What Your CGM Can (and Can’t) Tell You About Food
“Bananas spike my blood sugar. Should I stop eating them?” “Oatmeal sends my glucose through the roof. Is it bad for me?” “I guess I can never eat rice again!”
As a registered dietitian and diabetes care and education specialist, I hear questions like these increasingly often. With continuous glucose monitors (CGMs) becoming more accessible, people have more information about their glucose levels than ever before. But more data doesn’t always mean better understanding.
Here’s what I want us to remember: A glucose excursion is data, not a food grade.
Rather than labeling foods as good or bad based on a single glucose reading, let’s get curious about how portion sizes, meal pairings, physical activity, and individual physiology influence glucose responses, and how understanding these factors can help us make more informed food choices.
Five Nutrition Questions, One Practical Series
I recently had the honor of presenting at Colorado’s Association of Diabetes Care and Education Specialists annual conference. As diabetes care expands to include cardiovascular, kidney, and metabolic health, I was asked to discuss what’s new and what’s next in nutrition therapy.
That conversation inspired this five-part series, “Five Nutrition Questions Your Patients Are Asking.” Each article explores a common question, what the evidence says, and how to translate it into practical, person-centered guidance.
Catch up on Part 1: Are Artificial Sweeteners Safe? and Part 2: Can Eating Too Little Stall Weight Loss?
What Your CGM Measures (and What It Doesn't)
A CGM measures glucose levels in the fluid surrounding your cells, giving you insight into how glucose changes throughout the day, including after meals.
But your CGM doesn’t measure a food’s nutritional value. It can’t tell you how much fiber, protein, vitamins, or minerals you’re consuming. It certainly can’t measure satisfaction, cultural significance, or overall diet quality.
And importantly, a rise in glucose after eating is normal, even in people without diabetes.
Why Context Matters
Your glucose response isn’t determined by food alone. Portion size, meal composition, timing, physical activity, and individual physiology all influence what happens after you eat.
For example, a bowl of oatmeal eaten alone may produce a different glucose response than oatmeal paired with Greek yogurt and nuts. A banana before physical activity may look different on your CGM than one eaten while sitting at your desk.
Neither response automatically makes the food good or bad.
Experiment, Don't Eliminate
Instead of removing foods based on a single glucose spike, use your CGM as a tool for curiosity. Try a smaller portion of rice alongside vegetables and protein. Add nuts or seeds to your oatmeal. Take a short walk after eating.nThen observe what happens.
Research suggests that CGM-guided experiments involving food choices, portions, and activity can support meaningful behavior changes.
And remember to look beyond a single peak. The American Diabetes Association emphasizes broader glucose patterns, including time in range, when evaluating glucose management.
Here's How I Respond to My Patients
“Your CGM isn’t calling this a bad food. It’s showing how your glucose responded to that food, in that amount, in that meal, on that day.
Let’s get curious about what happens when we change the portion, pairing, or activity afterward. Then we’ll look for repeatable patterns while considering the food’s overall nutritional value.”
The bottom line: Your CGM is a powerful tool for understanding your body’s glucose response. Use it to make informed decisions, not to create unnecessary food rules.
Frequently Asked Questions About CGM and Blood Sugar Spikes
Yes. Blood glucose naturally rises after eating, even in people without diabetes. The size and duration of the increase vary based on food choices, activity, and individual physiology.
No. A CGM measures glucose responses, not nutritional quality. A food that raises blood sugar can still provide valuable fiber, vitamins, minerals, and other nutrients.
Oatmeal contains carbohydrates that raise blood glucose. Portion size, preparation, and toppings can influence your response. Pairing oatmeal with protein, fat, or additional fiber may help moderate the rise.
Try adjusting portions, pairing carbohydrates with protein and fiber, or taking a short walk after meals. Use your CGM to observe how these changes affect your glucose patterns.
Not necessarily. Rather than eliminating foods based on a single reading, look for repeatable patterns and consider your overall nutrition needs and glucose management goals.
Ready to Strengthen Nutrition Services in Your Practice?
Are you looking to build, refine, or expand nutrition services within your practice? I offer flexible, consultative support designed to meet the needs of busy clinics and healthcare organizations.
Nutrition is central to my work across prevention and chronic disease management. My approach focuses on translating evidence into clear, practical strategies that help patients understand not only what to do, but why it matters for their health.
Let me help you develop patient-centered nutrition services that integrate seamlessly into clinical care. Book a discovery call to explore how we might work together.
- American Diabetes Association Professional Practice Committee for Diabetes. 5. Facilitating positive health behaviors and well-being to improve health outcomes: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49 (suppl 1). doi:10.2337/dc26-S005
- Jarvis PRE, Cardin JL, Nisevich-Bede PM, McCarter JP. Continuous glucose monitoring in a healthy population: understanding the postprandial glycemic response in individuals without diabetes mellitus. Metabolism. 2023;146:155640. doi:10.1016/j.metabol.2023.155640
- Ettestad TM, Willis HJ, Johnson E, Green CR, Bergenstal RM. Continuous glucose monitoring as a behavior modification tool: a case series on CGM-guided nutrition in people with type 2 diabetes not using insulin. Clin Diabetes. 2025;43(4):610-617. doi:10.2337/cd24-0106
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