More fiber, less starch, linked to lower diabetes risk
This article was adapted from a recent issue of the Tufts Health & Nutrition Letter, a publication of the Friedman School of Nutrition Science and Policy at Tufts University
You already know to avoid added sugars, but now the evidence is mounting that another type of carbohydrate may also be implicated in weight gain and diabetes risk -- starch. That's tricky, because identifying high-starch foods requires doing a little arithmetic on the Nutrition Facts label, but the health rewards may be worth breaking out the calculator.
A large study published last year in the American Journal of Clinical Nutrition spotlighted the role of starches in promoting weight gain, with potatoes the No. 1 culprit. Now another large observational study has linked higher starch consumption to greater risk of Type 2 diabetes in women. But higher intakes of total fiber, cereal fiber and fruit fiber were all associated with lower diabetes risk, emphasizing the importance of making smart carbohydrate choices in your diet.
"This study adds to the evidence that carbohydrate quality matters," says Nicola McKeown, Ph.D., director of the Friedman School's Nutritional Epidemiology Program. "It's also consistent with results from other studies showing that higher dietary fiber, particularly from cereal fiber, is linked to lower risk of Type 2 diabetes."
The new study looked at data on 70,025 women participating in the long-running Nurses' Health Study who reported on their diets every four years. During 24 years of follow-up, 6,934 women developed type 2 diabetes.
Overall carbohydrate intake was not associated with diabetes risk one way or the other. But after accounting for other attributes of diet, different types of carbs were significantly associated with greater or lesser risk of developing diabetes:
- Starch, increased risk by 23 percent
- Total fiber, decreased risk by 20 percent
- Cereal fiber, decreased risk by 29 percent
- Fruit fiber, decreased risk by 20 percent
Higher ratios of carbohydrate to cereal fiber and especially starch to cereal fiber were most strongly linked to increased diabetes risk. These measures generally reflect a diet high in processed and refined grain products (such as white rice, crackers, many ready-to-eat breakfast cereals, and bread and pasta that's not made from whole grains) and greater intakes of starchy foods such as white potatoes and corn, along with low intake of fiber from whole-grain cereals.
It makes sense that fiber could reduce diabetes risk, because eating foods high in fiber improves post-meal insulin and blood-sugar responses. Fiber slows sugar absorption and helps you feel full, in turn reducing hunger and subsequent calorie intake.
The American Heart Association advises using the ratio of total carbohydrates to fiber as a quick gauge of a food's carbohydrate quality. (I participated with the AHA in developing this guideline.) A good ratio should have no more than 10 grams of carbohydrates per 1 gram of fiber. A food with 14 grams of total carbs and 2 grams of dietary fiber, for instance, would be a good choice at 7:1. In this new study, nearly 85 percent of participants had an overall dietary carbohydrate-to-fiber ratio above the desirable 10:1.
McKeown cautions that this 10:1 ratio is a guideline, not a hard and fast rule:
"It's really a metric for deciding on the quality of processed whole-grain food products. While the ratio largely detects healthier grain options, it's important that you don't let the numbers distract you from other nutritional attributes of a food, good or bad, such as sodium levels."
Moreover, she says, don't let this math keep you from choosing healthy whole grains whose slightly lower dietary fiber content means they don't quite make the cut. Wild rice (11:1), brown rice (16:1) and sorghum (11:1), for example, still deserve a place on your plate.
"Eat a variety of whole grains, including those like bulgur, wheat berries, steel-cut oats, and so-called 'ancient grains,'" McKeown adds. "Replace refined grains with whole grains - don't just add whole grains to a diet already high in refined grains. Minimize your intake of potatoes; choose puréed cauliflower or steamed broccoli instead. And don't forget sugar intake: Cut down on fruit juice and eliminate sugary drinks."
CHECKING THE LABELS
When calculating the starch content of a one-cup serving of corn flakes, subtract the fiber (1) and sugar (3) grams from the total carbohydrates (24): 24-1-3=20 grams of starch (about the same amount as in a cup of potatoes). The carb-to-fiber ratio would be 24:1, more than double the recommended 10:1. Remember, when looking at labels, a general rule is to check for at least 1 gram of fiber for every 10 grams of total carbohydrates.
For more information, see the Tufts Health & Nutrition Letter, a publication of the Friedman School of Nutrition Science & Policy at Tufts University: Editor-in-Chief, Dariush Mozaffarian, MD, DrPH, and Executive Editor, Alice H Lichtenstein, DSc.
About the school: The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy is the only graduate school of nutrition in the United States and provides a unique environment for trusted scientific research with real-world impact.