Carmichael, California, USA - April 10, 2014: Cars parked in front of the Subway restaurant located at 4005 Manzanita Ave #54 in Carmichael, California. Subway is fast growing restaurant franchise with close to 40,000 restaurants in over 100 countries.

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Why Subway's New Low Carb Bread Is So Concerning

Subway’s new health-conscious Hero Bread contains 0 grams of sugar, 1 gram of net carbs, and 100 calories, and 26 grams of fiber per serving — and these numbers are concerning dietitians. Eat This, Not That! reports that any item that contains more than 5 grams of fiber can put considerable strain on your digestive system.

Trista Best, Registered Dietitian at Balance One Supplements, adds that Hero Bread can be "an excellent option" for those who are watching their blood sugar. However, she warns against Hero Bread's primary ingredient of modified wheat starch, a kind of starch that is modified to have very little nutritional value besides large amounts of fiber.

Best explains that "the method by which this starch is modified [...] means there can be contamination from harmful compounds like sulfuric acid or chlorine." For Subway customers who usually choose refined bread, Hero Bread could still be beneficial, but it's a different story for diners who usually choose whole-grain breads.

Best explains, "For those that would typically eat whole grain breads, [Hero Bread] is a poor nutritional decision." Unlike Hero Bread, standard whole grain bread contains "un-modified, non-processed, fiber and ingredients," as Best says; if you already choose healthy, whole-grain bread options, Hero Bread won't do you any favors.