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How To Manage High Blood Sugar During Cancer Treatment

Cancer comes with a lot of uncertainties, and one of those is how the body will respond to treatment. For some people, the side effects of treatment cause problems with blood sugar and can even lead to diabetes. As a long-time cancer specialist and registered dietitian nutritionist, I get a lot of questions about this topic and have a lot of experience educating people on how to manage high blood sugar during cancer treatment.


The relationship between cancer and blood sugar is so complex but the bottom line is this: there’s nothing you can’t have. It’s what your diet and food habits look like as a whole that really matters. Are they balanced? Are they meeting your needs during treatment? Are you enjoying what you eat? I’ll share some evidence-based tips below to help you create a pattern of eating that supports you through treatment.


People have different needs and preferences during treatment, so one of the most important things I can tell you is to work with an experienced professional who can give you individualized information tailored to your specific circumstances.


How does treatment impact blood sugar?


Before I get to tips and recommendations, I want to explain how treatments like chemotherapy, radiation, and surgery can impact blood sugar.


  • Side effects: Things like nausea, vomiting, and poor appetite can make it difficult to keep blood sugar levels in a normal range. For example, if you don’t feel like eating during chemo, you’re more likely to skip meals or not enough enough, which can cause a drop in blood sugar.

  • Steroids: A class of medications that are given as part of chemo or to manage side effects like nausea, steroids can lead to high blood sugar for a couple of reasons. They cause the liver to release glucose (sugar) into the blood, and also slow down the delivery of sugar into muscle and fat cells. This means blood sugar levels will stay elevated in the body. Steroids come with their own side effects, too -- things like increased appetite, mood changes, and difficulty sleeping -- which also impact blood sugar.

  • Stress: I’ve seen how stressful the treatment experience can be -- on the body, on relationships, on finances, on emotional health -- and stress causes the body to release hormones that directly raise blood sugar.

Now you can see how treatment impacts blood sugar on a few different levels. Now let me explain why it’s so important to learn How To Manage High Blood Sugar During Cancer Treatment.




Why is it important to manage blood sugar?


Treatment is already a lot to handle and uncontrolled high blood sugar is just another hurdle to overcome. Keeping blood sugar in a normal range matters because it takes an extra load off the body and can help you feel better during treatment. That extra load I’m referring to is all of the side effects that come with high blood sugar, like frequent urination, dehydration, unintentional weight loss, infection, and damage to other organs.


For some people, uncontrolled high blood sugar can even lead to diabetes if they were already at risk before treatment started. (To be clear, cancer doesn’t cause diabetes but it can develop as a side effect of treatment.) As if that’s not enough, high blood sugar and diabetes left untreated for too long can also lead to serious organ damage and its complications -- things like blindness, cataracts, nerve damage leading to amputation, and kidney failure leading to dialysis.


I don’t say all of this to scare you but to help you understand how important it is to stay on top of this issue. These are all long-term complications that can be prevented and managed. When you do that, you’ll see a big improvement in your physical health, your mood and energy, and, ultimately, your quality of life during and after treatment.


How do carbohydrates impact blood sugar?


Since all carbohydrates are made up of complex chains of sugars, eating carbohydrates will eventually cause blood sugar to rise. It sounds pretty straightforward but it’s important to know that not all carbohydrates impact blood sugar the same way. And I do not want to hear you ever say “all carbohydrates are sugar” because it’s way more complex than that. Before I get to that, let’s start with a simple explanation of how carbohydrates become sugar that enters the blood.


  • The carbohydrates we eat are broken down into simple sugars that enter the bloodstream, causing blood sugar to rise.

  • The pancreas senses this increase in blood sugar and releases a hormone called insulin.

  • Insulin moves sugar from the blood into cells so they can use it for energy.


This process can go faster or slower depending on what kind of carbohydrate you’re eating, and this matters for your health and your risk for developing high blood sugar. Carbohydrates are classified as simple or complex, and they affect blood sugar levels in different and important ways:


  • Simple carbs are digested faster than complex carbs so they cause blood sugar and insulin levels to rise and fall more quickly. This gives you an immediate boost of energy that’s quickly followed by a drop in blood sugar, which is why you’re more likely to feel hungry soon after eating a meal of mostly simple carbs. When you think of simple carbs, you might think of that white (table) sugar found in desserts, sugary cereals, and soda. But simple carbs are naturally present in a lot of healthy foods like fruit and milk.

  • Complex carbs raise blood sugar more slowly because they take longer to digest and enter the bloodstream. They provide a greater sense of fullness because they contain fiber. Complex carbohydrates are found in foods like whole grains, vegetables, quinoa, lentils, and beans. They should make up most (45-65%) of your total calories every day. Whole grains and beans are literally linked to decreased rates of certain cancers (like colorectal) so don’t underestimate the power of eating these foods!


What’s the bottom line on eating carbohydrates?


You can and you should eat carbohydrates during treatment for several reasons. First of all, carbohydrates are the body’s main source of energy. If the body doesn’t get enough sugar from carbohydrates, it has to work extra hard to make sugar from other sources like protein and fat. This process is really stressful for the body, and by now you know that stress makes it extra hard to keep blood sugar under control.


Not only is cutting out carbohydrates unnecessary, it can be harmful for people undergoing treatment. Weight loss and malnutrition are major concerns for people with cancer, and carbohydrates provide important calories and nutrients that help maintain weight while dealing with side effects of treatment. Many nutritious foods like whole grains, fruits, vegetables, and beans are sources of carbohydrates. By eliminating these foods, you’re also eliminating important vitamins, minerals, fiber, and disease-fighting plant nutrients.


Food restriction in general is one of my biggest concerns with the cancer population. Not only do restrictive diets make the body work really hard to get the fuel it needs, but they take a lot of time, energy, and careful planning to ensure you’re getting enough food and cancer-fighting nutrients. Some people might even develop orthorexia, which is an extreme fixation of healthy eating that can harm our physical and emotional wellbeing.


The bottom line is that no foods are off limits, including sugar and carbohydrates. It’s so important not to deprive your body of the calories and nutrients it needs to make it through treatment, and the stress of carb-restrictive diets is counterproductive to managing blood sugar. With that said, it’s true that we want to focus on eating complex carbohydrates from plant foods as much as possible. More on that below.


What about the Ketogenic Diet ?


I get so many questions about Keto that I wrote a whole blog post on it. Keto has been growing in popularity as a way to treat certain cancers and cancer-related diabetes. Some studies support the use of Keto during cancer treatment, but there’s a lot we don’t know and experts haven’t agreed on its safety or effectiveness. Keto might show promise but it comes with a lot of challenges and complications. At this point, none of the major cancer organizations recommend Keto because research is limited and the diet contradicts many evidence-based guidelines for cancer treatment and prevention. But listen, if you’re going to try it anyway, please, please reach out because I can help you do it better and safer.


How To Manage High Blood Sugar During Cancer Treatment


Research shows that the best diet for cancer and blood sugar control is a plant-based diet. This doesn’t mean you have to eat only plants, but it does mean that you should eat plenty of them because they have lots of beneficial plant nutrients, like antioxidants, that help fight cancer and stabilize blood sugar.

Below are some tips to get you started. Keep in mind that these are general guidelines, and everyone will have different food tolerances during treatment. Eat what you like and what makes your body feel good!


  • Fill ⅔ of your plate with fruits, vegetables, and whole grains

  • Fill ⅓ of your plate with plant-based proteins like soy products (tofu, tempeh, edamame), beans, lentils, nuts, and seeds. If it speaks to you, you can include some animal proteins; everyone’s preferences are different.

  • Eat small, frequent meals throughout the day

  • Eat carbohydrates with healthy fats, fiber, and protein. This will slow stomach emptying, stabilize blood sugar, and provide a sense of fullness

  • Choose snacks that have both carbohydrates and protein. For example, raw vegetables with hummus or an apple with nut butter

  • Drink mostly unsweetened drinks like still or sparkling water, tea, coffee, or flavored waters without added sugar


If you need plant-based meal inspiration, check out my recipes for Vegan Tempeh Tacos, Simple Spicy Vegetarian Chili, and Simple Edamame Pasta Salad.


I’d rather have my clients focus on what they can have and can do, but there are some foods to eat less of as you’re trying to stay well during treatment and manage your blood sugar. These foods tend to have less fiber, vitamins, and minerals, and higher amounts of sugar, salt, saturated, and trans fats:


  • Sugar-sweetened beverages like sweet tea and soda

  • Red and processed meats like bacon and sausage

  • Highly-processed foods and refined grains like white bread


A word on alcohol: Most studies show that alcohol increases cancer risk and that limiting alcohol intake is important for both cancer and diabetes care. Experts agree that men and women should consume no more than one drink per day. That’s a 12-ounce can of beer, a 5-ounce glass of wine, or 1.5 ounce shot of liquor.


How Physical Activity Helps Manage Blood Sugar


Food isn’t the only way to manage blood sugar. Physical activity also contributes to normal blood sugar levels because it boosts the body’s ability to use blood sugar and clear any excess from the blood. It’s understandable if you don’t have the energy to perform long or intense workouts during treatment. The good news is, you don’t have to go all-out to see the benefits. Here are a few of my recommendations:


  • Aim for 30 minutes every day or 150 minutes each week. Feel free to break this up into smaller bouts, like three 10-minute walks

  • If going to the gym isn’t for you, think outside of the box. Walking up stairs, vacuuming, or gardening are all excellent options to get the body moving.

  • Whatever you choose to do, make it something that you enjoy and that feels good to your body. That way, you’re more likely to stick with it over time.


If you’re struggling to manage blood sugar or have developed diabetes as a side effect of treatment, I understand this is tough stuff and I’m here to help. I’ve spent years as a dietitian supporting people going through active treatment by educating them on plant-based diets and offering individualized plans for managing blood sugar. Feel free to contact me or drop a question or comment below!