DEAR DR. BLONZ: I am working on many angles to avoid Type 2 diabetes, which runs in my family. I have borderline blood sugar issues, but unlike others in the family, I have improved my diet and now go on daily walks that involve hills or stairs.
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My question relates to a lecture in which the physician speaking said that a common additive in bread, calcium propionate, can interfere with how glucose is metabolized and contribute to insulin resistance. A study was cited to support this, but I did not note the author. I am writing because I noticed that the high-fiber, whole-grain bread I now enjoy has this as one of its ingredients. I wanted your take on whether I need to shift to another brand. -- M.M., Phoenix, Arizona
DEAR M.M.: When we hear about a specific substance being suspected of helping or hurting a certain function, it is vital to know the amount of the substance associated with the effect. A closer look at this issue may spare you some concern.
Calcium propionate is a salt of propionic acid, a natural acid found in raisins and other fruits. Propionic acid, or its synthetically made calcium propionate salt, acts as an inhibitor of microbial growth -- most notably of the molds that tend to make themselves at home on breads. At the same time, these substances do not prevent leavening yeasts, which are also microorganisms, from doing their job. This explains why mold inhibitors are used in many breads to prolong shelf life. Some brands, particularly organic ones, use raisin juice as a mold inhibitor -- so propionate may be there even if you don't see "calcium propionate" on the ingredient list. (Read more on calcium propionate at b.link/hxgdw9.)
However, the practical concern about the impact of propionate on glucose metabolism seems a bit exaggerated.
One study reported that calcium propionate did impact glucose metabolism. But when checking the methodology, I noted that the experiment involved giving almost 1,500 mg of calcium propionate (or a placebo) to the subjects on an empty stomach after an overnight fast. That is a hefty amount! As calcium propionate typically makes up about 0.2% of dry flour weight, it would take about six cups of flour to provide that much calcium propionate. That's enough to make over a loaf and a half of bread -- more than anyone should have at one time, especially someone concerned about their blood sugar level.
A subsequent meta-analysis published earlier this year in the American Journal of Clinical Nutrition looked at 13 studies examining the effects of calcium propionate on glucose metabolism. Not surprisingly, that paper, which included the one mentioned above, concluded there was no significant effect on insulin and glucose metabolism.
No need to change bread brands because of this. My congratulations on your diligence; keep up the excellent work.
Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.