I had a discussion about nutrition with my brother yesterday. As often happens in a discussion about nutrition, he made reference to the scene in the Woody Allen movie Sleeper in which a character wakes up in the future and discovers that nutritionists think that steak and ice cream is good for you, while health food should be avoided.

I’ve never seen Sleeper but everyone who talks about nutrition seems to know about that scene. It’s usually brought up as an example of how today’s nutrition advice will probably be the opposite of tomorrow’s. I don’t buy it.

Consider the following nutrition advice that hasn’t changed for as long as nutrition has been studied scientifically:

  • Too much or too little of any nutrient is dangerous. Too few calories and you starve, too many and you become obese. The same is true for salt, carbs, vitamins, water, oxygen… you name it. But in most cases it’s safe to give advice in one direction (“drink lots of water”) because the opposite is hard to do.
  • Eat a balanced diet. Exactly what that means is up to debate, but if you eat the same foods every day, there’s a good chance that you’re missing some valuable nutrient.
  • Don’t consume more calories than you use.
  • Eat high-calorie foods in moderation. Which follows straight from the advice above, unless you happen to be trekking across Antarctica.
  • Eat more fruits and veggies. It’s theoretically possible to eat too much, but it’s hard to do.

30 years after Sleeper, red meat and ice cream (high-calorie foods) are still bad for you. Fruits and vegetables are still good for you. And only the proponents of fad diets have ever said otherwise. Not just that, but nearly everyone can acheive their nutritional goals just by watching calories and eating lots of veggies.

The reason this is a pet peeve of mine is that it is indicative of people’s perceptions of science. The science hasn’t changed much in 50 years. We now know more about why veggies are good and we’ve discovered that some fats are better for you than others. But people seem to think it reverses every year. Why is that? I have some ideas:

  • The media often can’t tell a wacky hypothesis from established science. I’ll probably get back to that in a later blog entry.
  • Balance is too complicated. People want to hear that a certain food is good or bad, not hear about how much is too much or too little.
  • Science is complicated. Is red wine good for you, or bad for you? Both: it’s been proven to do good things and bad things. And the right advice depends on how likely you are to suffer from anything from heart disease to alcoholism.
  • People don’t want to hear the truth. If you think ice cream might turn out to be good for you tomorrow, you can allow yourself to eat it today.
  • It’s a cat-and-mouse game between diets and food manufacturers. This is true for fad diets as well as real science. Low-fat diets worked because people switched from snacking on cookies and potato chips to carrots. The industry response? New Rolled Gold Pretzels are fat free! The low-carb fad started, and the food industry found ways to create technically low-carb snack foods. Both were secretly restricted-calorie diets, (even ice cream gets boring) until loopholes where discovered. The same thing is happening now with trans-fats: scientists knew that people were consuming too much saturated fat, so everyone switched from butter to margarine. Not that scientists knew that the trans-fats in margarine were any better…