Dear Doctor: Does drinking coffee really increase the craving for sweets? I tend to drink a lot of coffee throughout the day, and if it's true, it explains a lot about my dietary choices.

Dear Reader: While recent studies have found a connection between caffeine and the urge for something sweet to eat, the cause and effect isn't quite that direct. It's not the coffee itself that somehow makes us long for the doughnut or Danish, but rather how caffeine affects certain chemical processes within our bodies. To get a fuller understanding of what's going on, let's take a closer look at the research -- and at caffeine.

Our daily coffee (or tea or cola or energy drink) habits give us that boost because the caffeine they contain cuts off access to the adenosine receptors in our brain. Adenosine is a chemical that helps to regulate our internal clocks. It gradually builds up throughout the day, and, as it reaches a certain level, we begin to feel sleepy. By blocking those adenosine receptors with caffeine, we get a sense of energy and alertness.

But scientists at Cornell University found that in addition to giving us a jolt, caffeine dulls our ability to perceive sweetness. When the researchers divided the study's participants into two groups, one that drank decaffeinated coffee and the other that drank regular coffee, the members in the caffeinated group were unable to accurately gauge the sweetness of a sugar solution. They rated it as markedly less sweet than the decaf group did.

Not only that, the caffeine drinkers' palates also remained dulled to the taste of sugar for at least 15 minutes after drinking their high-octane coffee. Because many people continue to reach for caffeinated beverages throughout the day, researchers suspect that the ability to taste sweetness remains suppressed.

This new insight dovetails with the group's previous research, which found that limiting a person's ability to taste sweetness actually creates a craving for it. The result is that people actively seek out sweet (and frequently high-calorie) treats.

Put the two together -- caffeine suppresses sweetness and a dulled palate leads to sweet cravings -- and your coffee habit could be laying the physiological groundwork for a serious sweet tooth.

The study also had some surprising news about how we perceive the effects of caffeine. Although neither group knew whether they were the ones drinking the decaf, almost all the study participants thought that they were the ones who got the caffeine. When they were asked to rate how alert they felt after drinking their particular beverage, both groups reported feeling equally energized.

And it turns out caffeine isn't the only thing that can influence taste. Previous studies by these same Cornell researchers found that mood plays a role. Sports fans in the throes of joy after a victory rated ice cream as markedly sweeter than did the followers of the losing team. Meanwhile, the despondent fans were measurably more sensitive to sour and bitter flavors than the happy ones.

Could the happiness boost cancel out the caffeine effect? That would make for an interesting study.

(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.)

(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 normally get a flu shot every year, but now I'm pregnant and have read that the vaccine might cause miscarriages. Is this true?

Dear Reader: First, let's explain why this is an issue: Pregnant women who contract influenza are more likely to develop complications from the influenza virus. The most striking example of this occurred during the H1N1 pandemic in 2009, when pregnant women accounted for 5 percent of virus-related deaths, but comprised only 1 percent of the population.

In general, pregnant women with influenza are more likely to require hospitalization and more likely to end up in the intensive care unit. They also have a greater likelihood of giving birth to children with cleft lip, neural tube defects (spina bifida), hydrocephalus (increased fluid within the brain) and heart defects. These complications of influenza led the Centers for Disease Control and Prevention in 2004 to recommend that all pregnant women get the influenza vaccine, regardless of trimester.

Now let's look at the safety of the vaccine itself.

A recent study in the journal Vaccine obtained data from health care organizations in five states about women who were pregnant during the 2010-2011 and 2011-2012 flu seasons. The authors determined which ones had been vaccinated with the standard influenza vaccine and which ones suffered a spontaneous abortion, or miscarriage. They found that 485 women had a miscarriage; they then compared these women to 485 pregnant women who didn't have a miscarriage.

The major difference was seen among women who were vaccinated the year before they were pregnant and then repeated the vaccination when they were pregnant. Of those, 17 women in the miscarriage group had the vaccine within 28 days prior to the miscarriage. Women in the group who didn't have miscarriages were five times less likely to have had the flu vaccine in that preceding 28 days.

It's possible that an inflammatory response could be to blame for the miscarriages. Because the first shot primes the immune system, the second shot gives a greater immune response, leading to inflammation. Excessive inflammation can then lead to a spontaneous abortion.

However, the authors stressed that their study found a correlation, not a causation. Here are some other factors that emphasize the far-from-conclusive nature of the study:

First, the number of women in this part of the study was small: 17 in the miscarriage group and four in a group who didn't have a miscarriage at the same time. Second, women at increased risk of miscarriage may be more likely to seek medical help and thus be more likely to get a flu shot.

Obviously, a larger study is needed to verify -- or repudiate -- the possible connection. But, ethically, this may be difficult. A researcher would have to compare pregnant women who had the flu vaccine the year before, and give one group the flu shot in the first weeks of pregnancy and not the other. Yet the risks of going unvaccinated are simply too great.

Until we have further data, I would recommend flu shots in pregnancy to prevent the risk of maternal death and birth defects.

Dear Doctor: Now that I've turned 50, I need to get a colonoscopy, but I just can't drink that disgusting prep solution. I've tried three different times, but I wind up so nauseated that I can't finish. Is there any other way to prepare?

Dear Reader: Let us reassure you that you're not alone in your struggles with preparing for a colonoscopy. Many of our patients say that the procedure itself is a breeze compared to drinking the solution. However, the preparation phase, which thoroughly empties the intestines, is vital to a successful procedure. Alternatives do exist, but they don't have the same effect, and therefore the results of the colonoscopy may not be as accurate or useful.

A colonoscopy is a procedure in which a gastroenterologist examines the inside of your colon and rectum using a long, flexible tube. Known as a colonoscope, it's equipped with a lighted tip and a camera. A colonoscopy can reveal whether colon tissues are irritated or swollen, if polyps have formed, and whether cancer is present. When polyps are found, a small wire loop on the colonoscope can be used to remove them.

For the best view, the colon must be clean. In fact, the state of your colon is the most important variable in the exam. Unless every last vestige of fecal matter has been eliminated, it's possible that polyps, which are small growths with the potential to become cancerous, or other abnormalities may be missed.

And here's where the dreaded prep solution comes into play. Available under brand names like Golytely, Colyte, Nulytely and Trilyte, these are powders that consist of a laxative, along with essential electrolytes like potassium and sodium. You mix the prep powder with 4 liters of water and drink it according to your doctor's orders.

The laxative, along with the volume of water, empties and cleanses the bowel. The added electrolytes compensate for those you are losing. Because electrolytes are basically salts, the prep solution tries to compensate for the taste with the addition of super-sweet flavorings. The mix of the two, as you have found, is challenging.

An alternative is a low-volume prep solution that you mix with significantly less water. You still have to drink a full 4 liters of fluid prior to the exam, but other than the 2 cups or so of the low-volume prep solution, the rest of that 4 liters can be water or any other clear liquid.

But -- and this is important -- low-volume prep solutions won't get the colon as clean. Also, there is the risk that your electrolytes can be sent out of balance. If there's really no other way, then discuss the low-volume prep with your doctor. And if you're willing to give traditional prep just one more go, try these tips:

-- Chill the solution well before drinking.

-- Sip it through a wide straw (it'll go faster) placed far back on your tongue.

-- Alternate gulps of solution with sips of something that tastes good.

It's not fun and it's not easy, but it's worth the investment because you'll get the best results from your colonoscopy. And, remember: When it's caught early, colon cancer can be successfully treated.

(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.)