by Marion Nestle
Mar 27 2012

Nutritionist’s Notebook: Importance of fiber

This semester I answer students questions about nutrition on Tuesdays in the student-run Washington Square News.  Today’s is about fiber.

Question: We tweeted and linked to the article you were cited in The New York Times on Tuesday, and you mentioned the importance of fiber in a diet. How much fiber is good to have in a daily diet, and what does it do for our bodies? What are good sources of fiber — cereal bars, granola bars? How much is too much fiber?

Answer: You, like most Americans, probably get less than half the fiber you need. You can fix that by eating more vegetables, fruits, nuts, beans, peas and whole grain breads and cereals. Fiber occurs only in plants.

Eating these foods at every meal will do wonders for your digestive system. They help protect you against obesity, heart disease, Type 2 diabetes and even some cancers.

Fiber refers to a bunch of plant carbohydrates that human enzymes cannot digest easily. These come in two types: insoluble and soluble. Insoluble fiber, the kind found in grains, almost completely resists digestion. It has no calories.

But soluble fiber from beans and other vegetables can be digested to some extent by bacteria in your colon. They produce a little energy you can use.

Research shows that people who eat plenty of vegetables, fruits and whole grains with both kinds of fiber develop less chronic disease. But these benefits do not show up in studies using fiber supplements.

This means you are better off eating vegetables than power bars. If you must eat those bars, choose the ones with fruits, nuts and whole grain — real foods — high up on the ingredient list. Watch out for misleading claims about “good source of fiber.”  Check the Nutrition Facts panels — 3 grams is minimal, 5 is better.

If you are not used to eating fruits, vegetable and grains, eating more of them may make you feel gassy. Gradually include more. Your digestive system will be happier, and you will be healthier.

  • brad

    If you’re trying to lose weight, fiber is also a great way to help you feel satiated while consuming fewer calories. I have a tendency to over-snack, but I find that a bowl of high-fiber cereal with low-fat milk or almond milk will prevent even slight hunger pangs for at least three hours, especially if I drink lots of water afterwards. An apple is good too. Surprisingly I don’t get the same results from steel-cut oats; I always feel ravenous within an hour of eating a serving, but maybe that’s just me.

  • Emma

    And it’s delicious! I’m eating kale chips right now.

  • A great ‘power bar’: Gnu flavor & fiber bar. 12 grams of fiber, no HFCS, 6 whole grains.

  • Jeff

    Dietary fiber is important, but supplemental fiber shouldn’t be dismissed. There’s plenty of science showing the health benefits of fiber supplements.

    1.Supplemental Fiber Helps Lower Cholesterol and Boosts Weight Loss:

    2. Fiber supplement lowers risk of complications from type 2 diabetes:

    3. Treating obese patients with fiber supplement results in improved metabolism and lower body-weight:

  • Brandon

    I like how you start going into specifics then make the huge akward transition of going into recommendations…

    “But soluble fiber from beans and other vegetables can be digested to some extent by bacteria in your colon. They produce a little energy you can use.”

    … And? …

    Hopefully that doesn’t come off as too mean. I was just saying, everyone has heard the recommendations, not too many people go into the why the recommendation is there, other than the vague statements “reduce risk of Type 2 diabetes, etc”. I think it would be beneficial to go into the reasons it reduces the risk of T2D, cancer etc. The energy (butyrate) bacteria make from soluble fiber can also prevent the colon cells from mass multiplying (cancer). You are good at articulating, who better to come up with a friendly easy to understand way of saying that.

  • Anthro


    The studies you cite are not well documented and appear on a commercial website that sells supplements. One of them is from 1984, one is undated and the third is from an undefined group that studied (apparently) its own specific product. We are left to wonder if any of this work has been replicated–the gold standard for acceptance by the science and medical community.

    It’s important to understand that good nutritional and medical advice is based on the preponderance of scientific evidence that is published in quality peer-reviewed journals. You, and the sites you link to have “cherry-picked” a couple of isolated studies in a Journal that may or may not be respected (I cannot say for sure–perhaps Marion would know). This hardly translates to evidence in the scientific sense.


    If you have to ask if something sounds too “mean”, it probably is. If not mean, then certainly unnecessary. If you weren’t taught the difference between constructive criticism and rudeness, I am sorry, but I hope you will endeavor to gain this critical adult skill.

    Just because you have some additional information to offer, it doesn’t follow that Marion is somehow wrong, or wrote in an “awkward” way for not having offered it.

    Professional people such as Ms. Nestle don’t take such things personally, so I’m not so much defending her as offering a bit of general advice that may help if you want to be taken seriously.

  • Peggy Holloway

    Eating more fiber is another nutritional red herring. By eating more fiber, people are being encouraged to eat more grains which is a very bad idea.
    The only benefit to fiber is that it is an undigestible carbohydrate and will not raise blood sugar, so a food with higher fiber is preferable to a similar food that is lower in fiber. For example, a piece of bread with 4 grams fiber is preferable to one with no fiber and an equal carbohydrate total because, if there are 12 g/carbs in one slice and 8 in the other, the lower net carb bread is better. But, even better would be to eat no bread at all. There is absolutely no reason to supplement with fiber. Ridiculous and another good example of the pseudo-science that produces most nutrition advice.

  • brad

    @Peggy: You might be under the impression that mainstream nutritionists and the medical community are blissfully unaware of the work of Gary Taubes and cling stubbornly to the findings of their flawed science. Nothing could be further from the truth. For example, Marion Nestle and Maldon Nesheim’s new book (Why Calories Count) has an entire chapter devoted to the evidence and arguments put forth by Gary Taubes, and in another section of the book they talk in detail about the limitations of observational studies, making many of the same criticisms that Taubes does. The mainstream tide of nutritional thinking hasn’t shifted toward the carbohydrate hypothesis, but it’s not due to ignorance. It’s because the evidence remains unconvincing, and there are too many other contributors to weight gain to single out carbs as the only (or even the leading) cause. The carbohydrate-insulin connection is clear, but the insulin-fat connection is still under scrutiny. The science is far from settled.

  • Jeff


    The first article is footnoted and provides a link to the abstract:
    “The effect of a fibre supplement compared to a healthy diet on body composition, lipids, glucose, insulin and other metabolic syndrome risk factors in overweight and obese individuals: British Journal of Nutrition 2011 January 105: 90-100.”

    Study no. 2 was posted by The American Diabetes Association (an undefined group?).

    Study no. 3 was originally published in The British Journal of Nutrition, certainly a quality peer-reviewed journal.

    Maybe you feel you have to denigrate the science simply because you disagree with it.

  • Brandon


    You’re silly. Because there’s no nonverbal communication going on over the internet, the message I send could be different than the message that is received. The fact that you may have interpreted rudeness proves that point. Also, many people often get defensive over criticism, constructive or not. Those are the reasons as to why I made the statement I made. I never said Marion was wrong, I was saying she could’ve done so much more, gone so much further. I even compliment her strengths in my post, so obviously there was no rudeness intended.

    Thanks though, and have a great day.

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  • Margeretrc

    Brad, have you ever known (of) anyone who gained weight who did not eat carbs? Neither Gary Taubes nor anyone else who espouses the carbohydrate hypothesis claims that carbohydrates will make anyone and everyone who eats them fat. That would be foolhardy. The hypothesis, based on uncontroversial, established knowledge of the metabolism of glucose, posits that those who do get fat, do so because their body is unable to properly process carbohydrates and thus need to eat them sparingly–especially the high glycemic ones like grains, tubors, and sugars. Are there other factors at work as well? Most likely. But the success of low carbohydrate diets in RCT (at least 16 that I know of from one site) comparing it to other diets for weight loss strengthens this position and will, I do not doubt, continue to do so. It is my hope that some day, mainstream nutrition will work with those who believe that it’s the carbohydrates, instead of against them, to test this hypothesis instead of dismissing it out of hand because the “science is far from settled.” It’s far from settled because mainstream nutrition isn’t even willing to entertain the idea that there might be something to it and test it, because they believe they already have all the answers–as in “eat less, move more” and other such tried and failed ideas.

  • brad

    @Margaretrc, nobody disputes that low-carb diets are more successful than others at achieving rapid weight loss, although there’s no evidence that I’m aware of to indicate they are any more successful than others at long-term sustainability and prevention of weight regain. “Eat less, move more” is in fact very effective (as millions of people who’ve tried it can attest), but like most diet strategies it fails in the long term because it’s hard work and people slip back to their old habits. Low-carb diets can get monotonous after a few years or even a few months, and monotony tends to lead people to stray.

    If you look more deeply at the carbohydrate hypothesis promoted by Taubes and others, you’ll see that the mechanisms are not as uncontroversial as you claim — for example, see Stephan Guyenet’s very detailed analysis on his “Whole Health Source” blog (it’s silly to cite blogs as sources for scientific information, but his analysis is all based on published, peer reviewed studies, which he cites in his posts).

    My post above was in response to Peggy, who claimed that telling people to eat grains and other carbs is a “very bad idea.” It might be a very bad idea for some people (people who are obese, have a propensity toward obesity, or are insulin-resistant), but for the rest of us eating carbs is no problem. I’ve maintained a fairly steady weight for the past 25 years on a varied diet that is high in carbs and low in fat, and many people around the world live on high-carb, high glycemic-index diets with low rates of obesity.

  • Margeretrc

    Brad, I’m familiar with Stephan Guyenet’s analysis. I read both that and Taubes. I think they are both valid and not necessarily mutually exclusive hypotheses. But regardless of what Stephan says, the fact is that insulin is the primary (though not only) fat storing hormone. Biochemistry textbooks everywhere discuss that and not as though it is in question. Type 1 diabetics cannot gain weight without the exogenous insulin that they have to take and, in fact, lose weight drastically without it. That’s hardly controversial. And you didn’t answer my question. Do you know (of) anyone, normal metabolism or otherwise, who gets fat without eating carbohydrates? Yes, there are those without broken metabolisms who can maintain weight or even lose it while eating carbs. Neither I nor Taubes ever claimed otherwise. The question, which neither Stephan nor you has addressed, is whether or not it is possible to get fat/gain weight without eating carbohydrates. Regardless of whether it is the reward principal or insulin, or both, it is the carbohydrates in the diet which cause weight gain. As to low carbohydrate being boring and unsustainable, that is patently not true. I’ve been on LC for nearly a year and know many who have been on carbohydrate restricted diets for decades. It is anything but boring and it is satiating. You say you can go for 3 hours without hunger pangs after a meal of high fiber cereal with almond milk or low fat milk. 3 hours is nothing. I can go 5,6,or even 8 hours without hunger pangs after a satisfying lunch (I don’t eat breakfast–just coffee with cream) of bacon and eggs, omelet with cheese and veggies, salad with meat and cheese, or any one of a variety of filling, satisfying meals. I almost never snack and survive easily on two meals a day. It’s a plan I intend to stick to for the rest of my life because it has allowed me to effortlessly lose the weight I gained on a low fat vegetarian diet and keep it off. If getting fiber means I have to eat grains, (it doesn’t) no thanks.

  • brad

    Margaretrc, you asked “Do you know (of) anyone, normal metabolism or otherwise, who gets fat without eating carbohydrates?”

    The answer is no, of course, but neither do I know of anyone who gets fat without eating fats and proteins, nor do I know of anyone who gets fat without overeating (eating more calories than they expend).

    It’s been shown that people can eat a diet of 100% refined carbohydrates and lose weight (e.g., see the “Twinkie diet”), but as you point out the reverse has yet to be demonstrated: as far as I know there are no examples of people who ate no carbohydrates and still became obese. There have been some overfeeding experiments, but as far as I know those were all done with diets that included fats, proteins, and carbs. Maybe someone should ask David Katz (the Twinkie diet guy) to see if he can put back on the pounds by overeating while eliminating carbohydrates from his diet.

  • Herman

    As a ‘european’ citizen, I am always amazed by the american view on ‘diets’ and the discussions around nutrition. Whilst being acutely aware of the obesity problem in the US (I travel to the US on a bi-monthly basis and, every time, it’s quite obvious), I never get the impression that the underlying problem is addressable because of the massive power that your industries have over your food supply. Isn’t the problem really simple: our bodies have evolved over thousands of years where the dramatic change in food pattern only occurred in the last 50-100 years. These days, we eat way too much stuff that our bodies are not at all equipped to deal with; refined stuff such as sugar, salt, meat, artificial sweetners, HFCS, soy derivatives and so on. And not just us but we even feed our lifestock stuff that they were never meant to eat (cows eat corn for crying out loud, same with chicken). Trying to find products in a supermarket that do not have ‘stuff’ added to them is pretty close to impossible. On top of that, we expect the same products all year around which is why I find aparagus from Peru in the winter in a supermarket here in Holland. We ruin our planet and we mess up ourselves in the process. In Holland, we are not yet messed up to the point where everything has additives to the degree that you find in other countries but we are heading there just as well.
    In all societies that have little obesity and more healthy people, you will find that people stick to what nature gives them. Whether Japanese, Eskimos (who have never even seen fibre as they used to eat raw seal and have little heart desease as a result), Italians, most farm communities, you rarely find obese people. They eat what nature gives them and their bodies get what they are used to. I buy most of my stuff organic and I never ever touch anything that anyone messed with (‘refined’) if I can help it. Real butter instead of the fake stuff (which drives my cholesterol down as long as the butter is made from cows that eat grass which, btw, is what cows are supposed to do in case anyone wondered), we make our own fresh pasta (well, my 11yo daughter loves to make it) and serve it with great olive oil and organic parmesan cheese and wild rocket salad. It’s absolutely brilliant. We hardly ever buy precooked food, food cans, packages with preintegrated spices. When we do, everyone is disappointed with the taste of the preservatives. I don’t want to sound patronising by any means but I do wonder what is so difficult about eating things the earth gives you without it being messed with and just buying that at a small local shop?
    Anyways, just a thought. My mantra: “don’t mess with mother nature”. And obviously, keeping your body in shape helps as math does work in losing weight (weight = food intake – combustion). I drink more wine? Then I run a couple more miles (but you will never see me in a gym as too depressing and not enough fresh air). Greetings from Holland.

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  • julie

    Seems a few of these low-carb gurus are managing to get plenty fat without overeating the carbs. Jimmy Moore? Laura Dolson, or whatever her name is, who writes blurb on low-carb? BTW, if your blog has a 4 year old picture, you’re not fooling anyone.

  • Helen

    It is true that people of today eat much less vegetables and fruits than they need, and get much less natural food fibers than their digestive system requires. The point is that food fibers are an effective cleansing means that allows to remove toxic residue from intestines, allowing clean inner walls to absorb all the nutrition that comes with food. It is very important that eating more food fibers does not mean making additional efforts, it just means consuming more grains, fruits and vegetables, especially if they have passed only minimal procession. Check this post to find the full information:

    Eating healthy food is able to give the body much more energy than junk that is rich in calories but low in nutrition.