Fiber can be classified by how well it dissolves in water. Most foods contain both types of fiber: soluble and insoluble. When a food is said to be a soluble or insoluble fiber it refers that majority of the fiber present in it is of that kind. The soluble fibers include gums, mucilages, pectin, and some hemicelluloses. They are generally found around and inside plant cells.
Soluble fibers dissolve in water. They are also viscous, forming a gel when wet, and fermentable; that is, they are easily digested by bacteria in the colon. Soluble fibers are typically found in citrus fruits, berries, oat products, and beans. Research suggests that the regular consumption of soluble fibers reduces the risks for cardiovascular disease and type 2 diabetes by lowering blood cholesterol and blood glucose levels.
In foods, soluble fibers add pleasing consistency, such as the pectin that puts the gel in jelly and the gums that add thickness to salad dressings. Pectins, which contain chains of galacturonic acid and other monosaccharides. Pectins are found in the cell walls and intracellular tissues of many fruits and berries. They can be isolated and used to thicken foods, such as jams and yogurts. Gums, which contain galactose, glucuronic acid, and other monosaccharides. Gums are a diverse group of polysaccharides that are viscous. They are typically isolated from seeds and are used as thickening, gelling, and stabilizing agents. Guar gum and gum arabic are common gums used as food additives. Mucilages, which are similar to gums and contain galactose, mannose, and other monosaccharides. Two examples are psyllium and carrageenan. Psyllium is the husk of psyllium seeds, which are also known as plantago or flea seeds. Carrageenan comes from seaweed. Mucilages are used as food stabilizers.
Food Sources of Soluble Fiber
| Food name | Weight | Soluble Fiber (g) |
| Asparagus | 125 mL | 1.7 |
| Avocado | ½ fruit | 2.1 |
| Green beans | 125 mL | 1 |
| Black beans | 175 mL | 5.4 |
| Broccoli | 125 mL | 1.5 |
| Brussels sprouts | 125 mL | 2 |
| Chickpeas | 175 mL | 2.1 |
| Collard greens | 125 mL | 1.3 |
| Eggplant | 125 mL | 1.3 |
| Grapefruit | ½ fruit | 1.1 |
| Kidney beans | 175 mL | 3 |
| Lima Beans | 175 mL | 5.3 |
| Navy beans | 175 mL | 3.3 |
| Oat bran | 175 mL | 2.2 |
| Okra | 125 mL | 1 |
| Orange | 1 medium | 1.8 |
| Passion Fruit | 125 mL | 6.5 |
| Pinto beans | 175 mL | 3.2 |
| Tofu | 150 g | 2.8 |
| Turnip | 125 mL | 1.7 |
Health Benefits of Soluble Fiber
Let’s take a closer look on health benefits of soluble fiber:
- Prevent diabetes
For people with diabetes, soluble fibers—especially pectin and gums—may perform another important function. By helping to control the rise of blood sugar levels after a meal, soluble fibers may reduce the need for insulin, or medication, for some people. Incorporating at least one or two servings of beans, oats, or other sources of soluble fiber as part of a total fiber intake of 20 to 35 grams per day may help to lower fasting blood sugar levels in some people with diabetes.
The reason why soluble fibers help lower blood sugar levels isn’t fully understood. Perhaps it’s because fiber makes the stomach contents more viscous (more sticky and gummy) and so prolongs its emptying time. Because carbohydrates break down more slowly, sugar is released and absorbed more slowly, too. That in turn slows the rise of blood glucose levels. Diabetic patients if wanted to use more soluble fiber to control blood sugars, consult to a registered dietitian.
- Manages weight
Foods rich in fibers tend to be low in fat and added sugars and can therefore prevent weight gain and promote weight loss by delivering less energy per bite. In addition, fibers absorb water from the digestive juices; as they swell, they create feelings of fullness, delay hunger, and reduce food intake. Soluble fibers may be especially useful for appetite control. In a recent study, soluble fiber from barley shifted the body’s mix of appetite-regulating hormones toward reducing food intake. By whatever mechanism, as populations eat more refined low-fiber foods and concentrated sweets, body fat stores creep up. In contrast, people who eat three servings of whole grains each day tend to accumulate less body and abdominal fatness over time. Commercial weight-loss products often contain bulky fibers such as methylcellulose, but pure fiber compounds are not advised. Instead, consumers should select whole grains, legumes, fruits, and vegetables. High-fiber foods not only add bulk to the diet but are economical, nutritious, and supply health-promoting phyto chemicals— benefits that no purified fiber preparation can match.
- Prevent heart problems
Another potential benefit: Soluble fibers (mostly beta glucan and pectin) may help lower the level of total blood cholesterol, mainly by lowering LDL cholesterol, or “bad” cholesterol. In the small intestine, soluble fiber acts like a sponge, binding cholesterol-rich bile acids. As a result, they can’t be reabsorbed, but instead pass through the intestine as waste. As a result, the body absorbs less dietary cholesterol, and the liver pulls more cholesterol from the blood to replace the lost bile acids. That makes blood cholesterol levels drop.
Research have shown that that soluble fibers in present in beans,oats, psyllium, flaxseed and oat bran lowers the level of blood cholesterol in some people. In fact, there’s enough sound research for the U.S. Food and Drug Administration to allow foods to carry health claims linking oats or psyllium with heart health.
Clinical studies show that a diet high in fruits, vegetables, beans, and grain products that contain soluble fiber can lower blood cholesterol levels and therefore lower the risk of heart disease. As it passes through the gastrointestinal tract, soluble fiber binds to dietary cholesterol, helping the body eliminate the cholesterol. This reduces blood cholesterol levels, a major risk factor for heart disease. Although research is not conclusive yet, insoluble fiber may protect the heart by reducing blood pressure or the risk of blood clots.
- Blood glucose control
High-fiber foods may play a role in reducing the risk of type 2 diabetes. The soluble fibers of foods such as oats and legumes help regulate blood glucose following a carbohydrate-rich meal. Soluble fibers delay the transit of nutrients through the digestive tract, slowing glucose absorption and preventing the glucose surge and rebound often associated with diabetes onset. In people with established diabetes, high-fiber foods can modulate blood glucose and insulin levels, thus helping to prevent medical complications. A later section comes back to insulin in diabetes.
- Protective Benefits
Soft, liquid foods may have fiber, too. Instead of giving a coarse texture to food, soluble fibers found in oat bran dissolved for forming viscous or gummy. They’re often used in low-fat and nonfat food to add texture and consistency. Fibers called gums, mucilages, and pectin are all soluble. Pectin is familiar with jam or jelly. Pectin gives them their thick, gellike consistency. In your body, pectin plays a different role, binding to fatty substances and promoting their excretion as waste. This quality seems to help lower blood cholesterol levels. Soluble fibers also help regulate the body’s use of sugars.
- Cancer prevention
Research studies suggest that a high-fiber diet protects against colon cancer. When a large study of diet and cancer examined the diets of more than a half million people in ten countries for several years, the researchers found an inverse association between dietary fiber and colon cancer. People who ate the most dietary fiber (35 grams per day) reduced their risk of colon cancer by 40 percent compared with those who ate the least fiber (15 grams per day). Importantly, the study focused on dietary fiber, not fiber supplements or additives, which lack valuable nutrients and phytochemicals that also help protect against cancer. Plant foods—vegetables, fruits, and whole-grain products—reduce the risks of colon and rectal cancers.
Fibers may help prevent colon cancer by diluting, binding, and rapidly removing potential cancer-causing agents from the colon. In addition, soluble fibers stimulate bacterial fermentation of resistant starch and fiber in the colon, a process that produces short-chain fatty acids that lower the pH. These small fat molecules activate cancer-killing enzymes and inhibit inflammation in the colon.
- Gut health
Soluble fiber provides relief from inflammatory bowel problems such as constipation and diarrhea. Soluble fiber acts as a regulator for people with irritable bowel syndrome, diarrhea, constipation and hemorrhoids. In case of diarrhea, soluble fiber adds bulk for avoiding watery stool and acts more on liquid nature for providing relief from difficult and hardened bowel movements. It is also noted that soluble fiber ferments in colon by promoting flora of beneficial bacteria in colon.
Daily Recommended Intake for Soluble Fiber
No guidelines are available for how much soluble fiber one should have to maintain a healthy diet. Alternatively recommendations are found for total dietary fiber including combination of both soluble and insoluble fiber. Men and women who are over the age of 18 should target for at least 21 to 38 grams of total dietary fiber regularly.