When counting calories for weight loss or maintenance, one question that often comes up is whether you should count calories from fiber. Fiber is a type of carbohydrate that is not digested and absorbed by the body in the same way as other carbs. So should the calories from fiber count towards your daily calorie intake goal or not?
What is Fiber?
Dietary fiber, also referred to as roughage, is the indigestible part of plant foods like fruits, vegetables, whole grains, nuts and legumes. It passes through the digestive system relatively intact. There are two main types of fiber:
- Soluble fiber – dissolves in water to form a gel-like material. It can help lower blood cholesterol and glucose levels.
- Insoluble fiber – does not dissolve in water. It helps food move through the digestive system and promotes regularity.
Most plant foods contain a combination of both soluble and insoluble fiber. Good sources of fiber include oats, beans, lentils, berries, nuts, seeds, whole grains and vegetables.
Calories in Fiber
Fiber contains calories, just like other carbohydrates such as sugar, starch and digestible fiber. The calorie content of fiber is estimated to be around 1.5–2.5 calories per gram.
However, most of these calories are not absorbed by the body. Fiber passes through the upper part of the gastrointestinal tract mostly intact. It is then fermented by bacteria in the large intestine. The calories from fermentation provide some energy to the cells lining the colon, but are not absorbed into the bloodstream.
For comparison, digestible carbohydrates like starch and sugar provide around 4 calories per gram. Protein and fat also provide 4 calories per gram.
Should You Count Fiber Calories?
The majority of fiber’s calories are not digestible, so they don’t count toward your net calorie intake. Net calories refer to the calories actually absorbed by the body.
Leading health and nutrition organizations, including the FDA, suggest not counting calories from fiber when calculating your total calories for the day.
Subtracting fiber grams from total carbohydrates gives you the number of digestible or “net” carbs. You can use net carbs along with protein and fat grams to get a more accurate estimate of the calories your body absorbs from food.
Reasons Fiber Calories Don’t Count
Here are some reasons why the calories from fiber don’t count toward your daily calorie intake:
- Most fiber stays intact through digestion – Unlike other carbs like starch and sugar, fiber strands are resistant to digestion by stomach acid, bile salts and enzymes in the small intestine.
- Fiber can’t be absorbed – The human digestive system lacks enzymes needed to break down and release calories from fiber.
- Fiber fermentation provides minimal calories – Fermentation by gut bacteria accounts for about 10% of fiber calories. The small amount of energy released is not absorbed.
- Fiber increases fullness – Soluble fiber forms a gel that slows digestion. This helps you feel fuller on fewer calories.
- More calories are excreted – More calories from fiber calories are excreted as waste compared to digestible carbs.
In short, since your body cannot fully break down or absorb fiber and its calories, they should not be included in your daily calorie count.
Fiber Provides Several Important Health Benefits
Eating plenty of high-fiber foods is associated with several health benefits:
- Improved digestive health
- Reduced cholesterol levels
- Better blood sugar control
- Increased satiety and weight loss
- Lower cancer risk
The adequate intake (AI) for fiber is 25 grams per day for women and 38 grams for men. However, most people fall short of this, only getting around 15 grams per day.
Focusing too much on fiber calories can discourage people from eating enough high-fiber foods. So counting fiber grams, rather than calories, is recommended for optimal health.
Should You Completely Exclude Fiber from Calorie Counts?
Given that some fermentation of fiber does take place and provides a small amount of absorbed energy, some argue that you should count a portion of fiber grams toward your daily calorie intake.
For example, you could count half the calories from total carbohydrates, including fiber:
- Total carbohydrates: 25 grams (100 calories)
- Fiber: 5 grams (10 calories)
- Net carbs: 20 grams (80 calories)
- Calories to count: 90 calories (half of total carbs)
However, keeping track of calories this way takes effort and can get confusing. It’s more realistic for most people to subtract all fiber grams to calculate net carbs.
Additionally, people following low-carb, ketogenic and diabetic diets should rely on net carbs since their main goal is keeping digestible carbs low enough to maintain blood sugar control and ketosis.
Should You Count Insoluble vs Soluble Fiber Differently?
Both insoluble and soluble fiber provide health benefits and contain calories. However, some argue insoluble fiber calories shouldn’t count since they’re less fermented.
While it’s true that soluble fiber tends to be more readily fermented than insoluble, both types do undergo some fermentation. Therefore, there’s no need to count them differently.
How to Determine Fiber and Net Carb Content
To determine net carb content and count fiber grams rather than calories, read nutrition labels carefully.
Food labels display total carbohydrates, which includes fiber, sugars, added sugars and starch. The fiber grams are listed separately below the total carbohydrate amount.
To calculate net carbs:
- Look at the total carbohydrate amount.
- Subtract the grams of dietary fiber.
For example, here’s the label from a loaf of bread:
| Nutrition Facts | Servings per container 16 |
|---|---|
| Amount per serving | |
| Total Fat 5g | |
| Sodium 160mg | |
| Total Carbohydrate 15g | |
| Dietary Fiber 3g | |
| Total Sugars 2g | |
| Protein 4g |
To determine net carbs:
- Total carbohydrates = 15 grams
- Dietary fiber = 3 grams
- Net carbs = Total carbs – Fiber = 15 grams – 3 grams = 12 grams
Focus on net carbs and fiber grams, rather than fiber calories, to ensure your carb and calorie intake aligns with your health goals.
Should You Count Calories from Soluble Corn Fiber?
Soluble corn fiber is a viscous, fermentable fiber produced from corn starch. It’s been showing up as an ingredient in more foods.
Soluble corn fiber contributes 1.6 calories per gram, or about 40% less calories than regular digestible carbs. But does this mean you should count these calories when tallying your daily intake?
Due to its high solubility and fermentability, some calories from soluble corn fiber are absorbed. However, it’s still a type of fiber. So for simplicity, it’s best not to count calories from soluble corn fiber on a weight loss diet.
Additionally, soluble corn fiber provides benefits similar to other soluble fibers. It can help normalize bowel function, lower cholesterol and control blood sugar levels.
Should You Count Calories from Synthetic Fibers Like Polydextrose?
Polydextrose is a common synthetic fiber added to foods like protein bars, baked goods and candies to mimic the properties of soluble fiber.
It contributes 1 calorie per gram, which is slightly less than digestible carbs. While polydextrose does provide some benefits like improving bowel function, most of it is excreted intact.
For these reasons, most health experts agree you should subtract polydextrose and other synthetic fibers from total carbs like dietary fiber. Including their calories in your daily intake is unnecessary.
The Bottom Line
Fiber provides about 1.5–2.5 calories per gram, but most of these calories are not absorbed. Your body lacks the enzymes needed to break down fiber from plants.
Leading health authorities recommend subtracting fiber grams, but not calories, from total carbs to determine net carbs. This gives a more accurate estimate of the calories your body absorbs.
Counting fiber calories along with those from sugar, starch and digestible carbs is unrealistic and can deter people from getting adequate fiber.
Focus on increasing high-fiber foods for better digestive health, satiety, weight control and disease prevention. Be sure to read nutrition labels closely to determine fiber and net carb content.
Counting Fiber on Keto and Low-Carb Diets
The ketogenic diet and other low-carb diets limit digestible carbs to achieve ketosis and other health benefits. Therefore, counting net carbs is essential.
To determine net carbs on keto:
- Look at total carbohydrate grams.
- Subtract fiber grams.
- Avoid foods with maltitol and other sugar alcohols to keep carb counts accurate.
Low-carb and keto dieters should aim for net carbs in the range of 20–50 grams per day. Consuming foods high in fiber like non-starchy vegetables can provide carbs in a way that’s healthy while maintaining carb limits.
Excluding fiber grams, but not calories, gives you wiggle room for fitting in a wide variety of veggies to optimize nutrition.
Sample Keto Net Carb Calculation
Here’s an example for determining net carbs on keto:
Food: 1 cup raw spinach (30 grams)
- Total carbs: 0.7 grams
- Fiber: 0.6 grams
- Net carbs: 0.7 grams – 0.6 grams = 0.1 grams
As you can see, subtracting the grams of fiber from total carbs provides an accurate net carb amount. This allows you to utilize the health benefits of fiber without going over carb limits.
Should You Count Fiber on Diabetic and Low-Glycemic Diets?
Calculating net carbs is also useful for people with diabetes and those following low-glycemic diets.
Fiber has minimal impact on blood sugar levels. Focusing on net carbs can help manage glycemic response and insulin needs.
To determine net carbs on a diabetic diet:
- Look at total carbohydrate grams.
- Subtract fiber grams.
- Focus on foods with a low glycemic index.
Modifying carbohydrate intake and emphasizing high-fiber, low-glycemic foods helps control blood glucose levels and reduces diabetes complications.
Should Fiber Supplements be Counted?
Fiber supplements like psyllium husks, glucomannan and methylcellulose are composed almost entirely of fiber. They provide few, if any, digestible carbohydrates or calories.
While these isolated fibers can help increase your intake, they shouldn’t be counted toward net or total carbohydrate grams.
Pros of Fiber Supplements
- Increase fiber intake if diet is lacking
- Provide benefits like improved regularity
- Unlikely to affect blood sugar
Cons of Fiber Supplements
- May cause side effects like gas and bloating
- Less beneficial than fiber from whole foods
- Generally not counted as net or total carbs
Aim to meet fiber needs through foods first before considering supplements. Fiber from varied whole food sources is best.
Should You Count Calories from Sugar Alcohols?
Sugar alcohols like erythritol, xylitol, sorbitol and maltitol are used to sweeten some low-carb and sugar-free foods.
They’re considered natural fiber supplements. However, sugar alcohols can raise blood sugar and provide 1.5–3 calories per gram — more than other fibers.
Given their calorie content and glycemic impact, most health experts recommend counting half or all of sugar alcohol grams as net carbs.
Reasons to Count Some Sugar Alcohol Calories
- Most provide 1.5–3 calories per gram.
- Can spike blood sugar and insulin levels.
- Less likely to cause laxative effect than most fibers.
- Often incompletely listed on labels.
For better blood sugar control and accuracy, count at least half the grams from sugar alcohols when tallying net carbs.
Takeaway: Prioritize Fiber Grams, Not Calories
Calculating net carbs allows you to take advantage of fiber’s health benefits without worrying about its calorie content.
Focus on getting at least 25–38 grams of fiber per day based on your gender and calorie needs. Emphasize fiber-rich foods like vegetables, avocados, berries, nuts and seeds.
Read nutrition labels carefully to subtract fiber grams, but not calories, when determining the net carbs and calories absorbed from a food or meal.