Fiber is easily one of the most misunderstood, overlooked, and underrated nutrients in our diets. Technically, it’s not considered a nutrient, since our bodies can’t directly break fiber down into energy. But don’t let that fool you. Fiber plays a massive role in proper nutrient absorption, energy production, blood sugar management, gut health, and, based on recent studies, weight management. If you think fiber is just for middle-aged people, think again!
According to consumer research, 95% of the U.S. population is below the recommended daily requirements for fiber. If that doesn’t shock you, maybe the financial impact of it will. It’s estimated that if Americans met their daily fiber recommendations, it would save up to $80 billion dollars annually in medical expenses just from the reduction in constipation-related issues alone. That doesn’t even include heart disease or type II diabetes, which are at the top of the list for healthcare costs – not to mention deaths.
Now, I’m not a doctor, and this certainly isn’t medical advice, but it seems pretty clear that if the average American simply increased his or her intake of soluble and insoluble fiber on a daily basis, the current statistics on obesity and weight-related health issues would look dramatically different.
That’s a bold statement, yes, but one I’ll stand by, as it underscores the undeniable super powers of fiber. Consuming the proper ratio of fiber to the total amount of carbohydrate you eat, as well as making sure you’re getting the proper ratios of your two types of fiber (soluble and insoluble), can potentially do wonders for your weight loss goals and overall health.
Soluble vs. Insoluble Fiber – What’s the Difference?
There are two major types of fiber we get from our diets: soluble fiber and insoluble fiber. To understand the difference between them, imagine you put both in a glass of water. The soluble fiber will dissolve, and the insoluble fiber will not. The same in our bodies during the digestive process.
Both types of fiber are beneficial, but for different reasons.
Soluble Fiber: A Critical Tool for Blood Sugar Levels and Weight Loss
Foods high in soluble fiber include: oats, beans, avocado, brussel sprouts, broccoli, apples, pears, blueberries and some nuts like almonds.
Soluble fiber gets broken down in our intestines and digested by bacteria. Although we can’t break down soluble fiber directly for energy, the bacteria does it for us, producing necessary short chain fatty acids (SCFAs), which are the main source of energy for the cells lining the large intestine, promoting good gut health.
Soluble fiber also plays a part in managing blood sugar levels, which in turn can lead to better insulin response – the ultimate goal for better weight and health management. As soluble fiber dissolves, it takes on a gel-like state that helps slow the digestive process, giving our digestive tract the opportunity to properly absorb nutrients. The slower your digestive process, the lower the chances of blood sugar levels spiking after a meal.
When you don’t have enough fiber, the food you eat tends to move from the stomach to the small intestines too quickly, causing sugars to be absorbed rapidly. This in turn causes the pancreas to produce large amounts of insulin to help regulate this sudden rise in blood glucose. Not only can high insulin levels trigger fat storage and block our ability to burn fat for energy, but the subsequent hypoglycemic crash after a big spike can also leave you feeling tired and hungry.
When blood sugar levels are low, the brain sends out a red alert to eat. This can leave you feeling hungry prematurely, even if you just ate. This is also why it’s so easy to overeat a high-carb, low-fiber food like potato chips – because you eat a bunch of them and still feel hungry, so you keep eating.
The digestion-slowing effects of a high-soluble-fiber diet, on the other hand, tend to make you feel full for a longer period of time, making it easier to reduce your food intake without feeling as hungry.
If that’s enough to convince you to arm yourself with soluble fiber as part of your weight loss strategy, consider this: The gel-like consistency of soluble fiber can also help reduce the absorption of fats. According to reports from the University of Illinois-Chicago, the viscous properties of soluble fiber bind with fats and cholesterol, escorting them through the digestive tract, where they’re eliminated in your stool.
Insoluble Fiber: The Perfect Team Player for Optimal Health
Foods high in insoluble fiber include: almonds, whole wheat, whole grains, brown rice, bran, potatoes, and vegetables like green beans and cauliflower.
Insoluble fiber also helps with weight loss by reducing hunger pangs. Other than that one similarity, insoluble fiber plays a very different, yet complementary, role to soluble fiber. The two fiber types are teammates, so to speak.
Digestive enzymes, fluids, and bacteria don’t break down insoluble fiber the same way they do soluble fiber. Instead, insoluble fiber remains intact throughout the digestive process. In the colon, insoluble fiber absorbs fluids that help in the processing and movement of waste. This fibrous material also acts as a binder with other digested materials to help form a normal stool.
The proper forming and processing of waste helps prevent blockages in the intestines that could otherwise lead to poor nutrient absorption and constipation. Insoluble fiber may not have as glamorous a role as its soluble counterpart, but it’s equally important for digestive and overall health.
Ideal Fiber-to-Carb Ratios
So, how much fiber should you be getting? It’s not just a matter of “the more, the better,” as too much fiber can lead to gastric discomfort and other digestive issues. The general recommended daily fiber intake is 21-25 grams for women and 30-38 grams for men – but this is just a reference point and doesn’t take into account variables like carbohydrate type and different body weights.
My prefered fiber formula on a moderate “carb conscious” diet is a 4:1 carbs-to-fiber ratio. For example, if you consume 120 grams of carbs per day, 30 grams of fiber would be an ideal amount; at 200 grams of carbs, you’d want right around 50 grams of fiber.
If you’re on a very low-carb diet, you’re going to have to shoot for a much higher fiber-to-carb ratio. This is when the traditional recommendations can be referenced. Remember that fiber does not affect your net carbs, so don’t worry about disrupting your low-carb plan. If you’re on a keto diet, fiber intake is even more important, as high-fat and moderate-protein diets are typically deficient in fiber. Your fiber-to-carb ratio may be as high as 1:1 if you’re only getting 30 grams of net carbs a day.
Although a 4:1 ratio is suggested for achieving weight loss and health goals, a 5:1 ratio may be better if you’re consuming more than 200 grams of carbs a day (which I don’t recommend for those trying to lose weight). With a higher carb intake, a 5:1 ratio will help you avoid getting intestinal discomfort from too much fiber. For example, 250 grams of carbs would mean 50 grams of fiber with a 5:1 ratio; at a 4:1 ratio, you’d be over 60 grams of fiber a day, which could get quite uncomfortable.
The 5:1 ratio should also be used when selecting individual foods for your nutrition plan. For instance, if a particular loaf of bread (preferably “whole” wheat) contains 20 grams of carbs per slice, the fiber in that slice should be right around 4 grams. This is why a whole grain bread is always going to be a better option, as the fiber content is higher.
Whole Fruit YES, Fruit Juice NO
The 5:1 formula is also a great rule of thumb for picking the right type of fruit. Perhaps the best example of how big of a difference fiber can make is an apple.
Even though an apple has a lot of natural sugars (fructose), it also has a lot of fiber (a medium apple contains 4 grams of fiber, with 25 grams of carbs – almost exactly a 5:1 carbs to fiber ratio). The fiber in the apple slows the digestive process, allowing nutrients to enter the bloodstream slower and raising blood sugar more gradually (this is a good thing). This is why an apple has a low glycemic index (GI). Now, take that same apple, juice it, remove the pulp (the fiber), and it suddenly becomes high glycemic. This punctuates the importance of fiber content in our diet.
Apple = good. Apple juice = bad.
This example doesn’t just pertain to apples. Juice in general is a poor carbohydrate choice. Let’s look at a couple more fruits. Grape juice: 37 grams of carbs and less than 1 gram of fiber per cup. Orange juice: 26 grams of carbs and 0.5 gram of fiber. Two more losers right there. Eat an actual orange instead (22 grams of carbs and over 4 grams of fiber).
Aiming for these ideal ratios helps ensure that you’re getting “good” carbs from quality sources like those mentioned above. It also helps you keep your total carb intake in check for the day, rather than shooting for only a set number for fiber and then eating a bunch of “bad” carbs like potato chips and white breads.
Best Ratio of Insoluble to Soluble Fiber
Most people don’t get enough fiber in their diets, so “eat more fiber” is often a good initial recommendation. That said, to experience the full effects of fiber on your overall health (and even weight loss), you’ll want to be mindful to get proper amounts of both major types of fiber. Remember, soluble and insoluble fiber are teammates.
The ideal ratio for fiber intake is somewhere around 3:1, insoluble to soluble. This means you’ll want to get slightly more fiber from food sources like whole wheats and grains, brown rice, and bran than from oats, apples, and beans.
Here’s a good example of what it would look like: Let’s say your total daily fiber intake is 30 grams. You’d want around 23 of those grams to be insoluble and 7 grams soluble.
Where are you going to get all that insoluble fiber? Here are some good options of high-fiber foods where nearly all of it is insoluble:
- Almonds: 3.5 grams of fiber per ounce
- Brown rice: 3.5 grams of fiber per cup
- Whole Wheat Bread: 2 grams of fiber per slice
- Wheat Bran: 6 grams of fiber per ¼ cup
- Potato: 4.7 grams of fiber per medium potato
As for soluble fiber, here are some options:
- Apple: 4.4 grams of fiber per medium apple
- Rolled or Steel-Cut Oats: 5 grams of fiber per ¼ cup
- Blueberries: 3.6 grams of fiber per cup
- Broccoli: 5 grams of fiber per cup
Fiber’s Other Superpower: Gut Health
Another enormous benefit of daily fiber intake is that it improves gut health, particularly gut microbiome. Not versed on gut health? Never even heard of microbiome? Well, it could be your key to sustainable weight loss and robust health. And it’s covered in this Carbs 101 article on UndersunFitness.com.
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Burton-Freeman, Britt et al. “Ratios of soluble and insoluble dietary fibers on satiety and energy intake in overweight pre- and postmenopausal women.” Nutrition and healthy aging vol. 4,2 157-168. 31 Mar. 2017, doi:10.3233/NHA-160018
Carneiro, Lionel & Leloup, Corinne. (2020). Mens Sana in Corpore Sano: Does the Glycemic Index Have a Role to Play?. Nutrients. 12. 2989. 10.3390/nu12102989.
King DE, Mainous AG 3rd, Lambourne CA. Trends in dietary fiber intake in the United States, 1999-2008. J Acad Nutr Diet. 2012 May;112(5):642-8. doi: 10.1016/j.jand.2012.01.019. Epub 2012 Apr 25. PMID: 22709768.
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