Belly fat is extremely unhealthy. In fact, it increases the risk of heart disease, type 2 diabetes and other health conditions (1).
Fortunately, belly fat can be lost, and recent research shows that a higher fiber intake is linked to a lower risk of belly fat (2).
But interestingly, it seems that this includes only one type of fiber — soluble fiber. This article explains how soluble fiber can help you lose belly fat.
Soluble Fiber Can Help You Lose Belly Fat
There are two types of fiber — insoluble and soluble fiber. They differ in how they interact with water in your body.
Insoluble fiber does not mix with water and acts mostly as a bulking agent to help form stool and pass it through the gut. This can help with constipation (3).
Soluble fiber, such as beta-glucan, psyllium husk and glucomannan, mixes with water to form a viscous, gel-like substance that slows down how fast the stomach releases digested food into the gut (4).
This gives nutrients and water more contact time with the walls of the gut, leading to better absorption.
Eating more soluble fiber can also help you lose belly fat and prevent belly fat gain. One study linked a 10-gram increase in daily soluble fiber intake to a 3.7% lower risk of gaining belly fat (2).
Several other studies also show that people who eat more soluble fiber have a lower risk of belly fat (5, 6).
In fact, soluble fiber may help reduce belly fat in several ways.
Summary: Soluble fiber differs from insoluble fiber in how it interacts with water and other areas of the body. Soluble fiber may help reduce belly fat.
Soluble Fiber Encourages Gut Bacteria Diversity, Which Is Linked to Less Belly Fat
There are over 100 trillion helpful bacteria living in your lower gut.
Unlike other bacteria, these bacteria are harmless and share a mutually beneficial relationship with humans.
Humans provide the bacteria with a home and nutrients, while the bacteria help take care of processes like producing vitamins and processing waste (7).
There are many different types of bacteria, and having a greater variety of gut bacteria is linked to a lower risk of conditions like type 2 diabetes, insulin resistance and heart disease, to name a few (8).
And although it's not clear why, many studies show that people who consume more soluble fiber have a greater variety of bacteria and better health outcomes (9, 10,11, 12, 13).
What's more, a recent study showed that people with a greater variety of gut bacteria have a lower risk of belly fat (14).
While initial research on bacterial diversity's effect on belly fat is promising, more studies are needed before a clear link can be made.
Summary: A greater variety of helpful gut bacteria may be linked to a lower risk of belly fat, but more research is needed to confirm this.
How Helpful Gut Bacteria May Reduce Belly Fat
Because your body cannot digest fiber itself, it reaches the gut largely unchanged.
Once there, specific enzymes in gut bacteria can digest soluble fiber. This is one important way in which gut bacteria promote optimal health. Meanwhile, soluble fiber acts as a prebiotic, providing the bacteria with nutrients.
This process of digesting and processing soluble fiber is called fermentation. It produces short-chain fatty acids, a type of fat that can help reduce belly fat.
One way short-chain fatty acids may help regulate your fat metabolism is by increasing the rate of fat burning or decreasing the rate of fat storage, although exactly how this works is not completely understood (15).
Regardless, many studies show a connection between a higher level of short-chain fatty acids and a lower risk of belly fat (16, 17, 18, 19).
Furthermore, animal and lab studies have shown that short-chain fatty acids have reduced the risk of colon cancer (20).
Summary: Your gut bacteria can digest soluble fiber. The process produces short-chain fatty acids, which are linked to a lower risk of belly fat.
Soluble Fiber Helps Reduce Appetite
One way to lose belly fat is to lose weight.
And given that soluble fiber is a powerful natural appetite suppressant, it can help you do that.
By suppressing your appetite, you are more likely to reduce your calorie intake, which can help you lose weight (21, 22).
There are several theories about how soluble fiber can help reduce your appetite.
First, soluble fiber helps regulate hormones involved in appetite control.
Some studies have found that eating soluble fiber reduces the number of hunger hormones produced by the body, including ghrelin and neuropeptide Y (23, 24).
Second, fiber can reduce appetite by slowing the movement of food through the gut.
When nutrients like glucose are released slowly into the gut, your body releases insulin at a slower rate. This is linked to a reduced sense of hunger (4).
Summary: Losing weight can help you lose belly fat. Soluble fiber can help you lose weight by curbing your appetite, which reduces calorie intake.
Sources of Soluble Fiber
Soluble fiber is easy to add to your diet and found in a variety of plant-based foods.
Foods that are high in soluble fiber include flaxseeds, sweet potatoes, fruits like apricots and oranges, Brussels sprouts, legumes and grains like oatmeal.
However, although soluble fiber may help you lose belly fat, it's not a great idea to eat lots of soluble fiber right away.
This can cause side effects, such as stomach cramps, diarrhea and bloating. It's best to increase your intake slowly, over time, to help improve your body's tolerance.
As far as recommended daily intake goes, the US Department of Agriculture recommends that men aim to consume 30–38 grams of fiber per day, while women should aim for 21–25 grams per day (27).
Summary: Great sources of soluble fiber include flaxseeds, legumes, grains, fruits and vegetables. Aim to increase your intake slowly over time.
Can Fiber Supplements Help Reduce Belly Fat?
Whole foods are the best way to increase your soluble fiber intake.
But if this isn't realistic for you, taking a soluble fiber supplement could be an option.
Various types are available, including psyllium husk, glucomannan and inulin, and some evidence shows they can help you lose belly fat.
For example, one six-week study in teenage boys showed that taking a psyllium husk supplement reduced belly fat (28).
Also, the viscous fiber glucomannan has shown mixed results for belly fat loss. One study in mice found that glucomannan supplements reduced belly fat, while a human study showed the same effect, but only in men (29, 30).
Yet despite these mixed results, glucomannan can also promote belly fat loss by slowing down digestion and reducing appetite (31).
Inulin is another type of soluble fiber. Even though it's not very viscous, it has been linked to belly fat loss.
One 18-week weight loss study in people at risk of type 2 diabetics gave participants either inulin or cellulose (insoluble fiber) supplements. Both groups received nutrition advice for the first nine weeks and followed a fat-loss diet.
While both groups lost weight, the inulin group lost significantly more belly fat, total body fat and total weight. They also ate less food than the cellulose group (32).
Overall, fiber supplements seem like a promising area for future research in belly fat loss. Yet, more research is needed before making a stronger recommendation.
Summary: Psyllium, glucomannan and inulin show promise for belly fat loss, though more research is needed to make supplement recommendations.
The Bottom Line
Eating foods rich in soluble fiber may help you lose belly fat.
Soluble fiber helps keep your gut bacteria healthy and promotes overall fat loss by reducing your appetite.
To further promote belly fat loss, combine your soluble fiber intake with other lifestyle changes, such as making healthier food choices and exercising more.