With all the competing commercial interests clamoring for our eyeballs and wallets - especially in the food arena - it's no wonder Americans are confused about what's healthy to eat and what's not. We obsess about eating enough protein, for instance, yet tragically, our OVERconsumption of animal protein significantly raises our risk of dying from all causes and specifically from heart disease, our #1 killer (1).
We DO face one serious nutritional deficiency, however, not from protein but from FIBER, for which 97% of Americans don't meet even HALF the minimum daily requirement (at 32/g) (2). Since the only source of dietary fiber is plants, our fiber deficiency exists because we eat such paltry amounts of vegetables, fruits, whole grains, legumes and mushrooms.
So why's fiber so important? That fiber facilitates digestion & elimination is not new news. We've known that eating fiber provides satiety, helping us lose weight. But fiber's role in human health is far more pervasive than we once thought. And it all has to do with our recent ability to analyze the human microbiome, which requires ample quantities of fiber to sustain healthy and diverse microbial colonies (3).
The microbiome is a diverse ecosystem of 100 trillion bacterial, viral and fungal microbes, mostly residing in the gut, that coevolved with early homo sapiens and became inextricably involved with the functioning of many of our human metabolic processes.
Though more research needs to occur to understand the mechanisms at work, we are beginning to learn how pivotal gut bacteria are to human health and disease. A few examples:
Gut bacteria develop and train our immune system, determining how ably we can fight infections, avoid asthma and allergies, and stave off cancer (4).
Pathogenic bacteria can activate systemic inflammation, raising our risks for metabolic disorders like obesity, diabetes and atherosclerosis. If beneficial bacteria dominate, they protect us from these inflammatory disorders (5).
Gut bacteria appears to be linked to the onset of neurological disorders like Alzheimers Disease (6), and solving this puzzle may provide new treatment options to prevent this devastating disease.
Gut bacteria manufacture neurotransmitters that travel from gut to brain, directly influencing mood and behavior and holding promise for new ways to treat depression, anxiety, OCD, schizophrenia, & autism. (7,8)
Choosing your Friends
The diversity and quantities of bacteria we harbor may have a profound impact on health. And what foods we eat determine whether bacteria that hold sway are more protective or destructive. Beneficial bacteria thrive on FIBER and RESISTANT STARCHES, found only in plants. They produce short-chain fatty acids (SCFAs) which promote health in remarkable ways: They lower systemic inflammation and oxidative stress. They optimize our immune defenses, protecting us from cancer. They sustain the delicate epithelial cell lining in the small intestine to prevent dysbiosis which can trigger a plethora of autoimmune diseases (9).
On the other hand, when our diets are deficient in fiber and centered on animal proteins, populations of bacteria that digest sulfur-rich animal amino acids increase. While most protein is digested in the small intestine, a small amount can reach the colon where it putrefies. There the bacteria that thrive on sulfur produce hydrogen sulfide (the rotten egg smelling gas) which has several deleterious health effects: It inflames the delicate epithelial intestinal cell lining, making us vulnerable to ulcerative colitis and Crohn's Disease (10); it's toxic to DNA, raising the risking of colon cancer (11); it promotes atherosclerosis (12).
In addition, when we eat animal protein we increase the prevalence of gut bacteria that metabolize carnitine and choline found in meat, dairy, eggs, poultry, fish and seafood into toxic TMAO, which builds up cholesterol in the inflammatory cells of atherosclerotic plaques in our arteries (13,14).
Tending Our Microbial Gardens Before Its Too Late
As if our looming epidemics of obesity, diabetes and heart disease weren't enough, we face an even greater societal risk -- the depletion of the human microbiome (15).
The commercial extraction of fiber from manufactured processed foods in the post-war era, the explosion of packaged and fast food industries globally, medical practices like Caesarean section and the overuse of antibiotics, the widespread use of baby formula over breastfeeding, the abuse of antibiotics in livestock, and proliferation of bacteria-free cleansers have all had a worrying effect on human gut microbial health.
Studies reveal a serious decline in gut microbial species' population density, diversity and resilience among individuals eating a "Western" diet (16). The precipitous rise of chronic diseases has been the consequence.
The growing popularity of high-fat, meaty, refined and processed Western foods among industrializing countries worldwide puts traditional, fiber-rich, plant-based culinary traditions at risk, and may ultimately threaten the collective human microbiome. Our scientists might be wise to consider a global microbial "bank" not just to study but to preserve microbial species biodiversity.
A ray of hope: Bacterial density in the gut can be remedied by shifting one's diet strongly towards whole unrefined plant foods; fortunately, bacterial colonies that still exist in the gut revive quite rapidly (17).
However, if individual bacterial species have died out, they cannot easily be revived.
There is already a race on to identify bacteria to develop more effective strains of probiotics to reintroduce beneficial bacteria in order to treat specific disorders. Fecal transplants from healthier hosts to patients are already in use and show promise.
These modalities succeed if the patient also adopts an unrefined plant-based diet that supports the health of these newly introduced microbes. Otherwise, he jeopardizes their survival and must rely on continual interventions.
This is a race against time, individually and collectively, as we try to protect the human microbiome biodiversity and stem the tide of chronic diseases worldwide ~ so costly financially and in terms of human suffering.
The cheapest, simplest, and most effective course of action, of course, is to put processed foods and inflammatory animal products aside and begin to eat a great deal more prebiotic plant-based foods -- but at triple the recommended levels. We may need closer to 70-100g of fiber/day as our forebears did and as some populations still eating traditional plant-based diets consume. These are the levels that best support and sustain the health of those salutary bacteria that have served us for millenia so very well indeed.
Huller MA, et al. Gut microbes, diet, and cancer. Cancer Treat Res. 2014;159:377-99.
Christiakov DA, et al. Role of gut microbiota in the modulation of atherosclerosis-associated immune response. Front microbiol. v6;2015.
Hill JM, et al. The gastrointestinal tract microbiome and potential link to Alzheimer’s disease. Front. Neurol., 04 April 2014.
Dash S et al. The gut microbiome and diet in psychiatry: focus on depression. Curr opin psychiatry. 2015 Jan;28(1):1-6.
Campbell AW. Autoimmunity and the Gut. Autoimmune dis. 2014 May 13.
Pitcher MC, Cummings JH. Hydrogen sulphide: a bacterial toxin ulcerative colitis? Gut. Vol39(1). 1996 Jul.
Cai WJ, et al. Hydrogen sulfide induces human colon cancer cell proliferation: role of Akt, ERK and p21. Cell Biol Int. 2010 Apr 14;34(6):565-72
Lynn EG, Austin RC. Hydrogen sulfide in the pathogenesis of atherosclerosis and its therapeutic potential. Expert Rev Clin Pharmacol. 2011 Jan; 4(1):97-108.
Wang Z. et al. Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature 2011 472(7341):57 - 63
Koeth RA, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013 May; 19(5): 576–585.
Deehan EC, Walter J. The fiber gap and the disappearing microbiome: implications for human nutrition. Trends in Endocr & Metabol. May 2016. v27, n5.
Segata N. Gut microbiome: westernization and the disappearance of intestinal diversity. Curr Biol. v25, i14, pR611–R613, 20 July 2015.
David LA, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–563 (23 January 2014).