You hear the advice constantly: you need fibre. It’s crucial to your health. Fine, but how much fibre, and how crucial is it? Maybe you’re wondering, What is fibre, exactly? Let’s start with the basics.
Fibre is a type of carbohydrate that makes up the structural material in the leaves, stems and roots of plants. But unlike sugar and starch – the other two kinds of carbs – fibre stays intact until it nears the end of your digestive system. This, it seems, is what makes fibre beneficial, and why you’ve probably heard you can’t eat enough of it. Now read on to separate the facts from the fiction.
All fibre is created equal
FALSE
There are two basic types of fibre, with different functions. Insoluble fibre is found in wheat bran, nuts and many vegetables. Its structure is thick and rough, and it won’t dissolve in water, so it zips through your digestive tract and increases stool bulk. Soluble fibre is found in oats, beans, barley and some fruits. It dissolves in water to form a gel-like material in your digestive tract. This allows it to slow the absorption of sugar into your bloodstream. What’s more, soluble fibre, when eaten regularly, has been shown to slightly lower LDL (bad) cholesterol levels.
Fibre has no kilojoules
FALSE
Fibre is essentially composed of a bundle of sugar molecules. These molecules are held together by chemical bonds that your body has trouble breaking. In fact, your small intestine can’t break down soluble or insoluble fibre; both types just go right through you. That’s why some experts say fibre doesn’t provide any kilojoules. However, this claim isn’t entirely accurate. In your large intestine, soluble fibre’s molecules are converted to short-chain fatty acids, which do provide a few kilojoules. A gram of regular carbohydrate has about 17kJ, as does a gram of soluble fibre. (Insoluble fibre essentially has zero kilojoules.)
Fibre can help you lose weight
TRUE
Fibre’s few kilojoules are more than offset by its weight-control benefits. The conclusion of a review published in the journal Nutrition is clear: people who add fibre to their diets lose more weight than those who don’t. Fibre requires extra chewing and slows the absorption of nutrients in your gut, so your body is tricked into thinking you’ve eaten enough, says review author and registered dietitian Joanne Slavin. And some fibres may also stimulate CCK, an appetite-suppressing hormone in the gut.
Fibre is all-natural goodness
SORT OF
Fibre is showing up in everything these days – yoghurt, orange juice, artificial sweetener. If this seems impossible, remember that these are molecules; you don’t have to see or feel fibre for it to be present. Scientists now have a new class of fibre they refer to as “functional” fibre, meaning it’s created and added to processed foods. “You can make fibre from bacteria or from yeast,” says Slavin. “And as long as you prove that it can lower cholesterol or feed the good bacteria in your gut or increase stool weight, it’s fibre.”
Supplemental fibre is healthy
TRUE
Foods with added fibre don’t necessarily provide the benefits you might expect. Inulin, for example, a soluble fibre extracted from chicory root, can be found in a range of products. In addition to boosting fibre content, it’s also commonly used to replace fat. Inulin is known as a rebiotic, which means it promotes the growth of healthy bacteria in your gut. That’s good, of course. “But,” says Slavin, “inulin doesn’t have the same cholesterol-lowering effect as the fibre found in oat bran.” Food companies are jumping on the fibre bandwagon
DUH In 2007, the US’s Food and Drug Administration (FDA) declared that polydextrose can be called fibre. Polywhat? Polydextrose is made from glucose, sorbitol (a sugar alcohol) and citric acid. It received FDA approval because it mimics some attributes of dietary fibre: it isn’t absorbed in the small intestine and it increases stool weight. Polydextrose mainly bulks up foods so they’re not as high in kilojoules. However, there’s no research to prove that polydextrose
is as beneficial as the fibre found in whole foods.
Fibre helps prevent colon cancer
MAYBE
This idea arose in the Sixties when it was noted that fibre-
scoffing Ugandans rarely developed colon cancer. But nearly five decades later, it still hasn’t been proven. In 1999, Harvard researchers found no link between dietary fibre intake and colon cancer. But a European study that tracked more than half a million people correlated a high-fibre diet with up to a 40 percent reduced risk of colorectal cancer. Then a 2005 review in the Journal of the American Medical Association found that people who ate the same amount of fibre as those in the European study didn’t experience any benefit. The American Institute for Cancer Research calls protection “probable”. This controversy aside, high-fibre diets are associated with preventing many chronic diseases, so it’s smart to boost your intake, says cancer expert Dr Arthur Schatzkin.
You need 38g of fibre a day
FALSE
That’s the recommendation from the US’s Institute of Medicine. Scientists there crunched data from three studies and squeezed out the number 38 in 2005. It equals four slices of wholewheat bread or 12 bowls of instant oats. (Most people eat about 15g of fibre daily.) The studies found a correlation between high-fibre intake and lower incidence of heart disease. But none of the high-fibre-eating groups in those studies averaged as high as 38g, and, in fact, people saw maximum benefits with a daily gram intake averaging from the high twenties to the low thirties. Also, it’s worth noting that these studies don’t show cause and effect, and that unless you’re taking a supplement, it’s hard for even those who eat the healthiest of diets to consume 38g of fibre. It’s fine to shoot for that amount, but you’re certainly not failing if you don’t meet it.
This is complicated
FALSE
A simple strategy: eat sensibly. Favour whole, unprocessed foods. Make sure the carbs you eat are fibre-rich to help slow the absorption of sugar into your bloodstream. “The more carbohydrates you eat, the more fibre becomes important to help minimise the wide fluctuations in blood-sugar levels,” says registered dietitian and nutrition researcher Jeff Volek.
