What food causes your A1C to go up? The definitive guide

October 21, 2025 •

4 min read

According to the Centers for Disease Control and Prevention, over 38 million Americans have diabetes, and many more have prediabetes, a condition marked by elevated A1C levels. Understanding what food causes your A1C to go up is crucial for managing or preventing these conditions. The primary culprits are foods high in refined carbohydrates and sugar, which cause significant spikes in blood glucose that negatively impact long-term A1C readings.

Quick Summary

This article details the specific types of food that raise A1C levels, focusing on processed items, refined carbs, and sugary products. It explains the metabolic process by which these foods lead to increased blood glucose and provides actionable dietary strategies for maintaining healthier A1C ranges. The content also addresses the impact of fiber, protein, and fat on blood sugar control.

Key Points

Refined Carbohydrates: Foods made with refined white flour, like white bread and pasta, cause significant blood sugar spikes due to a lack of fiber.
Sugary Beverages: Drinks such as soda and fruit juice deliver a high dose of simple sugars, which are absorbed rapidly and elevate blood glucose levels instantly.
Glycemic Index: The glycemic index of food is crucial; choose low-GI foods like whole grains, legumes, and non-starchy vegetables to avoid blood sugar surges.
Role of Protein and Fiber: Pairing carbohydrates with lean protein and soluble fiber slows down the digestion process, leading to a more gradual release of sugar into the bloodstream.
Processed vs. Whole Foods: Highly processed and packaged snacks, desserts, and ready-made meals are often loaded with refined sugars and carbs that negatively impact A1C; opt for whole, unprocessed foods instead.
Beyond Diet: Exercise, stress management, weight control, and adequate sleep all play vital roles in regulating blood glucose and improving A1C levels.

The A1C test, or glycated hemoglobin test, provides an average snapshot of your blood glucose levels over the preceding two to three months. When your blood sugar rises, glucose binds to the hemoglobin in your red blood cells, and the A1C test measures the percentage of hemoglobin with this attached glucose. A higher percentage indicates poorer long-term blood sugar control. Therefore, managing your A1C is about controlling the frequency and severity of blood sugar spikes caused by the foods you eat.

The Primary Culprits: Refined Carbohydrates and Sugary Foods

The most significant dietary factor that causes your A1C to go up is the consumption of foods high in simple or refined carbohydrates. These foods are broken down quickly into glucose, leading to rapid and dramatic surges in blood sugar.

Sugary Foods and Beverages

Sugary foods and drinks are arguably the fastest way to raise blood glucose. The body absorbs the simple sugars in these items very quickly, causing an immediate spike. Limiting these is a cornerstone of diabetes management.

Soda and sweetened drinks: Regular sodas, sweetened teas, and fruit juices (especially bottled varieties) are liquid sugar and are absorbed almost instantly.
Candy and desserts: Items like cakes, cookies, pastries, and ice cream are laden with added sugars and refined flour, both contributing to high blood sugar.
Hidden sugars: Many processed foods contain surprising amounts of added sugar. Examples include flavored yogurts, cereals, and many condiments like ketchup and BBQ sauce.

Refined Carbohydrates and Starches

These are complex carbohydrates that have been stripped of their fiber and nutrients during processing, causing them to behave much like simple sugars in the body.

White bread and pasta: Unlike their whole-grain counterparts, these products offer little fiber and are rapidly converted to glucose.
White rice: This staple grain is a very starchy carbohydrate with a high glycemic index, causing a significant blood sugar spike.
Processed snack foods: Chips, crackers, and other packaged snacks are typically made from refined flours and starches that elevate blood glucose quickly.

How Cooking and Preparation Affect Blood Sugar

It's not just the food itself but also how it is prepared. Cooking methods can alter a food's glycemic index, which measures how a specific food affects blood sugar.

Deep-frying: Frying increases the caloric content and can raise the glycemic index of foods like potatoes. For example, french fries spike blood sugar far more than a baked potato.
Ripeness: The ripeness of some fruits affects their sugar content. A ripe banana has a higher glycemic index than a slightly green one.
Processing: Dried fruits have a greater effect on blood sugar than fresh fruits because the sugar becomes more concentrated as water is removed.

Navigating the Glycemic Impact of Carbs

Not all carbohydrates are created equal when it comes to A1C. Complex carbohydrates, especially those high in fiber, are digested more slowly and result in a more gradual rise in blood sugar.

Comparison: High-Glycemic vs. Low-Glycemic Foods


Food Category	High-Glycemic Examples	Low-Glycemic Alternatives
Grains	White bread, white rice, sugary cereal, instant oatmeal	Whole-grain bread, brown rice, rolled oats, barley, quinoa
Starchy Vegetables	White potatoes (especially fried), corn, pre-made potato products	Sweet potatoes, non-starchy vegetables (broccoli, leafy greens)
Sweeteners	White sugar, corn syrup, high-fructose corn syrup, honey, jaggery	Stevia, monk fruit, xylitol, or limited amounts of natural sweeteners
Beverages	Regular soda, fruit juice, sweetened iced tea	Water, herbal tea, sugar-free drinks
Snacks	Chips, pretzels, processed snack cakes	Nuts, seeds, fruits with skin (apples), vegetable sticks

The Role of Protein and Fiber in Moderating A1C

While carbohydrates are the primary driver of blood glucose fluctuations, other nutrients can help mitigate their effects. Pairing carbs with protein and fiber can significantly improve blood sugar control.

Protein: Protein foods, such as lean meats, eggs, and legumes, have a minimal impact on blood glucose and slow digestion when paired with carbohydrates. A breakfast rich in protein and fat, for instance, can lead to better glycemic control throughout the day.
Fiber: This indigestible carbohydrate is crucial for blood sugar management. It slows the absorption of sugar, preventing rapid spikes. Soluble fiber, in particular, forms a gel in the digestive tract that slows glucose absorption. Excellent sources include legumes, oats, nuts, and many fruits and vegetables.

Other Lifestyle Factors That Influence A1C

Diet is a critical component, but it’s part of a larger picture. Other lifestyle factors also play a significant role in managing blood sugar and A1C.

Regular Exercise: Physical activity helps muscles use blood sugar for energy, which improves insulin sensitivity and can lower blood sugar levels for extended periods.
Weight Management: Maintaining a healthy weight is key, as excess body weight (especially around the abdomen) can lead to insulin resistance.
Stress Management: Stress hormones like cortisol can cause blood sugar levels to rise. Practices like meditation, yoga, and deep breathing can help reduce stress and support blood glucose control.
Adequate Sleep: Poor sleep habits can negatively affect blood sugar levels and insulin sensitivity. Aim for 7-8 hours of quality sleep per night.

Conclusion: Making Smarter Food Choices for Better A1C

Controlling your A1C levels is a continuous process of making informed dietary and lifestyle choices. The key is to reduce your intake of foods that cause rapid blood sugar spikes, particularly those high in refined carbohydrates and added sugars. Focusing instead on a balanced diet rich in whole, unprocessed foods like vegetables, fruits, whole grains, and lean proteins can help maintain more stable blood glucose. Combining these eating habits with regular exercise, proper hydration, and stress management offers a comprehensive approach to naturally lowering and managing your A1C. For personalized advice, it is always recommended to consult with a healthcare provider or a registered dietitian.

Authoritative Outbound Link: American Diabetes Association: Understanding A1C Test

Frequently Asked Questions

A1C is a blood test that provides an average of your blood glucose (blood sugar) levels over the past two to three months. Diet is crucial because the carbohydrates you eat are converted into glucose, directly impacting your blood sugar. Regularly consuming foods that cause significant blood sugar spikes will result in a higher A1C reading.

No, not all carbohydrates are bad. Complex carbohydrates found in whole grains, fruits, and vegetables are rich in fiber and are digested more slowly, leading to a more gradual rise in blood sugar. Refined carbohydrates, which lack fiber, are the primary concern for A1C management.

Simple carbs are sugars that are quickly absorbed by the body, causing rapid blood sugar spikes. Complex carbs, especially those with high fiber content, are digested more slowly, resulting in a more gradual and sustained energy release that helps prevent blood sugar surges.

Yes. Many savory processed foods contain hidden sugars, refined flours, and starches that are quickly converted to glucose, causing blood sugar spikes and contributing to higher A1C levels. It's essential to read nutrition labels carefully.

Protein and fiber slow down the digestive process, which means glucose is absorbed into the bloodstream more gradually. This helps to prevent the sharp blood sugar spikes that negatively impact A1C levels. Pairing carbs with protein and fiber is a smart dietary strategy.

Other factors besides diet can affect A1C, including a sedentary lifestyle, stress, and poor sleep. Lack of exercise can reduce insulin sensitivity, while stress hormones can elevate blood sugar. Managing these lifestyle factors is also important for A1C control.

For most non-diabetic adults, an A1C level below 5.7% is considered normal. A reading between 5.7% and 6.4% indicates prediabetes, while an A1C of 6.5% or higher on two separate tests points to diabetes.