Learn how diet affects blood sugar and discover practical tips for managing glucose levels. Find out which foods raise blood sugar, how macronutrients impact it, and ways to reduce spikes
Introduction
Does eating too much sugar raise your blood sugar? Why do so many people avoid carbs? If you’ve ever wondered how your diet affects your blood sugar, you’re not alone.
When you eat foods containing carbohydrates, your blood sugar rises. Normally, insulin—a hormone made by your pancreas—helps bring it back down to a healthy range. Your blood always contains some glucose (sugar) to fuel your cells for energy.
If you have diabetes or prediabetes, your blood sugar may stay elevated for longer. Certain foods will affect your blood sugar more than others. In this guide, we’ll explore how diet affects blood sugar, how different foods impact glucose, and simple tips to keep levels in check.
What is blood sugar?
Blood sugar, or blood glucose, is the amount of sugar circulating in your bloodstream. It’s your body’s main source of energy.
When you eat carbohydrates, they break down into glucose, which enters your bloodstream. Two hormones from your pancreas regulate these levels:
- Glucagon signals your liver to release stored glucose (glycogen) when needed.
- Insulin helps glucose enter your cells for energy.
What is a normal blood sugar?
Normal blood sugar ranges vary depending on the time of day.
For most people without diabetes:
- Fasting: 60–100 mg/dL
- 2 hours after a meal: less than 140 mg/dL
For most people with diabetes:
- Fasting: 80–130 mg/dL
- 2 hours after a meal: less than 180 mg/dL
- Bedtime: 80–140 mg/dL
Always check with your healthcare provider for your personal targets.
How Do Different Nutrients Affect Blood Sugar?
There are 3 macronutrients or “macros” in our diet that come from food: carbohydrates, protein and fat. In this section, we’ll discuss how each will impact your blood sugar.
1. Carbohydrates and Blood Sugar
Carbohydrates have the most direct effect on blood sugar. All carbs—whether from bread, fruit, or sweets—are eventually broken down into glucose.
- Simple carbohydrates (white bread, fruit juice, candy) raise blood sugar quickly because they lack fiber and are digested fast.
- Complex carbohydrates (whole grains, beans, vegetables) raise blood sugar more slowly because they contain fiber and are less processed.
The glycemic index (GI) ranks carbs on how quickly they raise blood sugar (0–100 scale).
Low GI foods: beans, bran cereal, hummus, yogurt
High GI foods: white rice, white bread, watermelon
2. Protein and Blood Sugar
Protein has a slower, more moderate impact on blood sugar. It helps:
- Stabilize blood sugar levels
- Increase satiety (fullness)
- Support muscle, immune function, and hormone production
Examples: chicken, fish, eggs, tofu, Greek yogurt, nuts
3. Fat and Blood Sugar
Fat has little immediate effect on blood sugar. However, high-fat meals can keep levels elevated for hours because fat slows digestion and may increase insulin resistance.
Examples of high-fat meals that can keep blood sugars higher: pizza, burgers with fries, fried foods, spaghetti with meatballs.
4. Fiber and Blood Sugar
Fiber is a carbohydrate your body can’t digest. It slows the absorption of glucose and reduces overall spikes.
Two types of fiber:
- Soluble fiber (oats, beans, apples) dissolves in water, forms a gel, and slows digestion.
- Insoluble fiber (vegetables, whole grains, nuts) adds bulk and supports digestion.
Daily fiber goals:
Men: 31–34 g/day
Women: 25–28 g/day
In short, fiber helps to lower blood sugar because it delays digestion and absorption of carbohydrate foods and since we don’t digest fiber, it reduces the overall amount of carbohydrate that turns into glucose in our blood.
Does portion size impact my blood sugar?
Yes—larger portions of carbs lead to higher blood sugar spikes, especially if you have diabetes. Pairing carbs with lean protein, healthy fats, and non-starchy vegetables can help reduce the spike.
How to Reduce Blood Sugar Spikes
- Work with a Registered Dietitian
A dietitian can tailor a plan based on your food preferences and lifestyle. - Follow the Plate Method
- ½ plate non-starchy vegetables
- ¼ plate lean protein
- ¼ plate complex carbohydrate
- Choose More Complex Carbs
Swap refined grains for whole grains, whole fruit for juice, and add beans, lentils, and veggies to meals. - Plan Meals and Snacks
Having a plan prevents impulsive food choices and helps maintain steady blood sugar levels.
How to Change Your Diet to Reduce Diabetes Risk
Even if you don’t have diabetes, balanced eating helps prevent blood sugar problems.
Set SMART goals—specific, measurable, achievable, relevant, time-bound—for long-term success.
Sample SMART goal: I will choose to eat whole grain bread instead of white bread when I make a sandwich 3 times per week
Final thoughts
What you eat directly impacts your blood sugar. Carbohydrates are the biggest influencer, but protein, fat, and fiber also play a role. Choosing complex carbs, eating balanced meals, and practicing portion control can help stabilize blood sugars.
If you want personalized guidance, working one-on-one with a registered dietitian can help you create a plan that works for you.