What Is Healthspan?

Healthspan describes the period of life spent in good health, free from the chronic diseases and disabilities of aging. It focuses on the period of good health and functionality in which individuals remain healthy, active, independent, and productive both mentally and physically. Ultimately, the goal of improving healthspan is remaining healthier for longer, ideally delaying the onset of chronic disease. (Masfiah 2025)

Why the Gut Barrier and Immune Resilience Matters

A healthy gut barrier is essential for maintaining immune balance and reducing the risk of chronic disease because it serves as a critical interface between the external environment and the internal immune system. The intestinal barrier is composed of the microbiota, mucus layer, epithelial cells with tight junctions, and immune components that collectively regulate the selective passage of nutrients while preventing pathogens, toxins, and microbial products from entering systemic circulation. When this barrier becomes compromised, microbial components such as lipopolysaccharide can translocate into the bloodstream, triggering systemic immune activation and contributing to chronic low-grade inflammation. This persistent inflammatory signaling has been linked to the pathogenesis of numerous chronic diseases, including metabolic disorders, liver disease, autoimmune conditions, and cardiovascular disease. (Di Vincenzo 2024) 

Since immune function and inflammation are central drivers of aging-related diseases, maintaining gut barrier integrity and immune resiliency plays a key role in extending healthspan. Healthspan refers to the portion of life spent free from chronic disease and functional decline, and preventing chronic systemic inflammation is a major determinant of achieving this goal. By preserving barrier integrity and regulating immune responses, the gut helps maintain metabolic and immune homeostasis, reducing the risk of inflammation-driven diseases that commonly emerge with aging. Therefore, strategies that support gut barrier function and immune resilience may help delay the onset of chronic disease and support longer periods of healthy, functional living. (Martel 2022) 

Purpose of the Clinical Guide

The Gut Barrier and Immune Resilience clinical guide was designed to:

1. Simplify decision-making using standardized, evidence-rated nutrient and lifestyle interventions.
2. Integrate laboratory and biomarker data to identify modifiable contributors to gastrointestinal and immune health.
3. Serve as the foundation for individualized care plans aimed at supporting gastrointestinal and immune health through the lifespan.

Essential Labs

Ranges for the following markers will vary based on laboratory. 

Fecal Calprotectin 

Fecal calprotectin is the most extensively validated and widely used fecal biomarker for gastrointestinal (GI) inflammation. It is a calcium- and zinc-binding protein found in neutrophils. Calprotectin in stool is a consequence of neutrophil migration due to inflammation in the GI tract. It is a sensitive marker for distinguishing inflammatory bowel disease (IBD) from functional GI diseases. A 2019 systematic review and meta-analysis of 18 trials found that fecal calprotectin has an 88% (95% CI, 80–93%) sensitivity and 72% (95% CI, 59–82%) specificity for distinguishing organic gastrointestinal diseases, including IBD, from functional GI disorders. (An 2019)(Pathirana 2018)

Fecal Secretory Immunoglobulin A (SIgA)

Secretory IgA is one form of IgA produced by plasma cells in mucosal tissues of the GI, genitourinary, and respiratory tracts as well as in saliva, tears, and breast milk. Its secretory component allows it to remain stable in harsh environments. As the primary antibody protecting mucosal surfaces, it is abundant in the mucosal layer of the GI tract, preventing pathogens and toxins from binding to epithelial cell receptors. This marker is considered a direct assessment of gastrointestinal mucosal immune function and indicates active intestinal inflammation when elevated. Fecal sIgA correlates with disease activity in both Crohn’s disease (CD) and ulcerative colitis (UC). Newer research demonstrates that it shapes the microbiome through subclass-specific coating patterns and metabolite-mediated bidirectional communication. It should be noted that fecal sIgA is influenced by many factors and should not be interpreted in isolation as a marker of inflammation. (León 2022)(Lin 2018)(Vaquero 2024)

Low sIgA is associated with: 

• Chronic GI dysbiosis
• Chronic stress
• Immunocompromised state
• Protein malnutrition
• Systemic IgA deficiency
• Chronic illness – celiac disease, IBD

High sIgA is associated with: 

• Chronic gastrointestinal dysbiosis
• Acute infection
• Acute stress
• Food sensitivities
• Intestinal permeability
• GI inflammation – irritable bowel syndrome (IBS), IBD (Pietrzak 2020)(Campos-Rodríguez 2013)

Microbiome Diversity

Microbiome diversity is often reported as alpha diversity, specifically Shannon’s Index (the richness of the bacterial community) and Simpson’s Index (the evenness). While increased microbial diversity has been shown to correlate with less systemic inflammation, cardiovascular risk, and mortality risk, alpha diversity alone is not a consistent marker of disease. Not all diseases are associated with reduced diversity. A 2018 observational study of >600 women found that higher microbiome diversity (as measured by the Shannon and Simpson indices) was significantly associated with lower arterial stiffness (as measured by pulse wave velocity). A 2026 prospective cohort study of >2,000 adults with hypertension found that individuals with higher oral microbiome diversity had significantly lower mortality risk (Simpson Diversity – HR 0.38, 95% CI 0.20–0.75, p<0.01; Shannon Diversity – HR 0.47, 95% CI 0.25–0.88, p<0.05). A 2025 observational study of 112 subjects hospitalized with severe COVID concluded that lower gut diversity was associated with more severe disease. The Shannon Diversity Index was significantly reduced in critically ill patients compared to those with mild disease (p<0.05). (Gupta 2020)(Menni 2018)(Zhou 2026)(Scalzo 2025)

Microbiome Testing 

The human gut microbiota is composed of approximately 1,000 bacterial species, the majority of which belong to six major phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, Fusobacteria, and Verrucomicrobia. Among these, Firmicutes and Bacteroidetes together account for roughly 90% of the total bacterial population. These phyla play critical roles in maintaining intestinal barrier function, supporting immune system development, producing short-chain fatty acids (SCFAs), and metabolizing dietary compounds. Disruptions in the balance of these microbial communities have been linked to conditions such as IBD, metabolic disorders, and immune dysregulation. (Patloka 2024)(Sędzikowska 2021)

Pancreatic Elastase 1

This is a proteolytic enzyme secreted by the pancreas that serves as a key biomarker for exocrine pancreatic function. It is a reliable stool marker because it remains stable throughout the GI tract. It reflects endogenous pancreatic function and is not affected by enzyme replacement. Severe exocrine pancreatic insufficiency (EPI) is diagnosed by pancreatic elastase 1 <100mcg/g and can be directly caused by chronic pancreatitis, cystic fibrosis, pancreatic cancer, autoimmune pancreatitis, and gallstones. Other conditions associated with EPI include celiac disease, IBD, diabetes, small intestinal bacterial overgrowth (SIBO), Zollinger-Ellison syndrome, excessive alcohol consumption, obesity, and smoking. 

SCFAs

SCFAs are organic acids with carbon chains less than six carbons. They regulate the mucosal layer of the GI tract, prevent intestinal permeability, contribute to mucus secretions, promote the production of antimicrobial factors, and influence absorption of water, electrolytes, and nutrients in the colon. They foster an anaerobic, acidic environment to inhibit the growth of pathogenic bacteria and yeast and encourage a balanced immune response through anti-inflammatory and antimicrobial mechanisms. Acetate, propionate, and butyrate make up 95% of the total SCFA level in the GI tract, with acetate being the most abundant (60%). A more diverse diet positively influences SCFA levels. (Fusco 2023)

Reference ranges for SCFA levels will vary based on laboratory. Generally, elevated SCFA levels are associated with SIBO, while low SCFA levels are associated with the following:

• Diarrhea 
• Constipation
• Chronic antibiotic use 
• Lower fiber intake
• Dysbiosis 
• Chronic diseases such as type 2 diabetes, obesity, chronic kidney disease, hypertension, IBD, colorectal cancer, metabolic dysfunction-associated steatotic liver disease (MASLD, previously called non-alcoholic fatty liver disease, or NAFLD), respiratory diseases, neurological disorders 

(McOrist 2008)(Reichardt 2018)

Ingredients

Probiotics 

Dosing: 

• Lactobacillus plantarum: A minimum of 1 billion CFU daily for 4–8 weeks
• Lactobacillus rhamnosus GG: 6 billion CFU daily for 8 weeks
• Bifidobacterium longum 35624: 1 × 10⁸ CFU daily for 4 weeks 

Supporting evidence: 

• A 2019 randomized controlled trial (RCT) of 21 HIV-infected children 2–18 years who took Lactobacillus plantarum IS-10506 2.86 × 1010 CFU/day for 6 days showed a significant reduction in blood lipopolysaccharide (LPS) (p=0.001). (Athiyyah 2019) 
• In a 2012 RCT of >200 patients with IBS, 10¹⁰ CFU Lactobacillus plantarum 299v daily for 4 weeks significantly reduced pain severity in the study population (0.68 + 0.53 vs. 0.92 + 0.57, P < 0.05) and daily pain frequency (1.01 + 0.77 vs. 1.71 + 0.93, P < 0.05) compared to placebo. (Ducrotté 2012)
• In a 2023 RCT of 307 adult 18–70 years with diarrhea-predominant IBS (IBS-D), the change in IBS-severity scoring system total significantly decreased in participants receiving both L. plantarum Lpla33 at 1 × 109 (-128.45 ± 83.30; P < 0.001) and 1 × 1010 (-156.77 ± 99.06; P < 0.001) for 8 weeks compared to placebo. (Martoni 2023) 
• In a 2026 systematic review with meta-analysis, Lactobacillus rhamnosus GG significantly reduced severity of abdominal pain in patients with IBS compared to placebo. Benefits were most consistent with doses around 6×109 CFU/day. Higher doses of 20–40 billion CFU/day did not consistently show improvements. Positive effects were mainly observed with at least 8 weeks of supplementation compared with 4–6 weeks. (Maslennikov 2026)
• In a 2024 systematic review of Bifidobacterium longum 35624 in patients with IBS, 1 × 10⁸ CFU/day significantly reduced abdominal pain at 4 weeks in the study population, while 10⁶ CFU/day and 10¹⁰ CFU/day were less consistently superior to placebo. (Andreev 2024) 
• Bifidobacterium and Lactobacillus strains have been consistently shown to improve markers of gut barrier function and systemic inflammation, including serum zonulin, LPS, c-reactive protein (CRP), tumor necrosis factor alpha (TNF-α), and interleukin 6 (IL-6). Specific strains demonstrate targeted benefits: Bifidobacterium lactis and Bifidobacterium breve enhance fecal sIgA levels and promote tight junction protein synthesis, while Bifidobacterium infantis reduces inflammatory cytokines and modulates T regulatory (Treg) cell activity. Among Lactobacillus strains, Lactobacillus plantarum has been shown to strengthen the mucosal barrier and reduce inflammatory cytokines at doses of 10–20 billion CFU. Lactobacillus rhamnosus GG (LGG) effectively decreases intestinal permeability, and Lactobacillus paracasei increases sIgA, reduces inflammatory cytokines, and enhances cellular immunity. Collectively, these strains support both local gut health and systemic immune regulation. (Zheng 2023)(Francavilla 2010)(Poon 2020)

Butyrate 

Dosing: 300–800 mg daily 

Supporting evidence:

• A 2025 multi-center, double-blind, randomized, placebo-controlled trial evaluated 98 adults with active mild to moderate UC. Participants received microencapsulated sodium butyrate at a dose of 300 mg twice daily for 8 weeks as an add-on therapy. The treatment group demonstrated significant clinical benefits, with 51% achieving clinical improvement defined as a ≥3-point reduction in Total Mayo Score compared to placebo (P = 0.005). Additionally, in the study population, 31.4% reached clinical remission (P = 0.004), and 42.2% achieved biochemical remission, defined as fecal calprotectin ≤250 µg/g (P = 0.009). Notably, there was a strong correlation between fecal butyric acid levels and clinical improvement, with correlation coefficients ranging from rho = 0.80–0.87. (Karłowicz 2025)
• A 2024 randomized, placebo-controlled trial evaluated 36 patients with active UC who received sodium butyrate at a dose of 600 mg per day for 12 weeks. The intervention resulted in significant reductions in fecal calprotectin and hs-CRP (both P < 0.001), along with marked improvements in quality of life (P < 0.001), highlighting its potential role in reducing inflammation and improving patient-reported outcomes in this population. (Firoozi 2024)
• An observational study in UC patients in remission demonstrated notable benefits of butyrate as an add-on therapy. Therapeutic success was achieved in 83% of patients in this study receiving butyrate in addition to standard care compared to 48% with mesalamine alone (P = 0.022). Even greater efficacy was observed with a combination approach, as 95% of patients in this study receiving butyrate alongside fructooligosaccharides (FOS) and probiotics achieved therapeutic success versus 57% with 5-aminosalicylic acid (5-ASA) alone (P = 0.009). Over a 12-month period, these interventions were also associated with a significant reduction in fecal calprotectin, suggesting sustained anti-inflammatory effects. (Vernero 2020)

Glutamine 

Dosing: 

• 30 g daily to reduce intestinal permeability (Abbasi 2024) 
• 5 g three times per day for post-infectious IBS-D (Zhu 2022)

Supporting evidence:

• In a 2024 systematic review and meta-analysis of 10 studies with 352 participants, the sub-group analysis showed a significant reduction in intestinal permeability with doses over 30g/day (WMD: −0.01, 95% CI −0.10, −0.08). (Abbasi 2024)

• In a small clinical trial with 10 healthy men, glutamine consumed 2 hours prior to exercise significantly reduced intestinal permeability in a dose-dependent way. The dose 0.9 g/kg fat-free mass saw the most benefit. For a 70-kg individual with approximately 60 kg of fat-free mass, the glutamine dose would be 54 grams. (Pugh 2017) These results were confirmed by a second similar study. (Zuhl 2014)

Fructooligosaccharides (FOS)

Dosing: 2.5–15 g daily 

Supporting evidence: 

• A 2022 systematic review and meta-analysis evaluated 8 RCTs involving over 300 participants to assess the effects of FOS on the gut microbiota. Across the included studies, FOS doses ranged from approximately 2.5 g–15 g per day, with intervention durations spanning 7–56 days. Overall, FOS supplementation significantly increased Bifidobacterium abundance. Subgroup analyses demonstrated that longer intervention durations greater than 4 weeks resulted in larger increases, while higher doses above 5 g per day produced the most pronounced effects. (Dou 2022) 
• A 2019 RCT evaluated 80 healthy adults aged 18–55 years who received daily FOS supplementation at doses of 2.5, 5, and 10 grams per day over a seven-month period. The study found that FOS significantly increased Bifidobacterium abundance at all doses. Lactobacillus levels also increased in a dose-dependent manner, with statistically significant changes observed at the 5 and 10 gram doses. Additionally, supplementation at 5 and 10 grams per day led to significant increases in butyrate-producing bacteria and improvements in alpha diversity, indicating enhanced overall gut microbial diversity at higher intake levels. (Tandon 2019)

Saccharomyces boulardii 

Dosing: 250–500 mg twice daily, 5–10 × 10⁹ CFU

Supporting evidence:

• A 2017 double-blind, randomized, placebo-controlled trial in 44 HIV-treated patients found that supplementation with Saccharomyces boulardii (6.5 mg living yeasts per capsule, 2 capsules three times daily) for 12 weeks resulted in a significant reduction in plasma lipopolysaccharide-binding protein (LBP) (p = 0.019) and serum IL-6 (p = 0.037), along with microbiome shifts including lower concentrations of Clostridiaceae. (Villar-García 2017) 
• A 2014 randomized, double-blind, placebo-controlled trial in 72 patients with IBS-D demonstrated that Saccharomyces boulardii at 750 mg per day for 6 weeks significantly reduced IL-8 and TNF-α, and improved mucosal immune markers, including reductions in lymphocyte and neutrophil infiltrates and intraepithelial lymphocytes. (Abbas 2014)
• A 2023 randomized, double-blind, placebo-controlled trial in 40 patients with multiple sclerosis showed that Saccharomyces boulardii at 50 mg daily (10¹⁰ CFU) for 4 months significantly reduced hs-CRP (p < 0.001), pain intensity (p = 0.004), and fatigue severity (p = 0.01), while significantly improving total antioxidant capacity (p = 0.004) and quality of life (p = 0.01). (Asghari 2023) 

Zinc Carnosine 

Dosing: 37.5 mg twice daily

Supporting evidence:

• In a 2006 randomized crossover trial of 10 healthy subjects, zinc carnosine at a dose of 37.5 mg twice daily combined with indomethacin 50 mg three times daily prevented increases in intestinal permeability, as measured by the lactulose:rhamnose ratio, whereas indomethacin alone increased permeability threefold. (Mahmood 2006) 
• In a separate 2016 double-blind, placebo-controlled crossover study of 8 subjects, zinc carnosine at the same dose of 37.5 mg twice daily reduced gut permeability by 70% over 14 days based on the lactulose:rhamnose ratio, although larger confirmatory trials are needed. (Davison 2016) 
• Mechanistically, zinc carnosine has been shown to increase occludin expression, upregulate heat shock proteins, and reduce apoptosis in heat-stressed intestinal cells. Clinically, it is also used as an anti-ulcer agent in Japan at a dose of 75 mg twice daily. (Matsukura 2000)

Lifestyle Recommendations

Nutrition

Risk Factors

Diet is a key modulator of the microbiome. Western dietary patterns high in ultra-processed products with sugar and fat and low in plant compounds increase the Firmicutes/Bacteroidetes (F/B) ratio. The western diet increases LPS and endotoxemia, while a Mediterranean diet rich in fiber and plants is associated with higher levels of Lactobacillus sp., Bifidobacterium sp., Prevotella sp., Akkermansia muciniphila, and Faecalibacterium prausnitzii, as well as less endotoxemia. (Ortega 2020) High-fat, high-protein, and low-fiber dietary patterns increase the F/B ratio. (Patloka 2024) 

Only 5% of Americans meet the dietary fiber guidelines. The mean intake is 17 grams/day, while recommendations range from 25–38 grams daily. (Dahl 2015) A 2025 umbrella review of 17 million people concluded higher fiber intake reduces cardiovascular disease mortality, diverticular disease, colorectal cancer, and all-cause mortality. (Veronese 2025) 

Interventions

Soluble Fermentable Fibers

The greatest risk reduction in all‑cause mortality, coronary heart disease, stroke, type 2 diabetes, and some cancers was seen when total dietary fiber intake increased up to about 25–29 grams/day. Soluble fermentable fibers undergo colonic fermentation to produce SCFAs such as butyrate, propionate, and acetate. These fibers serve as fuel for colonocytes, strengthen tight junctions, and modulate immune function. They also enhance gut barrier integrity by upregulating tight junction proteins, including occludin, claudins, and zonula occludens-1 (ZO‑1), as well as mucin-2, thereby reducing intestinal permeability and systemic endotoxemia. In addition, SCFAs exert broad immune-modulatory effects, regulating regulatory T cells, effector T cells, B cells, macrophages, and dendritic cells, promoting anti-inflammatory responses while suppressing nuclear factor-κB (NF‑κB) activation. (Reynolds 2019)

Mediterranean Diet 

The LIBRE (Lifestyle Intervention Study in Women with Hereditary Breast and Ovarian Cancer) trial demonstrated that the Mediterranean diet reduces endotoxemia through fiber, polyphenol-rich foods, and olive oil. Comparatively, traditional diet patterns high in alcohol and processed meats were associated with higher LPS burden in a 2021 cross-sectional study of 698 older, French community-dwelling individuals. (Seethaler 2022)(André 2021)

The following guidelines summarize dietary recommendations to minimize intestinal permeability and improve gut barrier function: 

• Minimize ultra-processed foods: These are the primary source of emulsifiers, artificial sweeteners, and microbial transglutaminase
• Reduce added sugars: Particularly fructose from sugar-sweetened beverages and HCFS
• Limit saturated fat: Replace with unsaturated fats (olive oil, nuts, fish)
• Moderate or eliminate alcohol: Even moderate intake impairs barrier function
• Read labels for emulsifiers: Avoid polysorbate 60/80, carrageenan, CMC
• Avoid artificial sweeteners: Particularly sucralose, aspartame, and saccharin
• Consider gluten reduction: Especially in patients with suspected barrier dysfunction or autoimmune conditions

Movement

Risk Factors

Sedentary behavior is associated with less favorable microbiome profiles, including lower diversity and SCFA-producing bacteria. (Pérez-Prieto 2024)

Interventions

Regular moderate-intensity exercise improves gut barrier function following a hormetic pattern. Acute, intense exercise transiently increases permeability, while chronic moderate exercise produces long-lasting barrier improvements through decreased LPS and increased beneficial bacterial species including Akkermansia, F. prausnitzii, and Bacteroidetes. 

Stress

Risk Factors

Human clinical data demonstrates both acute and chronic psychological stress significantly increase intestinal permeability through corticotropin-releasing hormone (CRH) and mast cell activation. CRH activates intestinal mast cells, causing the release of mediators that disrupt tight junctions. Increased intestinal permeability allows bacterial translocation and LPS entry into circulation, further stimulating the hypothalamus-pituitary-adrenal (HPA) axis. (Marwaha 2025)(Yue 2017) A 2018 clinical trial with 23 healthy subjects found that acute psychological stress (public speaking) significantly increased small intestinal permeability measured by the lactulose-mannitol ratio. (Vanuytsel 2014) In a 2023 trial with 16 subjects, dichotomous listening stress (a form of acute stress) significantly increased paracellular permeability in rectal mucosa. (Gerdin 2023) A 2018 trial with 40 men found disruption to zonulin within one hour after psychosocial stress induction. (Linninge 2018)

Interventions

Participating in physical activity can improve stress resilience. During exercise, the body releases endorphins, which can improve mood. Adults should participate in at least 150 minutes (2.5 hours) of moderate-intensity exercise each week to reap the many health benefits exercise offers. (Childs 2014)(Anderson 2013)(The Department of Health & Human Services 2019)

Meditation, mindfulness, and breathing exercises can help minimize feelings of stress. Meditation has also been shown to lower high blood pressure, reduce resting heart rate, and decrease the body’s stress hormone, cortisol. Encourage patients to set aside a few minutes each day to focus on their breathing without external distractions or listen to a guided meditation exercise online. (Sharma 2015)