Sourdough vs wholewheat bread: which is better for blood sugar?

We all love a lunchtime sandwich, but we’re not always fans of the energy spike (and inevitable fall) that comes from eating all that bread in the middle of the day. Both sourdough and wholewheat breads are often recommended for being easier on blood sugar, but which is the best choice to keep our energy steady?

To get to the bottom of this, we consulted two dietitians and the glycemic index itself. Here’s what we learned.

Why do blood sugars spike?

Our blood sugar level is affected by the amount of energy entering our bodies at any given time. When we eat simple carbs (ones that are easy to digest), our body quickly converts those carbs into sugars, which immediately hit our bloodstream and cause our blood sugar to spike. That energy hits us fast and hard, but it doesn’t stick around, so our blood sugar quickly drops. This rollercoaster isn’t great for our health over time – and it definitely doesn’t help our post-lunch productivity!

So, here’s the bottom line: the bread that’s best for our blood sugar is bread that our bodies take longer to digest. Both sourdough and wholewheat fall into this camp, but for totally different reasons.

Benefits of sourdough

Sourdough takes longer for our bodies to digest because it’s been fermented before baking. According to dietician and nutritionist Lauren Manaker, this fermentation process produces natural acids, which ‘slow stomach emptying’ and ‘reduce the speed at which the starch in the bread is broken down and absorbed’. As a result, those sugars enter the bloodstream more slowly and in a more controlled manner, which helps blood sugar levels stay steady. That’s why sourdough has a glycemic index of 54, as opposed to many standard commercial breads, which are closer to 70.

However, not all bread labelled and sold as ‘sourdough’ actually has these benefits. ‘It’s important to purchase sourdough that has actually been fermented,’ dietician Dr Emily A. Mahadeo shares. And, yes, there are brands of ‘sourdough bread’ out there that haven’t been fermented and have simply been treated with a ‘sour’ flavour – and those will spike your blood sugar just as much as any other bread.

Benefits of wholewheat bread

Sourdough might have those natural acids that slow down digestion, but wholewheat bread has the benefit of containing (you guessed it!) the whole grain – and its extra fibre. According to Lauren, this fibre ‘helps slow the digestion and absorption of carbohydrates’, which results in steadier blood sugar levels. Dr Mahadeo agrees, adding that the higher fibre also leads to ‘increased satiety’, meaning it helps us to feel full and stay full for longer.

Just as with sourdough, it’s important to purchase wholewheat bread that actually contains the whole grain to really get these benefits. Commercially sold wholewheat bread runs the gamut from refined bread that’s been simply tinted with brown food colouring (which has a glycemic index of 71) to bread that contains purely whole grains (glycemic index of 51). Lauren recommends looking for bread that’s labelled ‘100% wholewheat’ or ‘100% wholegrain’ to make sure you really get the benefits you’re looking for.

So, which bread is better for blood sugar?

If you’re looking purely at the glycemic index, a true wholewheat bread made with whole grains has a lower value (51 versus 54) and so would be considered ‘better’ for blood sugar. But with health, nothing is ever that straightforward. According to Lauren, our blood sugar response depends on the ‘full picture’, which includes ‘what it’s eaten with, portion size and your individual body’ – so there’s no one-size-fits-all choice.

For example, pairing bread with protein and healthy fats, such as eggs, tuna, avocado or nut butter, is better for blood sugar than pairing it with, say, sweetened jam.

And people with diabetes, prediabetes or other medical conditions related to blood sugar should follow clinician guidance.

At the end of the day, both sourdough and wholewheat bread are much better options for most people than many standard breads and both will help you achieve that steady blood sugar level. But if you’re still super determined to hit the highest nutritional marks you can, you can overachieve and do what Dr Mahadeo suggests: buy wholewheat sourdough and get the best of both worlds!