What are Cyanogenic Glycosides?
Many plants, including several fruit trees, produce natural chemical compounds known as cyanogenic glycosides. The most well-known of these is amygdalin, which is found in the seeds of certain fruits. Amygdalin is not toxic on its own. The danger arises when the seed is crushed, chewed, or otherwise broken, and enzymes are released that convert the amygdalin into hydrogen cyanide, a potent poison.
The Prunus Family and Common Fruits
The most prevalent sources of amygdalin are members of the Prunus family, which includes many popular stone fruits. These fruits have a hard, protective pit (stone) at their center. The toxic amygdalin is locked within the kernel inside this pit. Common examples include:
- Apricots: The kernels of apricots are known to have high concentrations of amygdalin, particularly in bitter varieties. Raw apricot kernels are considered unsafe and their sale is banned in some regions.
- Cherries: While much smaller, cherry pits also contain amygdalin. Like other stone fruits, chewing or grinding the pits is what releases the cyanide.
- Peaches and Nectarines: Both peaches and nectarines contain amygdalin in their pits. The amount can vary depending on the fruit's ripeness and variety, but the risk mechanism is the same.
- Plums: Plums, including prunes, are also members of the Prunus family and have cyanogenic glycosides in their pits.
- Apples and Pears: The small seeds inside the core of apples and pears also contain amygdalin. The amount is relatively low per seed, meaning a person would need to consume hundreds of crushed seeds to approach a toxic dose.
- Bitter Almonds: While most commercial almonds are 'sweet' and safe to eat, bitter almonds contain high levels of amygdalin. Bitter almonds are not typically sold for consumption due to this risk.
Understanding the Risk: Whole vs. Crushed Seeds
The distinction between accidentally swallowing an intact seed and consuming crushed or ground seeds is crucial for understanding the real-world risk. The key to cyanide release is tissue damage to the seed.
- Accidental Swallowing of Whole Pits: If you swallow a whole peach pit, cherry pit, or apple seed, the hard outer shell is unlikely to be broken down by your digestive system. The seed will simply pass through your body and be excreted without releasing any significant amount of cyanide. For this reason, accidentally swallowing a few seeds is generally harmless for healthy adults. However, whole pits can pose a choking hazard, especially for small children.
- Consuming Crushed or Ground Seeds: The danger increases significantly when seeds are broken or ground. This can happen accidentally, such as when using a high-speed blender for smoothies, or intentionally, when consuming ground kernels. Children and individuals with lower body mass are more susceptible to poisoning from smaller quantities.
Cyanide Toxicity and Symptoms
The severity of cyanide poisoning depends on the dose and the individual's body weight. Mild symptoms are often temporary, while severe poisoning can be life-threatening. The lethal dose of cyanide can vary but is generally estimated to be between 0.5 to 3.5 milligrams of cyanide per kilogram of body weight.
Symptoms of Cyanide Poisoning
- Mild Exposure:
- Headache
- Dizziness
- Nausea and vomiting
- Anxiety and restlessness
- Severe Exposure (requiring immediate medical attention):
- Difficulty breathing or rapid breathing
- Rapid or irregular heart rate
- Confusion or weakness
- Seizures or convulsions
- Loss of consciousness
The Cyanide Content in Fruit Seeds: A Comparison
Studies have measured the cyanogenic potential in the seeds of various fruits. It is important to note that these figures can vary based on the specific cultivar, ripeness, and environmental factors. Here is a comparison based on available data:
| Fruit Seed | Cyanogenic Potential (mg HCN/kg) | Notes |
|---|---|---|
| Plum | ~96 | Contains higher concentration than many other common fruit seeds. |
| Peach | ~70 | A single pit is unlikely to contain enough to harm a healthy adult. |
| Apricot (bitter) | Up to 55,000 | Highly variable. Some varieties have extremely high amygdalin content. |
| Cherry | Variable | Amount is generally very low. Toxin is released when crushed. |
| Apple | ~22-45 (avg) | Varies by apple variety. High volume of crushed seeds required for toxicity. |
| Bitter Almonds | ~2850 | Significantly higher than sweet almonds, making them unsafe to eat raw. |
The Misguided 'Vitamin B17' (Laetrile) Myth
In the mid-20th century, a synthetic derivative of amygdalin called laetrile was misleadingly marketed as "vitamin B17" and promoted as an alternative cancer treatment. This claim has been thoroughly debunked by the medical community. Scientific studies have found no evidence that laetrile is effective in treating cancer and have highlighted the considerable poisoning risks associated with it. Major health bodies, including the National Cancer Institute, do not approve or endorse its use due to lack of efficacy and safety concerns. Anyone considering alternative treatments should be wary of such unproven claims and consult with qualified healthcare professionals.
Safe Practices for Enjoying Fruit
To ensure your diet is both delicious and safe, follow these simple guidelines:
- Pit all stone fruits before blending them into smoothies or juices. This includes cherries, peaches, nectarines, and apricots.
- Do not chew or swallow the pits of any stone fruit. Instruct children to do the same and be mindful of them when eating.
- Eat around the core of apples and pears. While the risk is very low for accidental seed ingestion, it's best to avoid eating them altogether.
- Avoid eating raw apricot kernels, especially those sold as a health food supplement. Some countries have banned their retail sale due to the high risk of cyanide poisoning.
- Discard fruit pits and seeds responsibly, keeping them away from children and pets who might chew on them.
Conclusion
While the concept of what fruit has cyanide seeds might seem alarming, the risk of poisoning from typical fruit consumption is extremely low, provided proper care is taken. The key takeaway is to avoid chewing, crushing, or grinding the seeds or kernels of common fruits like apricots, peaches, cherries, and apples, as this is the mechanism that triggers the release of toxic hydrogen cyanide. For intact seeds, the hard outer shell offers sufficient protection, and they will likely pass through the digestive system harmlessly. By following safe preparation and consumption practices, you can confidently enjoy the nutritional benefits of fresh fruit without any fear of harm from their seeds. If you suspect that someone has ingested crushed seeds or shows signs of poisoning, contact a poison control center immediately.
