Five reasons why Fibre is a must for Gut Health and Optimal Metabolism
Fiber intake is closely tied to metabolic health and most people in developed nations aren’t eating enough of it. According to the USDA Dietary Guidelines, “More than 90 per cent of women and 97 per cent of men do not meet recommended intakes for dietary fibre,” in part because more than 85 per cent of adults don’t eat enough fruits, vegetables and whole grains. (Though whether whole grains are a good source of fibre is up for debate – more on that below. In addition, beans, legumes, nuts and seeds are among the best sources of fibre.) What’s worse, even those official recommendations (less than 30 grams/day) may be lower than we really need for optimal health (which may be 50 grams/day or more).
Fibre is a macronutrient that mostly comes from plants. (Other macronutrients are protein and fat.) Though it is considered a carbohydrate, your body mostly doesn’t break it down into glucose like other carbs; fibre mostly passes intact through the gastrointestinal tract. There, it feeds and maintains the gut microbiome, which has beneficial effects on metabolic health, such as improved glucose and insulin levels. It also keeps gut inflammation down, protects the gut’s mucus membrane and slows glucose absorption.
Fibre has been dubbed “half of the ‘antidote’ to the obesity pandemic.” (The other half is exercise.)
Fibre Fuels Your Gut
Many of the organisms that make up the gut microbiome (which include bacteria as well as protozoa, fungi, and viruses) feed on fibre. So, when you eat a diet rich in fiber, these organisms thrive, helping to maintain a diverse gut microbiome. This has a ripple effect on glucose absorption as well as insulin sensitivity.
1. Fiber Produces Beneficial Short-Chain Fatty Acids
When gut microorganisms ferment soluble fibre, they produce metabolites called short-chain fatty acids. In recent years, studies have linked higher levels of these molecules with improved insulin sensitivity and weight regulation. Butyrate, acetate and propionate are the major short-chain fatty acids produced when dietary fiber is fermented. Together, they make up 90-95% of the total short-chain fatty acids in the colon. Although you can get small amounts of butyrate from foods like butter, milk fat and vegetable oil, most of the butyrate your body uses comes from the fermentation of dietary fiber.
2. Fiber Keeps Inflammation Down
Fiber keeps inflammation at bay by feeding gut bacteria. Most prebiotics – which feed the microorganisms already in your gut—can be classified as dietary fibre (probiotics, in contrast, add new ones). Prebiotics help maintain the balance between the anti-inflammatory and pro-inflammatory gut microorganisms. Imbalances in the gut microbiota – a condition known as dysbiosis that occurs when some gut microorganisms flourish while others falter – have been linked to gut inflammation and metabolic changes and diseases like obesity, inflammatory bowel disease and malnutrition.
Diets high in fat and sugar and low in fibre – such as the Western diet – are associated with lower levels of certain beneficial bacteria. Fibre, in contrast, helps keep the gut microbiome in a healthy balance and increases the diversity of the microbiome, including bacteria that promote anti-inflammatory processes.
3. Fibre Helps Protect the Gut Lining
Another way fibre keeps inflammation down is by maintaining the gut’s mucus layer, a physical barrier that keeps pathogens out. If the mucus layer is compromised and pathogens can breach it, the immune system mounts an inflammatory response. These pathogens can be invading microorganisms, or they can be those that already exist in the gut.
Fibre Helps Prevent Metabolic Dysfunction
Fiber can also help blunt post-meal blood sugar spikes. Appetite signalling and the appearance of glucose in the small intestine are primarily triggered by gastric emptying, the movement of partially digested food into the small intestine. Soluble fibre binds liquids to make food more viscous, slowing this movement.
Individuals with diabetes who ate more fibre had lower HbA1c (a measure of average blood sugar over three months), fasting plasma glucose, insulin, and insulin resistance. Interestingly, the type of fibre (soluble or insoluble) didn’t seem to matter. Instead, the researchers have found the most significant improvements in people who switched their fibre intake from low to moderate (19 grams) to high (35 grams). Eating 35 grams of fibre a day, the authors wrote, could reduce the risk of premature mortality by 35% in people with prediabetes or diabetes.
“Most experts recommend we consume 50 gms of fibre per day. An average person gets 14 gms per day”
How Much Fiber Should You Eat?
Research suggests our ancestors may have eaten as much as 100 grams of fiber a day. Our modern diet is nowhere near this.
The American Dietetic Association recommends that 30 to 50 grams per day can promote lower blood sugar. A 2001 study similarly found that people with diabetes who ate 50 grams of naturally occurring fiber a day for six weeks had better lipid and blood glucose profiles than those who ate only 25 grams per day.
How to Get More Fiber in Your Diet
Getting more fibre, like maintaining a low-carb diet, can help lower blood sugar. While it may seem like these strategies are mutually exclusive—fibre is a carbohydrate, after all—it is possible to consume fibre as part of a low-carb diet. Here are some of the best sources of fibre:
- Chia: Two tablespoons of chia seeds contain 11 grams of fibre and just 2 grams of carbs.
- Flaxseed: The same amount of ground flaxseed contains barely any carbs and packs almost 4 grams of fibre
- Avocado: A little more than half of a large avocado (100 grams) contains 6.7 grams of fibre and 8.5 grams of carbs.
- Beans and lentils: Navy, lima, small white and yellow beans, and lentils are also high in fibre but lower in carbs than other beans.
Whole Grains: A popular way to get more fibre is to swap refined grains for whole grains, but some experts suggest that whole grains are not an optimal fibre source.
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