Eat Fiber - Live Longer?
When it comes to nutrition advice, it can be hard to know what and who to trust. It seems every other week there's conflicting information about the benefits or drawbacks of our favorite foods. Are eggs good or bad for us? Should we be eating more lean meats or is the fat good for us?
Ask 4 different health professionals and you're likely to get 4 different opinions.
Luckily, one aspect of nutrition that is pretty clear cut are the benefits of fiber.
Fiber is the parts of plant foods that our body can't digest or absorb, and while we can't specifically absorb them, they are crucial for the health of our gut and our overall health.
So what are the benefits of incorporating more fiber into your diet?
There is a ton of research on fiber, but we'll stick with a few of the largest studies. Now most of these studies are observational studies - meaning that they look at the specific nutritional intake of a group over time and then track the disease rates and death rates over that same period, then they do a large statistical analysis to find out what was related.
While it would be amazing to say, “If you eat 25 grams amount of fiber a day it will result in a specific decrease in mortality or diseases risk” - it’s simply not the case. What we can gather from these studies is that people that eat more fiber typically live longer and have better health outcomes. That by increasing your fiber intake your gut will be healthier and your overall health will improve and that there is a higher probability that if you stick with this higher fiber diet over time your risk of certain diseases will decrease and you might even live longer.
Let’s dive into the studies and look at what they found.
The first study looked at 107,377 French adults over 10 years.
What they found?
Those eating the highest level of fiber (29.4 grams daily) versus the lowest (12.6 grams daily) showed a 41% lower risk of Type 2 diabetes. They also found that insoluble fiber specifically had a 35% lower risk of dying from cancer or heart disease, and soluble fiber was associated with a 20% lower risk of cardiovascular disease.
The second study looked at 388,122 Americans over 9 years.
What they found?
The difference in mortality risk from those eating the most and the least fiber was substantial. Those eating the highest level of fiber (29 grams daily) versus the lowest (12 grams daily) had a 22% decrease in mortality risk for both men and women. They also had lower cancer death risk in men, and when looking at pooled data from multiple studies, there was a 19% lower risk of death from cardiovascular disease(CVD) per 10g daily increase. Essentially, for every 10g increase in fiber, men had a 12% lower CVD death risk and women had a 24% lower CVD death risk.
The third study was a massive meta-analysis that looked at 2,567,890 participants from 22 different studies. They broke down the benefits per 10-gram daily increase in fiber intake.
What they found?
The difference in mortality risk from those eating more fiber was substantial. For every 10 grams of fiber consumed daily, people had a 10% decrease in all-cause mortality risk. They also had 13% lower CVD mortality risk, 10% lower cancer mortality risk, and even greater benefits when looking at soluble fiber specifically (17% lower all-cause mortality).
The fourth study looked at 48,632 people in Iran over 13.8 years.
What they found?
Those eating higher levels of fiber (19-22 grams daily) versus lower intake (14 grams daily) had a 7-10% decrease in all-cause mortality risk.
One interesting aspect of the this study is the effect on individuals with chronic diseases, when these individuals were taken out of the analysis the benefits of fiber decreased. Essentially meaning that fiber mattered more for unhealthy individuals(type 2 diabetes, cardiovascular disease, cancer) than it did for the healthy individuals in this group of individuals.
Overall, when we look at research, the evidence suggests that individuals who eat adequate fiber(25+ grams a day) tend to live longer and develop fewer diseases.
Does this mean I should increase my intake to 25+ grams today?
Not quite. If you're someone that is currently eating 16 grams of fiber or less and then bump up to 30-35 grams overnight, you're likely to get stomach pain, gas, and bloating.
This occurs because you are literally changing the ecosystem of your gut, and when we increase our fiber intake by 3-5 grams in a day it takes 3-4 days for the gut microbiome to adjust. Instead of trying to reach that 25+ number overnight a smarter approach is to add 3-5 grams a day for a little less than a week and then after that time bump up the intake another 3-5 grams. By taking a slow, measured approach it will decrease the chance of developing gas, bloating, and discomfort.
But I Eat My Fruits and Vegetables—Isn't That Enough Fiber?
What feels like "a lot" of fruits and vegetables might be: an apple, a banana, and a salad with cherry tomatoes, but the fact is even when we hit the recommended fruits and vegetable intake of 2 cups of fruit and 2.5 cups of vegetables per day we are only halfway to our goal of 25-30 grams. Let’s break it down.
Recommended fruits (2-3 servings): ~7.5g fiber
Recommended vegetables (3-4 servings): ~7.5g fiber
Total from fruits + vegetables: ~15g fiber
Percentage of research-backed goal: Only 50%
The missing 15 grams come from:
Whole grains: Oats (4g per cup), brown rice (4g per cup), quinoa (5g per cup)
Legumes: Black beans (15g per cup), lentils (15g per cup), chickpeas (12g per cup)
Nuts and seeds: Almonds (3.5g per 1/4 cup), chia seeds (5g per tablespoon)
The Bottom Line on Fiber
Of all the conflicting nutrition advice out there, fiber is one of the rare areas where the science is remarkably consistent.
Study after study shows that people who eat more fiber live longer and get fewer diseases. Unlike many health interventions that are expensive or complicated, increasing your fiber intake is straightforward and affordable. You don't need special supplements or exotic superfoods—just more beans, oats, fruits, vegetables, and whole grains(see a list of foods and their fiber content below).
The key is being patient with the process. Your gut has spent years adapting to your current diet, so give it time to adjust to the new one.
Start with adding 3-5 grams a day, pay attention to how you feel, and remember that a little gas and bloating initially is normal as your microbiome shifts. Most people are surprised by how much better they feel once they consistently hit that 25-30 gram daily target, but it might take you weeks or months to get there.
Fiber Intake and Mortality Risk Reduction
Comparing highest vs lowest fiber intake across major studies
107,377 participants
388,122 participants
2,567,890 participants
48,632 participants
French Study
29.4g vs 12.6g daily
No significant all-cause mortality reduction*
American Study
29g vs 12g daily
22% mortality risk reduction
Meta-Analysis
Per 10g daily increase
10% mortality risk reduction
Iranian Study
19-22g vs 14g daily
7-10% mortality risk reduction**
*French study showed significant benefits for diabetes (41% reduction) and cardiovascular outcomes, but not overall mortality.
**Iranian study benefits were primarily seen in participants without chronic diseases.
Fiber Content in Common Foods
Your guide to reaching 25-30 grams daily
🍎 Fruits
- Apple: 1 medium (with skin) - ~4.5 grams
- Banana: 1 medium - ~3 grams
- Orange: 1 medium - ~3.1 grams
- Strawberries: 1 cup, whole - ~3 grams
- Blueberries: 1 cup - ~3.6 grams
- Pear: 1 medium (with skin) - ~5.5 grams
🥕 Vegetables
- Carrots: 1 cup, chopped - ~3.6 grams
- Broccoli: 1 cup, cooked and chopped - ~5 grams
- Brussels Sprouts: 1 cup, cooked - ~4 grams
- Green Beans: 1 cup, cooked - ~4 grams
- Sweet Potato: 1 medium, baked (no skin) - ~3.8 grams
- Spinach: 1 cup, cooked - ~4.3 grams
🥜 Legumes, Nuts & Seeds
- Almonds: 1/4 cup (about 23 nuts) - ~3.5 grams
- Pistachios: 1/4 cup (about 49 nuts) - ~3 grams
- Chia Seeds: 1 tablespoon - ~4-5 grams
- Lentils: 1/4 cup, cooked - ~4 grams
- Chickpeas (Garbanzo Beans): 1/4 cup - ~3 grams
- Sunflower Seeds: 1/4 cup, shelled - ~3.9 grams
🌾 Grains & Cereals
- Oatmeal: 1 cup, cooked (made from 1/2 cup dry rolled oats) - ~4 grams
- Whole Wheat Bread: 1 slice - ~3-4 grams (Always check the label as brands vary significantly)
- Brown Rice: 1 cup, cooked - ~3.5 grams
- Quinoa: 3/4 cup, cooked - ~3.9 grams
- Air-Popped Popcorn: 3 cups - ~3.6 grams
- Cheerios: 1.5 cups - ~4 grams
References
Ghorbani Z, Noormohammadi M, Kazemi A, et al. Higher intakes of fiber, total vegetables, and fruits may attenuate the risk of all-cause and cause-specific mortality: findings from a large prospective cohort study. Nutr J. 2023;22(1):60. Published 2023 Nov 17. doi:10.1186/s12937-023-00883-4
Park Y, Subar AF, Hollenbeck A, Schatzkin A. Dietary fiber intake and mortality in the NIH-AARP diet and health study. Arch Intern Med. 2011;171(12):1061-1068. doi:10.1001/archinternmed.2011.18
Partula V, Deschasaux M, Druesne-Pecollo N, et al. Associations between consumption of dietary fibers and the risk of cardiovascular diseases, cancers, type 2 diabetes, and mortality in the prospective NutriNet-Santé cohort. Am J Clin Nutr. 2020;112(1):195-207. doi:10.1093/ajcn/nqaa063
Yao F, Ma J, Cui Y, et al. Dietary intake of total vegetable, fruit, cereal, soluble and insoluble fiber and risk of all-cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies. Front Nutr. 2023;10:1153165. Published 2023 Oct 3. doi:10.3389/fnut.2023.1153165