[cimbal]

Well said. The size relations of inner organs for example vary betweeen people as far as i know. That is a big hint, althought it's not a proof in itself.

I want to add to that the nutritional needs within each person vary drastically during different times of year (or times of stress, even down to times of day). Athletes know this, for example, it is common to exhibit significant drops in performance during a year of training (recurring every year).

Now combine these simple observations with the way nutritional studies are done and you know why it looks as if we have no clue.

[itchyouch]

I've observed that a lot of diets tend to have similar effects on the populations that adopt them. People speak about feeling better on Paleo. Body builders/lifters optimize macronutrient intakes for muscle gain with similar results. There's also wide consensus on how certain micronutrient deficiencies cause certain conditions. e.g. Vitamin C deficiency leads to Scurvy. Vitamin A deficiency leads to night-time blindness, etc.

I would hypothesize that most arguments about nutrition revolve around observational discrepancies between the micro & macro levels. At the micro (individual) perspective, it feels like everyone has custom nutritional needs (which in a sense, they do), but when looking at larger trends, generally, consistent patterns emerge.

One of salient points that are made about nutrition by Dr. Terry Wahls is that it is fundamentally chemistry. If an individual hits some type of limiting reagent, the body will adapt in the absence of it until it can not and certain ailments occur.

The problem with a lot of nutritional studies is similar to the problems in a company faces. There is some type of prescription to adhere to at the micro-level without taking into context the larger picture. CxO's, if you get at least 5000IUs of DevOps per day, you'll get better performance! Consuming 100mg of Agile development makes you more agile! 1 gram of purpose/mission-driven team-building per week helps with the bad customer service ailment. While there may some truth to those statements, they are also absurd without properly being incorporated into a larger context.

Anyway, one of the interesting tidbits I read was the recommendation to increase salt & potassium intake when adopting a ketogenic (high-fat) diet, to prevent/alleviate headaches & fatigue during the ketosis transitional period. One can see that the advice is probably rooted in some chemistry.

Nutritional studies would probably have much better results if the populations could be subjected to a strict meal plan to control for other factors.

[ska]

   "People speak about feeling better on Paleo."

You really have to watch selection bias problem here, as (different) people speak of feeling better on pretty much every popular diet ever.

Anecdotal and self reporting data for things like diet/exercise & health are notoriously poor sources (and also often suffer from a host of generalization issues).

[cimbal]

My suspicion is that most of the population does not react too strongly or fast to a suboptimal diet, hence the general softness of this topic. But maybe a certain percentage does, and i consider myself one of them. It could well be that those who do are on the brink of a deficiency, but i'm not sure about that.

My experience, and there was i time i was really into this, doing interviews with mostly young people. The results fit the assumptions of William L. Wolcott very well, that most people basically fall into 2 groups, fast and slow metabolizers. They differ significantly when it comes to digestion. One group needing more of certain minerals then the other when eating the same foods (potassium making the biggest difference as far as i remember). I remember often guessing correctly what type of water brand people would prefer based on this (chosing between 2 favourite sources, one with high potassium content. the sample size was small, but i'm really sure you can replicate this).

If this is due to genetics or due to gut microbes or both at the same time - i really don't know.

So, i think that the macro level does differ between people. That every person needs an individual mixture of nutrients to keep the metabolism in balance.

Btw, you can modify your metabolism bye eating differently and the body can adapt for a long time before any clinical symptoms show.

Wolcott explains the differences between those 2 groups in the following way: either the sympathetic nervous system or the parasympathetic nervous system is stronger and determines your metabolic type. And those systems can again be influenced by the environment (climate, food availability etc.). https://en.wikipedia.org/wiki/Autonomic_nervous_system

As i could use his theory to predict food preferences, i never questioned the basic premise. Would be interesting to do some more digging again.

[feld]

Reminds me of the urban legend "japenese people have longer intestines" which may or may not be true :-)

http://www.biguglyreview.com/body/nonfiction_andy_raskin.htm...