The editor in chief of the Harvard Health Letter introduces a second 2011 edition of a special issue comprised entirely of "Ask the doctor" letters from readers.

Q. More and more nutrition advice seems to be anti-sugar these days. So are artificial sweeteners a good alternative?

A. Sugar in all its forms may be the single most important dietary cause of obesity and heart disease in the American diet today. Stripped of fiber and antioxidants, table sugar (sucrose) and high fructose corn syrup cause big jumps in blood glucose and insulin that raise levels of triglycerides, various inflammatory markers, and free oxygen radicals. In addition, the fructose found in most types of sugar may damage the liver and cause insulin resistance.

The FDA has approved five artificial ...

Q. I saw Harvard's Healthy Eating Plate and noticed that poultry was listed as a healthy protein. I am not surprised that you're recommending fish, nuts, or beans. But why poultry?

A. The main reason we listed chicken and turkey as healthy sources of protein is that they have relatively low levels of saturated fat compared with red meat, which, for nutrition purposes, includes beef, lamb, and pork.

Look at the chart below. You can see there's about half as much saturated as unsaturated fat in chicken and turkey fat. By comparison, beef and pork fat contain a good deal ...

Q. I am 70, have had sleep problems, and have started to take Ambien every night. It seems to be working very well. Is it okay if I keep on taking it?

A. When Ambien (the generic name is zolpidem) was approved by the FDA in the early 1990s, it was supposed to be an improvement over the benzodiazepines like lorazepam (Ativan) and triazolam (Halcion) because it acted in a more targeted way and didn't stay in the body as long. Other nonbenzodiazepines were subsequently approved, including Sonata (zaleplon) and Lunesta (eszopiclone).

But when I see patients who are taking ...

Q. Is the chemical BPA just another health scare, or is it really something we should be worried about?

A. BPA, which stands for bisphenol A, is estrogenic. That means that in some respects it behaves like the hormone estrogen. Although BPA was first developed as a synthetic estrogen, it was never used as a pharmaceutical because diethylstilbestrol (DES), another synthetic estrogen, was more potent. DES was pulled from the market in the 1970s after it was discovered that the daughters of the women who took it (extra estrogen was thought to reduce the risk of miscarriages and premature births) ...

Q. I sprained my ankle pretty badly a few weeks ago and was taken to the emergency room. It took three hours before I saw a doctor. Why are emergency rooms so crowded and the waits so long just to be seen?

A. The reasons for emergency department waits are complicated; our entire health care system is implicated. It is impossible to explain every aspect here, but one place to begin thinking about the problem is to separate waiting to be evaluated from waiting to be admitted to the hospital, if an evaluation shows that to be necessary. The reasons ...

Q. I have wet macular degeneration. I am trying to decide between Avastin and Lucentis. Which drug is better?

A. This is a complicated and very unsettled area. All of the professional organizations for ophthalmologists are struggling with it.

I should also mention right off the bat that I am on Genentech's scientific advisory committee. Genentech developed both Avastin and Lucentis. I am also the chair of the Phase 3 clinical trial of Eylea, another drug for wet macular degeneration, which I expect will be approved by the end of 2011.

Wet macular degeneration occurs when tiny blood vessels behind ...

Q. A friend has a condition called gastroparesis. Please explain what it is and how it can be treated.

A. Gastroparesis is the term used for sluggish emptying of food from the stomach into the small intestine. Normally, your stomach moves about half of an average meal into the small intestine within two hours after you eat, and about 90% within four hours. If you have gastroparesis, food stays in the stomach much longer. Nausea and upper abdominal pain are common symptoms. It may become difficult to keep a full meal down. People with serious cases may eat so little ...

Q. My wife's medication to treat atrial fibrillation recently was changed from warfarin to a new drug called Pradaxa. They say that the new medicine does not require regular INR tests and is just as effective. Is that so?

A. Yes, it is so. Before I explain why, let me provide a little background.

In people with atrial fibrillation, the small upper chambers of the heart (the atria) lose that strong beating action that keeps the blood moving. As a result, blood tends to collect in the atria, and when it does, clots are more likely to form. If a ...