While they're not essential in short-term survival, they're essential for long-term health:
https://www.ncbi.nlm.nih.gov/books/NBK559033/
We have enough peer-reviewed studies on this.
The US had for a long time a much too low recommendation of around 0.8 g of protein per kilogram of body weight per day.
That has been discredited by various studies. It is an amount that is sufficient to keep you alive, but it is not sufficient to keep you in good health until an old age.
It is not known with any certainty which is the optimum amount of protein intake. On certain lab animals protein restriction lengthens life, but for now there is no evidence that this also works for humans. Too much protein is known with certainty to be harmful for humans.
I believe that it is likely that the optimum protein intake is somewhere between 1.2 and 1.5 grams of protein per day and per kilogram of body weight, for a person with no overweight. For an overweight person, the protein needs do not increase proportionally to the total mass, i.e. the extra fat does not need much protein.
I wonder whether the so low protein recommendation of USA was actually intended for average Americans, which are likely to be overweight, in which case that number might provide an adequate protein intake.
We’ve already known fruits and vegetables are healthy. Fiber is the reason why eating an orange is good, but drinking a glass of orange juice is about equivalent to a bottle of coke. That’s not an exaggeration, by the way, it’s about the same sugar content.
If you want to eat the recommended 35g of fiber a day, you won’t be able to reach it with just supplements. You need to be eating fruits and vegetables at every meal. For my entire life, everyone has been saying to eat fruits and vegetables at every meal in large quantities.
But the fiber does not survive. The fiber alone is what makes the sugar intake okay - fiber slows and prevents blood sugar spikes, which, over time, is what causes insulin resistance and then diabetes. Drinking orange juice is diabetes fodder. Again, it’s basically soda. Eating oranges doesn’t have that effect because of the fiber.
Also, another note on vitamins: for most vitamins, once you get enough, the rest is wasted. It’s not like eating more vitamin C gives you more and more benefits. No, your body has an amount it needs, which is quite low. Past that, you pass it in urine. The amount you need you reach every day with no effort.
And, additional vitamins still have to be metabolized in the liver and go through the kidneys. Too much vitamin intake is damaging, many doctors can tell you stories of acute liver failure as a result of excessive vitamin intake. It’s basically impossible to do that via food. But when you see those vitamin supplements that are like “2000% daily value” - yeah, don’t take those. You’re not getting any benefit.
Also savannah human diet is chock full of fiber too: baobab pulp, grass seeds, tuber plants, etc
You just have to look to the belly of a healthy, non-obese human and compare it with the bellies of the apes. The bellies of the apes are much bigger, despite not having the fat of humans, because they have much longer intestines, which are packed in there, which are required for the fermentation of the large amount of fiber included in their diets.
The intestines of humans are not so reduced as those of the obligate carnivores, but they are still much shorter than of most apes or monkeys.
Our health is still dependent on eating a decent amount of "fiber", but the amount we need is not comparable with what an ape needs.
My point is just modern diet is severely lacking in fiber, when our gut evolved to process them.
It's not a surprise this evolutionary mismatch will cause so many problems in our body.
fiber is great and under-consumed (especially soluble) and is very well-studied on modern populations [0]. we don't really need to make mechanistic reasonings about evolutionary adaptations that occurred hundreds of thousands of years ago or rely on studies of a small, homogenized population whose lived realities are far from yours and mine
plus, following the the hierarchy of evidence, mechanistic guesses are considered extremely low quality, only ranking above things like mouse studies [1]
[0] https://www.uptodate.com/contents/healthy-diet-in-adults#H61... [1] https://en.wikipedia.org/wiki/Hierarchy_of_evidence
https://nutritionsource.hsph.harvard.edu/carbohydrates/fiber...
> Resistant starch – Soluble fermentable fiber found in legumes, unripe bananas, cooked and cooled pasta, and potatoes that acts as a prebiotic. Adds bulk to stools but has minimal laxative effect. May help to normalize blood sugar and cholesterol levels.
For stronger studies, these guys have you covered: https://www.ncbi.nlm.nih.gov/books/NBK559033/
This includes a part of the "resistant starch", which is poorly digested by humans, so a big part of it reaches the large intestine.
So yes, the "resistant" starch counts as "fiber", but not all of it, because some part of it is hydrolyzed into glucose, which is absorbed.
looking into RS's in general, it seems like there is a special carve-out after a lot of industry lobbying for very specific forms of RS's to be classified as fibers and only if they have physiological effects similar to the classic definition of fiber: https://www.fda.gov/media/113663/download
for practical reasons, I suppose I'm just not understanding why you don't eat more 'classical' fibers. psyllium husk, for eg, which is cheap and effective and has been utilized as a digestive aid in Chinese traditional medicine for centuries (one of the few to survive rigorous empirical evaluation, naturally)
But there's already a general advise on this: eat more fiber.
https://med.stanford.edu/news/all-news/2017/08/hunter-gather...
We're a great ape, our body evolved to process a lot of fiber from fruits and starches. It's the modern fiber-deficient diet that's really weird.
90g/day of fiber is similar to the Hadza tribe diet, where they can consume 100-150g of fiber per day.