Humans consume seeds as part of their regular diet, whether deliberately or incidentally. Seeds are present in many fruits, vegetables, grains, nuts, and legumes that people eat. With their hard outer coat, seeds often pass through the digestive tract intact. However, the human body is capable of digesting seeds to some degree. The digestibility of seeds depends on the type of seed as well as the individual’s digestive system. This article examines the evidence on seed digestion in humans.
Can Humans Digest Seeds at All?
Yes, humans can digest seeds to some extent, although the degree of digestion varies. When we chew seeds, we mechanically break down the outer coat, allowing digestive enzymes access to the interior. Human saliva contains amylase enzymes that begin breaking down starch within seeds. The acidic environment in the stomach continues digesting the seed contents, including proteins, fats, and carbohydrates. Further breakdown occurs in the small intestine by pancreatic enzymes.
However, the indigestible components of seeds, mainly dietary fiber, limit how thoroughly they can be digested. Fiber resistant to human digestive enzymes passes through the gut intact. The seed’s tough outer coat is also difficult to digest completely. Partially intact seeds are often visible in stool after being eaten. Nevertheless, the human digestive system is able to extract some nutritional value from seeds.
Factors Affecting Seed Digestibility
The degree to which humans can digest seeds depends on several factors:
Seed Structure
Seeds with softer outer coatings are more easily broken down by chewing and digestive enzymes. For example, tomato seeds have a soft seed coat that quickly releases the interior contents. Seeds with harder shells, like nuts, pass through more slowly.
Seed Composition
The nutrients and anti-nutrients in seeds impact their digestibility. Seeds high in protein, fat, and starch tend to be well digested. However, some seeds contain anti-nutrients like tannins, phytic acid, and enzyme inhibitors that reduce digestibility.
Processing and Cooking
Processing methods like grinding seeds into flours and cooking make seeds more digestible. Heat helps break down compounds that inhibit digestion. Ground chia and flax seeds, for instance, are more bioavailable than whole seeds.
Individual Differences
An individual’s gastrointestinal function influences how well they can digest seeds. Powerful digestion breaks down seeds more thoroughly. Impaired digestion from conditions like acid reflux limits seed breakdown.
Gut Microbiota
The bacteria in a person’s intestines, or gut microbiota, play a significant role in digesting fibers and compounds that human enzymes cannot breakdown. People with more robust microbiomes digest seeds better.
How Thoroughly Are Common Seeds Digested?
The digestibility of seeds varies widely depending on the type. Here is an overview of how readily some common edible seeds are digested:
Flax Seeds
Flax seeds have a hard outer coat and are high in fiber. One study found around 85% of whole flax seeds passed through the digestive tract intact. When ground, around 75% of flax seeds were digested. The omega-3 rich inner contents are fairly digestible.
Chia Seeds
Like flax seeds, chia seeds are difficult to break down and absorb in whole form. Around 85-90% of whole chia seeds can pass through undigested. When ground, chia seeds are more bioavailable, with around 70% absorption.
Sesame Seeds
Sesame seeds have a softer seed coat and higher fat content than flax or chia seeds. Chewing helps release the inner oil. Around 60-65% of sesame seeds may be digested.
Poppy Seeds
Tiny poppy seeds have a soft seed coat that is easily chewed up, aiding digestion. Around 80% of poppy seeds may be digested by enzymes in the stomach and small intestine.
Pumpkin Seeds
Pumpkin seeds have a tough outer shell. About 50% of whole pumpkin seeds tend to pass through intact. When chewed thoroughly or ground, more of the inner contents get absorbed, around 60%.
Sunflower Seeds
The soft hull around sunflower seeds is easy to chew, while the inner seed is more durable. Around 20-30% of sunflower seed contents pass through undigested. Sunflower butter is more bioavailable.
Quinoa
Quinoa is considered a pseudocereal or seed. Around 70-75% of quinoa’s protein content gets digested, more than true cereal grains. Rinsing quinoa removes some of the bitter saponins that inhibit digestion.
Tomato Seeds
Tomato seeds have a soft seed coat that quickly breaks down during mastication and digestion. About 85% of tomato seed nutrients are absorbed by the body.
Possible Digestive Problems from Seeds
Most healthy people do not experience major side effects from eating seeds in moderation. However, seeds may contribute to minor digestive discomfort or aggravate existing gastrointestinal issues in some cases, such as:
Intestinal Blockages
For individuals with narrowed intestinal tracts, seeds can potentially obstruct or block the intestines. Whole flax or chia seeds are more likely to cause impactions than ground seeds. Surgery may be required to remove obstructing seeds if severe.
Nut Allergies
Seeds from nuts and legumes can trigger allergic reactions in sensitive people. Tree nut allergies may cause symptoms after eating nuts like almonds, pine nuts, or pistachios. Peanuts and soybeans can also spur allergies.
Seed Poisoning
Some seeds naturally contain toxins that defend against threats in the wild. Poisoning from common seed foods is extremely rare, but undercooked kidney beans, for example, have caused poisoning. Processing and proper cooking destroys their toxins.
Anti-Nutrient Effects
Seeds like cereals, grains, and legumes contain anti-nutrients like phytic acid, lectins, tannins, and enzyme inhibitors that may hinder digestion at high doses for some people. Effects may include bloating, flatulence, and mineral deficiencies over time.
FODMAPs Effects
Some seeds and nuts are high in short-chain carbohydrates called FODMAPS. People with IBS or other gut disorders may experience gas, cramping, and diarrhea from eating high FODMAP foods like pistachios or cashews.
Irritation of the GI Tract
The fibrous, hardy structure of some seeds can irritate the lining of the esophagus, stomach, or intestines, especially when eaten in excess. The sharp edges of seed coats may scratch or abrade digestive tissues for some individuals.
Gallstones
High fat seeds may worsen problems in people prone to gallstones. The gallbladder contracts to release bile when digesting fats, which can induce gallstone related pain. Minimizing high fat seeds could help prevent attacks.
Improving Seed Digestion
Digestive discomfort from seeds can often be reduced by preparing them in more digestible ways:
– Soaking seeds like quinoa overnight in water can reduce anti-nutrients.
– Sprouting or germinating seeds helps break down fibers and inhibitors.
– Grinding seeds into flours increases the bioavailability of nutrients.
– Roasting and cooking seeds enhances digestibility by inactivating anti-nutrients.
– Chewing seeds thoroughly disrupts their seed coats before swallowing.
– Consuming seeds along with foods that contain digestive enzymes like pineapple may aid breakdown.
– Individuals with impaired digestion may benefit from limiting portion sizes of seeds.
– Taking digestive enzyme supplements can help better digest seeds.
– Probiotics and prebiotics help populate the gut with beneficial bacteria that digest seeds.
Digestive Fate of Seeds: Excretion in Stools
Many seeds withstand digestion, allowing them to pass through the gastrointestinal tract and be excreted whole in feces. Here is what happens to various undigested seeds:
Transit Time
How long seeds take to appear in stool depends on digestive motility. In most people, transit time ranges from 12-48 hours, but is highly variable. Fast bowel transit leads to shorter appearance times. Slow motility increases the time for seeds to appear.
Seed Structure
Intact seeds clearly visible in feces likely have tough outer coatings and durable internal structures. Seeds with softer shells generally get broken down more and are less discernible after digestion.
Fecal Composition
Seeds may be obvious against formed, solid stools. They can camouflage more easily into loose, watery feces. Seeds tend to settle to the bottom of toilet bowls after excretion.
Dosage and Frequency
Eating more seeds in a single serving increases the chances of seeing intact seeds later. Occasionally eating seeds leads to fewer showing up than a daily seed-heavy diet. The more consumed, the more that reemerge.
Chew Thoroughness
The oral digestion stage heavily influences seed breakdown. The more thoroughly seeds get chewed, the more ruptured and degraded they become in the GI system. Light chewing fails to rupture tough seed coats.
Bowel Health
Gastrointestinal issues that impair digestion like gut inflammation, dysbiosis, enzyme deficiencies, gallstones, or blockages leave more seeds undigested. Healthy bowel function facilitates nutrient absorption.
Do Intact Seeds in Stool Indicate a Health Problem?
Passing recognizable seeds in stool is normal and not necessarily a health concern. As long as intact seeds are not causing observable symptoms, their presence alone rarely indicates an underlying medical condition. Possible explanations include:
– Healthy people often excrete durable seeds like quinoa, chia, flax, poppy, sesame, and nut shells intact frequently. Their hardiness enables them to transit undamaged.
– Thoroughly chewing seeds before swallowing maximizes digestion and reduces intact excretion. Individuals who eat quickly may excrete more unbroken seeds.
– Transiting seeds do not necessarily mean poor nutrition. The human gut still extracts nutrients like proteins and fats from seeds reasonably effectively. Shells and fibers remain undigested.
– Gastrointestinal disorders like irritable bowel syndrome can reduce digestion but may not impair nutrient absorption. Seeds can pass through fast without fully breaking down.
– Damaged intestines from conditions like Crohn’s disease can cause malabsorption of some nutrients. But seeds themselves are unlikely to be the root cause.
– Excreting chia or flax seeds may not be preventable. Even when ground or prepared well, their tough structure limits digestion.
Overall, intact seeds in stools are normal for the majority of people. They become a concern if associated with worsening symptoms or compromising nutrient absorption long term.
When to Seek Medical Advice
While seeds in stool are usually harmless, it’s reasonable to consult a doctor about intestinal symptoms possibly related to seeds, such as:
– Ongoing diarrhea, constipation, or other bowel habit changes after eating seeds
– Intense abdominal pain or cramping that seeds may be aggravating
– Bloating, gas, distension for hours after consuming seeds
– Evidence of intestinal blockages or obstructions from seeds
– Blood in stool potentially caused by seed irritation
– Unintentional weight loss or malnutrition from reduced seed absorption
– Development of new seed, nut, or legume allergy
– Hives, swelling, or anaphylaxis triggered by seeds
– Family history of gastrointestinal disorders that may interfere with seed digestion
Doctors can evaluate symptoms, order testing, and provide personalized advice on dealing with seed-related digestive issues.
Improving Overall Digestive Health
Beyond seed digestion itself, several lifestyle measures promote better overall gastrointestinal wellness:
– Drink adequate water and fluids to support digestive function.
– Consume more prebiotic fibers from sources like garlic, onions, bananas, and oats.
– Eat fermented foods containing probiotics or take probiotic supplements to foster healthy gut flora.
– Limit fast food, processed items, and junk foods that hamper digestion.
– Reduce stress through practices like meditation, exercise, sleep, and socializing which aid digestive health.
– Get regular physical activity, which stimulates the bowels and metabolism.
– Consider digestive enzyme supplements if dealing with chronic indigestion.
– Talk to your doctor if experiencing lasting digestive troubles impacting health.
Following a balanced, natural diet and healthy lifestyle goes a long way towards supporting optimal digestion and allowing the human gut to effectively process seeds.
The Bottom Line
While human digestion cannot break down seeds 100%, we do gain partial nutritional benefit from many common edible seeds. The degree varies based on the physical and chemical properties of the seed. Processing methods like grinding seeds improves digestibility when intact seeds cause problems. For most people, transit of durable seeds through stools is normal and not indicative of health issues. But chronic digestive symptoms possibly related to seeds should prompt seeing a doctor. When prepared properly and eaten in moderation, seeds can be a well-tolerated part of a regular diet.
