Whether you buy them at the grocery store or pick them yourself, you don’t have much time to enjoy fresh blackberries. The so-called bramble fruit owes its short shelf-life to its design -- a single berry is actually made up of many seed-containing fruits arranged around a fleshy core and held together by minuscule hairs. While this aggregate structure makes blackberries somewhat delicate, it’s also what makes them high in fiber.

Blackberries are more than an excellent source of fiber, they’re one of the most fiber-rich fruits available. They also pack more fiber per calorie than many other high-fiber foods – a 1-cup serving of fresh blackberries provides about 60 calories and 7.6 grams of fiber, or 30 percent of the recommended daily value, according to the U.S. Department of Agriculture. Close to 80 percent of the fruit’s fiber -- or right around 6 grams per serving, according to Jackson GI Medical -- comes from insoluble fiber. The nearly 1.5 grams of soluble fiber in a serving of blackberries includes a substantial amount of pectin.

Eating blackberries promotes digestive function, bowel regularity, normal cholesterol levels and a healthy body weight. Insoluble fiber helps you feel fuller faster by absorbing water and taking up space in your stomach, while soluble fiber helps you feel fuller longer by slowing the rate at which digested food leaves your stomach. Once this digested material reaches your intestinal tract, insoluble fiber helps sweep it through and soluble fiber helps prevent simple sugars from entering your bloodstream too quickly. Pectin, the main soluble fiber in blackberries, is particularly effective at reducing high cholesterol levels. After pectin binds to cholesterol, insoluble fiber helps your body to excrete it.

You’ve probably heard the rule-of-thumb recommendation for dietary fiber -- most people should aim to consume 25 to 30 grams a day. Specific dietary guidelines advise young men and women to get at least 38 grams and 25 grams of fiber a day, respectively. Because fiber recommendations are based on caloric intake, older adults usually require less fiber -- most men and women past the age of 50 need about 30 grams and 21 grams a day, respectively. Getting enough fiber -- from natural food sources, not supplements -- is thought to protect against bowel disorders, heart disease and diabetes, according to the Harvard School of Public Health.

When you eat blackberries to increase your fiber intake, you’ll also boost your intake of several important nutrients -- a 1-cup serving delivers 50 percent and 36 percent of the daily values for vitamins C and K, respectively, and close to 10 percent each of the daily values for folate, magnesium and potassium. Opting for raspberries over blackberries gets you an extra half a gram of fiber per serving for about the same number of calories. Raspberries are often more widely available than blackberries, but both are in season at roughly the same time. Fresh blackberries are harvested throughout the United States from May to September, peaking for a short amount of time in June and July.