Dear Doctor: I've been reading that choosing foods that are low on the glycemic index is better for your health. What is the glycemic index and why should I pay attention to it?

Dear Reader: The glycemic index, also referred to as the GI, is a system that rates foods based on how quickly the glucose contained within them is absorbed into the bloodstream. Developed to help people living with diabetes to maintain steady blood glucose levels, the GI has become a useful tool for anyone who wants to avoid blood sugar spikes.

The food we eat is broken up into three main categories -- protein, fat and carbohydrates. Of the three, carbohydrates are our main source of energy. The body turns carbohydrates into glucose, a type of sugar, which powers bodily functions. It gives you energy for both mental (your brain is a heavy user of glucose) and physical activity.

However, not all carbohydrates behave the same way after they are ingested. Some, like sweets, baked goods and some fruits and cereals, will cause a sharp rise in blood glucose levels. More complex carbohydrates, like beans or legumes and most vegetables, are digested and absorbed slowly due to their fiber content. When you eat foods that are low on the glycemic index, it leads to a gradual and controlled rise in blood sugar. Foods high on the glycemic index cause blood sugar levels to rise and fall quickly.

The GI is based on a scale of 0 to 100, with pure glucose assigned a value of 100. The more rapidly that foods release their load of glucose into the bloodstream, the higher they rank on the scale. Candy and processed cereals have high glycemic index values. The lowest values are assigned to foods in which glucose is digested and absorbed slowly. For example, cauliflower, spinach, green beans and mushrooms all have a GI of 0.

Why does this all matter?

Chronically high blood sugar levels have been tied to a wide range of health problems, including the risk of developing diabetes, heart disease, nerve damage, cataracts and kidney disease. By learning the GI values of the foods that you eat, you can take control of your diet. You can add foods low on the GI scale that will steady your blood sugar, and eliminate -- or at least limit -- the foods that make your blood sugar jump.

It's important to note that a balanced and healthful diet will be made up of foods from all parts of the GI spectrum. There are several nutritious foods with a high GI value, such as sweet potatoes, which have a GI of 70. Meanwhile, foods with little nutritional value, such as milk chocolate, will rank lower on the GI scale, at about 40.

Foods high in carbohydrates are essential to a healthy diet, but quality matters. Stick with fresh vegetables, fresh fruit, whole grains, legumes and beans. Steer clear of processed foods, which are usually high in refined carbohydrates like white sugar or white flour. And before you make a radical change to the way you eat, be sure to check with your physician.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I've been taking niacin for years to lower my cholesterol. Do you think it really helps?

Dear Reader: First, let's look at niacin and its role in the body. Niacin is a B vitamin needed to create compounds crucial to cellular function. A shortage of niacin, or vitamin B3, can lead to diarrhea, nausea, vomiting, rash and, when severe, neurologic conditions that manifest as confusion and dementia. Fortunately, because of our varied and plentiful diet, not to mention food supplementation, niacin deficiency is rare in this country.

Some research does support niacin's ability to improve cholesterol levels. In 1955, in one of the earliest studies of niacin, researchers found that doses of 1,000 to 3,000 milligrams significantly lowered total cholesterol levels in men. Niacin has also been found to lower levels of LDL, the so-called "bad" cholesterol, while raising levels of HDL, the so-called "good" cholesterol.

Niacin has an impact in other ways as well. A 2007 study of 30 patients who took 1,000 milligrams daily showed a reduction in the thickness of their carotid arteries' interior lining and lower levels of CRP (C-reactive protein, a marker of inflammation) when compared to a placebo. Further, a 2009 study of a niacin-plus-statin regimen showed that it led to a reduction in a marker for atherosclerosis in the heart.

Such research suggests that niacin could decrease the risk of heart attacks and strokes. The science, however, is less than conclusive.

A 1986 study followed 1,189 men who had a history of heart attack and compared those who took niacin at 3,000 milligrams per day to those who got a placebo. After five years, the niacin group reported fewer heart attacks, but no difference in the death rate. After 15 years, however, the niacin group reported an 11 percent decrease in mortality rates, mostly from a decrease in heart disease.

Studies of niacin in addition to a statin have not shown benefit against either death rates or heart attacks. A 2011 study in the New England Journal of Medicine assessed the impact of 1,500 milligrams of niacin in addition to the drug simvastatin in those with cardiovascular disease. After three years, the authors found no impact on mortality. A 2014 study in the New England Journal of Medicine echoed these findings, with no benefit after 3.9 years of statin-plus-niacin treatment.

It may be that niacin, when taken with a statin, provides no additional bang for the buck. The significant decrease in heart attacks and strokes seen with statin therapy may overwhelm any potential benefit of niacin. Further, as the 1986 study showed, the benefit of niacin may take up to 15 years to show benefit; the trials of statin-plus-niacin were only for three to four years.

Overall, niacin does seem to have beneficial effects on cholesterol and on reducing atherosclerosis, or hardening of the arteries. However, it's not as powerful as a statin in decreasing rates of heart attacks, and the benefit might not become evident for years.

If you cannot tolerate a statin, niacin may be a good option. But discuss it with your doctor.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: We brought our first baby home from the hospital, and it seems as though all he does is sleep. Is this normal? How much sleep should a newborn be getting?

Dear Reader: First, let us reassure you -- as long as your son is feeding, urinating and eliminating regularly (about eight diapers per day) and is gaining weight, all is well. Newborns sleep a lot -- anywhere from 14 to 18 hours in a 24-hour period. Some super-sleepy babies may clock as much as 20 hours per day. Even experienced parents who bring a newborn home can be surprised all over again by how much time their newest addition spends in sleep.

In the beginning, your newborn's sleep patterns can be unpredictable. Day and night are meaningless concepts and can easily become interchanged. Whether your son sleeps in short stretches of 30 to 45 minutes each, or drops off for three or four hours at a time, it's all perfectly normal.

Thanks to his tiny stomach, hunger will often push your sleepy infant to wakefulness, probably every three hours. Newborns feed anywhere from eight to 12 times in a 24-hour period. However, it's not uncommon, particularly in the early weeks, to have to wake your baby for a feeding. We recommend that you don't let your newborn go for more than five hours between feedings.

Likewise, don't be surprised if he drifts off to sleep in the middle of a meal. Sometimes this is just for a 10- or 30-minute nap and he'll be ready to eat again. Other times he's down for the count and will go for another few hours before hunger awakens him.

If your son is consistently sleeping through his feeding times, you'll have to wake him up to eat. For the best results, it helps to recognize his sleep cycles. Just as for an adult, waking from a deep sleep is both difficult and unpleasant. Interrupting sleep during a lighter cycle is less stressful for all involved.

When a newborn falls asleep, he enters what is known as "active" sleep, a cycle similar to REM sleep in adults, the stage in which we dream. That is followed by a "quiet sleep," a cycle in which deep sleep takes place. When quiet sleep ends, typically after an hour or so, the baby either wakes up or starts a new cycle of active sleep.

For the best results in waking your sleepy boy, watch for his active cycle. It's a somewhat restless sleep with the same physical motion and rapid eye movement seen in adult REM sleep. When you see the signs of active sleep, you can begin to wake him.

If he's swaddled, loosening the blanket may rouse him. Use your voice and your touch to draw him out, easing him into the conscious world. Even if he's still sleepy, he can begin to feed. Meanwhile, know that within three months, the quiet life with a sleepy newborn will have become a faint memory.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)