Does Eating High-Fiber Foods Cause Weight Gain? Here's What a Dietitian Says

Fiber may not be considered the most glamorous nutrient, but it is certainly important. Dietary fiber, abundant in plants, is an indigestible type of carbohydrate that aids in keeping your bowels regular, pulls LDL cholesterol away from the heart, increases feelings of fullness, regulates blood sugar and more. The Centers for Disease Control and Prevention states that a fiber-rich diet is linked to a lower risk of heart disease, diabetes and certain types of cancer.

Hence, increased intake of fibrous foods like fruit, vegetables, nuts, seeds, legumes and whole grains is encouraged for health benefits. But does eating fiber help with weight loss? And could eating too much make you gain weight instead?

This article will discuss how fiber promotes weight loss, why you might feel it causes weight gain, fiber supplements, and 10 easy ways to increase your fiber intake.

Why Fiber Promotes Healthy Weight Loss

Despite fiber's many health benefits, over 90% of Americans do not consume the recommended amount of fiber (25 to 34 grams daily), according to the 2020-2025 Dietary Guidelines for Americans.

In addition to being heart-healthy and beneficial to your gut, fiber has been shown to promote healthy weight loss by several potential mechanisms. Eating fiber can increase feelings of fullness, reducing overall calorie intake. Fiber-rich foods contain resistant starch and prebiotics, which contribute to the health of the microbiome. In addition, eating fibrous food helps to regulate blood sugar.

How your body reacts to increasing fiber will be highly individual and can vary based on weight, overall health, diet quality and physical activity, to name a few.

Increasing Feelings of Fullness

Fiber has satiating power because it takes longer to chew, promoting saliva and gastric acid production, and it reduces gastric emptying (the rate at which food leaves the stomach). When you are fuller for longer, you are likely to eat less food, which can reduce your overall calorie intake (creating a calorie deficit) and lead to weight loss. Researchers note that the effects of fiber on one's perceived satiety will depend on certain factors like the amount of fiber, molecular size and solubility, as well as the food matrix (solid, semi-solid or liquid food), per a 2019 systemic review in Foods.

Fiber's ability to make you feel full can help you stick to a diet. In a 2019 study published in The Journal of Nutrition, researchers found that dietary fiber intake, independently of macronutrient (fat, protein and carbohydrate) and calorie intake, promoted weight loss and dietary adherence in adults with excessive weight or obesity when consuming a calorie-restricted diet.

This subset of The POUNDS Lost (Preventing Overweight Using Novel Dietary Strategies) collected dietary recalls from 345 participants who were prescribed four different types of calorie-restricted diets (low-fat/ high protein, low-fat/average protein, high-fat/average protein and high-fat/high protein). They were told to eat a minimum of 20 grams of fiber daily. Participants met with a dietitian every 8 weeks and were instructed to exercise for 90 minutes weekly. Researchers found that from baseline to 6 months, an increase in dietary fiber (about 3.7 to 8.3 grams daily) was strongly associated with dietary adherence and weight loss.

There were some limitations, though; adherence was based on self-reported dietary recalls, which can skew data, and the population wasn't very diverse.

Improving Your Gut Microbiome

Studies have shown that a certain type of dietary fiber, referred to as prebiotics, increases good bacteria like Bifidobacteria and lactic acid bacteria in the gut, according to a 2017 review published in the Journal of Translational Medicine.

An increase in good bacteria contributes to gut diversity (different types of microorganisms like bacteria, fungi, viruses). A diverse and healthy microbiome may assist in weight loss and reduce the risk of obesity. In a 2018 systematic review and meta-analysis in Genes, researchers evaluated the use of probiotics, prebiotics and synbiotics (a combination of probiotics and prebiotics) on weight loss. They found that compared to placebo, probiotics led to significant reductions in body mass index (BMI), body weight and fat mass, and prebiotics led to a significant decrease in body weight in some of the studies.

Helping Regulate Blood Sugar

Carbohydrates are the macronutrient that impacts blood sugar the most. When you eat food that contains carbohydrates, the body breaks them down into sugar or glucose. Next, insulin (a hormone) is secreted to bring the sugar to your cells to use for energy. Eating more fiber slows down how quickly glucose is metabolized, resulting in a slower output of insulin. Slow and steady after-meal blood sugar and insulin responses are linked to increased satiety.

Why You Might Feel That Fiber Causes Weight Gain

Suddenly or drastically increasing your fiber intake, especially without drinking enough water, can result in gas, bloating and constipation. When your stomach is bloated, or you do not have regular bowel movements, you might feel like you've gained weight. Being backed up with stool can cause temporary shifts in the scale. But how you gain sustained weight is to consume more calories than your body needs.

Are Fiber Supplements Good for Weight Loss?

Simply taking a fiber supplement will not address other behavioral factors contributing to weight, including stress, sleep, exercise and eating behaviors. Fiber supplements do not contain other nutrients, like protein and fat, that can impact weight. Therefore, a food-first approach to weight loss is usually recommended because of the variety of nutrients in foods. In addition, if they contribute to weight loss, fiber supplements may only yield modest results in certain people.

10 Ways to Increase Your Fiber Intake

As mentioned above, the Dietary Guidelines for Americans recommend, on average, 25 to 28 grams of fiber daily for adult females and 31 to 34 grams for adult males.

If you don't consume fiber-rich foods regularly, you'll want to increase your intake slowly and make sure you drink adequate amounts of water simultaneously. Doing so will help reduce gas and bloating and prevent constipation, nausea and dehydration. Fiber acts like a sponge; it needs water to plump up and move through the digestive tract smoothly.

Reach your fiber needs by increasing your intake of fruits, vegetables, whole grains, nuts, seeds and legumes. Here are some great ways to up your daily intake.

1. Start your day with a fiber-rich breakfast: For example, a Vegetable Omelet with whole-grain bread or corn tortilla, low-fat yogurt with fruit and nuts, a fruit or vegetable high-protein smoothie or fiber-packed overnight oats.
   
2. Add 1 serving of fruit or vegetables at each meal: The recommended intake of fruits and vegetables for adults is 1.5 to 2 cups of fruits and 2 to 3 cups of vegetables daily.
   
3. Eat the skins of fruits and vegetables: Think apples, pears and potatoes.
   
4. Add 1 serving of berries to your daily meal plan: One cup of raspberries, for example, contains 8 grams of fiber.
   
5. Eat 1 serving (1 to 1.5 ounces ) of nuts daily: Nuts contain fiber and omega-3 fatty acids, essential fats that are important for heart, eye, brain and skin health.
   
6. Practice USDA's MyPlate method: Fill half your plate with nonstarchy vegetables (greens, peppers, onions, broccoli, cauliflower, mushrooms), make one-quarter a source of protein (fish, chicken, turkey, lean beef, tofu) and the other quarter a starch (whole grains or starchy veggies like sweet potatoes, potatoes, pumpkin or butternut squash).
   
7. Add a tablespoon of seeds, which are packed with fiber, to a snack: Try adding chia, ground flaxseed, hemp or pumpkin seeds to your yogurt, cottage cheese, oats or nondairy yogurt alternative.
   
8. Make half of your grains whole grains: Some examples are whole-grain bread, whole wheat, oats, popcorn, maize, fonio, freekeh, farro, quinoa, barley, brown rice, wild rice and teff.
   
9. Add ½ cup of beans to your daily routine: For instance, you can snack on cut-up veggies with a bean spread like hummus. A half-cup of beans contains at least 5 grams of fiber.
   
10. Eat more avocado: Top sandwiches, veggie bowls, wraps or whole-grain crackers with fiber-rich avocado. Half of a medium avocado contains about 6 grams of fiber, per the USDA.

Frequently Asked Questions

Is fiber good or bad for weight loss?

Fiber is great for weight loss and overall health. Fiber-rich foods, like fruits and vegetables, help you to feel full, reducing your overall caloric intake. A calorie deficit is important for weight loss.

Does fiber cause you to retain water?

If you are making a major shift in your diet (for example, from a low-carbohydrate diet to a higher-fiber carbohydrate diet), you may retain some water, but this is usually temporary. This usually occurs when you eat more carbohydrates than you need, and they are stored as glycogen.

How does fiber affect your weight?

Trying to lose weight is a different journey for everyone. Weight isn't impacted by one nutrient alone but rather by a combination of many factors, including overall diet quality, physical activity, creating a calorie deficit and age, to name a few. However, including more fibrous foods in your diet may assist in creating a calorie deficit by increasing feelings of fullness, contributing to gut health and improving blood sugars.

The Bottom Line

Increasing your fiber intake can benefit your heart and digestive health. It may also contribute to your weight-loss goals by increasing the likelihood of dietary adherence and promoting weight loss and maintenance. If your diet lacks fiber, increase your intake slowly and steadily while drinking ample amounts of water. Drinking water simultaneously will reduce the risk of digestive symptoms like gas and bloating. If you need assistance in meal planning or have an underlying condition, reach out to a registered dietitian for education and support.