Packaged diet foods have come a long way since Metamucil drinks and Fibre One bars, but one line of thinking has remained true even as our understanding of diet culture evolves: If you want to lose weight, you should eat fibre, and lots of it.
These days, you can find tasty protein bars packed with more than half of your daily recommended allowance of fibre, as well as easy-to-eat fibrous flatbread crackers for avocado toasts. There are even celebrity-endorsed fad diets — NutriSystem and F-Factor — that encourage people to load up on fibre because it keeps you full for very little calories. But of course, nutrition and weight loss are way more nuanced than just calories. So, what's so special about fibre, and are these fibre-full snacks the answer to all your nutritional concerns?
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Fibre is a unique carbohydrate because our bodies can't digest it, says Wendy Dahl, PhD, associate professor in the department of food science and human nutrition at the University of Florida, who studies fibre. When fibre eventually reaches the large intestines, it's broken down by bacteria in the gut. That fermentation process has a lot of beneficial effects, namely decreasing your risk for a number of chronic diseases, like cardiovascular disease, cancers, type 2 diabetes, and chronic kidney disease, she says.
Compared to other carbohydrates, like sugar, fibre keeps you full for a long time. But the benefits of fibre "go far beyond just having a full stomach," Dr. Dahl says. Studies have shown that fermentation in your gut also leads to hormonal changes that can suppress or regulate your appetite, she says. So, for many people looking to lose weight by eating less food, filling up on fibre seems like logical solution.
In truth, we all could stand to eat more fibre, period. "There'll be some vegans and vegetarians that would definitely be getting adequate amounts of fibre, but less than 5% of the U.S. population achieves what we have as recommended adequate intake for fibre," Dr. Dahl says. The average intake is around half of the recommended 25 grams per day for women.
Ideally, you'd get your dietary fibre from legumes, nuts, fruits, vegetables, and whole grains rather than processed foods like protein bars, Dr. Dahl says. It's not that these high-fibre packaged foods are dangerous, but isolated fibre doesn't have exactly the same important effect on your gut, she says. "If you're consuming multiple processed food bars with some added [fibre], they're super fermentable," she says. In excess amounts, isolated fibre can lead to uncomfortable gas and bloating.
So, basically dietary fibre is great for you, and eating more of it is great. "There's no upper limit for dietary fibre — fibre that comes from fruits, vegetables, nuts, legumes," Dr. Dahl says. "No amount is too much for that." But if you're only eating fibre foods as a way to lose weight, that might backfire on you. Eating fibrous bars or crackers might make you feel full, but you may feel deprived of other important nutrients. "Fibre is an important component of fullness, but so is protein and fat," Alissa Rumsey, MS, RD, an anti-diet registered dietitian nutritionist and intuitive eating coach in New York City told Refinery29. "It's not just about fullness either — satisfaction is even more important."