Fiber is an important nutrient that is often overlooked.
Simply put, fiber refers to carbohydrates that cannot be digested by your gut. It is classified as soluble or insoluble, depending on whether it dissolves in water (soluble) or not (insoluble).
Insoluble fiber primarily functions as bulking agents, adding content to your stool. In contrast, certain types of soluble fiber can significantly affect health and metabolism, as well as your weight (1).
This article explains how soluble fiber can promote weight loss.
An estimated 100 trillion bacteria live in your gut, primarily in the large intestine (2).
Along with other microbes in your digestive system, these bacteria are often referred to as the gut flora or gut microbiome.
Like other organisms, bacteria need to eat well to stay healthy.
This is where fiber – soluble, for the most part – comes in. Soluble fiber passes through your digestive system almost unchanged, eventually reaching your good gut bacteria, which digest it and turn it into usable energy.
Certain insoluble fibers, such as resistant starch, also work as prebiotics.
Fiber is not digested and tends to reach your large intestine relatively unchanged. There, some soluble fiber helps feed the good gut bacteria that are essential for good health.
Gut bacteria are well known for their effect on chronic inflammation (
They produce nutrients for your body, including short-chain fatty acids that fuel your colon cells.
While acute (short-term) inflammation is beneficial because it helps your body fight off foreign invaders and repair damaged cells, chronic (long-term) inflammation is a serious concern because it can begin to attack the own tissues of your body.
Inflammation is associated with many life conditions, including obesity. Fiber consumption has been associated with reduced inflammation.
You have to be in a calorie deficit to lose weight. This means that more calories (energy) have to leave your body than enter it.
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 less appetite, you can lose weight without even having to think about it.
Fiber is often thought to suppress the appetite. However, evidence suggests that only a specific type of fiber has this effect.
A recent review of 44 studies showed that while 39% of fiber treatments increased satiety, only 22% reduced food intake (
The more viscous the fiber, the better it reduces appetite and food intake. The viscosity of a substance refers to its thickness and stickiness. For example, honey is much more viscous 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 (1).
This gel slows the emptying of your stomach, increasing digestion and absorption times. The end result is a prolonged feeling of fullness and a significantly reduced appetite (
Some evidence indicates that the weight loss effects of fiber specifically target belly fat, which is the harmful fat in the abdominal cavity strongly associated with metabolic disease (
High viscosity fiber can provide increased fullness, reduced appetite and automatic weight loss. Low viscosity fibers seem to have no influence on these factors.
Fiber supplements are usually made by isolating fiber from plants.
Although these isolated fibers may have some health benefits, the evidence for weight control is mixed and inconclusive.
A very large review study found that psyllium and guar gum — two soluble, viscous fibers — are ineffective as weight loss supplements (
A notable exception is glucomannan, a fiber extracted from konjac root.
However, supplementing with isolated nutrients rarely makes a big difference on its own. For maximum impact, you should combine fiber supplements with other healthy 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.
Fiber supplements are generally ineffective for weight loss, with the exception of glucomannan. However, getting your fiber from whole plant foods is preferable to supplementation.
Viscous fiber occurs exclusively in plant foods. Rich sources include:
If you’re considering switching to a high-fiber diet, remember to do so gradually to give your body time to adjust.
Abdominal discomfort, cramps, and even diarrhea are common side effects if you increase your fiber intake too quickly.
Viscous, soluble fiber is only found in plant foods. Whole plant foods such as beans, asparagus, Brussels sprouts and oats are high in viscous fiber.
Eating more foods high in fiber, especially viscous fiber, can be an effective weight loss strategy.
However, like many weight loss methods, this will only lead to long-term results if you pair it with a lasting lifestyle change.
Keep in mind that fiber supplements probably have less of an impact on overall health than fiber-rich whole foods.
Also, remember that health is not just about body weight. Eating plenty of fiber from real foods can have many other health benefits.