A recent study shows that fiber intake is strongly associated with muscle maintenance and function after the age of 40. Here's what you need to know.
When the average person thinks about fiber, they think about pooping. That's because they're thinking about insoluble fibers, the "roughage" type: bran, nuts, bean and veggie skins, and whole grains. This is the type of fiber most associated with digestion and stool bulk.
The average person might know a little about soluble fibers, too, the type that dissolves to form a gel, slows digestion, lowers cholesterol, and helps with blood sugar control. Think oats, apples, and the psyllium husks used in Metamucil.
If a person really knows their fiber, they also think about specialty fibers like beta glucan, a prebiotic fiber that boosts immunity, feeds good gut bacteria, and leads to fat loss.
But here's what almost no one thinks about: fiber's effect on muscle and strength. A recent study discovered some surprisingly strong associations.
The Study
Researchers looked at over 6,000 Americans, aged 40-plus, using data from NHANES collected over seven years. They analyzed diet records, DXA scans, and grip strength tests to see if there was a link between how much fiber people eat and their muscle health. Here's what they found:
- People who ate the most fiber had more lean body mass (muscle and bone) and especially more appendicular lean mass (arm and leg muscle).
- Fiber intake was also linked with stronger grip strength, a standard marker of overall muscle function.
- High-fiber eaters generally had lower fat mass and lower BMI, while holding on to more muscle.
- Fiber munchers also had better blood sugar and insulin levels, showing that fiber also supports metabolism.
And yes, the researchers adjusted for total calories, protein, fat, and other nutrients, so the effect wasn't just because fiber-rich foods also carry other benefits.
They didn't break down the types of fiber consumed, only total fiber intake. Generally, low-fiber eaters consumed about 12 grams a day, while high-fiber consumers consumed closer to 34 grams.
Wait, How Does Fiber Intake Affect Muscle?
Fiber helps muscles by stabilizing metabolism, reducing inflammation, and supporting a gut environment that favors strength and leanness. Fiber slows carb absorption, reduces insulin spikes, and improves insulin sensitivity. Stable insulin helps preserve muscle mass.
Fiber also feeds gut bacteria, producing SCFAs (like butyrate) that reduce inflammation and directly support muscle metabolism. High-fiber diets are linked to lower systemic inflammation, which accelerates muscle breakdown with age. Finally, fiber promotes satiety (fullness), lowers fat gain, and helps maintain a leaner body – indirectly supporting healthier muscle-to-fat ratios.
Now, the study doesn't say that fiber directly builds more muscle. Rather, it shows that fiber intake is strongly linked to maintaining muscle mass and function as we age. So, fiber is more like a "muscle protector."
How to Use This Info
To replicate the pro-muscle benefits experienced by the high-fiber eaters, shoot for around 30 to 35 grams of fiber daily from a variety of soluble and insoluble sources.
Already doing that? Then ramp up your fiber game and add the immune-boosting fiber beta glucan:
- Increased intake of beta glucan leads to fat loss, improved metabolic health, and improved insulin sensitivity.
- Beta glucan forms a gel-like structure in the digestive tract. Its viscosity allows it to lower bad cholesterol levels by binding bile acids (which are then excreted) and reducing cholesterol reabsorption. It also slows carb absorption, reducing glucose spikes and regulating blood sugar.
- It feeds your good gut bacteria. Beta glucan is fermented by gut microbiota, producing short-chain fatty acids like butyrate.
- Beta glucan enhances immune function by activating immune cells like macrophages, neutrophils, and natural killer (NK) cells. This boosts your body's ability to prevent and fight infections.
- Emerging research shows that beta glucan may enhance immune surveillance against tumor cells. And by reducing oxidative stress, it could help ward off cancer.
- Beta glucan improves skin health due to its ability to stimulate immune responses and promote healthy tissue replenishment.
Specifically, the type of beta glucan you want is beta-1,3-glucan, extracted from Euglena gracilis, which is easy to absorb and utilize. Biotest Beta Glucan (Buy at Amazon) contains 600 mg per serving, derived from Euglena gracilis algae.
Learn more about beta glucan HERE.
Reference
- Frampton, Jason, et al. "Higher Dietary Fiber Intake Is Associated with Increased Skeletal Muscle Mass and Strength in Adults Aged 40 Years and Older." Journal of Cachexia, Sarcopenia and Muscle, vol. 12, no. 6, 2021.