So, do you get confused by what seems to be a changing plethora of dietary and nutritional advice? Does science seem to keep changing its mind? Fear not! It's not that complex, actually. After reading this I hope you'll have a clearer idea of basic dietary advice, its stability, and why following it in the media might seem confusing.
A key distinction is between general advice on food, and specific research results on various food factors, often in large doses and considered out of the context of a normal diet. Food advice has actually been stable for at least the last fifty years: eat more fruits and vegetables and whole grains, eat less red meat, don't overdo sugary or fatty foods. Eat less, overall. And move more. "Eat less, move more."(1) Sound familiar, like you've been hearing it all your life? That's because you have. And science hasn't been vacillating on this; all the trends of research consistently point in that direction. I'll expand on that later, along with why the message may be drowned out or confused.
Food factor results, on the other hand, do spin around. Here I'm talking about the reported efficacy of megadoses of vitamin C for fighting colds, or vitamin E for fighting heart disease, or B-vitamins for boosting energy levels, or oat bran for fighting heart disease, or tomato sauce and ketchup for fighting cancer, etc. etc. All of it looking at unnaturally large spikes of single vitamins, or single foodstuffs, often based on one research study, or one researcher's enthusiams (Linus Pauling for vitamin C), or some corporate funded research, and trumpeted by a media eager to headline news of some new miracle food, encouraged by whatever company might be in a position to sell the food. (Quaker Oats for oat bran, Heinz for ketchup, although that one didn't last long.)
And then other researchers look more closely, and find that vitamin C turns into the placebo effect, and that oat bran has no more effect than eating more of other whole grain cereals, and that the sugar and salt in ketchup make it hardly a health food (although tomato sauce in general is still recommended.) And the public wonders whether it should take vitamin C or not and concludes scientists can't make up their minds and maybe don't really know anything.
Well, as far as individual ingredients go, no, science doesn't know that much. Food is complex, with many interacting components, and it's hard to tease out the effects, even without worries about financial biases distorting reportage. On the other hand, precisely because food is complex, science can risk a bet that there are no miracle ingredients, that even if some food is good for you then megadoses of some component of that food are not likely to make up for a lousy diet in general. Your body is a highly complex machine, designed by evolution over a few million years to work with highly complex food. It may be possible someday to live on sugar, fat, and a bunch of pills, but don't expect that day to be soon. For now, stick to the basic and stable food advice: vegetables, grains, fruit, beans, fish, in descending order, and anything else in strict moderation. And don't overeat in general (although it's hard to get fat just on vegetables.)
Why is it so hard to get this message? Look at the interests of the food companies, who influence federal regulators and legislation, influence nutritional researchers, advertise heavily (through mass media and through packaging) and increasingly have access to schoolchildren through school funding deals. America produces a lot more food than it eats, which is great for not starving, but the companies have to try to sell all this food. And even taking into account the expanding waistlines of America, food is a basically limited demand -- there's only so much we can eat.
So first off, any advice so stark and simple as "eat less" will be fought tooth and nail. That attacks the core goal of the food industry, which is to get us to eat more. Second of all, advice to eat less of specific foods, such as red meat, or dairy products, will naturally get attacked by the producers of those foods. If people eat less beef, everyone connected to beef production and processing -- including many grain farmers, since most grain goes to feed livestock -- stands to lose sales. And all these food producers have a lot of clout in Congress, especially with the boost our Senate gives to low-population farm states. And this isn't theoretical -- much of Food Politics is documentation of things like FDA advice starting out as "eat less red meat" and being forced down into "choose foods lower in saturated fat".
Thirdly, the people with an interest in healthier foods don't have that much clout. Governmental and non-profit budgets for diet advice pale compared to individual corporate advertising campaigns, never mind the aggregate. And corporate money accumulates with "value added", and the foods we're supposed to eat more of -- unprocessed fruits and vegetables, minimally processed grains, dry beans, in short stuff without added salt or sugar or special flavor ingredients or packaging or labor -- don't have much room to have 'value' added. Plus, apparently produce farmers view each others as competitors -- apples vs. peaches -- and don't unify advertising the way dairy and pork producers have been.
So, finally, what are the converging trends of evidence for the basic healthy diet? The DASH study, which found that eating more fruits and vegetables correlated with lower heart disease. A study which found cancer rates increased with latitude -- and with latitude comes colder winters, and a shortage of fresh produce in the winter. Studies of Okinawan centenarians and near-centenarians (and unlike the Caucasus elders, their ages are documented -- Japan's competent bureaucracy has been keeping track since 1879) who mostly eat vegetables, rice, soy, fruit, and fish, and have much lower heart disease, stroke, and cancer rates than Westerners -- or their own children and compatriots eating more Western diets.
And the calorie restricted diets studied in a wide spectrum of lab animals, so far extending lifespan (and health in age) in all of them, thus pointing to a diet with a high nutrient to calorie ratio, and low total calories. The foods which most match that are vegetables, many of which are nearly complete foods (as in if you got all of your 2000 calories from tomatoes, say, you'd have more than enough protein, fiber, iron, and vitamins A & C). It's expensive and physically hard to live on just vegetables, though, so grains come in to supply more calories, protein, fiber, and B-vitamins. Beans can supply more protein and fiber as well, although if you lived on them I suspect you'd have protein overdose. Fruits supply some more vitamins and minerals, but basically just taste sweet, and are shifting the nutrient/calorie ratio down. Meat has nutrients and calories, and saturated fat to clog the arteries. A great food for growth and reproduction, as female chimps know, but not optimal for long individual health.
12 March -- According to this article obesity
raises health costs more than smoking or drinking. Note this demonstration of
food politics at work:
"The U.S. Surgeon General in a December report placed the blame on diet and
urged people to cut back on sugar and fats. The recommendation was
criticized by the Sugar Association, which thought the report should have
stressed fitness more."