First, let's get clear on what fiber is.
It is a type of carbohydrate that passes through the body undigested. It is not broken down into sugar molecules as most of the other carbohydrates are. It can be found in most whole, unprocessed plant foods, including legumes such as beans, peas and lentils along with vegetables, fruits, nuts, seeds, and grains. Most of these foods have both soluble and insoluble fiber in varying amounts and we need both. Soluble dissolves in water whereas insoluble fiber does not. Because fiber expands, it requires a sufficient intake of water to do its job of moving waste out of the body through a bowel movement.
While fiber's role in preventing constipation should be enough of an incentive for us to pay attention to the fiber content of the foods we eat, there are many other reasons why we need a sufficient amount of fiber in our diet. Relevant in our case is fiber's ability to help shrink our waistline. How does it do that?
Many experts summarize what fiber can do as follows:
Fiber promotes a feeling of fullness which can curb appetite and in turn, this helps to reduce overall calorie intake. Excess calories are a major factor in resistance to weight and fat loss.
Through what's referred to as the "fiber flush effect", fiber can eliminate calories from the foods we eat through the excretion of fecal matter. When this toxic waste stays in the body, it creates an environment for other toxic buildup and blockages throughout the body. Some of the toxins settle inside fat cells around the belly. The more toxins hide inside cells, the more weight and the bigger the waistline as well.
High fiber foods slow the body's conversion of carbohydrates to sugar. By doing so, fiber supports stable blood sugar levels which is required to prevent insulin resistance. Failing to keep blood sugar in balance means that excess sugar is stored as fat. In other words, since insulin is a fat-storage hormone, the more stable the blood sugar levels, the less insulin is released and the lower the risk of fat buildup from a diet that causes consistent hikes in blood sugar levels (Brenda Watson with Leonard Smith, 2007: 22).
Others including the Mayo Clinic and hrtnet.org websites concur, noting that fiber intake supports hormonal balance. According to a recent hrtnet.org blog post, a “…healthy dose of fiber in the diet will assist you to get rid of excess estrogens that…increase weight gain." Estrogen dominance is a known factor in belly fat accumulation. This occurs when dirty estrogen is not removed from the system.
Low fiber intake in the diet can also impair leptin. This hormone is known for its ability to suppress a strong appetite and can therefore prevent overeating (Mayo Clinic 2021; see also St. Pierre 2009), a factor in fat buildup and weight gain. This means that a high fiber intake will help to lower appetite through the increased production of hormones that make you feel full (Landes 2022). Because soluble fiber such as pectins, beta-glucans, psyllium, glucomannan and guar gum all thicken in water, it forms a gel-like substance that sits in your gut, this "slows the emptying of your stomach, increasing digestion and absorption times. The end result is a prolonged feeling of fullness and a significantly reduced appetite" (Joe Leech 2021).
Fiber may reduce inflammation in the body, which benefits the gut, a known factor in weight management efforts and in reducing abdominal obesity. “A high-fiber diet potentially lowers inflammation by modifying both the pH and the permeability of the gut” (Swann 2020). Reducing inflammation is important when trying to reduce belly fat, and it is especially important for those struggling with obesity (Ellulu 2017). The IRAS Family Study that included 1,114 people, African American and Hispanics who attended both the baseline and 5-year follow-up describes the impact of lifestyle factors on changes in visceral adipose tissue (VAT) or abdominal fat deposits concludes that "increased soluble fiber intake and vigorous physical activity significantly decreased the rate of VAT accumulation.”
Fiber improves the diversity of good bacteria in your gut, which enables your body to more easily process foods and have regular bowel movements. People with a healthy supply of good gut bacteria tend to keep a healthy weight as well. Soluble fiber passes through your digestive system mostly unchanged, till it reaches your friendly gut bacteria most of which live in your large intestine. Fiber is microbiome's favorite food helping them create short chain fatty acids (Joe Leech 2021).
Fiber can also help reverse insulin resistance, improve mood and memory.
So, how do you increase your fiber intake?
The easiest way is to focus on a diet that is rich in unprocessed plant foods as much as possible. The more of these consumed with each meal, the easier it is to meet daily fiber requirements. Fruits, nuts and seeds, whole grains and legumes are the main sources of fiber. So, making these the bulk of one's diet can help ensure we get not only a good supply of nutrients that whole unprocessed foods have, but also the required amount of fiber as well. When foods are processed, they tend to lose many of these nutrients. When buying processed foods such as cereal, bread, or crackers, aiming for those with 5 grams of fiber per serving can help us to meet our daily fiber needs. On average, Watson and Smith (2007) recommend 35 grams of fiber per day.
Caution: Not everyone can freely increase fiber intake without side effects. Therefore, always check with your healthcare provider before changing your diet or taking any supplements to ensure none of them will interfere with medications or other supplements you may already be taking. Some health conditions, such as Crohn's disease can make a high intake of fiber quite challenging. Otherwise, meeting the average recommended daily intake of fiber can be beneficial for anyone who is generally in good health. Low-fiber diets in fact can interfere with the body's normal metabolic processes and may require that your body uses its precious and most likely limited supply of vitamins and minerals to digest them.
Here is a list of some of the best sources of fiber to guide you as you plan your next time food shopping trip.
Veggies: Artichokes, collard greens, broccoli, beets, swiss chard
Fruits: Raspberries, kiwi, avocados, apples, blackberries, guava, persimmons
Legumes: Red lentils, kidney beans, chickpeas, black beans, lima beans
Grains: Steel cut oats, wild rice, brown rice, quinoa, teff, whole rye
Nuts and Seeds: Almonds, chia seeds, flax seeds, pistachios, sunflower seeds, pumpkin seeds
Potatoes: Sweet potatoes, red potatoes
So, if you are looking to support your body to shrink your waistline, increasing your fiber intake can support you along the way.
Here's another tip. The next time you want to cook potatoes, don’t get rid of the skin as this is where most of the fiber is. Also, cooked potatoes, especially those with red skin, are less starchy and less impactful on blood sugar levels. Still they need to be consumed in moderation. Once cooked and cooled, potatoes can serve as a healthy source of resistant starch or a prebiotic that feeds the good gut bacteria.... “[c]ertain insoluble fibers, such as resistant starch, also function as prebiotics” (Leech 2018). Cooked and cooled potatoes can be eaten as a healthy snack. With a little drizzle of olive oil, a couple of tablespoons of hummus or half an avocado, a few bites of these potatoes can satisfy your hunger until your next meal.
My favorite sources of fiber are legumes, including white beans and red lentils, fruits such as green apples, under ripe bananas, avocados, pears, raspberries, blackberries, blueberries and whole kiwi fruit. That's right! Kiwi's skin is edible and in fact most of the fiber is in the skin. It's a bit hard and chewy but it is beneficial. Try adding the whole fruit into a smoothie. Kiwi is not only a great source of vitamin C which supports the immune system, but it is also an excellent source of insoluble fiber that keeps things moving through the digestive tract and prevents constipation. Among nuts and seeds, my favorites are almonds, pistachios, walnuts, pecans, pumpkin seeds, chia seeds, flax seeds, and sunflower seeds. Among grains, my choices are gluten-free steel-cut oats, amaranth, sorghum (when I can find it) and teff.
I use some of these high fiber foods in my smoothies. Try this high fiber smoothie recipe for a nutrient-dense, high-fiber satisfying meal in a glass. It's a great for detoxifying!
1/2 cup raspberries
1/2 a banana
2 handfuls of fresh spinach
1 cup fresh celery, chopped
1/2 a beetroot cut in small pieces
1 medium carrot, cut in small pieces
1-2 tablespoons of ground flax seeds
1/2 a small avocado
A small piece of fresh turmeric or 1 tsp of ground turmeric
A small piece of fresh ginger or 1 tsp of ground ginger
1/2 fresh lemon (cut in small piece and collect the juice that may come out while cutting and add to the smoothie)
2 cups of filtered water (or 1 cup almond milk or any other dairy milk substitute and 1 cup of water)
Place all ingredients in a blender and blend till smooth.
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I discuss the importance of fibers and other foods in detail in my upcoming online course, which teaches women in midlife about dietary and lifestyle choices that support belly fat loss and promote a healthy balance. More details to follow!
“Fiber Can Help You Lose Weight — But Only a Specific Type” by Joe Leech. Updated November 18, 2021. https://www.healthline.com/nutrition/fiber-can-help-you-lose-weight. Accessed May 17, 2021
“Lifestyle Factors and 5-Year Abdominal Fat Accumulation in a Minority Cohort: The IRAS Family Study” by Kristen G. Hairston et al. In Obesity (Silver Spring), 2012 Feb: 20(2). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3856431/. Accessed October 17, 2022.
"9 Hormones That Affect Your Weight — and How to Improve Them” by Ellen Landes. Updated January 22, 2022. https://www.healthline.com/nutrition/9-fixes-for-weight-hormones. Accessed October 18, 2022.
“The Role of dietary fiber in hormonal balance and anti-aging.” April 25, 2020.
http://www.hrtnet.org/the-role-of-dietary-fiber-in-hormonal-balance-and-anti-aging/. Accessed October 18, 2022.
“Dietary fiber: Essential for a healthy diet”, by Mayo Clinic Staff. January 6, 2021. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983. Accessed October 18, 2022.
“Fiber intake predicts ghrelin levels in overweight and obese postmenopausal women,” by David H. St. Pierre, et al. April 15, 2009.https://pubmed.ncbi.nlm.nih.gov/19369431/. Accessed October 18, 2022.
“Dietary fiber and its associations with depression and inflammation,” by Olivia G. Swann, et al. In Nutr Rev, 2020 May 1;78(5). https://pubmed.ncbi.nlm.nih.gov/31750916/. Accessed October 18, 2022.
“Obesity and inflammation: the linking mechanism and the complications,” by Mohammed S. Ellulu, et al. In Arch Med Sci. 2017 Jun; 13(4). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5507106/. Accessed October 18, 2022.
Brenda Watson with Leonard Smith. The Fiber35Diet: Nature's Weight Loss Secret. Free Press, New York. 2007.