Link Between Insulin and Cancer: What Most People Aren’t Being Told

When someone is diagnosed with cancer, there’s often an immediate and overwhelming focus on treatment: surgery, chemotherapy, radiation, immunotherapy. All of that is valid and necessary. But something equally important often gets completely overlooked—your hormones and your metabolism, specifically insulin.

Insulin is most often talked about in the context of diabetes or weight. But what many people don’t realize is that insulin is also a powerful growth hormone. And when it’s elevated for too long or too often, it can create the kind of internal environment where cancer cells thrive.

Unfortunately, this still isn’t part of the standard conversation in oncology. Hyperinsulinemia—chronically elevated insulin levels—has been clearly linked to a higher risk of developing cancer and a higher risk of dying from it. This isn’t speculation. It’s documented, published, and has been known for decades. Yet it continues to be overlooked in most cancer care settings.

Insulin: More Than a Blood Sugar Hormone

Insulin’s job is to help move sugar (glucose) out of your bloodstream and into your cells to be used for energy. That’s a good thing—until it’s happening too frequently, for too long, and in too large of amounts.

Why does this matter in cancer?

Because insulin doesn’t just help your cells absorb sugar. It also sends a strong message to your body to grow. That includes fat cells. That includes muscle. And unfortunately, that includes cancer cells too.

Insulin also stimulates IGF-1 (Insulin-like Growth Factor 1), which encourages cells to grow, divide, and multiply. This is useful—for example, during childhood, puberty, or injury recovery—unless it’s elevated all the time. In the presence of cancer or precancerous cells, elevated IGF-1 and excess growth signaling can accelerate the spread of disease.

What the Research Says

A growing body of research has linked elevated insulin levels and insulin resistance to increased cancer risk and worse outcomes in a variety of cancers, including:

• Breast cancer
• Colorectal cancer
• Prostate cancer
• Endometrial cancer
• Pancreatic cancer

It’s not just about body weight. Many people with normal weight can still have chronically elevated insulin, but most don’t realize because doctors only test A1c.

What’s Missing in Cancer Care

I say this with care and respect, because I’ve been on the inside. I interned at a cancer center for several months. And while there was deep compassion, cutting-edge care, and a strong emphasis on survival—there was very little, if any, discussion about diet and insulin resistance.

In fact, my main role was to educate patients on how to eat more calories and protein during treatment—which is important. Cancer and cancer therapies can cause intense weight loss and muscle wasting. Getting enough nutrition is critical.

But what was never discussed was where those calories and protein were coming from.

• Whey and casein-based protein shakes were strongly recommended even though they’re some of the most potent stimulators of insulin and IGF-1.
• Sugar and starch—whether from juice, processed snacks, or even “healthy” sources like oatmeal or whole wheat bread—were rarely discouraged. Yet all of these spike insulin, sometimes dramatically.

The message was, “Just get the calories in.” And I’ve often heard patients say things like, “My doctor told me life is short—just eat what you want and get in as many calories as you can.”
But for some, that advice might actually be making life even shorter—especially if those calories are fueling the very growth pathways we’re trying to shut down with treatment.

How Sugar and Starch Fuel Cancer’s Environment

Cancer cells are metabolically different from healthy cells. Many rely heavily on glucose (sugar) for fuel—a concept known as the Warburg Effect. They absorb and use sugar at a much higher rate than normal cells.

So when insulin is high—whether from sugar or starches—glucose is being shuttled into cells quickly, and growth signals are being amplified. This creates a metabolic environment that can favor tumor growth and proliferation.

Even “healthy” starches like brown rice, sweet potatoes, and whole oats can contribute to this problem because they’re constantly spiking insulin throughout the day.

Insulin and Cancer Outcomes: A Tug of War

Here’s something that rarely gets discussed with patients: High fasting insulin levels at the time of cancer diagnosis have been linked to worse outcomes, including a greater risk of recurrence and death from cancer.

Why? Because insulin is telling cancer cells to grow, while chemotherapy and other treatments are trying to make them stop growing, shrink, or die. It’s a tug of war inside the body—growth vs. destruction—and when insulin is high, it can actually work against the very treatments being used to fight the cancer.

Yet fasting insulin isn’t routinely measured in cancer patients. Most oncologists aren’t trained to look at it, even though it could hold powerful insights into prognosis and recovery.

So What Should We Focus On Instead?

The goal isn’t to deprive patients or make life harder. The goal is to support the body’s healing by lowering insulin, reducing excess growth signaling, and creating a metabolic environment that is less hospitable to cancer.

Here’s what that might look like in practice:

Focus on Whole Food Proteins

• Eggs, poultry, fish, shellfish, grass-fed meat balanced with non-starchy plant proteins like nuts, seeds, and hemp hearts
• Avoid protein powders, especially whey, casein, and soy isolates

Limit High-Insulin Spiking Carbs

• Minimize sugar and starch, including whole grains and starchy vegetables like potatoes and corn
• Prioritize non-starchy vegetables like leafy greens, cruciferous veggies, carrots, tomatoes, peppers, mushrooms, and zucchini

Support Stable Blood Sugar and Insulin Levels

• Eat meals filled with healthy fats, protein, and fiber
• Avoid frequent snacking and grazing
• Incorporate gentle movement like walking, when possible

Why This Isn’t Standard Yet (And Why That’s Not Okay)

Most oncologists are not trained in nutrition or metabolic health. And most cancer centers don’t test for fasting insulin or insulin resistance. That doesn’t mean they don’t care—it just means the system hasn’t caught up with the science yet. The research is there, but the doctors just don’t know yet.

We expect that our doctors are reading the research. That they’re staying up to date. That they’re doing what’s best for their patients.

But when it comes to insulin, metabolism, and cancer, most oncologists are completely in the dark—not because the science isn’t available, but because they were never taught to look.

Let’s be clear: This isn’t new.
We’ve known for decades that insulin is a growth hormone, that it fuels cancer cell proliferation, and that high fasting insulin is associated with worse cancer outcomes.

So there’s no excuse.

The research is there. The data is there. The impact is real.

Yet most cancer centers still aren’t measuring insulin, aren’t screening for insulin resistance, and aren’t educating patients on how the food they eat might be helping—or hurting—their recovery.

And that’s not just unfair. It’s unacceptable.

Because this isn’t about replacing chemotherapy, surgery, or radiation. It’s about supporting those treatments—making them more effective, giving them a better environment to work in, and reducing the chance of recurrence down the road.

Patients deserve more than a standard protocol. They deserve a strategy that addresses not just the tumor, but the environment the tumor is growing in.

They deserve to know that insulin matters—not just in diabetes or weight loss, but in cancer development, treatment response, and long-term survival.

It’s time for this to be part of standard care. Because lives depend on it.

Bottom Line

We cannot keep ignoring insulin when it comes to cancer. It is a key hormonal driver of cell growth—and that includes unwanted growth. More calories may be necessary during treatment, yes. But the type of calories matters much more than quantity.

Supporting someone through cancer isn’t just about attacking the disease—it’s about changing the internal environment that allowed it to grow in the first place. If we want treatments to work better, we have to make the body more responsive to them.

It’s time for a more complete conversation. One that includes not just medicine, but metabolism. And it’s long past time for insulin to stop being ignored and start being treated like the critical factor it is in cancer care.

References

Gallagher EJ, et al. Hyperinsulinaemia in cancer. Nat Rev Cancer. 2020. Read more

Janssen JAMJL. Hyperinsulinemia and Its Pivotal Role in Aging, Obesity, Type 2 Diabetes, Cardiovascular Disease and Cancer. Int J Mol Sci. 2021. Read more

Tsujimoto T, et al. Association between hyperinsulinemia and increased risk of cancer death in nonobese and obese people: A population-based observational study. Int J Cancer. 2017. Read more

Goodwin PJ, et al. High insulin levels in newly diagnosed breast cancer patients reflect underlying insulin resistance and are associated with components of the insulin resistance syndrome. Breast Cancer Res Treat. 2009. Read more