Understanding FibRE: A Key to Better Blood Sugar

When people first consider reducing their carb or calorie intake or trying intermittent fasting to improve blood sugar, a common worry is: “Will I get enough fibre?”

Good news! The answer is yes. No matter which approach you try — low carb, low calorie, or intermittent fasting — you can meet your fibre needs. In fact, focusing on whole, nutrient-dense, minimally processed foods for your meals, especially leafy greens, colorful above-ground vegetables, and low-sugar berries, provides plenty of fibre without the blood sugar spikes that some other foods can cause.

Let’s dig into the whole issue of fibre in our diets, the different kinds and where to find them.

Total Carbs vs. Net Carbs: What’s the Difference?

Fibre comes from plants and is non-digestible carbohydrate. On nutrition labels, carbohydrates are listed as total carbs, which include:

Sugars
Starches
Fibre

However, fibre doesn’t raise blood sugar because it isn’t digested the same way as sugars and starches. That’s why many people track net carbs, calculated as:

Net Carbs = Total Carbohydrates – Fibre

This gives a more accurate picture of how much carbohydrate actually affects your blood sugar.

Types of Fibre: Soluble vs. Insoluble

Soluble Fibre:

Dissolves in water and forms a gel-like substance in the gut. It helps slow digestion, can lower cholesterol, and supports stable blood sugar.

It’s found in foods like chia seeds, flaxseeds, psyllium husk, avocado, and some vegetables, such as Brussels sprouts, sweet potatoes, carrots, broccoli, artichokes, peas and beans. Some of these vegetables, because they also contain starches, may raise blood sugar in certain people with type 2 diabetes.

It is best if you test your blood sugar after eating each of these vegetables, either by a trial with a Continuous Glucose Monitor (CGM) or pricking your finger to test a drop of blood on a glucometer CGM

Insoluble Fibre:

Does not dissolve in water. It adds bulk to stool and helps keep digestion regular. It is also filling. It’s found in vegetables, nuts, seeds, and the skins of many plants. It passes right through the body without being digested and so usually does not raise blood sugar.

Both soluble and insoluble fibre are important for gut health, digestion, and metabolic health.

Why Some High-Fibre Foods Still Raise Blood Sugar

Foods like whole grains, brown rice, oatmeal, and bran cereals are often recommended as “healthy” high fibre options for people with type 2 diabetes. But they also come packaged with significant starch, which digests down into glucose.

For many people with insulin resistance or type 2 diabetes, these foods still cause significant blood sugar spikes, despite their fibre content. Sweet potatoes, corn, beans, peas and legumes are also good fibre sources (and in some instances protein sources), but can also raise blood sugar in some insulin resistant people.

Similarly, highly processed “high fibre” products like granola bars, crackers, or breads often contain enough refined carbs, sugars, or starches to raise blood glucose, even if the label boasts about their high fibre content.

One way to tell how these higher fibre foods impact you is to wear a continuous glucose monitor (CGM) and check what happens to your blood sugar when you eat the food. Check out our article on the pros and cons of CGMs.

The Best Fibre Sources for Blood Sugar Control

You don’t need to eat grains or processed foods to meet your fibre needs. Focus on:

Leafy greens like spinach, kale, arugula, romaine, chard, lettuce

Above-ground vegetables like broccoli, cauliflower, zucchini, cabbage, and peppers

Low-sugar berries such as raspberries, blackberries, and strawberries (all relatively high in fibre)

Need a little extra? Try:

Psyllium husk; pure soluble fibre, great for digestion, easy to add to baking and other dishes

Chia seeds: high in both soluble and insoluble fibre; make a chia pudding by adding a milk or nut milk to chia seeds.

Hemp hearts: fibre plus healthy fats and protein; great on salads)

These fibre boosters are blood-sugar friendly and easy to add to smoothies, salads, or yogurt.

The Bottom Line

Eating to lower your blood sugar can absolutely be a high-fibre lifestyle. Ditch the processed “high-fibre” claims on cereal boxes and breads. Instead, fill your plate with real, whole foods with plenty of above-ground vegetables and low sugar fruit that support both gut health and blood sugar stability.