It’s common to see headlines that say increasing your fiber can help you lose weight. But is it true? I took a look at the latest scientific studies to find the answer.
What the science shows
In 2020, a group of scientists conducted a massive review. They looked at over 60 studies that included nearly 4,000 participants. The studies were randomized controlled trials, so that means they were most likely quality studies. These studies looked at fiber’s effect on body weight, BMI, waist circumference, and body fat - and the most important thing about these studies is that they were not calorie or carb restricted. The participants were able to eat what they wanted. All they did was increase fiber. So what were the results - did the fiber help?
There was a small drop in body weight, BMI, and waist circumference, but no difference in body fat. And the drop in weight was just a couple of pounds over a month period. Other studies also show that fiber promotes weight loss, but the loss is always very tiny - a few pounds only. It’s more likely that people who focus on eating fiber probably already have healthier habits or are focusing on eating well. That means other factors may account for or contribute to weight loss - not just fiber.
Nutrition studies are almost always flawed
One problem with nutrition studies is that researchers often require the participants to fill out food logs or to keep a food journal. They either have to recall what they ate over the past few weeks or months, or they are asked to record what and how much they eat. This is problematic for two reasons:
People forget what they ate. Food recall questionnaires used in nutrition studies often ask ridiculous questions like, “How many times did you eat peaches over the last six months?” Or “How often did you eat whole wheat bread over the past month?” Who on earth can accurately remember?
People lie on their food questionnaires. They are embarrassed about what they ate, or they exaggerate their healthy foods and minimize their unhealthy foods. Food questionnaires can’t really be trusted.
This means that nutrition studies often cannot be trusted.
Does fiber help at all?
One good thing about fiber is that it feeds your gut bacteria - your microbiome. When you have happy gut bacteria, they can reduce inflammation in your body, which can help your body lose weight. Because of that, fiber can be helpful, but it’s not going to make all the difference.
Some people cannot handle fiber well. While many studies show that fiber helps people have normal bowel movements and avoid constipation, for others, fiber makes it worse. In one study, they divided the participants into three groups. First, they all cut out fiber-rich foods. Then, each group ate differing fiber amounts: one group went back to their normal diets, the second group ate a high-fiber diet, and the third group remained fiber-free. The results showed that the group that ate no fiber had less constipation, less gas and bloating, and more regular stools.
Fiber does help some people with their gastrointestinal health, but it bothers other people. For regularity, you can ask your coach or doctor about magnesium citrate or magnesium sulfate. Increasing your sodium can also help ease constipation.
The bottom line
The takeaway is that fiber is not the magic solution for weight loss. It may help a little, but it most likely won’t be drastic. Virta is a pretty low-fiber plan, which worries some people. If you struggle with bathroom issues, you may need more fiber, less fiber, more magnesium, or more salt. Each person is different and you’ll need to experiment and talk to your coach or doctor. But sadly, as far as weight loss goes, it probably won’t help you lose more than just an extra pound or two.