Diet, Sugar, Cancer - What You Need To Know For Prevention & Active Treatment

How Everyday Eating Shapes Cancer Risk

Cancer does not arise overnight or from a single “bad” choice; it builds slowly from a mix of inherited traits, cellular changes, environmental exposures, and lifestyle patterns. Diet has been shown to have a major effect on cancer risk by affecting hormones, immune responses, inflammation, and metabolism.

Instead of viewing food through the lens of strict rules or “cancer diets,” it can be more helpful to think about how meals shape the body’s internal environment. When blood sugar is stable, inflammation is low, the gut microbiome is well-fed, and nutrient needs are met, the body is less inviting to abnormal cell growth. When these systems are overwhelmed by excess sugar, ultra-processed foods, and chronic low grade inflammation, the terrain becomes more favourable to disease.

The goal is not a perfect, rigid regimen but a way of eating that supports healing and energy-whether someone is trying to lower risk or navigating chemotherapy, radiation, or immunotherapy.

Where Sugar Hides in the Modern Diet

Most people associate sugar with desserts, but fast-digesting carbohydrates appear in many everyday products that don’t look like sweets. These “quick sugars” rapidly raise blood glucose and prompt repeated insulin surges.

Common contributors include:

• Sweetened drinks: sodas, commercial iced coffees, flavoured waters, sports and energy drinks, fruit juices

• Processed and packaged foods with added sugars or syrups

• Bakery items: muffins, pastries, cookies, donuts, and many breakfast bars

• “Healthy” granola or protein bars and meal replacement shakes that contain multiple sweeteners. One of the most well known meal replacement drinks has fructose corn syrup in the top three ingredients- yikes!

• Flavoured yogurts and sweetened plant milks

• Refined starches such as white bread, white pasta, crackers, and many snack foods

• Alcohol

A simple starting point is label reading: scanning for “added sugar,” syrups, fructose corn syrup, and ingredients ending in “‑ose” can help reduce sugar intake without feeling deprived.

Why High Sugar Intake Matters for Cancer

Cancer nutrition conversations often come back to sugar reduction, not because sugar “feeds” cancer in a simplistic way, but because of the metabolic and hormonal changes that follow chronic high intake. Diets rich in added sugars and ultra-processed carbohydrates are associated with higher rates of several cancers, including colorectal, breast, and pancreatic cancers.

Populations adopting a Western-style diet—high in refined carbohydrates, processed fats, and low in fibre-show rising rates of early-onset colon cancer and other malignancies. This highlights how lifestyle can amplify or offset underlying genetic risk.

Immune Health, Inflammation, and Blood Sugar

The immune system is constantly patrolling for viruses, bacteria, and emerging abnormal cells. When blood sugar runs high, white blood cells become less efficient at migrating and engulfing threats. Over time, frequent glucose spikes encourage a state of low-grade, chronic inflammation and immune imbalance.

This combination—dampened surveillance and ongoing inflammatory signalling—creates conditions in which precancerous cells may be less likely to be recognized and cleared. Keeping blood sugar more stable is one way to support the body’s natural monitoring and repair systems.

Insulin, IGF‑1, and Cell Signalling

Carbohydrates stimulate insulin release, and repeated large surges can eventually contribute to insulin resistance and type 2 diabetes—both linked to elevated cancer risk. But insulin is only part of the story. Insulin also interacts with insulin-like growth factor‑1 (IGF‑1), a hormone that promotes growth and inhibits programmed cell death (apoptosis). IGF‑1 is crucial for muscle maintenance, bone integrity, and brain health, yet persistently high levels may encourage cancer cells to grow and survive when they should be eliminated. Research has connected higher IGF‑1 activity with increased risk of cancers such as prostate, ovarian, colorectal, and lung.

Supportive strategies include:

• Emphasizing minimally processed, high-fibre, low-glycemic foods

• Maintaining healthy vitamin D status

• Using green tea or matcha as a regular beverage

• Avoiding non-medical use of growth hormone or hormone-like supplements

Low-Glycemic Eating in Practice

The glycemic index (GI) ranks carbohydrate foods by how quickly they raise blood sugar, but in real life, people eat meals, not isolated ingredients. A helpful concept is glycemic load, which reflects both the type and amount of carbohydrate eaten.

Low-glycemic patterns focus on:

• Choosing intact whole grains and legumes rather than refined flours

• Filling most of the plate with non-starchy vegetables

• Including protein, healthy fats, and fibre with carbohydrates to slow absorption

• Being mindful of portion sizes, even for foods considered “healthy”

For instance, pairing a baked potato with lentils and leafy greens or having corn tortillas with black beans results in a more gradual blood sugar rise than eating the starch alone. The emphasis is on balance and combinations, not strict avoidance.

Fasting, Caloric Load, and Cancer Care

Modern life makes it easy to overeat and under-move, leading to weight gain, insulin resistance, and metabolic stress—factors closely tied to cancer risk and recurrence. This has sparked interest in intermittent fasting and fasting-mimicking diets as potential tools.

Emerging research suggests that, in specific situations, structured periods of reduced intake may:

• Improve insulin sensitivity and blood sugar control

• Shift metabolic signalling away from constant growth mode

• Enhance some cancer treatments and reduce certain side effects

Early clinical studies in glioblastoma and triple-negative breast cancer, for example, have explored fasting-mimicking approaches alongside chemotherapy, with some encouraging signals in terms of tolerance and response.

Fasting, however, is not benign or appropriate for everyone. Individuals who are underweight, losing weight unintentionally, experiencing muscle wasting, or dealing with complex medical issues may be harmed by caloric restriction. In many people undergoing treatment, maintaining strength, muscle mass, and adequate nutrient intake is the top priority. Any fasting strategy should be individualized and medically supervised.

Beyond Food: Metabolic Health and Medications

Nutrition is fundamental, but not the only lever. Movement, muscle-building activity, restorative sleep, and stress reduction all help improve insulin sensitivity and lower chronic inflammation.

In some cases, medications used for type 2 diabetes have also shown associations with lower cancer risk or improved outcomes, likely through their effects on metabolic pathways. These aren’t replacements for lifestyle changes, but they illustrate how central metabolic health is to cancer biology and survivorship.

Cancer Fuel, its Not Just Carbs

While cancer cells often preferentially use glucose for energy (the “Warburg effect”), carbohydrates are not the only stimulus for insulin release, nor are they the only fuel source available to cancer cells.

Insulin is released in response to all macronutrients, not just carbohydrates.

• Carbohydrates stimulate insulin rapidly and strongly due to rising blood glucose.

• Proteins also stimulate insulin through amino acids such as leucine and arginine, although this is typically accompanied by glucagon release, which tempers blood sugar changes.

• Fats produce a smaller and slower insulin response, but they still contribute to overall insulin signaling, particularly in the context of mixed meals and chronic intake. Importantly, eliminating carbohydrates does not metabolically “starve” cancer cells. Cancer cells are metabolically flexible and can adapt by:

• Using amino acids (especially glutamine) to fuel growth and energy production

• Oxidizing fatty acids via beta-oxidation

• Utilizing ketone bodies in certain tumor types

• Engaging alternative pathways such as gluconeogenesis, where the body converts protein and fat derived substrates into glucose—maintaining circulating glucose even on a strict ketogenic diet

This means that even in a very low-carbohydrate or ketogenic state, glucose and insulin signaling do not disappear, and cancer cells may simply shift fuel sources rather than being deprived of energy. For this reason, metabolic strategies in cancer care are best viewed as supportive and context-dependent, rather than as stand-alone therapies. The focus is often on improving metabolic health, insulin sensitivity, inflammation, and overall resilience, rather than attempting to “starve” cancer through dietary restriction alone.

Long-Term Eating Patterns That Support Resilience

Instead of chasing single superfoods, it is more effective to look at overall patterns. Two dietary styles consistently linked with lower cancer risk and better survivorship are:

• Mediterranean-style eating, centred on vegetables, fruits, legumes, whole grains, olive oil, nuts, seeds, and regular fish intake

• Pesco-vegetarian eating, which emphasizes plant foods while including fish and seafood as primary animal proteins

These approaches naturally:

• Reduce reliance on added sugars and refined grains

• Boost fibre intake, feeding a diverse gut microbiome

• Provide anti-inflammatory fats and a wide array of plant compounds (phytonutrients and antioxidants)

Practical Ways to Add More Protective Foods

• Aim for a broad spectrum of plant foods across the week: different colours, textures, herbs, and spices

• Choose fish, skinless poultry, eggs, legumes, nuts, and seeds as go-to protein sources

• Work toward roughly 30 grams of fibre daily from vegetables, fruits, whole grains, beans, and lentils

• Include fermented foods, such as yogurt, kefir, sauerkraut, kimchi, or miso, several times a week to support gut health

Gentle Strategies for Cutting Back

• Keep red meat to modest portions a few times per week and avoid processed meats when possible

• Swap sugary drinks and packaged sweets for water, herbal teas, and fruit with nuts or yogurt

• Replace white bread, white rice, and pastries with whole-grain options that are higher in fibre

• Treat alcohol as an occasional indulgence, recognizing that even moderate intake can influence cancer risk

A Flexible, Compassionate Approach to Food

After a cancer diagnosis—or when trying hard to prevent one—it is easy to become hyper-focused on “perfect” eating. This can create fear around food, social withdrawal, and a sense of failure when choices are not ideal.

Food, however, is also about connection, culture, comfort, and celebration. Making room for joy—a slice of cake at a family event, a special meal out, a holiday tradition—can support emotional health, which is part of the healing process. The aim is to lean toward nourishing, blood sugar–friendly choices most of the time, while allowing room for flexibility without shame.

When the plan honours both metabolic health and quality of life, nutrition becomes not a burden but a powerful, sustainable ally in cancer prevention, treatment support, and long-term well-being. If you are interested in learning more contact to book an initial with Dr. Kyla Stewart.

Medical Disclaimer: This content is for educational and informational purposes only and is not intended as medical advice, diagnosis, or treatment. It should not be used as a substitute for professional medical guidance. Always consult a qualified healthcare provider for any medical concerns