Sugar loss during baking means calorie counts could be off

When you’re on a diet, counting calories usually means paying close attention to labels. But you might be surprised to learn that labels often provide the nutritional information of the recipe – not the final product. What goes in and what comes out during food processing aren’t necessarily the same.

To better understand the changes that occur during baking, researchers at UBC measured how much of a recipe’s sugar is lost when cakes are browned. They published their findings in the most recent issue of the Journal of Nutrition and Food Sciences.

Lead author Ningjian Liang, a food science PhD student, and professor David Kitts of UBC’s faculty of land and food systems, explain their findings.

What did you learn during this study?

DK: We found that the sugar content in baked goods is not always the same as it was before baking. This is due to two browning processes we refer to as the Maillard reaction and caramelization. We also found that the amount of sugar lost during baking depends largely on the type of sugar used, the baking temperature, and other attributes of the recipe — for example, the amino-acid content in the dough.

How did you conduct the study?

NL: We made cakes using two different types of sugar, then compared the amount of sugar retained in each type of cake after baking. The first cake was made with invert sugar, which is a mixture of glucose and fructose. The other was made with sucrose, table sugar, which is a disaccharide containing glucose bound to fructose. After baking, we recovered the portions of the cake that had a molecular weight lower than 3,000 and measured the gross energy from those portions, to give us a measurement in calories.

Why the limit on molecular weight?

DK: Browning reactions convert sugar into compounds that can have a higher molecular weight and are not easily digestible. These are usually just excreted.

How did the two types of cakes differ after baking?

NL: With invert sugar as the added sugar, we got significant browning, and lost as much as 20-25 per cent of the sugar when baking at 180 C. In contrast, with sucrose we lost up to 10 per cent. So the cakes made with invert sugar ended up containing fewer digestible calories derived from sugar than those made with sucrose. It was no longer sugar — it had been converted.

What does this tell people who might be counting calories?

NL: The calories from sugar indicated on a label may not accurately reflect the actual calories you consume from sugar. They’ve been calculated based on the composition of the recipe, not how much energy is actually available to your body. When we talk about the energy metabolism of carbohydrates, we’re talking about the potential energy if it is absorbed throughout the digestive system. But the gross energy you see on a label doesn’t tell you how much is digestible, and how much will be lost to fecal matter or urine. That lost energy doesn’t contribute to your metabolism. Digestion is not that efficient.