Newsflash: Fiber Provides Calories to Humans
But there is another effect of fiber on energy balance that often goes unappreciated. Backing up, it***8217;s often stated that fiber provides no calories to the body since humans lack the enzymes necessary to digest it. This has often been taken even further to claim that high-fiber vegetables are ***8216;negative calorie foods***8217;, that is they take more calories to digest than they provide (assumed to be zero).
Here***8217;s the thing: it***8217;s not true. Not entirely anyhow.
Above I discussed the issue of fermentation of some types of fiber to short-chain fatty acids which are then reabsorbed by the body. Well, those fatty acids provide calories to the body. While there is still some debate in the area, researchers have assigned a caloric value to fiber of 1.5-2 cal/gram (depending on the specific type).
Admittedly this is an average and will depend on the specifics of the diet and the type of fiber but, simply, the idea that fiber provides no calories to the body is not true. While the caloric value of fiber is still lower than starchy carbohydrates (4 cal/g), it is not zero.
As I mentioned, our evolutionary diet is thought to have contained absolutely massive amounts of fiber on average, intakes of 100-150 grams/day has been thrown around in some scientific papers. I would note again that this would have come from the intake of massive amounts of fruits and vegetables, providing numerous other nutrients (especially minerals and vitamins) that wouldn***8217;t be found if you tried to get that much fiber from supplements.
In that context, it***8217;s worth mentioning that high-fiber foods, typically fruits and vegetables, contain tons of other nutrients important to health or what have you so looking only at the fiber content can be a bit misleading. Getting adequate amounts of high-fiber fruits and vegetables on a daily basis has benefits far beyond just the fiber content; getting some at each meal would seem to be a good thing.
And yes, I am waffling on this. There is very little hard and fast data on optimal fiber intakes for any goal. Too little is bad, too much is probably bad. Somewhere between those two extremes is about right. People eating the modern diet get too little fiber and should increase it. I***8217;ve seen some meal plans that, frankly, included absurd amounts of fiber (folks with eating disorders often do this type of thing to stave off the gnawing hunger). Find balance, people.
Depending on meal frequency, somewhere between 5-10 grams of fiber per meal would seem a decent place to start. That should provide anywhere from 30-60 grams of fiber per day, covering average recommendations without being excessive.
