Dear Doctor: Are there foods and drinks that can help firm up loose stool, so that there isn't an occasional "surprise" when passing gas? Probiotics haven't helped, and multiple tests have proven negative for anything but chronic inflammation.

Dear Reader: We're glad to hear that your doctor has ruled out a medical cause for your experience with loose stools. And since you haven't referenced diarrhea, we'll assume that's not relevant to the issue you're having.

In many cases, this is the result of something in the diet, so let's start with the basics of digestion.

For the most part, digestion is a "wet" process. Food goes into our mouths and we chew, adding saliva to substances that, to some degree or other, already contain moisture. In the stomach, the chewed food gets further broken down by powerful acids, which deliver a liquid slurry to the small intestine.

Here, digestive juices from the pancreas, liver and intestine finish the dismantling process. The digested nutrients are then absorbed by the walls of the small intestine, where they enter the blood and are delivered to the rest of the body.

As the waste products that are left behind begin to move through the large intestine, the stool is formed. The job of the large intestine is to absorb water from these waste products, along with any stray nutrients. This process changes the waste from a liquid form into the firm mass of the stool. This is then stored in the rectum until a bowel movement occurs.

The upshot is that loose stool is the result of excess water that was not removed by the large intestine. Since illness and infection aren't the cause, let's look at diet.

Dietary sugars, which can increase the absorption of water, may exacerbate loose stools. That's in part because sugar is hygroscopic, which means it attracts and absorbs water. In addition, some people lack adequate enzymes to digest certain sugars. These sugars can include sorbitol, which is found in prunes, peaches and apples; mannitol, which is found in pineapples and asparagus; and xylitol, a sugar present in lettuce and strawberries. Each of these can have a laxative effect. The sugars in wine and beer can cause loose stools, as can lactose, the sugar found in milk products.

Caffeinated beverages, fried foods, fatty meats and additives like MSG and artificial sweeteners can also cause problems. In fact, for many individuals who experience digestive problems, the question may be not what to add to your diet, but what to eliminate from it.

If you're up for it, you might try an addition diet. Start with a small but nutritious range of foods that result in normal bowel movements. Think lean meats, small portions of vegetables, and potassium-rich foods like bananas. Then, one by one, begin to expand the range of foods in your diet. There are probably certain foods that your body absorbs better than others.

By proceeding slowly and keeping a food diary, you may be able to pinpoint the culprits and tailor your diet to your specific needs.

(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: Our older sons both played football in high school, but that was before all the publicity about concussions. Our youngest son is now old enough to try out for the team. Is it really that dangerous?

Dear Reader: Sports offer kids a lot of benefits. There's the physical exercise, the social aspect of being part of a group with a common goal, the lessons about teamwork, leadership and work ethic, and how to win -- and lose -- with grace. The tradeoff, of course, is the risk of injury.

In a competitive atmosphere, you're going full tilt, throwing yourself into the moment with everything you have. Even in a game as seemingly genteel as badminton, you can sprain an ankle, strain a muscle, break a bone or, if you run into another player or object, even sustain a concussion.

That said, football is in a category of its own. Collisions aren't accidental; they're an integral part of the game. Specialized equipment like helmets and braces and pads do offer a measure of protection. But, as you realize, there are variables at play that can have grave and lasting consequences.

We checked with the Centers for Disease Control and Prevention, and it turns out that 2.6 million children and young people under the age of 20 seek treatment in the ER each year for sports injuries. In football, knees and ankles are the most frequent sites of the injuries. A common sports-related injury we see in our practices is a tear to the ACL, the anterior cruciate ligament. That's one of two ligaments that help to stabilize the knee joint. This happens when the lower leg is firmly planted and momentum of some kind sends the body moving in an opposing direction.

Additional injuries sustained by football players include bruises, sprains and strains, broken bones, bruised or damaged internal organs, back injuries, spinal cord injuries and, of course, concussion.

Concussion may not be the most common football injury, but it can be among the most serious. That's because instead of just a bump on the head, a concussion is actually a mild form of traumatic brain injury. In a concussion, the blow to the head is severe enough to cause the brain to literally move back and forth within the skull. This results in physical and chemical changes to the brain tissue that can leave lasting damage.

Some school football programs have successfully limited the amount of head impact among their players by instituting specific safety rules for both practice and play. Advances in protective helmets have also proved helpful. However, as we all know, in an actual game situation, young athletes don't hold back. Football is a contact sport. No matter the precautions taken, the risk of injury -- including concussion -- still exists.

We recommend that you check with the school and the coach and learn what protections are in place. Bring your family doctor into the discussion. The truth is, football offers both risk and reward. With adequate information, you'll know which decision is right for your family.

(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 had back pain since my 20s and have gotten to the point where I can't use aspirin or other pain relievers because they tear up my stomach. My sister-in-law wants me to try meditation, which sounds a little nutty. Do you think it can help?

Dear Reader: The power of the mind over the body is a concept that has been explored, questioned, promoted and ridiculed for centuries, if not millennia. However, the latest studies on the subject offer intriguing insights. Researchers are uncovering evidence that techniques such as meditation and mindfulness can be an effective means of dealing with pain. This is good news for the estimated 11 percent of Americans who live with chronic pain.

Several recent studies have focused on meditation and mindfulness techniques to alleviate lower back pain, with some surprising results. Not only did researchers add to the growing body of evidence that mind-based techniques can be effective, but they also discovered that the relief from pain comes via unexpected pathways.

One study involved 342 adults between the ages of 20 and 70 who had lower back pain for three or more months, a length of time for it to be considered chronic. None of the individuals could attribute the onset of their pain to a particular cause, such as injury, overuse or disease.

The participants were divided into three treatment groups -- one that followed the traditional medical approach of rest, activity modification, heat or ice, and over-the-counter pain relievers. A second group learned a technique called cognitive behavioral therapy, or CBT, which addresses thought and behavior. The third group was taught something the researchers called "mindfulness-based stress reduction," which included several types of meditation as well as gentle yoga practice.

Six months later, 61 percent of each mind-based treatment group reported improved physical function. About 45 percent of them said they had less back pain. That was measurably better than the group assigned to traditional medical practices. In that group, 44 percent reported improved function, and 27 percent said they had less pain.

While the results may not be extraordinary, they are significant. And as acceptance of this novel pain relief pathway grows, the hope is that continued research will lead to greater understanding and to new techniques that are even more effective.

Speaking of understanding, the results of a study published in the Journal of Neuroscience last year also offered a few surprises.

When you hurt yourself -- stub your toe or scrape your knee -- your body responds with a flood of natural opioid compounds that make the resulting pain more bearable. But for the participants in this study, researchers blocked that pain relief pathway. Yet patients involved in meditation still reported feeling less pain in response to unpleasant stimuli than those who did not meditate. This led researchers to conclude the pain relief mechanism of meditation occurs independent of the opioid receptors in the brain.

Bottom line: Your sister-in-law has a point regarding meditation. With a bit of research, you can find a class or program in your area. And if you do follow through, please let us know how it goes.

(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.)