[rdmcfee]

There are two core issues with nutrition science.

The first issue is that it's extremely difficult to run a long term controlled study on nutrition. Adherence to diet interventions is difficult to measure and it drops off over time. As a result most nutrition studies are epidemiological cohort studies which are not particularly good at determining causality.

The second issue is a question of funding. Diet and exercise interventions are not something that are typically monetized be the pharmaceutical industry. As such there is little private sector funding going into nutrition studies. Couple that with the fact that they're extremely expensive and you have a serious deficit in studies.

[andrei_says_]

Once I found out that food calorie count today is still determined by literally burning the food in a calorimeter and measuring the heat, a practice started in the 1800-s, I realized that I am on my own.

I get that the laws requiring calorie content on labels have lead to finding an efficient way to measure and provide the numbers, but it is obvious to me that the measuring system is completely broken or very inaccurate at best.

http://www.scientificamerican.com/article/how-do-food-manufa...

[squidfood]

I'm not sure what your problem with this method is, given that the amount of heat given by burning is the definition of a food calorie.

That's like saying "once I learned that voltage was measured by the deflection of a coil in a current (a practice started in the 1800s)" or "once I learned that heat was measured by the expansion of a liquid in a glass tube..."

You could argue that the heat definition of calorie doesn't really reflect the health function of the food (for example, maybe glycemic index is more useful), but I'm not sure why complaining that a calorie isn't a calorie is really insightful.

[andrei_says_]

My problem with this method is that my body does not burn the food in the same way. And, it doesn't burn every food in a way similar to every other food.

I get that it's the best scientists could think of 100+ years ago. But putting averaged numbers derived from this absurd method on labels as if they are how my (!!) body works, and deriving all kinds of "food science" conclusions and recommendations from it is imo willful ignorance in the name of convenience.

[x0x0]

Your body isn't actually burning the food. Therefore, why is this an important measure, other than it is easy to measure?

Bioavailability / metabolizable energy varies not only in the small, ie composition and cooking of food, but in the large, as long run diet choice changes gene expression.

[squidfood]

Actually, respiration is burning the food, it's literally the same energy release, and the methods of calculation take into account the portion of the food that's burnable but non-digestable. If you're saying that the corrections for indigestible food are the subject of scrutiny, that's true, but that has nothing to do with the fact that "burning" is a problem for calculating caloric content.

I used to work in aquaculture, where we measured the amount of food going into a fish (via the bomb calorimetry that we're talking about, directly), the amount of energy spent by the fish in respiration (by measuring carefully increases in water temperature in their tank), and then we measured how much energy the fish had at the end (by burning the fish).

And quite simply, calories in was equal to calories out. It was a good relationship within very acceptable experimental error.

Now of course, the fish were growing very rapidly and we could control their food exactly. Humans, growing over a longer period, can be subject to different metabolic pathways, and we can't measure their respiration directly of these pathways [Edit: this is where the gene expression you mention comes in] - this is a far, far bigger source of error than the calorimetry, so calories alone can be less predictive of outcome. But this doesn't take away from the basic definitions of thermodynamics.

[PeterisP]

1) respiration is burning the food, but it's not burning all the food; "calories in" refers to calories absorbed, not calories put in your mouth; and the proportion between those two varies depending on all kinds of things, including e.g. gut microbiome and temporary changes to that due to various drugs; so if you strictly count calories put in mouth you still get a hard-to-measure variability in actual "calories in" (unless you put a respirator on the subject and measure it that way).

2) All other things being equal, changing "calories in" will make you lose/gain weight. The trouble is, all other things are not equal - simply changing how much you eat will significantly change those other things, it has an effect on your metabolism and eagerness for physical activity, thus directly affecting also "calories out" if you don't carefully monitor that and work to keep that stable.

3) All other things being equal, changing "calories out" will make you lose/gain weight. The trouble is, all other things are not equal - simply starting/stopping working out will significantly change your natural appetite, how hungry you are and how often you're hungry, and which types of food you have cravings for, thus directly affecting "calories in" unless you carefully track what and how much you eat everything and actually do keep that schedule exactly the same.

[squidfood]

Yes, this is a good partial list of all the "bigger sources of error" that I mention above!

[whiddershins]

Ok but if my body takes for example an amino acid and uses it as a building block for repairing a muscle, that building block hasn't been burned, correct? So that "calorie" is functioning in a completely different way than as an energy source.

It's like we didn't burn the wood or store it for fuel, we used it to repair the walls of the house.

Right? Or am I confused.

[squidfood]

Yep. Though it's still counted as a "calorie" that's stored in your body as a certain number of grams of protein. If your body later decides to lose that muscle, then the calorie is spent.

Since fat and protein each have different amounts of calories stored per gram, that's why if you want to get really accurate about weight loss/gain, you track your body's %fat & %muscle and not just your weight.

Edit: to clarify your analogy, just because we use wood to build a part of the house, doesn't mean we won't take it and burn it if we're desperate for heat and have used all the other fuel.

[andrei_says_]

> respiration is burning the food

Are we accepting that the complex biochemical mechanisms of the cells are identical to burning things in an open flame?

And, that every living human's body processes all foods in exactly the same way, regardless of age, ethnicity, gender, time of day etc? Just like the open flame would?

[whiddershins]

I think the idea is, on a cellular level, it's actually the same chemical reaction.

[jmde]

I generally agree with your two issues 100%, but one thing I've found interesting about these discussions is that no one seriously questions the fundamental hypotheses involved, that typical diet bears any relationship to long-term health.

That is, it's assumed it does, but we just can't pin it down because of poorly done studies.

My guess is that that's true, but the other very real possibility is that our bodies are designed to process a very wide variety of foods in a very robust manner, such that as long as you're not eating something obviously poisonous, it doesn't matter as long as you're not depriving yourself of something important nutritionally (as in scurvy).

Similar arguments can me made with regard to weight and exercise, although there it seems like the effects are clearer in certain ways (e.g., I doubt anyone would argue that being in shape isn't better than being physically deconditioned).

[mendelsd]

> our bodies are designed to process a very wide variety of foods in a very robust manner

There are indications that various health conditions can impair glucose regulation, and those affected would tolerate less dietary carbohydrate than healthy people. I'm aware of two conditions, elevated cortisol [1] and elevated blood iron [2] (which can be caused by regular alcohol consumption, btw).

[1] http://www.ncbi.nlm.nih.gov/pubmed/11724664

[2] http://www.ncbi.nlm.nih.gov/pubmed/26618110

Also, type 1 diabetes of course.

[Noseshine]

The third issue is the food categories are way too broad and ill-defined. For example "meat" and "fat". There is meat and there is fat that tastes good (incl. hours later, when the gut had a chance to sample it more thoroughly - there's a "brain" and there are taste receptors down there).

There's meat and also fat that doesn't (taste good). It's not just the meat/fat itself, it's also the combination with other foods and the preparation that can change completely how my body perceives a food. Since those "feelings" have developed for a reason - we didn't have science to tell us what is good to eat for the 1st million years of humans (and pre-humans) - I dare claim it is significant for ones long-term health.

But studies don't make any such distinction. To assume everybody eats what tastes best is a stretch, not just because circumstances in our stressful lives, but also because the brain can only ask for food that it knows, and I remember the stories from that British chef who showed American kids tomatoes and potatoes and they had no clue what that was, they only knew processed food.

So how can you seriously leave it at "they ate x amount of meat" when such a person eats "meat" compared to someone who had opportunity to taste "traditional" (pre-industrial) foods and prepares him- or herself a good piece, including a good combo with other stuff and well-prepared?

Am I seriously to believe a McDonalds burger's "meat" is correctly put into the same place - as "meat" - as a real meal?

Of course, if you acknowledge this difficulty you have to give up on studies because I see now way to reliably collect that information on a scale large enough and long-term enough for a useful study. As the article suggests, actually (to give up going down this path). The story of that guy looking for his car keys under the street light even though he lost them somewhere else comes to mind, in the desire to study this at all this seems to be what happened.

It isn't about giving up as some readers took away from that paragraph, it's about choosing another path. For example, get down to understand what's actually happening instead of high-meta-level studies and see if that gives us new ideas.

Oh and here's a nice article related to the subject: http://www.vox.com/2015/3/23/8264355/research-study-hype (I hope nobody tries to count the dots on each side of the plot to use that to draw conclusions... it's an example and incomplete and even if it had dots for every single study could not be used for that purpose)