Q: I watched a television talk show on which one of the guests claimed that fruits should be eaten before a meal and that starch should not be eaten with protein. Is there any truth to either claim?
A: No. The idea of "ordering" the foods we consume has been included in dietary prescriptions to improve digestion, lose weight and even as part of regimens associated with spiritual beliefs. Some foods may taste better if eaten alone, and some foods seem naturally appealing in combinations, but that is a matter of individual taste. If you reflect for a moment on past dining experiences, you will recall unlikely combinations that turned out to be surprisingly good, and others that were unacceptable, even though other people at the same table might have liked them. The point is that all these reactions occur at the sensory, not the physiologic, level.
The digestive process is dependent on the availability of enzymes that split the energy-containing nutrients, carbohydrates, protein and fat into simple units that can be absorbed. The normal, healthy digestive system provides the necessary enzymes and maintains the internal environment in which to function without regard for the combinations in which it receives them.
Finally, from a practical point of view, the idea of eating foods containing mainly carbohydrates apart from protein-rich foods would make eating an inordinately time-consuming process. (Few foods contain only one or the other of these nutrients.) For most individuals, it would also be an aesthetically unappealing way to eat.
Q: Can you explain why the nutrition label on a product lists the requirements for vitamins and minerals as percentages of the U.S. RDA, but does not do the same for fat? For example, when a yogurt carton says that it contains three grams of fat, what does this mean in terms of my fat allowance?
A: The answer lies in the fact that there are U.S. Recommended Daily Allowances for 12 vitamins and 7 minerals, as well as for protein, but there is no U.S. RDA for fat.
No doubt you are referring to the recommendation that is part of the Dietary Guidelines for Healthy Americans. It states that no more than 30 percent of our calories should come from fat. Since caloric needs vary from person to person, just how much the fat in a single serving of food contributed to that amount also would vary. In other words, to apply this information you must first know how many calories a day you consume.
If you are eating 2,000 calories and trying to follow this guideline, no more than 600 of them should come from fat. But there is still a gap between calories from fat and the labeling information, which is given in grams. Since each gram of fat has nine calories, this would mean that your fat intake should not exceed 65 grams. Thus the three grams of fat in the yogurt would provide a little over 4.5 percent of the day's fat.
If you are interested in finding out what percentage of your calories come from fat, you will need to keep a careful record of everything you eat for a period of several typical days, estimating portion sizes as accurately as possible and remembering to account for fat that might have been used in preparing food. Use nutrition-labeling information wherever possible to fill in both the grams of fat and the number of calories in each food you ate.
To glean other information, you can turn to one of the paperback volumes now available that list facts about fat and calories. Or use a government publication titled "Agricultural Handbook 456, The Nutritive Value of American Foods in Common Units," by Catherine F. Adams. It is available from the Superintendent of Documents, Washington, D.C., 20204, for $8.50.
Q: Recently my young daughter bought a package of frozen juice bars. On the ingredients list was something called annatto extract. What is that?
A: Annatto extract is a natural coloring substance that comes from the seeds of a tropical American tree of the same name. The extract gets its color from a carotenoid pigment. This is the same class of compounds that is responsible for everything from the color of carrots to the spectacular foliage of a New England autumn. But the value of some of these pigments is more than aesthetic. Some, like the carotene in carrots, are split by the body and used as a source of vitamin A.
Annatto extract is sometimes added to cream before churning to deepen the yellow color of butter.