Spotlight on Sourdough

The Blue Zones Solution: Eating and Living Like the World’s Healthiest People, is a 2015 book by Dan Buettner that looks carefully at what the longest living communities on earth all have in common. The shared characteristics of these cultures—which are as diverse as Akaria, Greece (an island near Turkey in the Aegean), Loma Linda, California, and Okinawa, Japan among others—are, in part:

  • a built-in, active lifestyle
  • strong communities reinforcing healthy behaviors
  • a habit of eating only to 80% of fullness

Foods Associated with Healthy Communities
A sampling of abundantly eaten foods in these communities, which boast the highest concentrations of centenarians in the world, includes:

  • beans
  • wild greens
  • fruit
  • fish
  • brown rice
  • sourdough bread
  • barley
  • almonds
  • avocados
  • soy milk
  • tofu

As well as:

  • little if any added sugar
  • only occasional meat and only in small 3-4 oz. portions
  • zero or just 1-2 glasses of alcohol daily

Most of these habits and foods are well known to be reliable promoters of good health. Yet sourdough bread stands out as a somewhat unlikely addition to the vitamin-rich, fibrous, low- or healthy fat, whole-food diets.

It turns out that there is much to know about how this particular type of yeast offers unique health benefits. The bread that is its product should never be mentioned in proscriptions to avoid white bread as a blood-sugar-spiking, marginally nutritious, refined carbohydrate we can all do with a lot less of.

Types of Bread Starters
A bread starter is simply a mixture of water and flour that has been colonized by yeast to provide fermentation for new batches of bread. The added yeast can be either “active dry,” or the flour mixture can be allowed to collect naturally occurring wild yeast and bacteria from the environment.

This is the principle difference between sourdough bread and other types: sourdough is made with wild yeast, and it is more microbiologically complex than active dry yeast. Among the healthy bacteria found specifically in sourdough yeast are lactobacillus and acetobacteria.

Sourdough starters have been used for centuries, and unlike other starters, are often maintained in stable colonies for long periods of time—even centuries—since it is simpler to maintain this type of starter than to remake it. This is likely one way that some healthy cultures wind up relying primarily on sourdough to make their bread.

Sourdough as Health Food
Here are some of the key characteristics that make sourdough bread a health food:

  • Sourdough breads are made from whole wheat flour.
  • Fermenting with wild yeast converts sugars into lactic acid, lowering the bread’s glycemic index (and imparting that trademark slightly sour taste).
  • Buettner’s colleague Gianni Pes, a senior researcher at the University of Sassari, Italy, has demonstrated that this type of bread is able to lower the glycemic load, reducing after-meal glucose and insulin blood levels by as much as 25% percent.
  • This helps protect the pancreas and may help prevent obesity and diabetes.

Other studies have shown that yeast in general has probiotic effects, including treatment of intestinal diseases in part due to the removal of mycotoxins as they bind to the yeast cell wall.

Yet sourdough appears to be the champion among rivals when it comes to nutrient bioavailability. One study compared the effects of different kinds of bread fermentation on subjects’ mineral absorption ability.

Over the course of three weeks, laboratory rats were fed either: reconstituted whole wheat flour (white flour plus bran), yeast bread, sourdough bread or none (controls). The favorable results for sourdough were as follows:

  • Magnesium absorption was significantly greater in rats fed the sourdough diets than in those consuming whole wheat flour and yeast bread.
  • Sourdough bread enhanced iron absorption.
  • Zinc absorption was strongly depressed in the presence of unprocessed whole wheat flour in the diet, whereas
  • Sourdough bread led to maximal zinc absorption.
  • Copper absorption increased significantly when rats were fed the sourdough bread.

It’s evident that sourdough bread belongs in an entirely different category from white and even whole wheat bread, and should be made a delicious, regular addition to a healthy diet.

National Geographic, Apr. 2015, Book Talk with Dan Buettner, author of The Blue Zones Solution,

NPR, Eat to Break 100, Apr. 2015,

Nutrition, 2003, Vol. 19, No. 6, pp. 524-30,

Nutrients, 2010, Vol. 2, No. 4, pp. 449-73,

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