For people with coronary heart disease, losing weight will not prolong life, a new study reports, but increasing physical activity will.

To their surprise, Norwegian researchers found that in some coronary heart disease patients — those of normal weight — weight loss actually increased the risk for death. The study, in The Journal of the American College of Cardiology, included 3,307 patients followed for an average of 16 years, with 1,493 deaths.

Lowering body mass index by more than 0.10 in a year was associated with a 30 percent increase in the risk for death, but only in those of normal weight at the start. Weight gain was not associated with mortality.

Compared with inactive patients, those who did 150 minutes of moderate exercise a week reduced their risk by 19 percent. Those who exercised more than that had a 36 percent reduction.

The lead author, Trine Moholdt, a research fellow at the Norwegian University of Science and Technology, said it was possible that people who lost weight were sicker than others, which might explain their increased mortality. Still, she said, “Being active has large effects.”