Dear Doctor: I hate dieting and have been putting off losing these last 12 pounds of baby weight. My husband says I should at least start exercising because it makes your fat healthier. Can this really be true?

Dear Reader: For all the bad press the fat within our bodies receives, it's actually a vital resource. With more than double the calories per gram than proteins or carbohydrates, it's an efficient system for storing energy that helped our ancient (and not-so-ancient) ancestors survive uncertain times. And while we tend to think of body fat in terms of its physical manifestation, as in the bulge of a waistline, it's actually a dynamic nutrient with multiple forms and functions within our bodies.

In addition to being an energy source, fat helps to manage temperature, cushion vital organs, regulate hormone production, build cell membranes and stockpile certain vitamins. It plays an important role in immune function and brain chemistry, as well as many other metabolic processes. Of course, too much stored fat is problematic, and can lead to adverse health consequences, including diabetes, heart disease and metabolic syndrome, to name just a few.

The complex cycle of how the various fats within our bodies are formed, stored, mobilized and metabolized is still not completely understood. (It's only a decade ago that we learned about the existence of "brown fat," which are fat cells within our bodies that burn rather than store lipids.) Now the results of recent studies have shed light on another question that has long puzzled scientists. That is, why do some overweight individuals develop insulin resistance, which is often a precursor to diabetes, and others do not?

One of the problems with stored fat is that it tends to release fatty acids into systemic circulation. This leads to inflammation, which is a common denominator in developing insulin resistance. But it turns out that not everyone who is overweight or obese has the same degree of release of fatty acids. A study last year from researchers at the University of Michigan found that certain individuals, despite being obese, have low rates of fatty acid release, few markers for inflammation and therefore do not develop insulin resistance. But why?

In a second study, the Michigan researchers looked at whether exercise might play a role. When they compared a group of overweight individuals who exercise regularly with a similar group of overweight individuals who did not exercise, they found that the subcutaneous fat of the active group contained more blood vessels. The two groups then took part in a session of aerobic exercise. Post-exercise biopsies of subcutaneous fat revealed that, after that single session, the stored fat in both groups became less "leaky," and this was considered healthier.

While it's important to note that these were both small studies, the results are intriguing. They add to what we already know about the health benefits of exercise and suggest some interesting directions for future study. In the meantime, we agree with your husband that no matter what you're doing with your diet, adding an exercise component to your daily life is a good idea.

(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: Considering the recent news coverage of how hot-air hand dryers do little more than blow bacteria around, am I better off just wiping my hands on my pants when using a public restroom?

Dear Reader: First, let's consider why this would have seemed a ridiculous question only two decades ago -- before bathroom hand dryers had proliferated throughout the developed world. The use of paper towels in bathrooms had created concerns about environmental impact, both in connection to the trees used to make the paper towels and in the amount of trash produced. Bathroom hand dryers, although they used energy, decreased the use of, and trash from, paper towels -- not to mention they were (and remain) -- very cost-effective. The operation of bathroom hand dryers is only one-tenth to one-twentieth the cost of a year's worth of paper towels.

But, yes, now there are concerns about bathroom hand dryers and hygiene. In short, air hand dryers can aerosolize bacteria. A recent study at the University of Connecticut School of Medicine evaluated whether hand dryers contaminated the area around them with bacteria. The authors looked at three buildings within the school and placed bacterial growth plates (supplemented with sugar) in the bathrooms underneath the hand dryers. Each plate was placed 12 inches from the outlet of the hand dryer, left open to air for 2 minutes and then closed.

After 48 hours, the growth of bacteria was then measured. The plates near non-operating hand dryers grew 0 to 1 colony of bacteria. Those plates exposed to 30 seconds of air from operating hand dryers grew 18 to 60 colonies of bacteria, depending on the bathroom. That's a very big difference.

Multiple strains of bacteria, from 21 different species, were seen on the growth plates. The bacteria appeared not to come from the hand dryer itself, but from bacteria in the bathroom that was sucked into the air coming out of the fan. The reason: A high volume of air passes through these driers (19,000 linear feet per minute at the nozzle).

Two interesting notes: First, researchers saw no difference between women's and men's restrooms. Second, placing a HEPA filter within the hand dryer led to a fourfold reduction in the number of bacteria seen on the plates.

But because the hand dryers disperse bacteria does not necessarily mean they will increase the risk of infections, at least for most people. Those who have compromised immune systems, disruptions of the skin or intravenous lines, however, could potentially develop invasive infections. Furthermore, if you're washing your hands to prevent passing an infection to others, using a hand dryer may make the action moot. When you shake someone else's hand, you may transfer bacteria from the dryer air to them.

It may defeat the purpose of washing your hands in the first place, right? Not quite. The logic behind that conclusion is still hypothetical. A better study would be comparing the bacteria upon the hands of people who used either hand dryers or paper towels.

Until then, we're still not willing to suggest you dry your hands on your pants. It's simply better to use paper towels. Perhaps, sometime in the future, hand dryers with HEPA filters will become widely available.

(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: Years ago, I was told not to consume grapefruit or grapefruit juice with statins. Now I understand that this restriction no longer applies. Is this correct?

Dear Reader: The reason people are warned to steer clear of grapefruit when taking statins, which are drugs that lower cholesterol, is that certain compounds within the fruit and its juice affect the way the medications are absorbed. Known as furanocoumarins, they interfere with the metabolic processes that break down a range of medications, including statins. And while you're correct that there are now a few brands of statins that don't interact with those compounds, it's important to check with your pharmacist or physician regarding your particular prescription before adding grapefruit to your diet.

Statins are a class of drugs that get broken down with the help of an enzyme known as CYP3A4, which is found in the gastrointestinal tract and liver. It's a process that controls how much of a drug is released into the bloodstream, and it is factored into the calculations used to determine drug dosages. What happens in the presence of furanocoumarins, which are found not only in grapefruit but also in pomelos and Seville oranges, is the work of that key enzyme is inhibited. As a result, a larger amount of the drug than is intended enters the blood and accumulates in the body. In the case of statins, too much of the drug in the body can lead to grave complications, such as increased risk of damage to the liver and muscles, which can lead to kidney failure.

Grapefruit is a good source of vitamin C and has a bit of potassium as well, so patients often ask if there's a minimum amount they can safely consume while taking statins. Unfortunately, with many statins, the answer is still no. That's because we each secrete a different amount of the CYP3A4 enzyme in the small intestine. The same glass of grapefruit juice that would be safe for one person would be dangerous for someone else.

Interestingly, that same compound that generates an overabundance of statins in the blood will decrease the available amount of a few other drugs, including fexofenadine, an allergy medicine sold under the brand name Allegra. Apple juice and orange juice have the same effect on fexofenadine, which is why the labels on both the prescription-level and over-the-counter varieties of the drug carry a warning against taking it with any fruit juices.

An estimated 20 percent of the population between the ages of 45 and 70 are prescribed statins, so the fact that several of the brands now available do not appear to affect the CYP3A4 enzyme is good news. The statins that remain on the no-grapefruit list are atorvastatin (Lipitor), lovastatin (Mevacor) and simvastatin (Zocor). And while the current literature suggests that rosuvastatin (Crestor) and pravastatin (Pravachol) as well as a few other statin drugs have limited or no interaction with furanocoumarins, we urge you to check with your pharmacist or physician before adding grapefruit to your diet.

(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.)