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Tuesday, November 17, 2009

Dietary consequences

Brainsucker by Kevin Steele from flickr (CC-NC)

This post is a follow-up to The myth of 5 a day - people never ate that much fruit and veg.

"Because" is not a logical connective of classical logic, it's not possible to construct a truth table for "A because of B" statement. Even when A and B are true, it's really quite difficult to prove that causality flows from B to A - correlations, no matter how strong, don't prove causality.

On the other hand, while proving such statement true is hard, proving it false can be very simple - if either A or B is false, "A because of B" must necessarily be so too. So "crime is on the rise because of violent video games" can easily proven to be false, because the consequence part ("crime is on the rise") is false - therefore collapsing the whole argument before we get anywhere near analyzing causality.

"Guns prevent crime" / "death penalty prevents crime" arguments collapse equally fast - countries with more guns and more executions don't have less crime - so we don't even need to think much about causality here. That doesn't mean that reverse statement "gun control prevents crime" is necessarily true, causality might be missing even if correlation exists. By the way there is actually some pretty good research indicating that violent movies deters violent crime, at least in short term - apparently because violence-loving young males go to theaters to watch violent movies instead of getting into real crimes. It's not too unlikely that it might be the same with violent video games.


Now that we're past the obligatory cat and the obligatory detour, let's get back to diets. There's a widely repeated claim, which basically goes "people are fatter than in the past because their diets have much more fat, especially animal/saturated fat than in the past, and nowhere near as much fruit and vegetables as in the past". The consequence is undoubtedly true - obesity is on the rise pretty much everywhere.


On the other hand, the part about too much (saturated/animal) fat, and not enough fruit and veg is entirely wrong. We actually eat a lot less fat; the fat we eat is increasingly unsaturated vegetable fat; and we eat a lot more fruit and vegetables than in the past.

Take a guess - what are the biggest sources of calories in American diet? Here's the list for 1961 and 2003, in kcal/day. I don't believe 1961's diets were perfect, and I'd love to have data earlier than 1961, but that's as far back as FAO statistics go.


Vegetal products consumption increased a lot - 1871 (65%) to 2708 (72%) kcal/day, while animal products consumption stayed constant in absolute terms, and decreased a lot proportionally - 1010 (35%) to 1045 (28%).

Top vegetal products:
  • cereals without beer - 627 to 832 (of which wheat - 504 to 603; rice 26 to 94)
  • sugar and sweeteners - 515 to 657 (of which sugar 453 to 320; HFCS 56 to 331)
  • vegetable oil - 276 to 606 (of which soybean oil 157 to 492)
  • alcoholic beverages - 108 to 150 (of which beer 68 to 100)
  • "fruits" without wine - 79 to 117 (of which oranges 14 to 32)
  • potatoes - 77 to 100
  • maize (without HFCS, maize oil etc.) - 59 to 98
  • "vegetables" - 63 to 77
  • beans - 32 to 30
It's quite surprising list - foods which can be considered traditional like wheat, potatoes, and beans, are a really small portion of the whole. Modern vegetal products like soybean oil (unsaturated fat), sugar+HFCS (sugar, obviously not fat) dominate the list.

And for animal products:
  • meat - 335 to 451 (of which poultry 64 to 197; pork 127 to 132; beef 125 to 115)
  • whole milk - 304 to 199
  • animal fat products (butter etc.) - 199 to 116
  • cheese - 48 to 149
  • eggs - 67 to 55
  • butter - 65 to 40
  • fish and seafood - 19 to 28
Total fat and protein consumption in g/day:
  • Animal fat - 69g to 71g (63% to 46%)
  • Vegetable fat - 40g to 83g (37% to 63%)
  • Total fat - 110g to 155g
    What increased here was poultry - the approved lean meat; and cheese - the most vegetarian of animal products; what decreased most was whole milk, butter, eggs, and animal fats as whole category.

    This is as far away from the conventional story as it gets. Proportionally to their diets, people eat less fat, a lot less of the supposedly "unhealthy" saturated animal fat, less milk and butter (saturated fat), vastly more "healthy" vegetable fat, more lean meat, more vegetables, more fruit. Sugar+HFCS consumption increased a lot in absolute terms, but stayed fairly constant proportionally, even decreasing slightly from 17.8% to 17.5% of all calories.

    So it's not that people lack personal responsibility - people adjusted their diets to follow every single point of conventional dieting advice. To keep blaming people's eating habits for obesity epidemic is to blame the victim. You cannot claim that people are fat because they don't follow dietary advice, as they actually do!

    The only alternative is that the conventional advice doesn't work. Eating more fruit and veg, switching from animal to vegetable fats, reducing proportion of fats in diet and so on - does not make you slimmer. I won't answer the question if the advice is merely useless or actually harmful in this post (causality in reverse direction) - that would require a lot of research. But we sure know it doesn't work.

    I doubt that another round of minor adjustments to the advice (look at all reversals on butter vs margarine), let's say by insisting on more fish oil this time, are likely to magically make it work now, in spite of consistent track record of failure.

    I don't have enough data to give you reliable advice, but the most obvious alternative would be eating reasonably-sized portions of the most delicious food you can think of. This will usually be something fairly traditional (even not necessarily from your culture), often but not always with plenty of animal products in it, and extremely rarely with much sugar or vegetable oil. If type of food doesn't matter, and only portion size does, then you can as well enjoy it, instead of torturing yourself with diets.

    For the record, author of this post has BMI 23. Never trust overweight people to give you diet advice.

    8 comments:

    Mark Dominus said...

    Have you seen The No-S Diet? It is a very slightly refined version of your own diet advice. It says: "No *S*nacks. No *S*weets. No *S*econd helpings. Except on days that begin with *S*."

    It seems to me like generally good advice.

    taw said...

    Mark: Are there any published studies that No-S kind of advice works? I'm just saying that conventional advice doesn't work, for what evidence is plentiful, unfortunately I don't have any alternative I'd be willing to bet my money on.

    Everything I have read on pubmed says that major long-term fat loss by dieting or exercise is really unlikely regardless of specifics (gastric bypass surgery and drugs work much better), so the best thing would be not to get fat in the first place. By the time you want to go "on diet", you already lost.

    bosie said...

    taw, does your comment suggest a mental/psychological problem (which only fat ppl have/get) then?

    Xianhang Zhang said...

    "because the consequence part ("crime is on the rise") is false - therefore collapsing the whole argument before we get anywhere near analyzing causality."

    This is not accurate. It's possible to claim that "government policy has lead to higher broadband prices" while also acknowledging that broadband prices have been falling over time.

    The claim is that broadband prices are above what they would be absent government policy, not against historical broadband prices.

    Bragi said...

    In Poland we have a "ŻP" diet (that would be "DH" in English). It stands for "żryj połowę" ("devour half").

    Cut your meals in half and stay there. You will become and remain slim :)

    taw said...

    bosie: That it can be reliably fixed by surgery implies that it's probably not a purely psychological issue. One obvious mechanism is that supposedly fat cells multiply when you're fat, but don't die when you slim, so ex-fatties supposedly have more empty hungry fat cells than people who've never been fat (but I haven't even properly verified this, so don't rely on this comment). This only explains difficulty of getting slim, not why so many people get fat in the first place.

    Xianhang Zhang: If you have comparable countries with different government policies, then you can compare to these countries instead of historical record.

    If you don't, then you have a problem. Unless you have some data showing some positive correlation, evidence will be hard to get, and it's not purely theoretical problem - the entire field of macroeconomics was based on such counterfactuals and collapsed last year.

    In theory saying "government policy has led to slower decline in broadband prices" might be valid in such case, but convincingly proving causality in such situation will be really hard, as you already know there are some other factor that are much stronger than the one you analyze, as total change is opposite of one you predict. The best you can do is to use statistical tricks to extract residual influence of your factor in question after removing influence of leading factors, but methods like that depend on far too many assumptions, and are prone to fail.

    Bragi: Yes, standard portion sizes increased a lot with time. I don't know which way causality goes.

    bosie said...

    taw, obviously a gastric bypass works because you can't eat ;) although i know a few people who had gastric bypass surgery and they liquefied the chocolate .... or just ate tiny bites, but a lot of them.
    have to look up your fat cell theory and hope you are wrong ;)

    as to why we get fat, you might try
    http://www.amazon.com/End-Overeating-Insatiable-American-Appetite/dp/1605297852/ref=sr_1_1?ie=UTF8&s=books&qid=1258554210&sr=1-1-catcorr (regular amazon link, not an affiliation link)

    taw said...

    bosie: Even milder version of stomach size reduction seem to work like magic.

    Wikipedia seems to mildly confirm the theory of fat cells number increasing for fat people, and not decreasing after they slim down.