Question: I’m a bit wary of the fibre claims of products that contain whole seeds. We know that seeds can pass through undigested. Does this mean we have to chew every single seed to get the full fibre content?
Answer: High-fibre plant-derived foods, such as whole grains and seeds, are typically the source of undigested food fragments that pass through our digestive system unchanged. But that does not mean they are useless; it’s quite the opposite – seeds and fragments of grains play an important role by travelling undigested through our gut.
Indeed, scientists define dietary fibre as the fractions of the edible parts of plants that are resistant to digestion and absorption in the small intestine. Although these fibrous fragments aren’t digested there, they’re still beneficial to our gut health. First, dietary fibre absorbs water and adds bulk to bowel motions, softening them and helping them pass more easily through the gut. In turn, this helps to reduce the transit time of food through our gut and the risk of constipation. By bulking up stools, they also dilute the contents of bowel motions that can contain harmful compounds, reducing the risk of harm to our gut. And at the opposite end of the spectrum, if you have loose, watery stools, dietary fibre can help solidify them by absorbing the water and adding bulk.
Those actions likely contribute to the link between higher-fibre diets and a reduced risk of developing haemorrhoids and pouches in your colon (diverticular disease).
The World Cancer Research Fund says there is also strong evidence that consuming foods containing dietary fibre decreases the risk of colorectal cancer. Dietary fibre also plays a role in lowering blood cholesterol levels and assisting with blood sugar control (which is vital for those with prediabetes and diabetes).
And, of course, we have become increasingly aware of the important link between our gut microflora and health in recent decades. For example, high dietary fibre consumption is associated with increased gut microbiota diversity. A healthy and diverse gut microflora population enables our body to function at its best. Dietary fibre is fuel for the gut microbiome, with microbes in the large intestine fermenting certain fibres and producing short-chain fatty acids and gases that improve glucose and lipid metabolism in our body, a 2021 review published in the journal Nutrients found.
So, yes, seeds and wholegrain fragments pass through your digestive system undigested and turn up in your stool. The same situation can occur when scientists analyse food to determine its fibre content, says Carolyn Lister, food and health information science team leader at Plant & Food Research.
“Usually, the food is homogenised and extracted for the analyses. However, the amount different seeds are disrupted will depend on their size.” In other words, even when scientists analyse food products to determine the fibre content for the nutrition label, not all of the seeds are necessarily ground up or fragmented. Some remain whole, just as when we eat food containing seeds.
There are still many questions about the bioavailability of nutrients from different foods, says Lister. But we do know there is evidence that regular consumption of seeds has health benefits, and there are advantages to passing intact seeds through the digestive tract.
However, chewing or a good food blender comes in handy when you want to access the other nutrients – aside from fibre – inside the seed, such as good fats, protein and minerals. Chewing or grinding the hard shell of the seeds allows you to access these other nutrients, though it may alter the action of the dietary fibre. And depending on the type of fibre in the seed, grinding them up may increase or decrease fibre fermentation by gut bacteria – but that’s another topic for another day.
