Opinions about what constitutes "healthy eating" vary and even change through the years.
Remember when the makers of one brand of margarine used to advertise that doctors recommended eating that in place of butter to protect against heart disease?
Now most dietitians seem to think that artificially hydrogenated fats like margarine are terrible. Butter is much healthier.
And when we baby boomers were growing up, not much was considered more healthful for a kid to drink than milk. But the Push Start Your Metabolism eating guidelines used by the Fittest Loser contestants urge us to drink no more than a half glass per day.
Just a few years ago a Center for Science in the Public Interest report congratulated some theater chains for making their popcorn in healthy soybean oil instead of the usual coconut oil, which the writer described as one of the unhealthiest of all cooking oils. Now some healthy-eating books recommend bathing cooked vegetables in coconut oil because the type of saturated fats in it is an especially healthy type.
Like so much in science and medicine, ideas about nutrition change almost monthly.
All those millions who switched from sugary pop to diet pop now read that according to one study, people consuming artificial sweeteners gained more weight than people drinking regular Coke or Pepsi.
Apparently sugar screws up our cholesterol, but artificial sweeteners screw it up even worse. And did you read that they also might cause dementia?
There are two reasons I've been reluctant to go along with all the rules of the Push Start eating regimen. One, of course, is that I love fruit juices and candy and bread and rolls and milk, while I hate vegetables and salads.
But two, some of the diet's rules -- especially the expensive and labor-intensive urgings never to eat processed foods (not even homogenized milk) and always to choose "organic" -- seem kind of New Agey to my 64-year-old ears.
When we were in fifth-grade health class in the 1960s, the textbook said we should eat four groups of healthy food every day. Dairy foods not only were not forbidden, they were considered some of the most sacred, along with meat; fruits and vegetables; and bread and grains.
Until 2015, even the official food guidelines recommended by the U.S. government said a solid diet should be built around six to eight servings of whole grains a day. Go easy on meat, it said, especially fatty red meat. And eat fats and oils only "sparingly."
But Push Start comes from a new strain of thinking.
Much new research says love handles and clogged arteries -- even excess poundage -- don't come from eating butter and oils and meat after all. They come from eating sugar and starches. Even starches like those previously sacred whole grains.
Zeroing in on what eating various things do to the production of insulin and the burning of sugars, diets like the Paleo Diet say that eating lots of meat and eggs and fish -- even a lot of fats -- is actually a good idea because it does great things for our inner chemistry.
PBS recently ran a TV show on which Dr. Mark Hyman, director of the Cleveland Clinic Center for Public Medicine, urged us to "Eat Fat and Get Thin." And now my physician-assistant sister Pat says everyone in the E.R. where she works is into a Fasting Diet that emphasizes resetting our metabolism by not eating anything at all for up to half the hours in the day.
In fifth-grade health class, most of the emphasis was on making sure we took in enough of the right things, like vitamins and minerals and protein. We have discovered some new "right" things since then, such as non-vitamin antioxidants.
But now more of the emphasis seems to be on not eating the wrong things. And on balancing what we eat together, such as the way the Push Start plan tells us to always eat a protein (such as meat or eggs or a health-food-store protein powder) and a fat (such as nuts or fish oil capsules or olive oil) along with any fruit or vegetables or … horrors, bread or starch.
All this leaves a would-be weight loser's head spinning.
Eggs? Used to be a heel because of all their cholesterol. Now a hero because we make almost all our cholesterol inside us, and having enough good cholesterol is more important than not eating bad cholesterol.
Milk? Scientists have found it has about as much sugar as pop, and lots of fat. But guess where that protein powder in the health-food store comes from? Yep, milk, which also boasts a kind of protein that helps us burn up sugar instead of storing it away as fat.
Meat? Eat lots, that fifth-grade health book advised me. Eat only lean cuts, and as little as possible of that, the government diet charts now say. Replace it with fish and cheese, the Mediterranean Diet folks would say. Eat lots because the cave men did, the Paleo Diet would say.
Bread and pasta? The staff of life, according to a popular saying. Eaten constantly in Bible times. A terrible source of insulin spikes and a likely cause of Type 2 diabetes, more recent researchers say.
Chocolate? Coffee? Wine? Terrible for us, the conventional wisdom says. Three good sources of antioxidants, some researchers now argue.
What then should we believe?
Most of us -- including me -- tend to just pick out the theories and facts that go along with what we want to do anyway. We use science more as an excuse for the behavior we like than as a guidepost for what behavior we should be willing to accept. And there's a lot of different science to choose from.
But I'm still trying to find some study that says drinking Mountain Dew Live Wire is healthier than drinking tap water.
•Dave Gathman is a Daily Herald correspondent. He is undergoing the same physical workouts and nutritional counseling as the Fittest Loser contestants as he writes about their journey.