Eating soluble fiber may help promote weight loss and have other health benefits. But fiber from whole plant foods is better for weight loss than fiber supplements.

Fiber is the carbohydrates that your gut can’t digest. Fiber is classified as either soluble or insoluble depending on whether it dissolves in water (soluble) or not (insoluble).

Insoluble fibers function mostly as bulking agents, adding content to your stool. In contrast, certain types of soluble fiber can significantly affect your health and metabolism — as well as your weight.

An estimated 100 trillion bacteria live in your gut, primarily in the large intestine.

Along with other microbes found in your digestive system, these bacteria are often called the gut flora or gut microbiome.

Different species of bacteria play important roles in various aspects of health, including:

  • weight management
  • blood sugar regulation and management
  • immunity
  • brain function

And just like other organisms, bacteria need to eat well to stay healthy. This is where fiber — soluble, for the most part — steps in.

Soluble fiber passes through your digestive system mostly unchanged, eventually reaching your friendly gut bacteria, which digest it and turn it into usable energy.

The fiber that benefits your gut bacteria is known as prebiotic fiber, or fermentable fiber. It’s considered very beneficial for health and body weight.

Certain insoluble fibers, such as resistant starch, also function as prebiotics.

Gut bacteria are well known for their effect on chronic inflammation.

They produce nutrients for your body, including short-chain fatty acids that feed the cells in your colon. This reduces gut inflammation and improves related inflammatory disorders.

While acute (short-term) inflammation is beneficial because it helps your body fight foreign invaders and repair damaged cells, chronic (long-term) inflammation is a serious concern because it may begin to attack your body’s own tissues.

Chronic low level inflammation plays a major role in many chronic diseases, including:

  • cancer
  • Alzheimer’s disease
  • metabolic syndrome

Observational studies also demonstrate that a high fiber intake is linked to lower levels of inflammatory markers in the bloodstream.

To lose weight, you need to be in a calorie deficit, which means you need to burn more calories than you consume.

Counting calories helps many people, but it may not be necessary if you choose the right foods.

Anything that reduces your appetite can decrease your calorie intake. With a smaller appetite, you may lose weight without even having to think about it.

Fiber is often believed to suppress your appetite. However, evidence suggests that only certain types of fiber have this effect. The more viscous the fiber, the better it is at reducing appetite and food intake.

Viscosity refers to a substance’s thickness and stickiness. For example, honey is a much more viscous substance than water.

Viscous soluble fibers such as pectins, beta-glucans, psyllium, glucomannan, and guar gum all thicken in water, forming a gel-like substance that sits in your gut.

This gel slows the emptying of your stomach, increasing digestion and absorption times. The end result is a prolonged feeling of fullness and reduced appetite.

The weight loss effects of fiber may specifically target belly fat, the harmful fat in the abdominal cavity associated with metabolic disease.

Rich sources of viscous fiber

Viscous fibers occur exclusively in plant foods. Rich sources include:

If you’re planning to switch to a high fiber diet, remember to do it gradually to give your body time to adjust.

Abdominal discomfort, cramps or bloating, and even diarrhea are common side effects if you ramp up your fiber intake too quickly.

It’s recommended to increase water intake on a high fiber diet. Fiber needs more water to digest properly.

Fiber supplements are typically made by isolating the fiber from plants.

While these isolated fibers may have some health benefits, the evidence for weight management is mixed and unconvincing.

A 2022 systematic review found that guar gum — a soluble, viscous fiber — was not effective as a weight loss supplement in 3 out of 5 studies reviewed.

One notable exception is glucomannan, a fiber extracted from the konjac root. This dietary fiber is very viscous and shows promise for weight reduction in adults with overweight and obesity.

However, supplementing with isolated nutrients rarely makes much difference on its own. For the greatest effects, it’s best to combine fiber supplements with other weight loss strategies.

Although glucomannan and other soluble fiber supplements are a good option, it’s best to focus your diet on whole plant foods.

Eating more foods rich in fiber — especially viscous fiber — can be an effective strategy to lose weight.

However, like many weight loss methods, it won’t lead to long-term results unless you pair it with a lasting lifestyle change.

Keep in mind that taking fiber supplements likely has less overall health effects than eating fiber-rich whole foods.

Additionally, don’t forget that health isn’t all about body weight. Eating plenty of fiber from real foods can have numerous other health benefits.