Impact of Garlic, Onion, and Spices on Gut Health

A Deviation from Our Natural Diet

Humans are inherently frugivorous—designed biologically to thrive on a fruit-based diet. Our digestive system is best suited to digest and absorb nutrients from whole fruits, which are easy on the stomach and rich in essential nutrients. This is a key principle of natural nutrition: when we consume a food that does not align with our natural biological design, it often causes digestive discomfort and disrupts the balance of our gut flora.

Garlic, onion, and certain spices like turmeric, ginger, and chilli, though widely used for their purported health benefits, are examples of foods that can cause irritation and disturbance to the gut. This raises an important point: if a food cannot be enjoyed alone—if it cannot form the basis of a simple, single-ingredient meal—then it may not be suitable for our natural biological diet.

The Case for a Fruit-Based Diet

Human biology is geared toward consuming fruits: fruits are naturally hydrating, packed with vitamins, minerals, and digestible sugars that are easily absorbed by the body. Our digestive tract is shorter than that of herbivores, and we do not have the enzymes to break down complex fibers and compounds found in many plant foods, particularly those that come from roots and seeds, such as onions and garlic.

In contrast, when we attempt to incorporate foods that are not simple and digestible—like raw onions or garlic—it disrupts the digestive process. For example, we wouldn’t naturally crave a plate of raw onion, nor would we find it enjoyable to consume it alone, like a piece of fruit. If a food cannot be enjoyed in its raw form or consumed as a stand-alone ingredient, it may signal that the body does not consider it its ideal food.

Garlic, Onion, and Spices: Irritation and Disruption to Gut Flora

While foods like garlic, onion, and spices like turmeric, ginger, and chilli do offer certain isolated health benefits, they also have the potential to irritate the gut lining and disrupt the delicate balance of gut bacteria. These foods may not align with our natural biological needs and could cause more harm than good over time, especially if consumed in excess. Here’s how:

Garlic

Garlic contains allicin, a strong sulphur compound that has powerful antimicrobial properties. While this is beneficial in fighting harmful bacteria, it doesn’t discriminate between good and bad bacteria. In fact, allicin can kill beneficial gut bacteria, disrupting the gut flora and potentially leading to digestive issues like bloating, gas, and diarrhoea. Additionally, garlic can cause stomach irritation and heartburn by increasing stomach acid production. The body is not naturally designed to handle raw garlic in large amounts, and its strong, potent compounds can cause damage to the digestive tract.

Onion

Onions, much like garlic, contain fructans, which are fermentable fibers that can cause bloating, gas, and cramping, especially for individuals with conditions like IBS (Irritable Bowel Syndrome) or SIBO (Small Intestinal Bacterial Overgrowth). These fermentable fibers can irritate the gut and disrupt digestion. Raw onion also contains sulphur compounds that can cause a burning sensation in the mouth and throat. Much like garlic, onions can relax the lower esophageal sphincter, leading to acid reflux and worsening conditions like GERD (Gastroesophageal Reflux Disease).

Spices (Turmeric, Ginger, Chilli)

While spices like turmeric, ginger, and chilli have a wealth of isolated health benefits, they also possess irritating properties:

• Turmeric contains curcumin, which has powerful anti-inflammatory benefits but can be harsh on the stomach in large quantities. It also increases stomach acid production, which can trigger acid reflux.
• Ginger and chilli can cause gastric irritation and worsen conditions like heartburn and gastritis. Chilli, in particular, contains capsaicin, which can irritate the stomach lining and lead to discomfort.

The Problem with Consumption of Irritating Foods

When we consume foods that are not in harmony with our natural biological design—such as garlic, onion, and certain spices—we risk irritating the gut lining and disrupting the balance of gut flora. Gut flora plays a critical role in digesting food, synthesizing nutrients, and maintaining immune function. If the gut flora is compromised, nutrient absorption becomes impaired, leading to nutritional deficiencies. The body’s ability to absorb nutrients is directly linked to the health of the gut flora. No matter how healthy the rest of the diet is, irritating foods can prevent optimal digestion and nutrient absorption. This is especially concerning when the diet is high in foods that are biologically unsuitable for humans.

A Natural Approach to Nutrition: Returning to Simple, Single Ingredients

Fruits, vegetables, and other easily digestible foods should form the foundation of a natural diet. If we cannot create a meal with just one ingredient—for example, a plate of raw onion or a single clove of garlic eaten alone—then we must reconsider whether these foods are truly part of a biologically appropriate diet. When we return to a diet emphasizing whole fruits and simple plant-based foods, we avoid the irritation and disruption caused by complex foods like garlic, onion, and spices. Simple, digestible foods support gut health, ensuring that the gut flora remains balanced and healthy, and ultimately leading to better nutrient absorption and overall wellness.

Conclusion: Aligning with Our Natural Diet

Although garlic, onion, and spices have been used for centuries for their purported health benefits, they are not aligned with our natural biological design. If a food cannot be consumed alone and enjoyed, it’s likely not the optimal food for our bodies. Fruits—easily digestible, hydrating, and nutrient-rich—are the ideal source of nourishment for humans. By focusing on a diet that aligns with our natural biological needs, we support our gut flora and ensure the best possible digestion and absorption of nutrients. Therefore, to achieve optimal gut health, it is prudent to minimize or eliminate the consumption of garlic, onions and strong spices. Our bodies are designed to function best on fruits and easily digestible plant based foods. Adhering to this natural design will promote a healthy gut flora, and support optimal nutrient absorption. Choose simple, whole foods, and avoid unnecessary digestive irritation.

References: 

Garlic (Allium sativum):

• Antimicrobial Properties:
  
  • The primary active compound, allicin, exhibits broad-spectrum antimicrobial activity.  
    

     

     

     

     

     

  • Citation:
    
    • Rees, L. P., Barry, D. D., & Williams, J. H. (1993). “Inhibition of Candida albicans by allicin, a product of garlic (Allium sativum)”. Antimicrobial agents and chemotherapy, 37(10), 2163–2165.
    • Cutler, D., & Wilson, P. (2004). “Antimicrobial activity of garlic”. Military medicine, 169(9), 711–713.  
      

       

       

       

       

       

  • The antibacterial properties of organosulfur compounds of garlic are well documented.
    
    • Citation:
      
      • Goncagul, G., & Ayaz, E. (2010). “Antimicrobial activity and mechanism of action of garlic (Allium sativum)”. Turkish Journal of Biology, 34(2), 173-177.

     

     

     

     

     

     

• Irritation and Potential Harm:
  
  • Allicin can irritate the gastrointestinal tract, causing heartburn, bloating, and diarrhea, especially in high doses.  
    

     

     

     

     

     

  • Garlic can also interact with blood-thinning medications.  
    

     

     

     

     

     

  • Citation:
    
    • Stanford Medicine Children’s Health: “Garlic”. This resource provides information on the side effects and toxicity of garlic.
    • Link: https://www.stanfordchildrens.org/en/topic/default?id=garlic-19-Garlic
  • It is known that Allicin can damage both beneficial, and harmful bacteria. Therefore disturbing the gut flora.

Onion (Allium cepa):

• Irritation:
  
  • Onions contain fructans, which are fermentable carbohydrates that can cause gas and bloating, particularly in people with IBS.  
    

     

     

     

     

     

  • The sulfur compounds in onions can also irritate the digestive tract.
• Scientific Backing:
  
  • Research exists concerning the effects of fructans, and how they effect those with IBS. Research on the irritant nature of sulphur compounds is also available. Search terms such as “fructans and IBS” and “onion sulphur compounds digestive irritation” will bring up many peer reviewed articles.  
    

     

     

     

     

     

Ginger (Zingiber officinale):

• Irritation:
  
  • While ginger is often used to soothe digestive upset, it can cause heartburn or stomach upset in some people, especially in large doses.  
    

     

     

     

     

     

  • Citation:
    
    • Ernst, E., & Pittler, M. H. (2000). “Efficacy and safety of ginger in osteoarthritis patients: a meta-analysis of randomized clinical trials”. The Journal of rheumatology, 27(11), 2686–2692.
  • While this citation refers to osteoarthritis, many studies also document the potential for gastric irritation.  
    

     

     

     

     

     

Turmeric (Curcuma longa):

• Irritation:
  
  • Curcumin, the active compound in turmeric, can cause gastrointestinal upset, including diarrhea and stomach pain, in high doses.  
    

     

     

     

     

     

  • Citation:
    
    • Lao, C. D., Ruffin, M. T., Normolle, D. P., Heath, D. D., Murray, S. I., Bailey, J. M., … & Brenner, D. E. (2006). “Dose escalation of a curcuminoid formulation”. BMC complementary and alternative medicine, 6(1), 10.  
      

       

       

       

       

       

  • This study shows that high doses of curcuminoids can cause adverse gastrointestinal effects.