This week's column turns to questions from readers.
Q: I suspect that my sugar-sweetened breakfast cereal is the reason I'm yawning at the computer terminal in the morning. Without resorting to caffeine, what can I eat to help me stay alert and concentrate on my job?
A: While there's no diet that can counteract the tedium of a repetitive task, what you eat can help determine whether you're awake or ready to fall asleep on the job.
We know, for example, that large meals, or those high in sugar or fat, will encourage drowsiness.
The tired feeling comes on in three stages. First, as you're eating, the pattern of blood flow begins to shift away from the muscles and toward the digestive tract -- this in preparation to receive all the nutrients from the food.
Next, as sugar from the meal enters the bloodstream, insulin gets released by the pancreas. In reaction to these events, the brain, through its homemade tranquilizer, tells the body to sit back and relax.
There's logic to this as the body is not equipped to do a good job on digestion and muscular work at the same time. The warning to not go swimming soon after a meal is based on this principle.
But while such involuntary relaxation might be welcomed after a long day of work, it can be a real nuisance at 10 a.m. or 2 p.m.
Often, though, we make it happen.
The day begins with a coffee and pastry breakfast. The caffeine plus a rapidly absorbed sugar provides an immediate surge of energy. But as insulin is released, energy dwindles into the doldrums, and in a couple of hours you're ready to lay your head down on the desk.
Lo and behold, it's then time for the coffee break. Time for the snack machine and another jolt of java and it's up again for the next ride on the energy roller coaster.
If the cycle sounds too familiar, shift to smaller meals of complex carbohydrates and protein. For breakfast this could be a whole grain, unsweetened cereal with low-fat or skim milk. If a sweetener is needed, opt for fruits over table sugar. Fructose, the carbohydrate found in most fruits, is not as quickly absorbed as sucrose and it doesn't have the same insulin-stimulating effect.
By this same logic, fruits and sliced raw vegetables, such as apples, oranges and carrots, make excellent selections for the coffee break.
On the job, look for ways to break the monotony. If your job involves repetitive tasks with little movement, take periodic breaks for stretches, shoulder shrugs and head rolls. Get up for a brief walk -- even if it's only around your work station. If you are lucky enough to have a choice, tackle the boring tasks when energy is high, and schedule the more stimulating jobs for the times you traditionally feel energy on the wane.
Q: Will taking a vitamin C pill help with the absorption of iron from a beef or meat dinner?
A: Vitamin C, or ascorbic acid, can help the body absorb minerals such as iron and calcium. The vitamin C works by helping the mineral dissolve -- a necessary step before these nutrients can pass through the walls of the digestive tract.
In meats, though, much of the iron is inside "heme," a compound used to transport oxygen in animal cells. When food containing heme iron is digested, heme gets absorbed as an intact compound. Only then, after it's already "through the door," is the heme broken apart and the iron released for use by the body.
Because it's different from the usual way iron is absorbed, taking vitamin C isn't of much help. Where vitamin C can be of help is with non-heme sources of iron. Having vitamin C-rich foods or taking a vitamin C supplement significantly increases the amount of iron that's absorbed from dietary sources such as fruits, vegetables and iron-fortified foods.
Ed Blonz is a nutrition scientist based in Berkeley, Calif.