Digestive discomfort: The FODMAP connection
For a large portion of the population, the most common side effect of eating onions and garlic is digestive upset. Both are high in fructans, a type of fermentable carbohydrate known as a FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). For people with sensitive digestive systems or Irritable Bowel Syndrome (IBS), these compounds are poorly absorbed in the small intestine. Instead, they travel to the large intestine where they are fermented by gut bacteria, leading to a host of uncomfortable symptoms.
Symptoms of FODMAP sensitivity often include:
- Excess gas and flatulence
- Abdominal bloating and cramping
- Stomach pain and general discomfort
- Changes in bowel habits, such as diarrhea or constipation
Cooking onions and garlic can help reduce some of these effects by breaking down a portion of the fructans, making them easier to digest. For those with severe sensitivity, however, even cooked alliums may cause problems, and it may be necessary to remove them from the diet. Alternatives like garlic-infused oil can offer flavor without the fructans.
Why raw alliums are more problematic
Raw onions, in particular, are harsher on the digestive system than their cooked counterparts. The volatile sulfur compounds that cause the pungent flavor are more concentrated in the raw state. Lightly cooking onions and garlic can make them more tolerable for many people with milder sensitivities. In contrast, raw onions are a much more likely trigger for gastrointestinal issues and even migraines in some individuals.
Bad breath and body odor
Perhaps the most well-known social side effect of eating onions and garlic is the lingering odor they cause. This is due to the same sulfur compounds responsible for their potent flavor. When consumed, these compounds are absorbed into the bloodstream and released through the lungs and sweat glands.
This process is why:
- Brushing your teeth or using mouthwash may not completely eliminate bad breath, as the odor is coming from the lungs.
- Body odor can develop, as the compounds are secreted through your pores along with sweat.
Certain foods, like apples, mint leaves, or green tea, may help neutralize some of the odor-causing compounds. However, the smell may persist for several hours, or even a day, depending on the quantity consumed and individual metabolism.
Acid reflux and heartburn triggers
For those prone to acid reflux or GERD (Gastroesophageal Reflux Disease), onions and garlic are common dietary triggers. They can relax the lower esophageal sphincter (LES), the muscle that prevents stomach acid from moving back into the esophagus. This relaxation can lead to:
- A burning sensation in the chest and throat (heartburn)
- Nausea
- Regurgitation of stomach acid
Raw onions are particularly notorious for triggering heartburn, and the intensity can vary depending on the onion type. More pungent varieties, like red and yellow onions, have higher sulfur content and are more likely to cause issues than milder, sweeter varieties.
Allergic reactions and intolerances
While relatively rare, some individuals have a true allergy or more common intolerance to allium vegetables. Allium intolerance is different from a FODMAP sensitivity and can manifest with a range of symptoms from mild to severe, including:
Common Allium Intolerance Symptoms:
- Stomach ache or cramping
- Bloating and flatulence
- Diarrhea or nausea
- Skin rashes or hives
In very rare cases, a true allergy to onions or garlic can occur, triggering an immune response that can cause severe symptoms like:
- Difficulty breathing
- Swelling of the lips, tongue, or throat
- Anaphylaxis, a life-threatening reaction
Potential medication interactions
High consumption of onions and garlic, especially in concentrated supplement form, may interact with certain medications.
Anticoagulants (Blood Thinners)
Both alliums have mild blood-thinning properties. Excessive intake, particularly from supplements, could potentially increase the risk of bleeding, especially for individuals already on blood-thinning medications like warfarin. This is a concern for those undergoing surgery, who are often advised to stop taking garlic supplements beforehand.
Diabetes Medication
Onions and garlic have been shown to potentially lower blood sugar levels. While this can be beneficial in moderation, large quantities could cause blood sugar levels to drop too low, especially for those on diabetes medication.
Comparison: Onions vs. Garlic Side Effects
| Side Effect | Onions (especially raw) | Garlic (especially raw) |
|---|---|---|
| Digestive Discomfort | High in fructans, a FODMAP; common trigger for gas, bloating, and cramps in sensitive individuals. | Also high in fructans; can cause bloating, gas, and abdominal pain in those with FODMAP sensitivity. |
| Bad Breath/Body Odor | Sulfur compounds cause pungent breath and can be released through the lungs and skin, causing lingering body odor. | High concentration of sulfur compounds leads to strong, lingering breath and can be secreted through sweat glands. |
| Acid Reflux/Heartburn | A known trigger, especially when raw, due to relaxing the lower esophageal sphincter (LES). | Can trigger acid reflux by decreasing LES tone in sensitive individuals. |
| Blood-Thinning | Contains compounds with mild blood-thinning properties; large amounts should be avoided with certain medications. | Higher risk of bleeding with excessive consumption or supplements, especially when combined with anticoagulants. |
| Allergies | Rare, but can trigger skin reactions or, in severe cases, breathing difficulties. | Rare allergy, but intolerance is more common. Cross-reactivity with onion allergy is possible. |
Conclusion: Moderation is key
Onions and garlic are not inherently unhealthy; in fact, they are packed with vitamins, antioxidants, and compounds that offer numerous health benefits, including supporting heart health and having antibacterial properties. However, for certain individuals, consuming them, especially in large, raw quantities, can lead to unpleasant side effects. Paying attention to your body's signals is crucial. If you experience digestive distress, bad breath, or other adverse reactions, consider reducing your intake, consuming them cooked rather than raw, or consulting a healthcare provider. Ultimately, the best approach is to enjoy these flavorful alliums in moderation and prepare them in a way that aligns with your individual tolerance. A great resource for further reading on FODMAP sensitivities is the Monash University Low FODMAP Diet, which provides detailed guidance on managing trigger foods.
Final thoughts on managing side effects
If you find yourself experiencing adverse reactions, here are some actionable steps:
- Cook Thoroughly: Heat helps break down the problematic compounds. Caramelized or sautéed onions are often much better tolerated than raw ones.
- Reduce Quantity: Try using smaller amounts of onion and garlic in your cooking to see if that helps manage symptoms.
- Identify Triggers: A food diary can help pinpoint which alliums and preparation methods are causing the most issues.
- Explore Alternatives: Infused oils offer the flavor without the FODMAP content. Alternatively, try other spices like asafoetida (hing) for a similar savory flavor profile.
By being mindful of your consumption and preparation, you can enjoy the benefits of these kitchen staples while minimizing the negative impacts.
