Why is so little known about Nutrition?

Factual Questions
1

This is not a thread to raise points about nutrition and defend or argue them. It is to discuss why medical science knows so little about nutrition.

Even doctors, at best, have only the vaguest notions about nutrition, usually limited to what is advised in connection with their particular specialty, which they have uncritically assumed to be true because they read it in a single research article.

A number of nutrition questions are ongoing, and have been for decades. Why can’t medical science answer them? Why can’t they find out if refined cane sugar is better or worse than other sugars? Why can’t they find out if fresh veggies lose nutrients quickly if unfrozen and if freezing locks them in? Why can’t they find out how much salt is dangerous?

2

Think of how complicated a person’s diet is. Think of every single food you’ve every had, all the breakfasts, lunches, and dinners, all the snacks and fast foods and drinks and noshes and grazing and stuff at the office. Now think about every single ingredient and additive and method and mode of processing that is in each one. And think about your personal health and the diseases you’ve had, the allergies you suffer from, the deficiencies you’ve gotten, the level of exercise you get, the kind of house you live in, the climate of your hometown, and any external factors like pollution. When your head is thoroughly dizzy, add in your individual genetic heritage which is different from everybody else on earth’s. And remember that this mixture, except the last - though who knows?, changes with time, both over days and over years.

So you’re asking why people can’t isolate out one single element of that beyond-complex stew? Because it’s impossible. The best that can be done is to try to tease out correlations from the background noise. That best is mostly way too little. Nor I can see any good reason why this should improve in any foreseeable future.

3

We know more about livestock nutrition than about human nutrition. I suspect because science has fewer ethical obstructions to doing scientific experimentation on livestock nutrition. And there is more to be economically gained by maximizing understanding of livestock nutrition.

4

Exapno’s and your post really provide the complete answer. Following the long term impact of isolated changes across a lifespan is very difficult to do in the broad range of human genetic subpopulations engaged in a wide variety of diets, exercise habits, living in a host of cultures. Livestock, with shorter lifespans, controlled genetic variability, and control over all aspects of their lives and where the points of interest are how cost effectively you can get them to grow, not maximizing lifespan or preventing dementia … not as difficult.

BTW the research is pretty well settled on two of your questions asked* … the fact that media hype and people marketing books pretend it is not is not the fault of the science.

*Added refined sugar is harmful with the exact magnitude and form of the harm still being fleshed out.

5

At least traditionally, a doctor’s job is to fix whatever’s wrong with you. Providing lifestyle advice (including nutrition) really isn’t a big part of their training.

The answers depends on so many other factors. Refined cane sugar is good for you if you aren’t otherwise getting enough calories. It’s just as bad as any other sugar if you’re already consuming too many calories.

6

:confused:

It isn’t. We know huge amounts about nutrition. You could (and people do) fill libraries with what we know about nutrition.

Whatever makes you think we know less about nutrition than about any other field of science?

You had best start first by explaining why you believe that medical science knows so little about nutrition? Compared to what does it know so little? And how did you do this comparison?

:confused:

Doctors know a huge amount of very specific information about nutrition. If you ask about the metabolic fate of fructose or the physiological effects of protein deprivation the average doctor will be able to provide you with enough information tot fill a small book.

Can you provide any evidence at all that this is true?

As have a number of astrophysics questions, a number of biochemistry questions, a number of civil engineering questions, a number of ecology questions, a number of…

If this is your standard of “knowing so little” then we “know so little” about literally every field of study.

For the same reason that astrophysics can’t answer why the Voyager probes are slowing down and why ecology can’t answer why or even if bee populations are declining.

It’s because the differences, if they exist art all, are relatively tiny compared to the background fluctuations in any possible control in natural system. As such, it’s almost impossible to separate out any putative effects form random variation.

This isn’t especially true of nutrition compared to any other field of science. All the low hanging fruit have been plucked. All the questions that were amenable to easy study have already answered. All we have left are, of course, questions that are difficult to answer.

In many cases the questions are ones, like your sugar question, where we aren’t even sure that there *is *a question. There may not *be *a difference between different types of sugar. Even if there is, the effect is so tiny compared to genetics, exercise, age, the rest of the diet and so forth that it isn’t showing up reliably in controlled studies. Every field of study has these types of questions and, of course, always will. This isn’t evidence of “knowing so little”. It’s just evidence when you’ve resolved all the big, easy-to-study issues you will be left with little hard-to-detect issues.
Others, like your salt question, are not even a question but an issue of ever-increasing accuracy. All nutritionists agree that one pound of salt per day is injurious. All agree that 1 mg per day is not. So we actually do have agreement on how much is injurious. You just aren’t satisfied with the accuracy off the answer. And if the answer fell between 100mg and 5 mg, would you be satisfied then? Why? Or if it fell between 1mg and 1.00001mg? You are simply setting an arbitrary level of accuracy that you require and claiming that we know “so little” because the current state of knowledge doesn’t have enough decimal places. But once again every field of study has these. The speed of light or the circumference of the Earth, for example, aren’t known to an infinite number of decimal places. Do you take this to mean that we know “so little” about relativity or geology?

7

If we know so much about nutrition, why does what we know change every five or ten years. Twenty years ago, eggs were considered next to poison (not that it stopped people from eating them); now they are considered the perfect food. Ten years ago, low fat and hi carb was considered ideal; now it isn’t and maybe the reverse is true. Professional nutritionists still go around saying that a calorie is a calorie is a calorie, despite increasing evidence that it might not be so. Who ever heard of gluten intolerance ten years ago? Now it is the latest fad.

My doctor recommends a “balanced diet”, which is really an admission that he doesn’t have a clue. Oh, he does want to limit sugar and salt. As for the latter, he says the evidence that it contributes to high blood pressure is weak and it may do so in only about 20% of people, but it is hard on the kidneys in any case.

8

As Blake says, we know a lot about nutrition. Much of what that is comes from studying individuals or small groups of people with specific complaints. You can say that started with the discovery of vitamins, because vitamin deficiency diseases are noticeable and easily rectifiable.

What we don’t know a lot about is what to recommend to your basic average human to extend health and life. That’s where the enormous complexity of ingredients and foods overwhelm the data.

When you do hear about recommendations you normally are hearing about the findings of large-scale longitudinal studies. One famous one is Harvard’s Nurses’ Health Studies, which has followed 238,000 nurses since 1976.

This is valuable because it’s large enough to include many variables in lifestyle and nurses presumably have the education and training and inclination to do the tedious work of precisely chronicling their intake over years of time. At the same time, it is a study only of woman, not men or teens or children. The woman are American. They are likely to have higher incomes, live in better homes and neighborhoods, and enjoy the other benefits of middle class lives. They are also subject to the whims of fads in cooking and diet, of earlier dietary advice, and of the lack of information about basic ingredients in foods. (Are they likely to have any clue about the quantity of polyols in foods? Yet this is a promising new area of food sensitivities.)

In the late 19th century serious scientists - the best of the best - were saying confidently that they would soon be able to produce synthetic food that would be better and healthier than anything grown. We now know they understood close to nothing about what makes food healthy. It took 100 years just to get started on that and more is learned all the time.

Translating knowledge about food into dietary advice requires much more than just knowing food. We have to understand genetic and environmental influences as well. Again, this is a constantly changing background. You might as well ask why we can’t predict next summer’s weather on a daily basis. The answer isn’t that we don’t know anything about meteorology; it’s that forecasting is really, really hard.

9

Woo, woo, woo, woo /
Fakin’ ‘em out / Fakin’ 'em out
Woo, woo, woo, woo, wooooooo…

10

Part 1 – Most of what fills those libraries is contradictory, written by hacks with economic or ulterior motives, in the absence of well-researched scientific data…

Part 2 – Do we know more about the Periodic Table, or the Food Pyramid, and with what degree of scientific certainty?

11

I’m not sure this is true.
Most current human nutrition issues are about extending lifespan.
Livestock nutrition is about putting on as much mass as possible in a short timeframe. If the process for doing this decreases the animals’ lifespan, nobody cares, since it’s going to be slaughtered as a young adult anyway.

12

Actually, that one was solved a few years ago. It’s due to uneven heating of the spacecraft. The first clue was that the anomolous acceleration was radial to the Earth, not radial to the Sun, indicating that it had something to do with the direction the antennae were pointing. Models of heat production, absorption, and transfer in the craft confirmed it. But of course, unsolved problems are sexier than solved ones, so the broader press never reported on this.

13

The problem is, as Blake says, we know a lot about specific nutrient items and what they do in the body, what processes they go through to be metabolized. How that contributes to overall fitness and good health (or bad health) is in flux because the human body is incredibly complex and variable. One person smokes and is spry and relatively healthy at 99, another dies of lung cancer in their 50’s. Some people eat high-fat diets and do not get heart attacks. A friend of mine, for example, was 300lb with an incredibly bad diet yet had a fairly low cholesterol - just the opposite of all the diet hype. What specifically about Japanese or Mediterranean types reduces the risk of heart disease (or is that a myth?)

The answer is the body is very very complex, and can operate very differently on the same inputs from one person to another. Of course, true experiments are also very hard to perform on human subjects living in the real world. We know a lot about how to keep rats healthy.

14

Per what Blake and others said we know a ton about human nutrition in terms of what happens to food once it gets into the body, we know less about what specific foods and precise amounts an individual should eat in combination with each other to get X physical result because there are gazillion other variables re exercise, age, drug use (cigs, alcohol caffeine) etc., food allergies, personal metabolism, etc. that effect the way food will processed by a specific individual.

As just one example relatively small differences in metabolism between individuals can yield huge differences over time in the amount of weight a person carries around. There is no “best for all people” food combo or intake level.

And beyond this it’s not really a pressing issue in terms of public health in industrialized counties. Sure, nutrition is important, but human biology is adaptable to an extremely wide variety of foods. If your fat, carbohydrate, protein and vitamin and mineral intake ratios are within reasonable specs most human beings will be perfectly healthy on a huge range of diets. Obviously eating too much or intaking too much salt etc. can be harmful but these are known issues.

Re your questions

Based on what is known about the metabolism of fruit and plant sugars I believe the answer is that the differences are (on a biological level) infinitesimal at best.

This could be answered relatively easily with testing and I suspect the answers here are already known. Please cite that this is some big mystery.

A lot is known about how sodium levels effect health. This varies hugely by individual genetic disposition, there is not specific “answer” here that applies to all people.

15

You know I had some empathy for your intial OP … I understand the level of certainty of answers that people want regarding health issues and that they want them yesterday … and the frustration the public experiences when best understanding at one particular moment morphs into a different understanding as more is learned.

And there is to some degree a GQ answer (or really answers), as given by several now, for why we do not possess the level of certainty at the level of precision that many desire: humans are a varied bunch, a motley crew, with different presidpostions and different combinations of habits. Neat long term experiments altering only one factor followed over lifetimes with enough subjects to be adequately powered to give definitive answers just cannot be done. So extrapolations are made from animal models that sometimes hold up and sometimes don’t. Associations are observed and confounders controlled for as best as can be. Studies are sometimes replicated and sometimes they contradict each other. The results from one animal model are different than in another and the apparent findings in one population diverge from the findings in another. Moreover the public is not satisfied with the broad answer about nutrtion that we do know and that we have known: Lots of veggies and probably fruits, not too much processed crap, not a lot of added sugars and added salt. After that the differences can get to be angels dancing on the head of a pin. 10% protein or 25%? Vegan, Paleo, low carb? All so much better than the Standard American Diet that any differences between them are relatively inconsequntial. HFS vs sucrose? Both are bad when added to food that already provide enough energy, one worse? If so inconsequentially so. As far as nutrtion goes it really is simple: couple lots of veggies and fruits and other high fiber foods of your choosing (whole grain, legumes, nuts, whatever) with a decent protein source and avoid the processed/highly refined crap; add in a moderate amount of exercise to help it go where it can serve you best. That is as well established and as solid as the Periodic Table.

But this post of yours bespeaks for an agenda that is not really a GQ. Maybe you really meant to put this in GD or The Pit? Simply put contradictory findings is how science works and susses things out. To call most of nutrition science to be the product of “hacks with economic or ulterior motives, in the absence of well-researched scientific data” is beyond the understandable frustration with the ongoing work in progress; it is tin foil hattery.

16

I just want to make sure this is perfectly clear:

Nutrition science in relation to health and medicine has a created a massive fund of verified hard science knowledge and that knowledge base has been increasing exponentially in recent years. Of course answering questions in this regard is like battling a hydra: every question answered only raises six or more new ones. And anyone who claims to understand the whole edifice is either delusional or lying.

Every active field of science contains controversy and debate and minority perspectives. Medicine is no different. And sometimes the previously minority perspective ends up becoming the new consensus opinion … in every field of science.

Oh, well established that frozen and canned veggies are fine nutritionally btw. How much a fresh vegetable loses nutrtionally as it sits in transport, on the shelf, and in your fridge, varies by the vegetable and the nutritional factor under consideration. The details are known but fairly unimportant to most of us.

17

DSeid put it much better than I would, so I’ll be blunt: this is pure and simple nonsense, written out of obvious and utter ignorance.

18

Practicing physicians know quite a bit about nutrition, and are able in general to give sound dietary advice and talk about the importance of various components of diet. I just had one of my infrequent medical checkups and conversed with my primary care doc about the significance of vitamin D supplementation.

I have found when engaging in “dialogue” with alt med advocates, that when they say “physicians don’t know much about nutrition”, what they really mean is “physicians don’t buy into my bizarre beliefs about nutrition”. :smiley:

19

Is nutrition science the same as dietetics? The stereotypical impression in my mind of a dietician is someone employed by an institution to determine what various patients, etc. should eat, and stereotypically is a busybody who goes around and reminds people to eat more vegetables, etc. “Eat healthy, yeah, that’s what we believe here!” In other words, a practitioner. Is the field similar to psychology in the sense that you have some people who specialize in clinical practice and others who specialize in more theoretical research, or is nutrition science a separate, theoretical field?

20

No, not the same. Your impression of dieticians is pretty much the same as mine. The people who do the research are usually PhDs in a host of different areas and then there are expert panels that parse out the research according to now accepted standard levels of evidence quality, hopefully doing that job critically. Of course the typical practicing internist or pediatrician is not a medical scientist any more than dieticians are. We are informed (and to variable levels, critical) consumers of scientific information. And some of us are more informed about some things and some others. Given the vastness of what is known about the interection of nutrition and health and medicine I plead guilty to having, relative to that vastness, only vague notions about nutrition. And I have a pretty strong interest in it.