Most teens eat far less fiber than recommended, and this nutritional deficit may lead to a higher risk of diabetes and high blood pressure in the future, a U.S. study suggests.
Researchers questioned 754 teens from Augusta, Georgia, about their eating habits on at least four separate occasions. Researchers also tested participants' blood pressure and blood sugar levels and looked for insulin resistance, which happens when the body is less effective at using the hormone insulin to convert sugars in the blood into energy for cells.
Only two teens in the study consumed the minimum amount of daily recommended fiber - 38 grams for males and 25 grams for females - researchers report in the European Journal of Clinical Nutrition. Overall, participants consumed an average of 10.9 grams daily.
"Our adolescents had very low intakes of soluble and insoluble fiber," said senior study author Haidong Zhu of the Medical College of Georgia and Augusta University.
"Both lower soluble and insoluble fiber intakes were associated with higher insulin levels; furthermore, lower soluble fiber intake was associated with higher systolic and diastolic blood pressure," Zhu said by email.
Dietary fiber can be found in a variety of fruits, vegetables, whole grains, beans, nuts and seeds. It can help people feel fuller when they eat, aiding with weight management, and it has also been linked to a lower risk of heart disease and diabetes, according to the U.S. Department of Agriculture. Most Americans eat far less fiber than recommended, however.
For the study, researchers looked at total fiber as well as each of the two types of fiber people need in their diet. Insoluble fiber, often called roughage, can be found in grains, nuts, fruits and veggies and helps prevent constipation. Soluble fiber in beans, oats, barley and avocados helps soften stool and also helps slow down the amount of sugar absorbed in the blood.
Males in the study had average total daily fiber intake of 12 grams, the study found. Increasing this to the recommended daily minimum of 38 grams could lead to decreases in blood pressure, blood sugar and insulin resistance, the study team estimated.
Teen boys who increased their fiber intake to the daily recommended amount, for example, could see their systolic blood pressure - the top number that shows what happens when the heart beats — drop by an average of 6.3 mmHg (millimeters of mercury). They could also see their diastolic blood pressure — the bottom number that shows what happens when the heart rests between beats — drop by an average of 5.2 mmHg.
Adolescent girls who increased their fiber intake to the recommended 25 grams a day could see their systolic blood pressure drop by an average of 3.7 mmHg and their diastolic pressure decline by 3.0 mmHg on average.
While these teens didn't have high blood pressure, reductions of that magnitude might be enough for some adults with elevated blood pressure to reduce it back to a healthy range.
The study wasn't a controlled experiment designed to prove whether or how fiber intake might directly impact blood pressure or risk factors for diabetes, and it also wasn't designed to show how teen eating habits or lab results might lead to specific health outcomes in adulthood.
"It is really likely the entire lifestyle that is operating here - physical activity and dietary choices," said Dr. Margo Denke, a former professor of medicine at the University of Texas Southwestern Medical School in Dallas who wasn't involved in the study.
"This paper reiterates key elements of the theoretical relationship between dietary intake and metabolic syndrome," a cluster of risk factors for heart disease and diabetes, Denke said by email.
Teens are likely missing a lot of fiber in their diets because they consume too much processed food and not enough whole grains, fruits, and veggies, Denke added.
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