A recent study[ref url=”http://www.cell.com/cell-host-microbe/fulltext/S1931-3128(17)30498-5″] published in Cell Host & Microbe reveals that good gut bacteria – specifically bifidobacteria – rely upon fiber as a nutritional source to maintain a healthy mucus layer in the colon. This layer protects against gut permeability, which can lead to leaky gut syndrome as well as a host of other digestive concerns. While the findings demonstrate that fiber contributes to colonic health, many people still are not getting adequate fiber in their diets. Past research shows that low-fiber diets can lead to weight gain and diabetes. However, not all types of fiber are created equal. Here’s what you need to know to make sure you are getting enough of the good stuff.

Bifidobacteria and fiber promote a healthy colonic mucus layer

In the two-part experiment, mice subsisting on a low-fiber diet quickly developed a leaky colonic mucus layer after only three days. This gut defect is a risk factor for inflammatory bowel disease and other disorders. In the second part of the experiment, the fiber-deprived mice received a gut bacteria transplant from normally fed rodents, and regained some of the protective coating necessary for a healthy mucus layer. When the mice received a probiotic supplement of bifidobacteria, their mucus layer grew, but it did not repair the gut’s permeability. Adding inulin, a type of dietary fiber found in chicory root and vegetables, to their diets did keep gut bacteria from leaking into the body. As a result, the researchers suggest that fiber supplements need to be investigated further as a treatment protocol.

Not all fiber is created equal

In the meantime, recall that fiber is actually just a carb, though unlike sugars and starches, your body cannot break it down. In fact, fiber makes it all the way to your large intestine undigested. What it does to benefit or harm your gut is totally dependent upon the type of fiber you eat.

Eating foods with refined fiber – think packaged cereal or high-fiber bread laden with cellulose as its fiber source – can actually be harmful, irritating the gut lining, especially if it’s already compromised by leaky gut syndrome, IBS, or any other inflammation. Cellulose, FYI, is a fancy term for wood pulp, which the human body is not meant to digest. Side note: here’s how to tell if you have a compromised gut and how to fix it. Even fiber supplements may cause similar irritation, so it’s best to opt for natural sources of fiber – i.e. piles and piles of veggies.

Why vegetables will make you feel 100% better

To keep your colon lining robust and your gut bacteria healthy, reach for vegetables like collard greens, green beans, celery, cabbage, broccoli, and brussels sprouts at every meal. Vegetables are packed with beneficial fiber that will help you burn fat and build a stronger gut. When your gut bacteria are out of whack, it makes you weak, tired, and moody. Leaky gut has even been linked to depression.

Read Next: How to Own Your Gut Bacteria and Fix Leaky Gut Syndrome

Just when you thought it couldn’t get better for fiber, another boon: though it’s a carb, fiber won’t take you out of ketosis – that state your body enters when it burns fat for fuel instead of carbs.