Most of us know we need to eat more protein, that processed food is bad for us and that we should avoid excess sugar, but when it comes to what constitutes a healthy diet, fiber is often mentioned in passing—overlooked for more fashionable nutritional fads and reminiscent of a bygone era of Bran Flakes.
Not only is a high-fiber diet the key to keeping slim, it has also been found to improve our gut microbiome, reducing the risk of illnesses such as diabetes, heart disease, cancer and Alzheimer’s. Fiber also helps to lower cholesterol and balance blood sugar levels.
And we are lacking in it more than ever, according to the latest figures from the British Dietetic Association (BDA). The average adult’s intake of fiber today is 18g a day—60 percent of the government guideline of 30g. Only 9 percent of the population are getting enough of it, according to the Food and Drink Federation.
“The huge uptake in high-protein, low-carbohydrate diets in recent years means fiber is often forgotten and has gained an unfair reputation for being the preserve of bland foods,” says the nutritionist Laura Southern. “But it’s critical to our health.”
Getting into the habit of eating more fiber is easier than you might think and can pay dividends surprisingly quickly. “Clients are always surprised how quickly a higher-fiber diet can work—I often see a reduction in their body fat percentage, better blood sugar control and digestive health in as little as two weeks,” Southern says.
One recent year-long study of dieters published in the journal Obesity Science and Practice found “participants with higher-fiber-density diets resulted in greater weight loss.” Here’s everything you need to know about fiber and how to increase your intake.
Different Types of Fiber Serve Different Functions
Fiber is contained in the parts of plants not digested by our small intestine. Instead, it is completely or partially broken down (fermented) by bacteria in our large intestine.
There are several types, but one of the main two is insoluble fiber—or “roughage”—that passes straight through our body, increasing stool bulk and aiding the digestive process. Good sources are nuts, vegetables and whole grains such as brown rice and flour.
Soluble fiber, dominant in oats, beans and legumes, dissolves in water in the stomach and intestines to form a gel, keeping stools soft. It has been linked to lower cholesterol, better blood sugar balance and satiety—it can delay the stomach emptying, keeping you feeling fuller for longer.
“Most fibrous foods contain a mixture of these two types of fiber,” says Southern, of londonfoodtherapy.com, who adds that the key to increasing fiber intake is to build up tolerance gradually to avoid bloating, as anyone who has been bent over double after eating too many dried apricots knows. “When people say fiber gives them a stomach ache it’s often because they’re eating too much too quickly. Your gut needs time to adapt.”
How Fiber-Fueled Short-Chain Fatty Acids Can Transform Our Health
Given that most carbohydrates, proteins and fats are absorbed into our bloodstream before they get to the large intestine, fiber provides essential food for the beneficial microbes that live there. “These give off waste products known as short-chain fatty acids [SCFAs] as they feed on it,” Southern says.
SCFAs not only support our digestive system but the lining of the large intestine, reducing inflammation in the gut. “This inflammation can increase the risk of conditions from joint pain to dementia, cancer and heart disease—they all have inflammatory pathways,” Southern says.
Last year a review in the journal Nature found a high intake of fiber was associated with a reduced risk of several cancers, including those of the stomach, colon, prostate and pancreas, and there is increasing evidence SCFAs can improve mental health.
Research published in General Psychiatry this year found that SCFAs “alleviate depressive symptoms” by regulating the central nervous system. “One 12-week study of patients diagnosed with clinical depression found 32 percent of those who followed a high-fiber diet went into remission,” Southern adds.
Why Fiber Is Key to Weight Loss and Managing Blood Sugar Levels
Because food high in fiber travels more slowly through the digestive tract, our body extracts sugar from it at a slower rate, “so you’re not getting blood sugar spikes. This reduces cravings, making it easier to resist sugary food and lowers the risk of constant high blood sugar leading to high insulin and diabetes,” Southern says.
A three-month study published in the journal Science last year on 43 participants found the 27 who followed a high-fiber, whole grain diet had a greater reduction in blood sugar levels and lost more weight than the 16 in the control group, even though their calorie intake was similar.
Last year research in the journal Cell Reports Medicine found those on a high-fiber diet also had less of a bile acid called isoUDCA that is linked to increased appetite. “This study highlights the key role that fiber plays in appetite regulation and metabolism, harnessed by specific gut microbes,” said the report’s co-author, Tim Spector, professor of genetic epidemiology at King’s College London. “The gut microbiome and its chemical products such as these bile acids hold huge promise for reducing obesity without the need for invasive surgery.”
How Fiber Helps to Lower Your Cholesterol and Balances Hormones
Soluble fiber can lower the amount of low-density lipoprotein (LDL) cholesterol—the “bad” type of cholesterol that can harden arteries, increasing the risk of heart disease—absorbed into our bloodstream.
SCFAs, meanwhile, decrease the production of cholesterol in the liver. A 2016 study showed a diet high in soluble fiber—present in foods such as oats, flax seeds and apples—could reduce LDL cholesterol levels by up to 10 percent.
A review of 31 studies in the Journal of Chiropractic Medicine discovered that those who ate the highest amounts of fiber reduced their risk of having a stroke and developing coronary heart disease by up to 24 percent. “A high-fiber diet also lessens the amount of excess estrogen we don’t need being re-absorbed by the colon, which is why studies link it to a reduced breast cancer risk,” Southern says.
How to increase your fiber intake
Stop Peeling Fruit and Vegetables
One of the easiest ways of increasing your fiber intake is to leave skin on as many foods as you can. An apple with its skin contains 4.4g fiber, for example, but only 2.1g without it. More food can be eaten unpeeled than you might think.
“I’ve eaten kiwi fruit with its skin on, which increases the fiber content by 50 percent, since I was a child,” says Southern, who also eats the skin of mangos and figs, and advises eating the entirety of a vegetable where possible too.
“Stalks, stems, leaves and roots of vegetables such as carrots, broccoli and beetroot can be roasted, boiled or fried. The skin of vegetables such as carrots and butternut squash can be washed instead of peeled,” Southern says. “Buy as many different varieties of each vegetable as you can—tender stem broccoli instead of purple sprouting broccoli, or shallots instead of white onions, for example, as the structure of fiber in each will be different.”
Start Eating Oatmeal for Breakfast
Studies show SCFAs can stimulate the secretion of leptin, a hormone that signals satiety, and the release of hormones that make us feel full. Oats are beneficial in this process because they are abundant in a form of soluble fiber called beta-glucan.
This produces a SCFA called butyrate, which in turn stimulates the release of glucagon-like peptide 1 (GLP-1), a hormone that suppresses appetite in a similar, albeit less powerful, way to Ozempic, a “GLP-1 receptor agonist” drug that mimics the hormone’s effect.
A rodent study published in the Journal of Nutrition this July said that mice whose high-fat, high-sugar diets were supplemented with 10 percent beta-glucan showed less weight gain and better blood sugar levels. Other good sources of beta-glucan include rice and mushrooms.
Switch to Whole Grain Bread and Reheat White Pasta
According to the BDA, a food is high in fiber if it contains 6g or more per 100g, and a source of fiber with 3g per 100g. The unrefined versions of many of our staple foods contain 6g or more of fiber per 100g and are sources of high fiber, so it’s worth training our taste buds to enjoy them.
Whole grain bread, for example, has 7g fiber per 100g compared with white bread, which has just 2.7g. “Or buy bread made from rye, oat or millet flour, all of which are high in fiber and should be available in most supermarkets,” Southern says.
Contrary to what you might assume, sourdough bread isn’t necessarily higher in fiber than regular bread: 100g of white sourdough contains about 3g of fiber, while 100g sourdough made of whole wheat flour contains about 6.5g.
“The benefit of sourdough is that the fermentation process produces prebiotics, a type of fiber that supports our good bacteria—and can also make the bread easier to digest,” says Southern, who adds that rye sourdough is another good high-fiber sourdough option.
Whole wheat pasta, meanwhile, contains 6g fiber per cooked 150g (white pasta contains 2.7g), which was found by research in the journal Applied Physiology, Nutrition, and Metabolism to potentially “promote fullness and reduce hunger.”
“Lentil, chickpea and brown rice pasta can be a good high-fiber alternative to whole wheat pasta and mung bean and buckwheat noodles, easily found in the world food sections of most supermarkets, are another good high-fiber option,” Southern says.
If you do eat white pasta, try cooling and reheating it, which turns it into resistant starch—now classified as a type of fiber that is fermented in the large intestine and linked to lower cholesterol and more balanced blood sugar.
In 2014 an experiment on Italian restaurant staff on the BBC show Trust Me, I’m a Doctor, led by the nutritionist Dr. Denise Robertson, found eating cooked pasta that had been chilled overnight then reheated caused a lower rise in blood sugar levels than eating cooked pasta or pasta that had been chilled. The process is thought to change the structure of starch, so it can’t be broken down by digestive enzymes as easily. “The same is true for rice and potatoes,” Southern says.
Make Vegetables the Focus of Your Dinner
Adding extra vegetables or legumes to your meal needn’t be complicated. “You can throw a packet of lentils or grate a carrot into a bolognese without making it taste too different,” Southern says. “Blitz vegetables into a curry sauce with a blender.”
Ratatouille is easy as there is no set list of vegetables to include, she says—dice what you have, fry until soft, stir in a can or two of tomatoes and simmer for 20 minutes. Onions, garlic and leeks are good sources of a type of fiber known as prebiotic, fermented in the large intestine and linked to lower cholesterol and more balanced blood sugar levels. Keep a constant assortment of vegetables in the freezer and stock up on canned beans.
“They’re brilliant coming into soup season,” Southern says. “Increase the fiber content of a shop-bought soup by throwing in a can of cannelloni beans, blitz chickpeas into hummus or add kidney beans to a salad.”
Cooking can reduce the fiber content of some vegetables, including carrots, cauliflower, radish and spinach, according to a study in Food Chemistry, with microwaving better at retaining fiber than pressure cooking. This isn’t necessarily bad, Southern says. “If you’re new to a high-fiber diet, eating a lot of raw vegetables can be challenging to your digestive system—I’d start by including more cooked vegetables.” Drink plenty of water to help fiber to pass through your digestive tract—Southern recommends five to six glasses a day.
Snack on Popcorn and Dark Chocolate
Popcorn is packed with 4.3g fiber per 30g serving—just stick to the air-popped version and try not to undermine the health benefits by drenching it in syrup. Good quality dark chocolate contains 3.9g fiber per 30g portion, and there are plenty of high-fiber alternatives to potato chips.
“I’m a big fan of lentil crisps, stocked in most supermarkets, and pea crisps by brands such as Off the Eaten Path, which contain more than 9g fiber per 100g, and chocolate-coated chickpeas are a good alternative to a chocolate bar,” Southern says.
With 3g fiber per 40g serving, dates are another sweet option, especially when paired with high-fiber nuts. Adding a tablespoon of peanut butter (1.3g fiber) to a sliced apple will provide further benefit to your gut health.
What About Supplements? Will They Work?
Available in powders, tablets and gummies, fiber supplements often contain psyllium, which is made from the husks of the psyllium seeds, a combination of soluble and insoluble fiber.
Although often marketed to ease constipation, they are increasingly being promoted as a weight loss aid. One, a powder psyllium husk fiber supplement sold by the brand Yerba Prima for about $15, went viral on TikTok this summer after Dr. Enaka Yembe described it as “the poor man’s Ozempic,” explaining that “both induce feelings of fullness.”
Psyllium, which binds to water to form a gel, was found in a review last year to aid weight loss in overweight and obese people. Meanwhile, a 2022 American study of three different fiber supplements found that among participants on a low-fiber diet, they positively changed the gene expression of participants’ gut microbes within a day, and that within a week they increased the production of butyrate.
“Emerging research is focusing on fiber supplements as a useful weight-loss tool,” Southern says. “They can support blood sugar balance and might be a useful intervention in helping reduce food cravings.”
Antonia Hoyle is a London-based freelance journalist whose work has appeared in the Daily Mail, The Mail on Sunday, The Telegraph, the Daily Mirror, Grazia, and Marie Claire, among other publications
