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Comment by sarchertech | Hacker News Reader

> Actual RCTs that randomly assigned subjects found no difference in polyp rates between high and low fibre diets.

As far as I know the only RCT that fits that description is one looking at people who had already developed adenomas and then tested for reoccurrence.

An RCT actually designed to answer the question would need to last decades and just isn’t feasible.

There are a large multitude of studies that show a negative correlation between CRC and fiber intake even when adjusting for diet, exercise, BMI, income, alcohol consumption etc…

> but the current consensus is that fibre, or lack thereof, is not a contributor behind the rise in colon cancer among younger subjects.

There’s not good evidence to say it’s the sole or primary factor, but saying there’s consensus that is not a contributor is way too strong.

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> but saying there’s consensus that is not a contributor is way too strong

In most cause hypotheses, fibre just doesn't rank at all. I mean, of course everyone should eat more fibre so that's good, but it isn't a credible cause for the rise of colon cancer rates among the young.

Most destructive to the fibre hypothesis is that fibre intake has actually increased over the past few decades, at the same time that youth colon cancer rates crept up[1]. I don't know what notion people have about common Western food practices decades ago, but in the 1980s, for instance, fibre was basically non-existent in the common diet: No one ate multigrain anything. Everything was loaded with sugar, trans fats and simple carbs (we literally considered that healthy, with hilarious products like Snackwells).

[1] Twice as many young people, per capita, are facing colon cancer now than in the 80s. Overall colon cancer rates are down significantly now, however this is most certainly due to the massive reduction in smoking and other behavioural issues that catch up to you after many decades, but kids today are in no way eating less fibre than kids in the 1980s.

> There are a large multitude of studies that show a negative correlation between CRC and fiber intake even when adjusting for diet, exercise, BMI, income, alcohol consumption etc…

Not really. Take any behaviour or practice that is common among the healthier cohort and it's easy meat for bullshit study results. It's why the nutrition field in particular is full of contradictory studies because "adjusting for" is carrying a lot of unmerited credibility.

> Not really. Take any behaviour or practice that is common among the healthier cohort and it's easy meat for bullshit study results. It's why the nutrition field in particular is full of contradictory studies because "adjusting for" is carrying a lot of unmerited credibility.

You’re the one that said that when studies adjust for these differences they no longer show a correlation.

That is just flat wrong. You used that exact phrase “adjust for”. You can move the goalpost if you want to “I don’t think they are correctly adjusting for all differences” but that’s a very different argument than the one you presented.

The preponderance of the evidence is that fiber has a protective effect against colon cancer and there are multiple plausible explanatory mechanisms.

“I don't know what notion people have about common Western food practices decades ago, but in the 1980s, for instance, fibre was basically non-existent in the common diet”

This is misleading.

1. There is a single gram per thousand calorie difference in aggregate between 1980 and today, so if it was non existent then, it’s non-existent now.

2. Percentage of ultra processed food and food away from home has gone up drastically since 1980, so the types of fiber consumed on average have changed drastically as well.

3. “Fiber” is now a much broader category than it used to be. Resistant starches can now be labeled fiber. If a tiny fraction of the population eats the equivalent a single low carb tortilla with 30g of resistant starch per day that’s enough to completely throw off the aggregate fiber stats. There is much less evidence that resistant starch is protective against colon cancer.

4. Stability in the aggregate doesn’t preclude changes in sub populations. Changes in the way we eat leading to a larger sub population with very little fiber intake.

We know that there have been changes in sub populations. For instance one study that found fiber consumption was stable overall between 1999-2017 found that it dropped among White adults, but the aggregate was stable because it rose among Black and Hispanic adults.

> You’re the one that said that when studies adjust for these differences they no longer show a correlation.

A large number of studies that fully adjust for lifestyle differences have found no meaningful difference in colon cancer rates. It is basically debunked.

https://pmc.ncbi.nlm.nih.gov/articles/PMC4250613/

This cynical piece covers quite a few of them. The evidence that fibre prevents colon cancer is akin to the evidence that red wine keeps you healthy. It disappears when properly analyzed.

> This is misleading.

The mean fibre intake in the 1980s was ~11 grams per day. Today the fibre intake is ~15g. A 36% increase in fibre, and youth colon cancer rates have more than doubled. The math isn't mathing.

I grew up in the 1980s, friend. I suspect you didn't, because anyone heralding those good old days of food quality is clearly simply clueless. A good diet was captain crunch (actually an entire aisle was just whatever cartoons or characters were big having their own cereal that was all coloured flour + sugar), miracle bread, bagged chips and an endless series of full-sugar products.

On the eating out thing: Food made by McDonalds or any other org is in no way empirically worse for you than similar foods eaten at home. Like I get far more veggies and fibre from a Wendy's burger than when I make the burger at home. This is one of those lazy correlation hand-wavy things people use to invent data where there is none. The one real change with eating out is higher sodium is more prevalent, but otherwise it isn't really illustrative of much at all.

That is a 20 year old editorial from 2 random doctors in Singapore in a 3rd rate GI journal that reads like an opinion piece in a newspaper.

Here is a list of 10 widely respected health organizations who state that a high fiber diet likely reduces the risk of colon cancer

World Cancer Research Fund

American Institute for Cancer Research

American Cancer Society

Cancer Research UK

National Health Service

Bowel Cancer UK

British Dietetic Association

American Gastroenterological Association

Dana-Farber Cancer Institute

Cleveland Clinic

Here is a list of 5 very large meta reviews that show a correlation between low fiber diet and colon cancer even after adjusting for diet, lifestyle etc… All published after your editorial in top tier journals.

https://www.bmj.com/content/343/bmj.d6617

https://jamanetwork.com/journals/jamanetworkopen/fullarticle...

https://pubmed.ncbi.nlm.nih.gov/30638909/

https://pubmed.ncbi.nlm.nih.gov/31495339/

https://pubmed.ncbi.nlm.nih.gov/34854791/

>fiber in the 80s

The mean fiber intake in 1989 was ~14g per day according to the USDA https://www.ers.usda.gov/sites/default/files/_laserfiche/pub...

I definitely remember the 80s. We eat healthier than my family did in the 80s. But my parents were working class and we’re upper-middle class.

Sample bias and confirmation bias are the reason that you can’t rely on memory and personal experience. If you look at the data we know that people consume far more of their calories from ultra processed foods than they used to. And we know they eat out far more often. We also know that the average restraint meal is lower in fiber than the average meal at home.

The USDA survey does show a minor increase in total fiber consumed, but there are large differences in sample methodology and as I said previously resistant starches are now labeled as fiber. It is common for low carb breads, tortillas and similar to contain 20-30g of “fiber” in the form of resistant starches.

>no way empirically worse for you than similar foods eaten at home. Like I get far more veggies and fibre from a Wendy's burger than when I make the burger at home. This is one of those lazy correlation hand-wavy things people use to invent data where there is none.

Here is a study from the USDA showing that the average at home meal has 30% more fiber per calorie than the average fast food meal. And the previous survey I posted shows a similar difference in the 80s.

https://www.ers.usda.gov/amber-waves/2013/february/americans...

If you eat hamburgers and French fries for every meal, then yes replacing that with fast food isn’t any different.

But according to the USDA that’s not what people are eating for every home cooked meal.

Away from home meals are higher in fat, higher in sodium, have less fiber, fewer vegetables, are more calorie dense, and are served in larger portions.

https://www.ers.usda.gov/sites/default/files/_laserfiche/pub...

> That is a 20 year old editorial from 2 random doctors in Singapore in a 3rd rate GI journal that reads like an opinion piece in a newspaper.

They're simply recapping various other studies, and attacking the messengers is pretty telling. In fact, every single one of the "studies" that you cited are meta analyses that simply take the already flawed data and outcomes of other observational studies, run them through magical Excel formulas, and then Dan Ariely the desired outcome. You're pretending there is a difference here that there isn't.

Regardless, from your very first meta study-

> It is possible that the weak inverse associations between dietary fibre or whole grain intake and risk of colorectal cancer could result from unmeasured or residual confounding by other dietary or lifestyle factors. Higher intakes of dietary fibre and whole grain are typically associated with other health behaviours, such as higher intakes of calcium and folate; higher levels of physical activity; lower prevalence of smoking, overweight, or obesity; and lower intakes of alcohol and red and processed meat.22 27 63 Many but not all of the studies adjusted for potential confounding factors, although not all potential confounders were adjusted for in every study. In analyses stratified by adjustment for confounding factors

This is junk nutrition science, and the field is rife with it (every week someone does this junk and you get another "super food XYZ protects against ABC"). A very weak correlation is found between a healthy practice and an outcome that tends to come from healthy living. Story at 11.

The funny thing is that I heavily lean towards fibre options, and ultimately have almost all ideal, healthy practices. Fibre is good for everyone. But the narrative around fibre and the rise in youth colon cancer is such a ridiculous non-starter, for virtually every reason, that it's just a gigantic distraction.

> LOL. They're simply recapping various other studies.

It was a review or meta analysis. There was no criteria for acceptance. It’s just 2 random doctors cherry picking studies. The authors refer to it as an editorial and not a meta analysis for that reason. The language even sounds like a newspaper editorial. They make far too many unsupported assertions for an academic paper.

It’s also 20 years out of date. And we’ve had 2 decades of additional research.

>It is possible…

Of course it’s possible there’s a hidden confounder. That’s possible with literally every single observational study.

A sufficient RCT in this case is essentially impossible and likely unethical.

But you failed to read the conclusion that

> Our results indicate a 10% reduction in risk of colorectal cancer for each 10 g/day intake of total dietary fibre and cereal fibre and a about a 20% reduction for each three servings (90 g/day) of whole grain daily, and further reductions with higher intake. These findings thus have important public health implications. Our results provide further support for public health recommendations to increase the intake of dietary fibre in the prevention of colorectal cancer.

Despite the fact that it may be wrong.

Read the other 4 very large meta studies.

Read the statements from essentially every relevant heath authority.

Read the theoretical science.

Of course it’s possible that there are hidden confounders. But the preponderance of the evidence is that high fiber == less colon cancer.

Specifically:

1. We don’t know for sure what the relationship between fiber and CRC is, and we likely can’t.

2. The majority of studies that correct for lifestyle and diet still show a correlation.

3. There are plausible explanatory mechanisms.

4. The most likely explanation is that there is some protective effect.

There is broad consensus among Doctors, health agencies, and researchers that the above are true.

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