduce recurrence risk, manage long-term treatment side effects, and optimize quality of life.
Return to Preventive Dietary Principles
Following treatment, return to the anti-cancer dietary framework (Section 19.2) with particular attention to:
- Gradual weight restoration if treatment caused significant weight loss (prioritize lean mass)
- Weight management if treatment caused weight gain (common with corticosteroid use or hormonal therapies for breast and prostate cancer)
- Gut microbiome restoration after antibiotic use and chemotherapy (fermented foods, prebiotic fiber)
- Bone health for survivors of hormone-deprivation therapies (breast cancer — aromatase inhibitors; prostate cancer — androgen deprivation therapy) → prioritize calcium, vitamin D, weight-bearing exercise
Exercise in Survivorship: Building Back
ACSM guidelines for cancer survivors:
- Aerobic: 150 min/week moderate or 75 min/week vigorous
- Resistance training: 2–3×/week — particularly critical for those who lost lean mass during treatment or are on hormone-suppression therapy (which accelerates muscle and bone loss)
- Progress gradually from low to moderate intensity over 8–12 weeks following treatment completion
Recurrence risk reduction through exercise: Evidence is strongest for breast, colorectal, and prostate cancer — the three most common survivable malignancies:
| Cancer | Exercise-associated recurrence reduction |
|---|---|
| Breast cancer | ~40% reduction in recurrence with regular post-treatment exercise (WHEL Study, HEAL Study) |
| Colorectal cancer | ~30–50% reduction in disease-specific mortality |
| Prostate cancer | Slowed progression; reduced PSA rise velocity |
The CHALLENGE Trial (Courneya et al.) demonstrated that a 3-year structured exercise program post-colorectal cancer surgery improved disease-free survival by 28% — one of the most compelling survival benefits ever documented for a lifestyle intervention in oncology.
19.6 Cancer-Specific Summary Reference
| Cancer Type | Highest-evidence dietary factors | Exercise priority |
|---|---|---|
| Colorectal | High fiber, limit red/processed meat, limit alcohol | Aerobic exercise (reduces transit time); resistance training |
| Breast (postmenopausal) | Maintain healthy weight, limit alcohol, low saturated fat, omega-3 | Aerobic + resistance (reduces estrogen; prevents weight gain from hormonal therapy) |
| Prostate | Tomato/lycopene, green tea, limit dairy excess, low saturated fat | Aerobic + resistance (especially during androgen deprivation therapy) |
| Endometrial | Weight management (most powerful single factor), low glycemic diet | All modalities; weight management emphasis |
| Pancreatic | Avoid obesity, limit processed meat, avoid heavy alcohol | Moderate aerobic; weight management |
| Lung | Cruciferous vegetables, carotenoid-rich diet; avoid beta-carotene supplements (if smoker) | Aerobic exercise — independent risk reduction |