10 of the worst foods for blood sugar—according to CGM data
These foods produced some of the worst blood sugar responses among Levels members. Here's how you can make them healthier.
Levels members log what they eat in the Levels app to see how their body responds. The app pulls in data from a continuous glucose monitor to measure blood sugar, then analyzes several aspects of the glucose response (rise from baseline, height of the peak, recovery time back to baseline) along with the activity around that meal that may impact glucose (say, a post-meal walk). Together, that yields the Zone Score, a simple 1-10 rating for that meal, 10 being the best.
In aggregate, those thousands of logs tell a story about some of the worst foods for our metabolic health; foods that frequently caused a significant glucose response had the lowest overall Zone Scores.
Some foods on the list, such as donuts, will likely not surprise anyone. But you may not expect to see something like sushi—fish, after all, is a protein, unlikely to spike blood sugar. However, the white rice under the fish is a processed starch that can cause a glucose rise in many people. Another surprise? Grapes made the list. Whole fruit is better than processed food (or juice) for sure, but some fruits contain more sugar than others.
This list has some caveats. First, people rarely log foods alone, and meal order and composition affect the glucose response. So a dinner log might consist of chicken, broccoli, and bread. The first two are unlikely to spike one’s glucose, but the bread almost certainly will. If you eat the protein first, it can blunt the bread’s impact. Had a glass of wine? That can further confound the results.
So we focused on entries where the listed food was the only thing in the log. That’s why it’s heavy on foods often eaten alone, like pizza or dessert, or just categories, such as Thai.
Second, this is by no means a definitive list of foods that can cause a blood sugar rise or negatively impact your metabolic health. That would include just about anything with added sugar, high-carb foods like bread, and most processed foods.
This is, however, the first time we’ve had data-backed confirmation that these foods are more likely to cause a negative metabolic response. Continuous glucose monitors are rare among people without diagnosed metabolic impairment. But it’s exciting to see the things that data can reveal as this kind of bio-monitoring expands to broader populations.
Five Surprising Foods That Spiked Blood Sugar—and How to Make Them Healthier
1. Grapes
Why it Likely Scored Low: Many fruits are high in sugar and will produce blood sugar spikes (although whole fruit is always better than juice). Grapes have 15g–20g of sugar per cup, and though they have a low glycemic index, many people find they raise glucose levels sharply.
How to Make it Healthier: Eat fewer grapes, pair them with fat or protein, or swap them for berries like strawberries, raspberries, or blackberries, which have around half the sugar.
2. Oatmeal
Why It Likely Scored Low: Often considered a go-to healthy breakfast, oatmeal surprises many Levels members as a glucose spiker. Heavily processed “instant” or rolled varieties break down more quickly, leading to a sharp blood sugar rise, and flavored varieties often contain added sweeteners.
How to Make it Healthier: Swap your morning bowl for a healthy smoothie topped with hearty toppings like hemp seeds, almond butter, chopped nuts, and chia. If you just can’t give up oatmeal, aim for steel-cut oats or groats, and pair with healthy fat and protein like walnuts, almond butter, and chia. We also love swapping oatmeal for grain-free granolas or a warm chia pudding.
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3. Sushi
Why It Likely Scored Low: Sticky white rice is refined and high in starch. Soy sauce also frequently contains sugar.
How to Make it Healthier: Order sashimi with no rice, and don’t drown it in soy sauce. Or, try cauliflower rice sushi, which is starting to appear at restaurants and is easy to make.
4. Acai Bowl
Why It Likely Scored Low: Acai berries are low in sugar (just 2g or 3g per 100g) and loaded with antioxidants, but they have a slight bitter taste, so commercial bowls tend to mix in sweeter fruits like bananas or mangos, sweeteners like honey, or sweetened nut milks, shooting the sugar through the roof. Blended bowls are even worse, reducing some of the fiber that can slow glucose absorption.
How to Make it Healthier: Mix your own at home, or go off-menu when you order. Reduce the sweeteners, add low-sugar fruits like berries, lemon juice or coconut, and mix in unsweetened milk. Even better, add veggies like spinach, and healthy fats like chia or flaxseeds.
5. Pho and Ramen
Why It Likely Scored Low: Though these are two distinct foods, the spike is most likely from the same culprit: noodles. (Note that we also see food logs for broad cuisines like Thai and Chinese food, but there too the glucose offender is a particular ingredient such as white rice or a sweet sauce. There are many, many healthy Thai and Chinese menu options.) Noodles (even rice noodles) are a processed food made with refined grains that tends to spike many people.
How to Make it Healthier: Look for dishes without noodles, or if you’re cooking at home, swap in alternative pastas made with konjac root or vegetables. Many pho and ramen restaurants now offer vegan options with spinach noodles, zucchini noodles, or tofu noodles. Also, avoid any sugary sauces or glazes.
Five Less-Surprising Blood-Sugar Bombs—and Some Healthier Alternatives
6. Chik-Fil-A and McDonald’s
Why It Likely Scored Low: Most items on these menus would fall under the ultra-processed food category. That means they likely have added sugars, refined carbohydrates with little fiber, and poor nutrient content, all of which can cause a rise in blood sugar. A Chik-Fil-A sandwich has sugar listed three times in its ingredient list and five types of flour! And these meals often come with a sugary drink like orange juice or soda.
How to Make it Healthier: Ideally, skip the fast-food joints altogether. If you’re stuck at one, look for whole foods without additives, like a salad with chicken breast (skip sugary dressings or croutons) or a burrito bowl without rice.
7. Donut
Why It Likely Scored Low: Whether a dense old-fashioned or fluffy glazed, donuts are a blood-sugar double-whammy. First, the dough is made with refined white flour, which strips grains of many of their nutrients and their microbiome-friendly fiber. This allows your body to absorb the carbohydrates more quickly, potentially spiking your blood sugar. Second, donuts can contain several grams of added sugar, even without glaze or frosting (which is often basically pure sugar).
How to Make it Healthier: To make any baked good more glucose friendly, swap refined flour for a nut flour, like almond, and use a natural alternative sweetener like allulose or monk fruit instead of sugar. At Levels, we love glonuts and these lightly sweetened almond flour donuts from Minimalist Baker.
8. Pizza
Why It Likely Scored Low: Pizza crust is another refined flour dough and often includes sugar. The tomato sauce and even processed meats like pepperoni and sausage may also contain hidden sugars.
How to Make it Healthier: Cauliflower pizza crust is now easy to find in the frozen section and even on some menus. For toppings, stick with healthy veggies and unprocessed, clean proteins like pastured raised chicken, grass-fed, grass-finished beef or pork, or tofu.
9. Pancakes
Why It Likely Scored Low: Pancake batter contains ultra-refined white flour and also typically contains sugar. Top it with maple syrup, and it’s a trifecta of glucose spiking. While maple syrup is a natural sweetener that does have some minerals, it’s still ⅔ sucrose.
How to Make it Healthier: Fortunately, there are so many delicious pancake mixes that are grain- and sugar-free. We like Pamela’s pancake and waffle mix made with coconut flour, pecan flour, walnut flour, and cassava flour (note: cassava does spike some people), and Birch Bender’s Keto pancake mix, made with tiger nut flour, almond flour, coconut flour, and cassava.
10. Cereal
Why It Likely Scored Low: Even the brands advertised as “healthy” (we’re looking at you, Cheerios) tend to list sugar as one of the first ingredients. Don’t be fooled by phrases like “whole grain”—cereals are processed foods that will likely raise blood sugar.
How to Make it Healthier: Keto-friendly cereals like Magic Spoon swap in alternative sweeteners and may lower the glucose response for some people. Or better yet, make your own grain-free granola or buy some at the store (we have tried this brand mixed with unsweetened cashew milk and have had minimal spike).
What a CGM can (and can't) tell you about your diet
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