What it is
Fiber is a class of indigestible carbohydrates. Your body has enzymes that can break the bonds between the individual sugar molecules in starches, but it doesn’t have enzymes that can break the bonds between the individual sugar molecules in fibers. However, some types of fiber can be broken down by intestinal bacteria.
What they do
There broadly are two types of fiber: soluble and insoluble fiber.
Insoluble fiber is essentially inert – it passes through your digestive tract largely unaffected. In doing so, it slows down digestion, helping you feel satiated for longer after a meal. It also adds bulk to your feces and helps make for more regular bowel movements.
Soluble fiber can’t be digested, but it can be broken down and fermented by bacteria in your digestive tract. So, soluble fiber helps feed the healthy bacteria in your intestines. The fermentation products include short-chain fatty acids which can be absorbed by your large intestine (thus yielding some energy), and a variety of chemicals that help keep your large intestine and colon healthy, thus reducing the risk of colon cancer.
Recommended intake
The recommended intake of dietary fiber is 14g per 1000 calories. For instance, if your total calorie intake is 2000 calories per day, you should be aiming for about 28g of fiber per day.
Likelihood of tracking completeness: Very high in the US and Canada, and low in many other places.
Nutrition labels in the US and Canada are required to list fiber content. So, the vast majority of American and Canadian foods in the MacroFactor database should contain dietary fiber information, making it easy to accurately track your fiber intake with consistent food logging.
However, in the EU, Australia, and many other countries, dietary fiber is a nutrient that is only reported on a voluntary basis. Many food manufacturers do not voluntarily list fiber content on nutrition labels, so many branded products in the MacroFactor database from outside the US and Canada lack fiber information. So, if you’d like to accurately track your fiber intake, you’ll need to make a point of mostly tracking “common foods,” which come from research-grade databases that have full nutrient reporting.
For more on when you can track using branded foods versus common foods when you’re trying to accurately monitor your intake of particular nutrients, you should check out this article.
Likelihood of insufficient intake: High
Most adults in developed countries don’t consume enough fiber. Americans generally consume <20 grams per day, and Europeans generally consume about 18-24 grams per day. Given typical levels of energy intake (2000-3000 calories per day), typical intakes should generally be around 30-40 grams per day.
For more on nutrients with a greater likelihood of insufficient or excessive intake, check out this article.
Signs of deficiency/insufficiency or excess intake
The most common acute signs of insufficient fiber intake are GI-related symptoms (constipation or diarrhea). The most common signs of excessive fiber intake are also GI-related symptoms (constipation, diarrhea, or excessive gassiness).
Most people have a happy range of fiber intake that keeps their bowels happy and moving along without diarrhea, constipation, or excess gas. The research supporting fiber intake targets is fairly imprecise, so if your happy range of fiber intake is a bit above or below the general recommendation of 14 grams per 1000 calories, that should be perfectly fine.
Good sources
Per 100g, some of the best sources of dietary fiber include:
Dried seaweed (nori) – 44.4g
Wheat bran – 42.8g
Cocoa powder – 37g
Flax seeds – 27.3g
Dried chile peppers – generally >25g (depending on the type)
Dark rye flour – 23.8g
Pumpkin seeds (pepitos) – 18.4g
Hulled barley – 17.3g
Roasted soybeans – 15.65g
Textured vegetable protein (TVP) – 14.59g
Per 100 calories, some of the best sources of dietary fiber include:
Artichoke – 20.9g
Rhubarb – 20g
Turnip greens – 17.5g
Sauerkraut – 15.3g
Kohlrabi – 13.3g
Jicama – 12.9g
Banana peppers – 12.9g
Raspberries – 12.5g
Lettuce – 12.4g
Blackberries – 12.3g
Collard greens – 12.1g
Most other whole grains, nuts, seeds, berries, peppers, and non-starchy vegetables are particularly great sources of fiber. Dried spices also typically have a ton of fiber, but I didn’t include them on these lists because you’re unlikely to consume them in large quantities.
Learn more
If you’d like to learn more about micronutrients generally, there’s a five-part series on the MacroFactor website you might enjoy.