In a large US study of men and women with a heart attack in their past, those who had upped their fiber intake the most afterwards had the lowest risk of death.
The pattern held true even after researchers accounted for medications that lower cholesterol, suggesting it's important not to rely just on drugs to cut future risks, the authors said.
"There are additional benefits that come from eating healthy," said Shanshan Li, the study's lead author and an epidemiologist at the Harvard School of Public Health in Boston.
Diet plays an important role in the development of heart and artery disease, Li and her co-authors write in the journal BMJ, but little is known about the difference dietary fiber might make after a heart attack.
The researchers analysed data from the Nurses' Health Study and the Health Professionals Follow-up Study, two long-term studies that follow the health and risk factors of women and men across the United States.
At the beginning of the study period the 2,258 women and 1,840 men included in the analysis had survived a first heart attack and had never had a stroke.
Before and after their heart attacks, all participants had filled out questionnaires about how often they ate common foods over the previous year, ranking them from "never" to "six or more times per day."
Researchers used this information to calculate total fiber intake and kept track of whether each participant's fiber came from grains, fruits or vegetables.
Participants were followed for a median of about nine years; in that time, 336 women and 451 men died from heart disease-related causes, such as a second heart attack, clogged arteries in the heart and stroke. A total of 682 women and 451 men died of any cause.
The study also took into account factors that could by themselves affect mortality, such as weight, exercise and taking medicines to lower cholesterol.
Li and her team found that for every 10-gram increase in total fiber intake, the risk of death from any cause dropped by 15 per cent. The recommended daily fiber intake for women is 25 grams and 38 grams for men.
The authors point out that only fiber from grains, including cereals, was linked to lowered risk, and a high intake of this type of fiber was associated with a 28 per cent lower risk of death compared to people who ate the least fiber.
Notably, the amount of fiber participants ate regularly before the first heart attack was not related to the odds of dying later. However, the more a person boosted fiber intake after the heart attack, the lower their risk of death.
The results line up with what was already known about fiber intake and heart disease, said Vivian Mo, a cardiologist and director of the Women's Cardiovascular Center at the University of Southern California in Los Angeles.
A high-fiber diet has been linked to lower cholesterol levels, which is associated with a lower risk of heart disease, Mo said.
Still, the study goes beyond that by showing that eating more fiber is associated with a lower risk of death - although it doesn't prove that it's the fiber itself that makes the difference, she said.
For example, people who eat lots of fiber likely practice healthy habits and eat an overall healthy diet as compared to those who don't eat much fiber, she said.
"There are so many differences between people who eat more or less fiber; it's not just the fiber," Mo told Reuters Health. But the fact that people who changed their diet the most after a heart attack had the lowest risk of death is encouraging.
"It's never too late to make a change, such as starting to eat healthier," Li said.