Several weeks ago I attended a party where the host, who must have a direct link to Martha Stewart, provided a variety of delicious foods for his guests to enjoy. I noticed that one of the guests, a water bottle carrying woman who introduced herself "a nutritionist" wasn't joining the rest of us as we moved through the buffet line sampling sumptuous goodies from every platter. When someone asked her why she wasn't partaking of the food (and was drinking only water) she began to espouse the famous but currently out of vogue "food combining" theory. According to this woman it's necessary to combine foods in a specific ways to assure better digestion and a higher level of health. She added that if you eat the wrong combination of foods at any meal you'll have a variety of problems because different foods require different enzymes for their digestion. For instance, if you eat protein with carbohydrates the protein won't be digested. Her theory, which mimicked a diet book popular some years ago, says that undigested protein will then ferment and putrefy, spending up to two years in the large intestine. She told listeners that when you don't digest foods properly you get fat.

This theory, like many erroneous ones, makes logical sense. However, anyone with a basic knowledge of biochemistry knows it is so laughable it's hard to believe anyone takes it seriously. In fact, exactly the opposite happens when you don't digest foods properly--you absorb fewer calories. And, contrary to the "enzymes can't mix" theory, digestion begins in the mouth, continues in the stomach and really cranks up in the small intestine. The body puts out a variety of digestive juices (enzymes) in all these locations to breakdown the carbohydrate, protein and fat you eat--regardless of the combination. For example, the pancreatic juice secreted into the small intestine contains enzymes that digest proteins, carbohydrates, and fats.

We have evolved to eat meals of mixed foods. No human population has ever subsisted on eating single foods at a time. But diets that support theories similar to these continue to be popular under a variety of names.

With few exceptions energy balance is still the fundamental issue when it comes to weight control. Burn more calories than you take in and you'll lose weight. Eat more calories than you burn off and you'll gain weight. There are a few exceptions due to prescription medications that alter metabolism, or the rare case when someone has an endorcrine abnormality. But for most of us the number of calories we eat, not the foods themselves, is what makes a difference when it comes to managing our weight.

I wanted to ask why, if her theory was true, there were so many lean people in the room (the party was hosted by a physically active elder citizen and the room was filled with his physically active friends). Instead I smiled, let her have her few minutes of attention then asked, "What's your exercise of choice?" As it turned out she doesn't exercise. Not much wonder she can't eat.

I rest my case.