When it comes to heathy foods, the rules are always changing. Fat was the enemy, then it was sugar. “Eat more protein” turned into “eat less meat.” But we’ve always seemed to agree that wheat bread is healthier than white bread. For better or worse, that too might be a myth.

In his new book, Modernist Bread, Nathan Myhrvold makes the bold claim that wheat bread is no better for you than white bread. Myhrvold, former Chief Technology Officer of Microsoft, has spent the last 15 years advancing the culinary field through science. His Modernist Cuisine team of scientists and chefs have been known to test 100 versions of a recipe or cut an entire oven in half if they think it will prove a point. Their first book, Modernist Cuisine: The Art and Science of Cooking, won the James Beard Award for Cookbook of the Year in 2012, ushering in a wave of science-based cooking. So when Myhrvold makes a declaration, it’s not just a hunch.

This particular declaration, however, turns our most basic thinking upside-down. “If you made a list of what everybody knows to be true about nutrition, one of those things would be that whole grain breads are both more nutritious and better for you, health-wise,” says Myhrvold. “And, unfortunately, there’s no evidence of either one, and kind of evidence to the contrary.”

After sifting through 50 years of studies, the Modernist Cuisine team found that all types of breads have pretty much the same result on your body. It starts with the difference between white and wheat bread. Every kernel of wheat has an outside (bran) and an inside (the large endosperm and a much smaller sprouting germ). White flour is made by separating the bran and germ from the endosperm by smashing it in a flour mill and sifting them apart, saving only the endosperm. For whole wheat bread, the two parts are still separated, but in the final product, they get mixed back together. The addition of the bran gives wheat its darker color.

It’s long been thought that the bran was the healthy part of bread because it contained more fiber and vitamins. But it was a theory that never held weight in any controlled study. “If you look on a nutrient-by-nutrient basis,” Myhrvold explains, “there’s a couple things that [wheat bread] would be slightly better on,” including vitamins like manganese, phosphorus, and selenium, “but they’re generally not important in the sense that they’re not things most people run a deficit of.”

If Myhrvold is right, how were the rest of us so wrong? The notion that wheat is better than white started with a doctor, Denis Parsons Burkitt, whose 1979 book Don’t Forget Fibre in Your Diet, became an international best seller. The book was based on the idea that fiber—which comes from the bran in wheat bread—prevented certain cancers. By the end of the next decade, health professionals were all on the whole-grain bandwagon, touting not just cancer prevention but the overall health benefits of whole wheat. But most of Dr. Burkitt’s research was based on anecdotal work he did as a missionary in Africa, and later studies (including the groundbreaking Nurses’ Health Study that followed more than 88,000 women for 16 years) proved this to be false.

As for the other health claims, through fecal analysis and blood tests, we can see that our bodies don’t absorb many of the vitamins and minerals in raw grain. “Human digestion doesn’t break down [whole wheat] in the same way that a chemical analysis does,” says Myhrvold. So a lot of the nutrients that are supposedly advantageous in bran aren’t actually absorbed by humans, such as vitamins like zinc, iron, and calcium. And a compound in bran called phytates can actually bind to some of the potentially beneficial minerals to block absorption. It’s called the antinutrient effect, and it’s just as depressing as its name suggests.

Many people reach for whole grains because they take longer to digest and don’t spike blood sugar the way refined carbohydrates do. Whitney English, MS, RND, explains that the fiber “causes starch to break down more slowly in the gut than simple sugar. Therefore, it is absorbed and released into the bloodstream more slowly. This prevents blood sugar spikes and results in a longer, steadier flow of glucose into the body.” Still, Myhrvold points out that even whole grain bread is only 11% bran, and he believes the effect on blood glucose is minimal.

Regardless, it’s important to remember that not all bread is created equal—loaves with added sweeteners like honey and corn syrup will certainly give a blood sugar spike, and there are preservatives and other additives in many grocery store brands. Whether you go white or wheat, the only ingredients in your bread should be words you recognize.