Fibre – How To Lose Weight IX

Fibre is the non-digestible part of food, usually a carbohydrate. A more formal definition is the “dietary constituents that are not enzymatically degraded to absorbable subunits in the stomach and small intestine”. These are generally plant foods, but occasional animal foods such as liver glycogen are included. Common types of fibre include cellulose, hemicellulose, pectins, beta-glucans, fructans, and gums. Whole grains, fruits, vegetables, legumes and nuts are all major sources of dietary fibre.

Fiber is classified as soluble or insoluble based on whether it is dissolvable in water.  Beans, oat bran, avocado and berries are good sources of soluble fibre. Whole grains, wheat germ, beans, flax seeds, leafy vegetables and nuts are good sources of insoluble fibre. Fibre can also classified as fermentable or non-fermentable. Normal bacteria residing in the large intestine have the ability to ferment certain undigested fibre into the short-chain fatty acids acetate, butyrate and propionate. These fatty acids can be used as an energy source. They may also have other beneficial hormonal effects including the decreased output of glucose from the liver. Generally, soluble fiber is more fermentable than non-soluble.

Fibre has multiple purported mechanisms of health benefit but the importance of each is largely unknown. High fibre foods require more chewing, which may reduce food intake. Horace Fletcher (1849-1919) believed strongly that chewing every bite of food one hundred times would cure obesity and increase muscle strength. This helped him lose 40 pounds, and “Fletcherizing” became a popular weight loss method in the early 20th century.

Fibre may decrease palatability and thus reduce food intake. Children seem to naturally gravitate towards the white bread and white pasta, rather than the whole-wheat varieties. Fiber bulks up foods and decreases energy density. Soluble fibre absorbs water to form a gel, further increasing volume. This fills the stomach, which increases satiety. Stomach distention may signal a sensation of fullness or satiety through the vagus nerve. Increased bulk may lead to increased time for stomach emptying.  This leads to a slower rise in blood glucose and insulin after meals. In some studies, half the variance of the glucose response to starchy foods depends upon the fiber content.

In the intestines, soluble fibre may ‘trap’ nutrients in the gel formed. This blocks contact with the intestinal walls, reducing absorption of fats and proteins. The mixing of food and digestive enzymes is disrupted. Indeed, some studies have shown that increased fibre intake lowers fat and protein absorption. Increased unabsorbed macronutrients in the distal small bowel may result in further delaying of stomach contents. The mechanism has been called the ‘ileal brake’. Presumably, this is an adaptive feature to allow more complete absorption of nutrients farther upstream. Hormones involved in this ‘ileal brake’ may include GLP-1, peptide YY and neurotensin.

In the large intestine, the increased stool bulk reduces the transit time.  The increased stools may lead to increased caloric excretion. On the flip side, fermentation in the colon may produce short-chain fatty acids. Roughly 40% of dietary fibre may be metabolized in this way. One study demonstrated that a low fiber diet resulted in 8% higher caloric absorption. In short, fibre may decrease food intake, slow down absorption in the stomach and small intestine, then exit quickly through the large intestines. All of these effects are potentially beneficial in the treatment of obesity.

Fibre intake has fallen considerably over the centuries. Fibre intake in Paleolithic diets is estimated to be 77-120 grams per day. Traditional diets are estimated to have 50g/day of dietary fibre. By contrast, modern American diets contain as little as 15 g/day. Indeed, even the US Dietary Guidelines only recommends 25-30 g/day. Removal of dietary fibre is a key component of the processing of foods. Improving the texture, taste and consumption of foods directly benefits the profits of food companies.

Fibre came to public attention in the 1970s.  Physicians doing missionary work with native populations mostly in Africa noted a consistent pattern of disease. The Diseases of Civilization, including heart disease, obesity, diabetes, stroke, and cancer were rare amongst natives that followed a traditional diet and lifestyle.  By contrast, in urban areas where native lifestyles became westernized, these diseases slowly appeared.

Some researchers believed that these diseases were caused by the increased consumption of refined carbohydrates – particularly sugar and white flour.  These could be stored at room temperature without fear of spoiling. This was a significant advantage when traveling without refrigeration.  Flour and sugar could be carried in great quantity over great distances.  Through the 1960s and 1970s, debate raged back and forth.  The pendulum finally swung in favor of lowering dietary fat, which necessitated an increase in carbohydrate consumption.  Since most of the carbohydrates in the Western diet are refined, the goal of reducing fat was incompatible with lowering refined carbohydrates.Diet-guidelines-2

Thus, the carbohydrate hypothesis quickly fell into disfavor.  But how to explain the Diseases of Civilization?  Perhaps, it was not the carbohydrate but the lack of fibre that was the problem.  Being compatible with the dietary fat hypothesis, this explanation quickly became accepted. Traditional unrefined foods that included carbohydrates tended to be very high in fibre. A missionary surgeon named Denis Burkitt became one of the leading proponents of the dietary fibre hypothesis.  By 1977 the new Dietary Guidelines made the recommendation to “Eat foods with adequate starch and fiber”.  With that, fibre was enshrined in the pantheon of conventional nutritional wisdom.  Fibre was good for you.  You should eat more fibre. But it was difficult to show exactly how it was good for you.

At first, it was believed that high fibre intake reduced colon cancer. The subsequent studies proved to be a bitter disappointment. The prospective Nurse’s Health Study followed 88,757 women over 16 years finding no significant benefit. A randomized study of high fibre intake failed to demonstrate any reduction in precancerous lesions called adenomas. The Nurses Health Study and found no benefit to cancer risk with high fibre. The huge Women’s Health Initiative study increased whole grains, fruits and vegetables, but failed to find a benefit for colon cancer, either.

If fibre wasn’t helpful in cancer, perhaps fibre might be beneficial in heart disease.  The Diet and Re-infarction Trial (DART) study randomized 2033 men after their first heart attack to three different diets.  To their astonishment, the American Heart Association low fat diet did not seem to reduce risk at all.  The Mediterranean diet (a high fat diet) on the other hand, was beneficial.  Dr. Ancel Keys had suspected this years ago from the Seven Countries Study. Recent trials such as the PREDIMED confirm the benefits of eating more natural fats such as nuts and olive oil.  So eating more fat is beneficial.  What about a high fibre diet?  No benefit.  Not only that, but increasing fibre may actually have increased the risk of dying!

But it was difficult to shake the feeling that somehow, fibre was good. Most correlation studies show lower BMI with higher fiber intake. This has also been found to be true in native Pima populations and native Canadians as well. More recently, the 10-year observational CARDIA study found that those eating the most fiber were least likely to gain weight. Short-term studies show that fibre increases satiety, reduces hunger, and decreases caloric intake. Randomized trials of fibre supplements show relatively modest weight loss effects with a mean weight loss is 1.3 – 1.9 kg (2.9 – 4.2 pounds) over a period of up to 12 months. Longer-term studies are not available.

Next Article: Fibre Reduces Insulin – How to Lose Weight X

Start here with How to Lose Weight I

2019-01-10T09:56:07-05:0015 Comments

About the Author:

Dr. Fung is a Toronto based kidney specialist, having graduated from the University of Toronto and finishing his medical specialty at the University of California, Los Angeles in 2001. He is the author of the bestsellers ‘The Obesity Code’ and ‘The Complete Guide to Fasting’. He has pioneered the use of therapeutic fasting for weight loss and type 2 diabetes reversal in his IDM clinic.

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Ted Hutchinson
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Ted Hutchinson

I think maybe you are being overly pessimistic about the potential benefits from dietary fiber.
http://www.ncbi.nlm.nih.gov/pubmed/25552267
Association between dietary fiber and lower risk of all-cause mortality
“A higher dietary fiber intake was associated with a reduced risk of death. These findings suggest that fiber intake may offer a potential public health benefit in reducing all-cause mortality”
I think we also have to consider the role of resistant starch and other fermentable fibers separately from non fermentable fibers from grain. The reasons for this are explained here.
Resistant Starch May Reduce Colon Cancer Risk From Red Meat http://jnci.oxfordjournals.org/content/106/10/dju341.long

melancholyaeon
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melancholyaeon

But the real reason most people don’t eat more fiber is the FODMAPs. No one is going to endure the horrible gas pain & bloat to meet some arbitrary unproven fiber goal that results only in a 3 pound weight loss. The real problem is an unhealthy microbiome. After folks have ditched the junk food, processed food, flour, grains and added sugars, they then need to tackle their microbiome. This is where the situation gets difficult. Further, many T2 diabetics and pre-diabetics are in such metabolic trouble that they can’t even eat the stuff like well-soaked cooked lentils that will… Read more »

Dena Mott
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Dena Mott

Aree with melancholyaeon…I am type T2 and am in metabolic trouble for sure. Some on told me to eat beans for the fiber and then a friend who lost 100 lbs said no to beans..way to much carbs and spiked my sugar! I cannot seem to get my number below 300’s. I just do not want to go onto insulin and thought I would somehow be able to get this under control. So discouraged. I def need help.

Apicius
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Apicius

I think there is a big difference between eating “real” fiber from “real food”, versus fake fiber from processed foods. For example, eating fiber that is locked in the vegetables in your salad is not the same as the fiber from a Metamucil drink or processed energy bar. Also, I would like to learn more about fiber from non vegetable or non fruit sources. I read that beef and other meat sources, for example, does indeed provide some fiber. But, it is difficult to find literature explaining what this means (quantity, type, effect on metabolism, etc).

erdoke
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erdoke

Maybe a short paragraph could have been devoted to the relationship of fibers and constipation. I have only found one (yes, 1, número uno) controlled study where the authors directly compared effects of higher and lower fiber intake from baseline on constipated individuals. Guess, what happened…

Colin
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Colin

Dietary fiber is unnecessary.

M. H
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M. H

Dear Dr. Jason Fung.
Your blog and lectures are amazing.

This real story is here:
http://www.ncbi.nlm.nih.gov/pubmed/9436530

Throughout 25 years in Israel, diabetes rates in the Yemenite community rose from 0.06% to 12.5% ( 20,000% growth in diabetic prevalence) and after five years in Israel the Ethiopian community began to exhibit diabetes at a rate of 5-8%.

20,000% growth is a “Maga signal” above noise level. Any nutrition research should explain the data.

sam kapoor
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sam kapoor

Dr Jason,

I really enjoyed your full lecture series on Diabetes —It was real eyeopener. As we have heard / read that Diabetes is hereditary disease –what is your view on that ? I did not hear word “Hereditary” in your presentation or may be I missed it.

Look forward to hearing from you.

Thanks,

Sam

kfacwpup
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There is clearly a large contribution of genetics to both obesity and type 2 diabetes. However, it is not something you can change. Further, our genetics have not changed, even as the diabetes epidemic has gained strength, so clearly, there is an environmental component. Genetics may explain the difference in risk between individuals, but not a population.

Simon Thompson
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Simon Thompson

“In the large intestine, the increased stool bulk increases the transit time”

Should that be reduces the transit time? I would imagine peristalsis would be promoted.

kfacwpup
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Yes,thank you. I’ve corrected it.

gloria
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gloria

dr fung- I have been following your IF plan for 1 month now I feel wonderful but I am constipated all the time. I drink lots of water and walk 30 min a day – what am i doing wrong?

Justin
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Justin

How to consume Konjac: Dr. Fung, I’m reading your “The Obesity Code” book right now and I’m so grateful to you for writing this book that has already changed how I eat and don’t eat. Could you please give me a recommendation on how to best consume glucomannan or konjac root? I gather that pills normally aren’t a good way to go, but is there a powder that would be a second best to actually using the whole root in foods? This is assuming that I look and can’t find a convenient way to get the whole root. If you… Read more »

Kim kingry
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Kim kingry

Same question! Please advise

Noor Ullah jan Jan
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Thank you for the comprehensive review of fibers. I have cleared my so many conceptions about the use of fibers from your perspective. Although the benefits of fibers for weight loss is simply physical and multiple studies have proven its effectiveness for weight loss. If we are the talking about the whole grains, fruits, and nuts, they are also loaded with fibers and maybe the benefits that one will get from these foods will be due to high fibers content. However, i appreciate your in-depth analysis of data available and you have posted it in a very presentable form.