Are Carbohydrates Essential?
The Gut Microbiome Says Yes
Carbohydrates are not essential for survival. The complex, fiber-rich carbohydrates in whole plant foods are essential for a healthy gut and a well-regulated immune system, and they are the pattern most consistently tied to lower long-term risk.
A viewer left a thoughtful comment on an older video, Nutrient Density Explained and What You Should Know (February 2018). He wrote that he is in the camp that believes carbohydrates are not essential, since the body can make the glucose it needs from protein. He asked to be corrected if he was wrong.
He is partly right. The answer depends on what we mean by “essential,” and on a group of organisms the textbook definition leaves out: the trillions of microbes living in our gut. This article walks through what the research actually says.
Where the skeptics are right
In the strict nutritional sense, no digestible carbohydrate is essential. An essential nutrient is one you must eat because your body cannot make it, like vitamin C or certain amino acids. Glucose does not meet that definition.
The Institute of Medicine, in the same report that set the official carbohydrate recommendation, states that the lower limit of dietary carbohydrate compatible with life is apparently zero, as long as enough protein and fat are eaten (1). The body makes glucose through gluconeogenesis, using amino acids, glycerol from fat, and lactate. The brain can also run on ketones for much of its fuel.
The Recommended Dietary Allowance of 130 grams per day is not a survival threshold. It is based on the glucose the brain typically uses (2). The report itself acknowledges that long-term data to define the ideal minimum simply do not exist.
So far, the skeptics have a point. The trouble is that this definition only counts what human cells need.
Not all carbohydrates are alike
Lumping a donut and a bowl of lentils together as “carbs” hides the most important distinction: who digests them. Our own genome encodes only a small number of enzymes for breaking down complex plant carbohydrates. Our gut microbes encode thousands (3). We have, in effect, outsourced most of that work.
| Type | Examples | Digested by | Why it matters |
|---|---|---|---|
| Sugars | Glucose, fructose, sucrose, lactose | You, in the small intestine | Intrinsic sugar in whole fruit behaves very differently from added sugar |
| Rapidly digestible starch | White flour, white rice, most packaged snacks | You | Absorbed high in the gut; little reaches your microbes |
| Slowly digestible starch | Intact whole grains, legumes | Mostly you | Structure slows absorption and blunts blood sugar spikes |
| Resistant starch | Cooked-and-cooled potatoes, rice, beans; green bananas | Gut microbes | Escapes digestion and is a major source of butyrate |
| Oligosaccharides (prebiotics) | Inulin in onions, garlic, leeks; oligosaccharides in legumes | Gut microbes | Selectively feed beneficial bacteria |
| Soluble fiber | Pectin (apples, berries), beta-glucan (oats, barley) | Gut microbes | Fermented into short-chain fatty acids; beta-glucan lowers LDL |
| Insoluble fiber | Cellulose, hemicellulose (whole grains, vegetable skins) | Largely undigested | Adds bulk and keeps things moving |
The last four rows are what this article means by complex, non-digestible carbohydrates. They are the part of the carbohydrate family the “not essential” argument overlooks.
Your microbes eat what you can't
When fiber and resistant starch reach the colon intact, gut bacteria ferment them into short-chain fatty acids: acetate, propionate, and butyrate. Researchers call these fermentable carbohydrates “microbiota-accessible carbohydrates,” and they are the primary source of carbon and energy for the microbes in our lower gut (4).
These short-chain fatty acids are far more than waste products. Butyrate is the main fuel for the cells lining the colon (7). Blood levels of butyrate stay low; most of it is used right there in the gut wall. The fatty acids also act as signaling molecules through dedicated receptors and influence gene expression (6). Claims about whole-body effects should stay modest and tied to those two jobs: feeding the colon lining, and sending signals.
Dr. Michael Greger of NutritionFacts.org — who advocates a plant-based diet, as we do here — frames this as a symbiosis: we evolved to depend on these microbes for fiber digestion, short-chain fatty acid production, and even some vitamins. He contrasts an estimated ancestral intake of up to about 100 grams of fiber a day with the roughly 16 grams typical today (8).
What happens when fiber disappears
Two landmark studies show what is at stake:
• The mucus barrier erodes. In a 2016 Cell study, mice deprived of fiber saw their gut bacteria switch to eating the protective mucus layer lining the colon. The thinner barrier left them far more vulnerable to a gut pathogen, which caused lethal colitis (5).
• Microbes go extinct across generations. In a 2016 Nature study, mice carrying a human gut microbiota were fed a low-fiber diet over several generations. Diversity declined progressively, and much of it did not come back when fiber was restored (4). The authors concluded that diet alone may not be enough to restore a depleted microbiome.
Diet also changes what gets fermented. In a human feeding study, an animal-based diet sharply lowered the microbes that break down plant polysaccharides and shifted activity toward protein and bile metabolism (19).
Beyond the gut: immunity, inflammation, and the brain
The effects of fiber fermentation reach well past the colon.
• Immune regulation. Short-chain fatty acids are absorbed into the bloodstream and bind receptors on immune cells, generally producing an anti-inflammatory effect (8). Dr. Rhonda Patrick of FoundMyFitness has discussed research showing these fiber-derived signals help regulate the production of regulatory T cells, which keep the immune system from overreacting (11).
• Inflammation from endotoxin. Patrick also highlights that an intact mucus layer helps limit the leakage of bacterial endotoxin, a major driver of chronic inflammation (11). This is the human side of the mucus-erosion findings above.
• Metabolism. Research describes direct effects of short-chain fatty acids on tissues throughout the body, not just the gut lining (6). Greger cites a study in which three days of whole barley kernels improved participants’ insulin levels by 25 percent (10).
• The brain. A 12-week randomized trial in adults aged 50 to 80 found that a Bifidobacterium probiotic taken with inulin, a prebiotic fiber, improved overall cognitive scores and lowered several inflammatory markers (12). That is one trial, not a prescription, but it fits the larger pattern: feed the microbes, and some of the signal reaches the rest of the body.
Short-chain fatty acids can also be produced by bacteria on the skin and in other body sites, though the gut is by far the dominant source and the one most directly shaped by diet (13).
Fiber alone isn't the whole story
A 2021 Stanford trial, one Rhonda Patrick returns to often, adds an important twist (14). Healthy adults were assigned for 10 weeks to either a high-fiber diet or a diet high in fermented foods such as yogurt, kefir, kimchi, fermented vegetables, and kombucha.
• The fermented-food group saw gut diversity rise, with larger servings producing larger effects, and a drop in inflammatory markers (15).
• The high-fiber group did not see diversity rise over those 10 weeks, which surprised the researchers. Their stool contained more undigested carbohydrate, suggesting their microbes could not fully break down the extra fiber (15). That is not evidence that fiber failed. It is evidence that 10 weeks may be too short, or that the microbes needed to use that fiber were already missing.
The investigators suggested two explanations: the microbiome may need longer than 10 weeks to adapt, or fiber-consuming microbes may need to be deliberately reintroduced. That fits the 2016 extinction study. Many modern Western guts may have lost the very microbes that make use of fiber.
The practical lesson is not to skip fiber. It is to increase fiber gradually and pair it with fermented foods that help restock the gut.
What the human outcome studies show
The largest human studies point the same direction: more fiber and whole-food carbohydrates, less risk.
| Study | What it looked at | Key finding |
|---|---|---|
| Reynolds et al., The Lancet, 2019 | 185 prospective studies and 58 clinical trials on carbohydrate quality | Higher fiber intake linked to 15–30% lower all-cause and cardiovascular mortality, plus less heart disease, stroke, type 2 diabetes, and colorectal cancer. Greatest benefit at 25–29 g/day, with more likely better above 30 g. |
| Aune et al., BMJ, 2011 | Meta-analysis of 25 prospective studies | Each additional 10 g of daily fiber linked to about 10% lower colorectal cancer risk, most consistently for cereal fiber and whole grains. |
| Seidelmann et al., Lancet Public Health, 2018 | 15,428 US adults followed for 25 years, plus a meta-analysis of 432,179 people | Lowest mortality at 50–55% of calories from carbohydrate. Low-carb diets built on animal fat and protein were linked to higher mortality (HR 1.18); low-carb diets built on plant fat and protein, to lower mortality (HR 0.82). |
The Seidelmann finding is especially relevant to the “carbs aren’t essential” debate. What replaces the carbohydrate matters as much as the carbohydrate itself (20).
Even researchers who favor low-carbohydrate eating treat fiber as non-negotiable. FoundMyFitness has featured ketogenic researcher Dr. Dominic D’Agostino on including fiber within a well-formulated ketogenic diet (21).
Honest caveats
Good science means acknowledging what the evidence can and cannot say.
• Mouse studies are not people. The mucus-erosion and multigenerational extinction findings come from mice carrying human-derived microbes. They are compelling mechanisms, not direct human proof.
• Observational studies have limits. People who eat more fiber tend to differ from those who don’t in many ways. Researchers adjust for this, but confounding can never be fully ruled out.
• Not every fiber study is positive. Patrick has reported a trial in which a low-gluten, high-fiber diet changed microbiome composition and reduced bloating but did not change blood glucose, lipids, or inflammation markers compared with a fiber-matched high-gluten diet (22).
• Low-carb diets have real short-term benefits for some people, including improvements in risk factors tied to insulin resistance (23). The open question is what they do over decades, and which foods fill the gap.
• Advocates have perspectives. Dr. Greger advocates a plant-based diet; Dr. Patrick limits whole grains in her own diet. Both summarize research well, but the primary studies cited here are the stronger evidence.
Where we land
For full disclosure, we eat a whole food plant-based diet here at Mindful Living Sanctuary. I don’t for a second think everyone needs to eat that way.
But I do believe complex, non-digestible carbohydrates are essential. Not essential for survival, but essential for quality of life and longevity. Our gut microbes depend on them, and we depend on our gut microbes.
Just as important is what we avoid. Minimizing ultra-processed foods, and the preservatives, additives, emulsifiers, and artificial ingredients that fill so much of our food supply, matters a great deal, especially here in the United States. Packaged foods with fiber added back in are not a substitute: the Stanford researchers Justin and Erica Sonnenburg have stressed that a resilient gut needs a wide variety of fibers from real plants (24).
On this farm that is not an abstract list. Beans, onions, garlic, oats, apples, berries, and cooled leftover potatoes and rice are already in the kitchen and in the garden. Those are the same plants that feed soil life when they go back on the ground as residue or compost. The principle is the same above the plate and below it: diversity of living plants, not a powder stirred into a processed bar.
Practical steps
1. Eat whole, minimally processed foods. This is the goal that matters most.
2. Aim for 30 grams of fiber a day or more, from beans, lentils, intact whole grains, vegetables, fruit, nuts, and seeds.
3. Increase fiber gradually. If you have been eating very little, add one extra serving of beans or one piece of fruit with the skin for a week before you add the next. Give the microbes time to catch up. People who get gas from raw salads and raw alliums often do better starting with cooked vegetables and cooked-and-cooled starches.
4. Add fermented foods such as sauerkraut, kimchi, or other fermented vegetables to help restock your gut.
5. Eat for variety. Different plants feed different microbes; onions, garlic, oats, barley, berries, apples, and legumes each bring something distinct.
6. Cook and cool some starches. Cooled potatoes, rice, and beans provide resistant starch, a favorite food of butyrate-producing bacteria (9).
Thank you to our viewer for a great question. Keep them coming.
Further reading
Primary sources and reviews
Institute of Medicine dietary reference intakes and the 130 g carbohydrate RDA discussion: lcreview.org/main/130g-carbsday-rda/ and Slavin & Carlson, Advances in Nutrition, 2014, pmc.ncbi.nlm.nih.gov/articles/PMC4224210/
CAZyme review (human genome vs. microbial enzymes): El Kaoutari et al., Nature Reviews Microbiology, 2013, nature.com/articles/nrmicro3050
Microbiota-accessible carbohydrates and multi-generation fiber loss: Sonnenburg et al., Nature, 2016, nature.com/articles/nature16504
Fiber deprivation and mucus-barrier erosion: Desai et al., Cell, 2016, doi:10.1016/j.cell.2016.10.043
Short-term animal- vs. plant-based diet and the human microbiome: David et al., Nature, 2014, nature.com/articles/nature12820
Stanford fiber vs. fermented-food trial: Wastyk et al., Cell, 2021, doi:10.1016/j.cell.2021.06.019
Carbohydrate quality and mortality: Reynolds et al., The Lancet, 2019, thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext
Carbohydrate intake and mortality, plant vs. animal replacement: Seidelmann et al., Lancet Public Health, 2018, doi:10.1016/S2468-2667(18)30135-X
On this site and channel
Nutrient Density Explained and What You Should Know (video, February 2018): youtube.com/watch?v=9Y2a90CoGU4
Soil Succession: From Barren Soil to a Thriving Forest Ecosystem — mindfullivingsanctuary.com/articles/soil-succession-from-barren-soil-to-a-thriving-forest-ecosystem
Weeding and Gardening — mindfullivingsanctuary.com/articles/weeding-and-gardening
References
1. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press, 2002/2005. Quoted in: 130g Carbs/day RDA, Low Carb Review. http://lcreview.org/main/130g-carbsday-rda/
2. Slavin J, Carlson J. Carbohydrates. Advances in Nutrition. 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC4224210/
3. El Kaoutari A, Armougom F, Gordon JI, Raoult D, Henrissat B. The abundance and variety of carbohydrate-active enzymes in the human gut microbiota. Nat Rev Microbiol. 2013;11:497–504. https://www.nature.com/articles/nrmicro3050
4. Sonnenburg ED, Smits SA, Tikhonov M, et al. Diet-induced extinctions in the gut microbiota compound over generations. Nature. 2016;529:212–215. https://www.nature.com/articles/nature16504
5. Desai MS, Seekatz AM, Koropatkin NM, et al. A dietary fiber-deprived gut microbiota degrades the colonic mucus barrier and enhances pathogen susceptibility. Cell. 2016;167(5):1339–1353. doi:10.1016/j.cell.2016.10.043
6. Kimura I, et al. Dietary gut microbial metabolites, short-chain fatty acids, and host metabolic regulation. Nutrients. 2015. https://pmc.ncbi.nlm.nih.gov/articles/PMC4425176/
7. Roles of short-chain fatty acids in inflammatory bowel disease. Nutrients. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10609902/
8. Greger M. How to Keep Your Microbiome Healthy with Prebiotic Foods. NutritionFacts.org, 2022. https://nutritionfacts.org/video/how-to-keep-your-microbiome-healthy-with-prebiotic-foods/
9. NutritionFacts.org. Short-Chain Fatty Acids (topic page). https://nutritionfacts.org/topics/short-chain-fatty-acids/
10. Greger M. How to Cultivate a Healthy Gut Microbiome with Food. NutritionFacts.org. https://nutritionfacts.org/video/how-to-cultivate-a-healthy-gut-microbiome-with-food/
11. Patrick R. Gut health’s important role in regulating inflammation (with Peter Attia). FoundMyFitness. https://www.foundmyfitness.com/episodes/gut-health-regulating-inflammation
12. Azuma N, Mawatari T, Saito Y, Tsukamoto M, Sampei M, Iwama Y. Effect of continuous ingestion of bifidobacteria and dietary fiber on improvement in cognitive function: a randomized, double-blind, placebo-controlled trial. Nutrients. 2023;15(19):4175. https://pmc.ncbi.nlm.nih.gov/articles/PMC10574581/
13. Health benefits and side effects of short-chain fatty acids. Foods. 2022;11(18):2863. https://pmc.ncbi.nlm.nih.gov/articles/PMC9498509/
14. Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137–4153. doi:10.1016/j.cell.2021.06.019
15. Fermented-food diet increases microbiome diversity, decreases inflammatory proteins. Stanford Medicine / ScienceDaily, July 2021. https://www.sciencedaily.com/releases/2021/07/210712122151.htm
16. Reynolds A, Mann J, Cummings J, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet. 2019;393(10170):434–445. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext
17. Aune D, et al. Dietary fibre, whole grains, and risk of colorectal cancer. BMJ. 2011. Discussed in: Patrick R. How Dietary Fiber Supports Gut and Colon Health. https://www.foundmyfitness.com/episodes/how-dietary-fiber-supports-gut-and-colon-health
18. Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 2018;3(9):e419–e428.
19. David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505:559–563. https://www.nature.com/articles/nature12820
20. Plant or animal food replacements in lower carbohydrate diet influence mortality risk. Diabetes on the Net. https://diabetesonthenet.com/diabetes-news/plant-or-animal-food-replacements-in-lower-carbohydrate-diet-influence-mortality-risk/
21. FoundMyFitness. Fiber tag page (including fiber as part of a well-formulated ketogenic diet, with Dominic D’Agostino). https://www.foundmyfitness.com/tags/fiber
22. Patrick R. Post on low-gluten, high-fiber diet trial. FoundMyFitness on X. https://x.com/foundmyfitness/status/1063825791220215808
23. Carbohydrates. Advances in Nutrition. 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11555338/
24. Found My Fitness Podcast: The Sonnenburgs on How the Gut Microbiota Interacts With Our Bodies. Podcast Notes. https://podcastnotes.org/found-my-fitness/found-my-fitness-podcast-the-sonnenburgs-on-how-the-gut-microbiota-interacts-with-our-bodies/
