DEAR DR. BLONZ: At a recent lunchtime discussion, someone strongly stated the opinion that we should not mix proteins and carbohydrates at the same meal. They also said we should always eat fruit all by itself. I expressed general skepticism, but the person offering this was very intelligent; I was not certain exactly how to counter these arguments. -- A.M., Santa Clara, California
DEAR A.M.: This "don't mix food types" argument is not new. It is based on the dubious "theory" that it is not so much the foods themselves, but the way they are combined, that holds the key to health.
Such ideas appeared in a 1922 book titled "Mucusless Diet Healing System" by Arnold Ehret. There have been many reincarnations since, the classic one being the 1951 "Food Combining Made Easy" by Herbert Shelton, who started Dr. Shelton's Health School in San Antonio, Texas.
According to this notion, easy-to-digest foods such as fruits or other carbohydrates should never be eaten with proteins or fatty foods, which take longer to digest. To do so would delay the digestion of the carbohydrates, and in the case of fruit, allow the fruit sugar to ferment and putrefy as it waits its turn. The theory then imagines that this is responsible for today's health issues.
Other forbidden combinations include starchy foods, such as bread or potatoes, together with proteins, such as meat or fish. The theory stems, in part, from the fact that the body uses an acid (low pH) environment to digest protein, while it relies on an alkaline (higher pH) environment to digest carbohydrates.
There might be more interest in the theory if all the foods we ate were digested in the same location at the same time, but this is not the way it works. There are separate digestive enzymes for the proteins, carbohydrates and fats in our foods, and they operate in different regions of the digestive system. The treatments given to one type of food do not interfere with the others.
Protein, for example, is first denatured in the stomach by subjecting it to an acid environment. This, plus the churning by the stomach muscles, helps to break down the protein tissue so that the digestive enzymes will have an easier job. Once out of the stomach, the body neutralizes the acid; the rest of the digestive process, including the digestion and absorption of protein, carbohydrate and fat, takes place in a more alkali environment. If starches are present in a protein-based meal, they just hang out, waiting for their turn. The idea that they would ferment makes little sense -- especially in light of the fact that the acid environment of the stomach is not conducive to fermentation.
No doubt, many of us have found that certain foods or food combinations work best for us, and our bodies do seem to get used to the way we eat. But this is more a product of habit-bred efficiency than a requirement of the human species. There appears to be no physiological reason that we have to refrain from including a variety of foods at every meal.
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to email@example.com. Due to the volume of mail, personal replies cannot be provided.