The Missing Carb That Could Be Protecting Your Brain
- Austin Perlmutter MD
- 23 hours ago
- 5 min read
Almost nobody eats the recommended amount
By Austin Perlmutter, MD
In recent years, carbs (short for carbohydrates) have been heavily criticized for their role in diseases, including brain issues. There’s a basis for this, as our modern diets are loaded with low-quality “empty carbs” like added sugars and refined baked goods, both of which may create issues in the brain when consumed regularly by way of metabolic and immune effects. Yet emerging research suggests that one of the most powerful nutrients for overall and brain health could be a carb, and almost nobody is eating the recommended amount. In this article, we’re breaking down the science on dietary fiber, and why it may still be one of the best-kept secrets for longevity, overall wellness and especially brain health and cover considerations around low-carb diets.
Dietary fiber is a carbohydrate (or carb) that’s indigestible to humans. This means we don’t break it down into sugar molecules, and that it passes through the stomach and small intestine to reach the large intestine intact. The data on fiber intake in the United States is sobering. Health guidelines recommend approximately 14 grams of fiber per 1,000 calories consumed — roughly 25 grams per day for women and 38 grams for men. Yet research consistently shows that the average American is consuming only about 10 to 15 grams per day, less than half the recommendation. More striking still, research suggests that only 5% of Americans are eating the recommended levels of fiber. This isn’t a US issue alone. Less than 10% of UK adults hit the recommended mark, and lower than optional levels of intake are seen from Mexico to European countries.
Fiber's link to health
Decades of research suggests that a higher fiber diet may help to prevent cardiovascular issues, improve blood sugar, increase lifespan and decrease risk for a host of other issues, including brain health conditions. These types of data were most recently confirmed in a massive review of over 17 million people across 33 separate meta analyses.
As it relates specifically to the brain, an observational study on nearly 4000 Japanese adults found that those eating more fiber had a roughly 20% lower risk for developing disabling dementia over the observational period, with the biggest benefits seen with soluble fiber. In a 2025 randomized, placebo-controlled trial looking at multiple interventions, researchers found that people who took fiber had changes in the gut microbiome and improved cognition versus the placebo. Finally, in another 2025 study, scientists found a link to cognitive improvements in those eating more fiber with a peak benefit between 22 and 30 daily grams of consumption. While there’s lots still to learn, a key mechanism seems to involve benefits to the gut-brain axis that come from eating more fiber.
Why are people eating so little fiber? Modern food is a big reason. As we moved towards industrialized food products, especially refined grain products, we kept the carbs but lost the fiber. Data show that in general, the more ultra-processed food we consume, the less fiber we consume. Contrast this with our ancesters diets which are believed to have added up to 100 grams of fiber a day to our diets!
What are the different forms of fiber?
Two types of fiber are commonly described, although the reality is that there’s a whole lot of nuance, even there. Insoluble fiber, found in whole grains, nuts and seeds, fruits (especially the skins) and leafy greens veggies doesn’t dissolve in water, and it helps aid in GI transit. Soluble fiber turns to a gel when we consume it and high in nuts, beans, fruits and chia seeds. It’s believed to help us feel full, in part by slowing digestion. As you can see, there’s considerable overlap in food sources, and a key consideration across the board here is that these foods are plant-based and mostly minimally processed whole foods.
Beyond these basics, some fibers are called “fermentable,” which means then can be digested by the microbes living in your gut. Many studies now additionally call attention to specific “functional” fibers like beta-glucans (which come from oats, barley, mushrooms and even algae) and resistant starch, which is high in unripe bananas and cooled rice. While there’s lots of interesting studies looking at various forms of fiber to consume, many expert sources like Harvard and the Mayo Clinic echo the same idea: focus on eating more fiber rich foods rather than hyper-focusing on nailing the specific forms of fiber.
Adding too much fiber into our diets, and especially if we do so quickly, is linked to increased bloating and other GI discomfort. This may be even more the case when we up our intake of fermentable fiber. Experts recommend increasing fiber intake by a few grams a day with adequate water, along with monitoring for tolerance. Additionally, those with preexisting GI issues or those undergoing or recently undergoing GI procedures may have more risk from increasing fiber intake.
What about all-meat or low FODMAP diets?
Fiber isn’t an “essential nutrient” in that don’t absolutely need it for survival, and there’s no defined “deficiency” state. That’s led many to challenge the idea that we need it at all.
For some individuals, particularly those with significant food sensitivities, elimination diets like carnivore can provide genuine short-term relief. Removing certain plant foods can meaningfully reduce bloating and GI distress for certain people with IBS — and that relief is real. It's also true that our understanding of the microbiome is still evolving, and not every aspect of it is settled science.
With this said, the data are increasingly clear that eating more fiber for most people is a good bet for better overall health. This is where it’s helpful to speak to a qualified nutrition and health professional (like your doctor or dietician) to better understand your body and needs.
Some general ideas on how to incorporate more fiber into your day:
1. Start your day with a fiber
Most people miss a huge opportunity at breakfast. Build in a higher fiber option with chia pudding, nuts, seeds, some greens or beans with your eggs, fruits or a fiber-rich smoothie
2. Add extra fiber on your favorite meals
Layer fiber onto your food with some ground flax seed on your yogurt, beans or lentils on your salad, or some extra veggies with your dinner.
3. Opt for plants with every meal
Distributing a bit of fiber into every meal can help you reach your fiber goals without being too concerned about any one opportunity. Think black beans with your morning eggs, seeded bread with your sandwich, and almonds with your dark chocolate for dessert.
Below is a list of some high fiber foods and the amount of fiber per serving
Vegetables
Broccoli (cooked) — 1 cup → ~5 g
Brussels sprouts (cooked) — 1 cup → ~6 g
Carrots (raw) — 1 medium → ~2 g
Sweet potato (with skin) — 1 medium → ~4 g
Spinach (cooked) — 1 cup → ~4 g
Fruits
Apple (with skin) — 1 medium → ~4 g
Banana — 1 medium → ~3 g
Raspberries — 1 cup → ~8 g
Pear (with skin) — 1 medium → ~5–6 g
Avocado — ½ fruit → ~5 g
Whole Grains
Oats (cooked) — 1 cup → ~4 g
Quinoa (cooked) — 1 cup → ~5 g
Brown rice (cooked) — 1 cup → ~3.5 g
Whole wheat bread — 1 slice → ~2–3 g
Barley (cooked) — 1 cup → ~6 g
Legumes
Lentils (cooked) — 1 cup → ~15–16 g
Black beans (cooked) — 1 cup → ~15 g
Chickpeas (cooked) — 1 cup → ~12–13 g
Kidney beans (cooked) — 1 cup → ~13 g
Split peas (cooked) — 1 cup → ~16 g
Nuts & Seeds
Chia seeds — 2 tbsp → ~10 g
Flaxseeds (ground) — 2 tbsp → ~4 g
Almonds — 1 oz (~23 nuts) → ~3.5 g
Pumpkin seeds — 1 oz → ~1–2 g
Hemp seeds — 2 tbsp → ~1–2 g
This content is for informational and educational purposes only and does not constitute medical advice. Please consult with a qualified healthcare provider before making significant changes to your diet or lifestyle.
