Adding Fiber to a Ketogenic Diet
When following a ketogenic diet, it is not uncommon for people to neglect eating quality
sources of fiber in an effort to avoid any carbohydrate intake. There is a chance this can
lead to constipation, poor digestion, and a lack of certain vitamins and minerals.
What is fiber?
Dietary fiber is the indigestible plant material that passes through our digestive system either
completely undigested, or broken down via microbial fermentation, in the large intestine.1
Fiber aids in the removal of waste via the colon and is important for maintaining healthy digestion.
Fiber is categorized as either soluble or insoluble, and each is digested differently.
Soluble fiber: Soluble fiber dissolves in liquids and becomes gel-like in the digestive tract.1 It slows digestion, increases satiety, and when consumed with carbohydrates can slow intestinal absorption and can help minimize increases in postprandial blood glucose.2
Soluble fiber is predominantly found in fruits and legumes, which are not advised on a ketogenic diet, and small amounts are found in vegetables.3 Soluble fiber ingredients are also commonly found in low-carb packaged foods, such as isomalto-olidosaccharides (IMOs) and soluble corn fiber.
Insoluble fiber: Insoluble fiber does not dissolve like soluble fiber does. This type of fiber stays intact and is responsible for what people refer to as roughage when speaking of fiber. This type of fiber aids in digestion and promotes elimination of waste by the colon.4
Insoluble fiber is the predominant type of fiber found in vegetables, especially the low-carb, nonstarchy options that are fitting for a ketogenic diet.
Taking in fiber on a ketogenic diet
Following a ketogenic diet is easy when you stick to fatty meats, eggs, oils, and full-fat dairy. However, by a strict intake of these foods, there is very little consumption of whole-food fiber in addition to a lack of micronutrient intake. Moreover, low-carb, keto-friendly packaged foods, although providing ease of entry into a ketogenic lifestyle, are typically filled with soluble fibers. These soluble fibers contribute toward the majority of the daily carbohydrate count and lead to a lack of insoluble fiber in the diet. Consequently, due to the attempt to meet daily macronutrient ratios, there is a tendency to neglect all vegetables, even low-carb options, and thus losing out on insoluble fiber intake. A well-formulated ketogenic diet should not be void of fiber; some may even argue it provides more fiber than other diets. This is because a well-formulated ketogenic diet includes regular amounts of low-carb vegetables on a daily basis, along with quality sources of fats and protein.
Intriguingly, the fermentation process of insoluble fiber during digestion can also contribute to ketogenesis (i.e. the production of ketones). Fiber is broken down by the gut microbiome into short-chain fatty acids, such as butyrate,5 a molecule that is very structurally similar to the ketone body, beta-hydroxybutyrate. Subsequently, butyrate can be converted to beta-hydroxybutyrate and has been shown to increase blood ketone levels in humans.6
Fiber sources on a well-formulated ketogenic diet
Low-carbohydrate fibrous whole foods, such as those listed below, are recommended as part of a well-formulated ketogenic diet to allow for entering and/or sustaining nutritional ketosis (defined as an elevation of beta-hydroxybutyrate (BHB) above 0.5 mmol/L). Consider adding these examples to your diet:
All leafy greens
Cruciferous vegetables (e.g. broccoli, cauliflower, Brussels sprouts, cabbage, kale)
Low-sugar berries (e.g. wild blueberries)
Nuts & seeds
Always consider carbohydrate content in examples above and portion accordingly.
Tips for consuming more fiber on a ketogenic diet:
This may be an obvious solution to a lack of insoluble fiber in the diet, and you may even be experiencing flashbacks from traumatic dieting memories you just cant shake. However, a ketogenic salad should be an exception to this bias. If you have ever had a good salad, you know salads are underrated; they only become boring when you take away the fatnot an issue on a ketogenic diet. Gone are the days when you ask for dressing on the side. When you find a high-fat dressing you enjoy, you will begin to enjoy your salads!
Recommended ingredients: leafy greens (all types), avocado, hemp seeds, boiled eggs, fatty cuts of beef, chicken thighs, fatty fish, olives, nuts & seeds, artichoke hearts, high-quality oils, high-fat dressings (see below)
Sautéed & roasted vegetables
While from a glycemic standpoint there is an advantage to eating vegetables raw (due harder access to carbohydrates stored inside plant cells), sometimes eating cooked vegetables can bring a sense of comfort, and could translate to better compliance to a ketogenic diet. The best oils for cooking that can handle heat contain saturated and monounsaturated fats such as butter, ghee, avocado oil, extra-virgin olive oil, MCT oil, and coconut oil. Use of fresh or dried herbs and spices such as garlic, parsley, cumin, chili, oregano, paprika, rosemary, coriander, etc. will add additional flavors.
Recommended ingredients for sautéing: spinach, onion, mushrooms, kale, zucchini, cabbage, Bok choy
Recommended ingredients for roasting: Brussels sprouts, broccoli, cauliflower, onion, mushrooms, celery (dont knock it til you try it!)
Yes, pudding! Ketogenic chia puddings are extremely easy, cheap, and convenient to make and, most importantly, are full of fiber. The carbohydrate content of chia seeds is primarily fiber, 86% to be exact, and most of it is insoluble fiber! When chia seeds are soaked overnight, they absorb the liquid and take on a pudding-like consistency. Spruce up the chia puddings with some of the recommended ingredients below to avoid a flavorless gel and make sure to include healthy fats!
Recommended ingredients: chia seeds, flax seeds, hemp seeds, low-carb nuts/nut butters, sugar-free chocolate chips, cocoa powder, cinnamon, vanilla extract, MCT oil/powder, full-fat coconut cream, coconut butter, shredded coconut, unsweetened nut-milks, coconut oil, sea salt, sugar-free/low-carb protein powders
Dressings & dips
Dressings and dips are like smoothies in that you can easily sneak ingredients into them. Adding fiber into dressings and dips makes food taste better, as well as being an easy way to get in those healthy fats! Use a blender to make these, and include dressings and dips with any savory snack or meal!
Recommended ingredients: spinach, kale, steamed cauliflower, raw or steamed zucchini, high-quality oils, tahini, herbs & spices, garlic, lemon juice, apple cider vinegar, full-fat yogurt (or dairy-free alternative), MCT oil/powder, avocado oil- or olive oil-based mayonnaise
Lattimer JM et al. Effects of Dietary Fiber and Its Components on Metabolic Health. Nutrients. 2010;2(12):1266-1289.
Chutkan R et al. Viscous versus nonviscous soluble fiber supplements: Mechanisms and evidence for fiber-specific health benefits. Am Acad Nurse Practitioners. 2012;24:476-487.
https://carleton.ca/healthy-workplace/wp-content/uploads/soluble-fibre.pdf. Accessed 10/5/18.
Lattimer JM et al. Effects of Dietary Fiber and Its Components on Metabolism. 2010;12:1266-1268.
Slavin J. Fiber and Prebiotics: Mechanisms and Health Benefits. 2013;5:1417-1435.
St-Pierre V et al. Butyrate is more ketogenic than leucine or octanoate-monoacylglycerol in healthy adult humans. J Functional Foods. 2017;32:170-275.