I want to be honest here: I never thought much about fiber. Growing up, my mother always emphasised the importance of eating more fruits and vegetables, much more so than eating more protein. As a result, I’ve never really had any issues with my bowel movements. Among all the daily recommended intake levels, my fiber intake has probably been on healthy autopilot for the majority of my life. I can’t confidently say that I hit the recommended 30 grams of fiber every day, and my commode usage has always been smooth sailing for as long as I can remember.

Along with the world’s protein obsession, fiber has suddenly become the next hot topic. It’s no longer just “have a serving of leafy greens or fruit with every meal.” I’ve seen quite a few meal-prep recipes, one in particular titled “stool slop”: a mushy mixture of oats, grains, chia seeds, fruit, nuts, milk and yogurt that apparently guarantees to unclog your pipes and probably cleanse part of your soul along with it. It might work for some people, and I’ve actually made that slop for myself. It’s not exactly enjoyable to have every single morning, and after a while, it made me crave other foods that aren’t slop.

I’ve also come to realise how much some of my lifters focus on protein without giving much thought to fiber. Heck, I’ll even admit that my own understanding of dietary fiber is embarrassingly limited, perhaps because it has never been a point of consideration with regard to my own diet.

In fact, fiber plays a far more important role than I previously assumed, especially when you’re trying to eat more protein while counting calories. Regardless of your diet masterplan – losing weight, bulking up or building muscle – it’s worth taking a closer look at whether you’re getting enough fiber.

What is dietary fiber?

Dietary fiber is a type of carbohydrate found primarily in plant foods that is not fully digested or absorbed by the human body. Instead of being completely broken down in the small intestine, fiber travels further along the digestive tract, where different types of fiber can perform different functions. Despite being more commonly known as a fix for irregular bowel movements, fiber does far more than service a highly anticipated poo.

There are many ways to classify fiber, but you’ll most commonly hear about two broad categories:

Soluble fiber dissolves in water and can form a gel-like substance. Some soluble fibers are viscous and can slow the movement of nutrients through the digestive tract, while others are readily fermented by gut bacteria.

Insoluble fiber does not dissolve in water and generally adds bulk to stool, helping to support regular bowel movements.

Foods usually contain mixtures of different fibers, and fibers can also differ in how viscous, fermentable and easily broken down by gut bacteria they are.

Benefits of fiber in a high-protein, low-calorie diet

A high-protein diet can contain plenty of meat, fish, dairy and other animal products. Tofu is also a useful source of protein, although unlike meat and dairy, soy foods can contain some fiber.

The bigger issue is what happens when these foods start displacing plant-based foods from your diet. When every meal is fixated on squeezing in more protein, while simultaneously reducing calories or carbohydrates to make room for more protein, it can become surprisingly easy to end up with very little fiber. Do this repeatedly over weeks and months, and you may eventually notice the consequences in a stressed digestive system.

Ensuring sufficient fiber can support a high-protein diet in several ways (Guarneiri et al., 2025):

Diet and satiety management

Fiber can help you feel fuller after a meal, which can be particularly useful when you are trying to control calorie intake. Different types of fiber can contribute to satiety through different mechanisms. Fiber-rich foods tend to add bulk and often require more chewing, while viscous fibers can slow gastric emptying and the absorption of nutrients. Fermentable fibers can also be metabolised by gut bacteria, producing short-chain fatty acids that may influence appetite-regulating signals, particularly handy when you are trying to eat fewer calories without feeling like you are permanently hungry, replacing some low-fiber foods with fiber-rich whole foods can make a surprisingly useful difference.

Supporting the Gut Microbiome

Your large intestine is home to a massive community of microorganisms, and some of them quite literally feed on the fiber that you eat. Certain fibers are fermented by gut bacteria, producing short-chain fatty acids such as acetate, propionate and butyrate. These compounds can interact with the cells lining the colon and participate in a variety of metabolic processes.

Different bacteria prefer different types of fiber, which is one reason why eating a variety of plant foods is more useful than finding one magical “best” fiber source. In other words, your gut microbiome doesn’t necessarily need you to eat the same bowl of chia seeds every morning for the rest of your life. It needs a diverse supply it can actually feed on.

Blood sugar and cholesterol

Certain viscous fibers can slow the digestion and absorption of carbohydrates, which can reduce the rise in blood glucose and insulin following a meal.

The same properties can also affect cholesterol metabolism. Some viscous fibers bind bile acids in the intestine and reduce their reabsorption, increasing the amount that is excreted. The liver then has to use more cholesterol to produce replacement bile acids, which can contribute to reductions in LDL cholesterol. Again, this isn’t a property shared equally by every type of fiber. “Fiber” is a category, not an individual substance with a singular effect.

Preventing constipation and supporting gastrointestinal health

This is the part everyone is most familiar with. Fiber can increase stool bulk and, depending on the type of fiber and your fluid intake, help produce stools that are easier to pass. This can support regular bowel movements and reduce the likelihood of constipation.

Adequate fiber intake has also been associated with a lower risk of several gastrointestinal and chronic health conditions. Higher fiber intake is associated with a lower risk of colorectal cancer, although it would be an overstatement to describe fiber as a guaranteed way to “prevent colon cancer.” Diet, genetics, lifestyle and other factors all contribute to disease risk.

Still, there is a reason that hospitals and dietary guidelines have been telling people to eat more fruits, vegetables, whole grains and legumes long before fiber became a social-media buzzword.

Adding fiber to your shopping list

So how much fiber do you actually need?

A commonly used recommendation is around 14 grams of fiber per 1,000 kcal consumed, which works out to approximately 28 grams on a 2,000 kcal diet. Singapore guidance from SingHealth recommends around 30 grams per day, while also noting that the average Singaporean consumes only around 13 grams per day (Singapore General Hospital, n.d.).

And if you’re counting calories, there is another reason fiber is useful. Fiber is technically a carbohydrate, but it isn’t metabolised in exactly the same way as digestible carbohydrates such as glucose and starch (Eat This Much, n.d.). Depending on the type of fiber and the system used to calculate food energy, fiber can contribute considerably less calories than digestible carbohydrate.

So you don’t have to choose between eating enough fiber and keeping your calories under control. In fact, fiber-rich foods can be particularly useful when you’re trying to get more food volume and satiety out of a limited calorie budget.

So what should you actually buy?

Instead of memorising an enormous list of “superfoods”, here is a short mental list for your next supermarket trip.

Fruits

If you’re not eating enough fruit, pick your favourite one and start having an extra serving each day: Two kiwis. An orange. An apple. A punnet of blueberries. Whenever possible, eat the edible skin. The skin of many fruits contributes fiber and contains various phytochemicals, although the exact nutrient composition varies considerably between fruits.

Vegetables

Vegetables are another straightforward way to increase your fiber intake.

Leafy vegetables, cruciferous vegetables and other whole vegetables can all contribute fiber. Cabbage, broccoli and spinach are perfectly good options.

You don’t need to start eating an enormous salad every night. Start with one additional serving a day.

Grains and carbohydrates

Look for whole-grain versions of foods you already eat.

Switch white bread for whole-grain bread. Try brown rice instead of white rice. Choose whole-wheat pasta. Making some of these swaps can increase your overall fiber intake, while whole grains can contribute other nutrients as well.

Beans and legumes

Beans are one of my favourite ways to add an inexpensive combination of protein and fiber.

It’s really easy: empty a can of drained cannellini beans into a chicken stew, or add a handful of frozen peas to your bolognese. Throw chickpeas into a curry. Mix lentils into your mince.

You don’t have to completely redesign your recipes. Just tweak what you’re already eating to make it slightly more fiber-dense.

Nutrient and fiber dense additions

Those things you see scattered over yogurt bowls – chia seeds, flaxseeds, pumpkin seeds and various nuts – are popular for a reason.

They’re small, easy to add to meals and can provide fiber alongside other nutrients, with some also contributing amounts of protein and unsaturated fats. Note that these foods are also relatively energy-dense, so “more fiber” doesn’t necessarily mean “eat unlimited quantities.”

There are huge numbers of lists online showing which foods contain the most fiber and how much fiber each serving provides. The U.S. Dietary Guidelines also provide a useful reference table of fiber-containing foods (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2024).

Eating more fiber is really, really easy

Adding fiber is really easy with small and slow steps! It starts with one more fruit, a little more vegetables, a serving of whole grains, or a handful of beans added to a dish you already enjoy.

Just remember that your digestive system may need some time to adapt.

A sudden dramatic increase in fiber can cause bloating, abdominal discomfort and excessive gas, particularly if you’re coming from a very low-fiber diet. SingHealth specifically recommends increasing fiber gradually over roughly two to three weeks to minimise this problem.

Water matters too. Fiber interacts with water in the digestive tract, and adequate fluid intake is particularly important when increasing your intake of fiber. So don’t go from eating 10 grams of fiber a day to suddenly trying to hit 40 grams tomorrow. Give your digestive system some time to catch up after a minor diet switch.

There are dietary supplements available as well, including psyllium husk and other fiber products. These can be useful in certain situations, but they shouldn’t necessarily be the first solution to a diet that contains very little fiber. 

Don’t worry about “fiber-maxxing”, just start with one more fruit a day!

References:

1. Eat This Much. (n.d.). How are the calories calculated? Why is fiber included in the calorie count? https://help.eatthismuch.com/help/how-are-the-calories-calculated-why-is-fiber-included-in-the-calorie-count

2. Guarneiri, L. L., Kirkpatrick, C. F., & Maki, K. C. (2025). Protein, fiber, and exercise: A narrative review of their roles in weight management and cardiometabolic health. Lipids in Health and Disease, 24, 237. https://pmc.ncbi.nlm.nih.gov/articles/PMC12255039/#CR51

3. Singapore General Hospital. (n.d.). High fibre diet. SingHealth. https://www.singhealth.com.sg/symptoms-treatments/high-fibre-diet

4. U.S. Department of Agriculture & U.S. Department of Health and Human Services. (2024). Dietary guidelines for Americans, 2020–2025: Food sources of dietary fiber. https://www.dietaryguidelines.gov/sites/default/files/2024-12/DA_Supplement_Food_Category_Sources_Dietary_Fiber_508c.pdf