As Fiber Intake Goes Up Metabolic Disease Risk Goes Down, According to New Study

Fiber may be one of the most talked-about nutrients, but most of us still don’t get enough of it. Specifically, 90% of women and 97% of men in the U.S. aren’t eating the recommended amount of fiber (28 to 34 grams per day, depending on age and sex).

Fiber is necessary for many reasons. It helps keep waste moving through your intestines and out of your body. During this process, fiber scrubs your intestines clean and even removes toxins. Fiber provides food for your beneficial gut bacteria (because even bacteria need to eat!), which helps to create a healthy, thriving microbiome. Fiber can also aid in healthy weight loss and management since eating plenty of it helps fill you up and slows down digestion, keeping you full and satisfied longer. 

Fiber has also been linked to living longer and a reduced risk of disease, including heart disease, cancer and type 2 diabetes. And now, a new study published on October 7, 2024, in Nutrients suggests getting enough fiber on a regular basis may decrease your risk of metabolic syndrome. Here’s what you need to know.

How Was This Study Conducted & What Did It Show?

Researchers from Australia and New Zealand drew data from a previous study called PROMISE (Predictors Linking Obesity and Gut Microbiome) that was conducted between July 2016 and September 2017. They used body mass index (BMI) data from 287 PROMISE participants who were Pacific Islander women (44% of participants) and New Zealand European women (56% of participants). They were 18 to 45 years old, free of chronic disease and had either a normal BMI (18-24.9 kg/m2) or a BMI indicating obesity (BMI >30 kg/m2). 

Because these researchers recognized that people with the same BMI can have dramatically different body composition, they were also placed into one of two body fat percentage groups: low BF% (<35%) or high BF% (>35%).

Data for the study was collected during two clinic visits, between 11 and 14 days apart, as well as home visits. 

Besides weight, height and body composition assessments, study participants underwent several other tests, including blood pressure and blood work testing for glucose and lipid profiles. Metabolic syndrome was assessed based on the accepted definition of having three out of five risk factors:

• Elevated waist circumference ≥ 80 cm
• Triglycerides ≥ 1.7 mmol/L
• Systolic blood pressure ≥130 mm Hg or diastolic blood pressure ≥ 85 mm Hg
• Fasting blood glucose ≥ 100 mg/dL
• Low HDL cholesterol < 1.3 mmol/L

Participants’ diets were assessed using a five-day nonconsecutive estimated food record that participants filled out themselves between clinic visits, which was then reviewed with a registered dietitian. They also completed an online food frequency questionnaire regarding the past 30 days’ food intake. This was then assessed using a food composition database to break down nutrient intake, including fiber. 

After several statistical analyses were run, researchers found that every 1-gram increase of dietary fiber consumed was associated with 9% lower odds of metabolic syndrome. In other words, as dietary fiber intake went up, the risk of metabolic syndrome went down. 

How Does This Apply to Real Life?

Aussies and New Zealanders aren’t the only ones at risk for metabolic syndrome. As many as one-third of Americans have the condition, too. If left unchecked, metabolic syndrome increases the risk of many diseases, including heart disease, stroke, diabetes and nonalcoholic fatty liver disease—to name a few.  

To know if you’re eating enough fiber, it helps to know how much fiber is in the foods you normally eat. The USDA has a handy online resource to help you with that. 

If you’re eating packaged foods, like bread, cereal and pasta, check the Nutrition Facts panel to see how much fiber is in the amount you’re eating. Do this sleuthing for five days and figure the mean (total amount of fiber over the 5 days, divided by 5) to get your average daily amount. Is it close to 28 grams? If so, keep it up! If not, what foods can you add to hit your target?

Foods rich in fiber include whole grains—like oats, whole-wheat bread, brown rice and quinoa—as well as fruits, vegetables, nuts, seeds and legumes.  

You might also be able to tell if you’re eating enough fiber based on your pooping habits. Are you pooping every day? Are you fully voiding—as in, do you feel like you got it all out? Are they well-formed poops? You may go every day, but if they come out looking like rabbit poops—little pellets—you’re probably constipated. Human poop should be soft, but not too soft, and ideally is uniform and sort of sausage-shaped.

It’s important to note, though, that pooping habits are influenced by several factors, not just fiber. For example, not getting enough magnesium may contribute to constipation—and getting too much of it might give you diarrhea. Sleep, exercise, stress and anxiety can also influence the speed at which your intestines empty out.

Because fiber helps stabilize blood sugar and fills you up, if you’re constantly ravenous and frequently getting that “hangry” feeling, you might not be eating enough fiber—or protein and healthy fats. And since fiber also feeds your gut’s beneficial bacteria, it can affect your gut health. You may know your gut bacteria is out of balance with a few key signs—like frequent headaches, persistent fatigue, eczema and increased stress or anxiety.

The Bottom Line

This study suggests that for those not already meeting the minimal fiber requirement, for every 1-gram increase in fiber intake, you may reduce your risk of metabolic syndrome by 9%. If you’re already meeting your fiber intake, you don’t want to go above that amount since this can create some unwanted side effects. 

Eat fermented foods—like yogurt, kefir, kimchi and tempeh—to add more beneficial bacteria to your gut. And include foods rich in fiber each day to feed those bacteria—including fruits, vegetables, whole grains, legumes, nuts and seeds. Eating a varied, balanced diet will help you get the nutrients you need for overall good health. Other habits that influence factors related to metabolic syndrome include regular physical activity, getting plenty of quality sleep and managing your stressors.