Some think fiber is awesome, and others want to avoid it like the plague for higher testosterone… so which is it?

Health benefits of dietary fiber.

Higher fiber intake significantly lowers the risk for developing:

  • coronary heart disease
  • stroke
  • hypertension
  • diabetes
  • obesity, and certain gastrointestinal diseases
  • high cholesterol levels
  • Increases nutrient absorption

Increased intake of soluble fiber improves:

  • glycemia
  • insulin sensitivity in non-diabetic as well as diabetic individuals

Prebiotic fibers (such as bananas and onions) appear to enhance immune function. (1)

So fiber is actually something you really need.

So why are androgen freaks afraid of fiber?

Fiber is known to increase SHBG, which lowers free testosterone.

What you also need to know is that the lower amount of fiber you consume, the less estrogen and the more testosterone it will excrete. Now that’s not a good thing.

Lets’s look at the studies.

1) Switching from a high fiber (61g/day), low fat diet to a low fiber (26.6g/day), high fat diet resulted in a 15% increase in SHBG-T binding, but also a 13% increase in testosterone and a 10% increase in free T. (2)

More SHBG-T binding even when following a lower fiber diet? 

Also, on the low fiber diet they had 13% greater urinary testosterone excretion and 12-28% less urinary estrogen excretion. That’s not good either.

2) In this study men switched from a low fiber (<20g/day), high fat diet to a high fiber (25-35g/day), low fat diet. Testosterone (-12%) and free T decreased, but SHBG only decreased minimally. I have to add they were in a caloric deficit as well which also reduces testosterone. Just by lowering your fats will impact testosterone negatively.

So even when increasing fiber, does not result in elevated SHBG.

Androgen excretion was not altered. So…when you want to lose weight, and you cut on your calories, increasing fiber a bit might be a good idea to reduce androgen excretion as much as possible.

3) Insoluble fiber reduces estradiol more than soluble fiber (3). 

  • Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower risk of heart disease. (4Soluble fiber helps against diarrhoea.
  • Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines. (5) Insoluble fiber helps against constipation.


The problem with all these studies are that they don’t compare the same amounts of fats with different amounts of fiber to see if it lowers T and free T.

It probably does, but the difference would be insignificant.

SHBG is positively associated with testosterone. So the more T you have the more SHBG you’ll have, however, fiber is not a major contributor to SHBG.


My advise, fiber is good as it helps the body to detox and the clean the colon, but don’t overdo it.

I actually advise people to rather stay away from fiber as it irritates the gut and increases endotoxin absorption and increases serotonin. This can lead to inflammation, autoimmune disease, fatigue, low motivation, no focus, and many other bad stuff. More about increase dopamine here, as it antagonizes serotonin.

Rather fix your gut, by doing a colon cleanse and putting in the right gut bacteria (yogurt, kefir, beet kvass, etc) and then you can ingest only raw low to moderate GI vegetables. 

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Published by Hans Amato

Hi, I'm Hans and I'm a physique, strength and nutrition specialist/coach. My passion is building the best physique naturally (both functional and super strong) and enabling others to achieve their dream physique and health goals as well. Nothing is impossible if you set your mind and heart to it - not even you're "genetic limit" will be able to stop you then.

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