Organ Systems and Performance – Episode 8: The Small Intestine

INTRODUCTION

The small intestine is where nutrition becomes fuel. It’s the site of absorption, signaling, and transformation. Every gram of protein, every micronutrient, and every calorie you consume must pass through this organ to be used by the body. If the small intestine is compromised, performance suffers, no matter how clean your diet or how disciplined your training.

For aging lifters and general population clients, supporting small intestine function is essential for recovery, energy, and long-term health.

STRUCTURE AND FUNCTION

The small intestine is divided into three sections: the duodenum, jejunum, and ileum. Each plays a role in breaking down food and absorbing nutrients. Enzymes from the pancreas and bile from the liver enter the duodenum to help digest fats, proteins, and carbohydrates. The jejunum and ileum absorb vitamins, minerals, amino acids, and glucose.

The surface of the small intestine is lined with villi and microvilli, tiny finger-like projections that increase surface area and maximize absorption. Damage to these structures, whether from inflammation, infection, or poor diet, reduces nutrient uptake and impairs recovery.

NUTRIENT ABSORPTION AND TRAINING OUTCOMES

You can eat the perfect meal, but if your small intestine isn’t functioning well, your body won’t benefit. Protein synthesis, glycogen replenishment, and hormonal signaling all depend on absorption. When absorption is impaired, you may experience:

• Muscle loss despite adequate protein intake  
• Fatigue due to poor iron or B vitamin absorption  
• Cramping or bloating from malabsorbed carbohydrates  
• Poor recovery and immune suppression

For lifters, this means slower progress and increased risk of overtraining. For aging adults, it means reduced resilience and increased vulnerability to illness.

GUT-BRAIN AXIS AND NEUROLOGICAL IMPACT

The small intestine communicates with the brain through the vagus nerve and chemical messengers. This gut-brain axis influences mood, focus, and stress response. When the gut is inflamed or dysregulated, it can trigger anxiety, brain fog, and poor sleep.

Supporting small intestine health improves not just digestion, but cognitive function and emotional regulation. This is especially important for clients dealing with chronic stress or sleep disruption.

IMMUNE FUNCTION AND INFLAMMATION

Over 70 percent of the immune system resides in the gut. The small intestine acts as a gatekeeper, deciding what gets absorbed and what gets rejected. If the gut lining becomes permeable, a condition often called “leaky gut”—toxins and undigested proteins can enter the bloodstream, triggering systemic inflammation.

This inflammation affects joints, recovery, and even hormonal balance. For aging lifters, reducing gut permeability is a key strategy for preserving mobility and energy.

DIETARY STRATEGIES FOR SMALL INTESTINE HEALTH

Supporting the small intestine starts with what you eat and how you eat it. Key strategies include:

• Prioritizing whole foods rich in fiber, polyphenols, and resistant starch  
• Including fermented foods like yogurt, kefir, and sauerkraut to support microbial balance  
• Avoiding excessive alcohol, processed sugars, and artificial additives  
• Eating slowly and chewing thoroughly to support enzymatic breakdown  
• Supplementing with digestive enzymes or probiotics when clinically appropriate

Hydration also matters. Water supports enzymatic activity and helps move nutrients through the intestinal lining.

COMMON LIMITERS AND COACHING INSIGHTS

Clients often overlook digestive health until symptoms become severe. But subtle signs, like bloating, inconsistent energy, or nutrient deficiencies, can signal small intestine dysfunction. Coaches can help by tracking food logs, identifying patterns, and encouraging gut-friendly habits.

For aging adults, digestive efficiency declines. Meal timing, food combinations, and stress reduction become even more important. Educating clients on how digestion affects performance can be a game-changer.

CONCLUSION

The small intestine is not just a digestive tube. It is a dynamic interface between the outside world and your internal systems. It determines how well you absorb fuel, regulate inflammation, and adapt to stress. Supporting its function is essential for anyone serious about performance, recovery, and longevity.

Eat with intention. Digest with efficiency. Protect the gateway that turns food into function.