Dear Doctors: I'm pretty good about eating a healthy diet. The exception is each month during my period, when all I seem to want is potato chips and ice cream. Is there something going on with my body, or is this just a good excuse for a few cheat days each month?

Dear Reader: Eating a healthful diet means putting a daily limit on the sweet treats and salty carbs that can wreak havoc on weight management, blood pressure and blood sugar. That kind of sustained discipline makes the occasional cheat day a welcome break. But when it comes to the intense food cravings that can occur during the menstrual cycle, years of research suggest that the many changes taking place in the body during that time are a significant factor. These include rising and falling levels of estrogen, progesterone, cortisol, serotonin and insulin. Levels of ghrelin and leptin, the so-called hunger hormones, also seesaw during the menstrual cycle. Ghrelin boosts feelings of hunger, whereas leptin promotes satiety.

Now, a small study from researchers in Germany, which was published last year in the journal Nature Metabolism, suggests that brain chemistry plays a significant role in period cravings. Specifically, the cycle of hormonal shifts that take place during a woman’s menstrual cycle cause the brain to become more sensitive to changes in insulin levels. The hormone insulin, which is produced by the pancreas, regulates blood sugar. It is also able to cross the blood-brain barrier. The body’s response to insulin has an effect on hunger and cravings.

The researchers conducted two experiments. In the first, they used a device known as a glucose clamp to measure changes to insulin sensitivity in the brains of 11 young women as they went through the phases of a menstrual cycle. They found that during the follicular phase, which is when the egg is being prepared to leave the ovary, the brain becomes more sensitive to insulin. Insulin sensitivity is associated with good blood sugar control and a stable appetite. But during the luteal phase, which is when the egg travels to the uterus and waits to be fertilized, insulin sensitivity in the brain measurably decreased. That suggested that this phase of menstruation, which is when food cravings typically occur, is marked by insulin resistance. This is a metabolic state that prevents the cells from absorbing glucose from the bloodstream, which in turn can cause an increase in hunger.

In the second experiment, conducted with a different group of 15 young women, the researchers again measured changes to insulin sensitivity throughout the phases of a menstrual cycle. The women underwent MRIs, which verified the original findings.

The idea that insulin resistance in the brain can have an effect on appetite is intriguing. It not only offers an explanation for the food cravings that many women struggle with during their periods, but it also points to new avenues of research in obesity and diabetes. However, as is true of all small studies, this is just a beginning. More research is needed to confirm these findings and to further explore their effects on the body.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: My father is 74 years old. He wants to stay healthy, so he has started taking a fitness class at his local community center. One of the exercises they do is to walk backward. The instructor says it’s good for your body, and also for cognition. Do you know if this is actually true?

Dear Reader: The health benefits of walking are well-established. Make it a regular part of your life, and walking helps with strength, endurance and balance; bolsters cardiovascular health; aids in blood sugar control; helps maintain a healthy weight; contributes to improved mood and emotional health; reduces anxiety and tension; and helps you get a good night’s sleep. Increasing distance, speed and frequency increases the benefits. And as your father has been told in his fitness class, so does a change of direction.

Known as retro walking, the practice of walking backward engages the same groupings of muscles as does forward motion. That is, the hip flexors and adductors, gluteal muscles, quadriceps, hamstrings, calf and foot muscles. However, when walking backward, each of the muscles involved must work in a different way and put forth different degrees of effort. The mechanics of maintaining balance are similarly challenged.

Researchers who study the biomechanics of walking backward found this change in direction has multiple benefits. It can strengthen the muscles in the back; increase strength and flexibility in the hamstrings; strengthen the ankles; improve balance, posture and coordination; and even ease lower back pain. Due to a decreased range of motion in the knees and hips, retro walking can be kinder to those joints. There is also evidence that walking backward can have a beneficial effect on cognitive health.

Several studies have found that when someone walks backward, activity in the prefrontal cortex increases. That is the region of the brain associated with problem-solving, logic and making decisions. In one particularly intriguing study, participants who simply visualized the act of walking backward, but were actually sitting still, improved their scores on a memory test.

The precise connection between retro walking and improved cognition is not yet clear. However, researchers suspect that the increased complexity of the physical aspects of the process somehow support the data processing centers of the brain.

When it comes to adding retro walking to your regular fitness regimen, the data shows that as little as 10 to 15 minutes per day can be beneficial. Safety is obviously an important consideration. When moving backward, it can be difficult to anticipate and compensate for obstacles. Glancing backward to assess the terrain can throw off balance, which can add an extra element of risk.

Walking backward on a treadmill gives you a stable base, allows you to set a steady and controlled speed and lets you track your distance and progress. Another option is working with a partner, each taking turns going forward and backward. If working alone, a hallway that is clear of rugs or obstacles can be an option. To maximize benefits and avoid injury, it is important to plan ahead and ease into the process.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I tripped on a tree root and almost did a face-plant. I landed on my hands with my arms stretched out, and now my right shoulder has started aching. My boyfriend thinks it’s a rotator cuff injury. I’ve only heard of that in baseball players. What is the rotator cuff? What is the treatment?

Dear Reader: Your rotator cuff is the group of muscles and tendons that help anchor the bone of the upper arm, known as the humerus, within the shoulder joint. This is a ball-and-socket joint, the architecture of which allows the arm to have a wide range of motion. Working together, the muscles and connective tissues of the rotator cuff hold the rounded end of the humerus -- that’s the ball -- in place as it moves within the shallow cup of the shoulder blade “socket.” They also contribute to the strength and stability needed to lift and rotate your arm.

Injuries to the rotator cuff can occur in a fall onto an outstretched arm, as happened in your case. This can damage not only the tendons, but also may bruise or tear the muscle. The area can also sustain harm due to repetitive overhead arm motions, which is why the injury is often seen in baseball and tennis players, swimmers and golfers. Professions such as house painting or construction work, and improper technique when lifting heavy weights, also put people at increased risk.

The most common symptom is a dull ache deep within the shoulder joint. This can be accompanied by weakness in the muscles of the arm and a reduced range of motion. Lifting a weight or rotating the arm can intensify discomfort. Pressure on the shoulder, as when sleeping on your side, may be painful. In some cases, damage to the connective tissues in the shoulder joint can create a sensation of friction during motion or cause a popping or crackling sound.

Diagnosis begins with a close examination of the shoulder joint to assess pain and identify areas of weakness or impaired motion. Imaging tests, such as an MRI or an ultrasound, may be recommended.

Treatment depends on the scope of the damage. In minor injuries, the connective tissues may be irritated or inflamed but are not torn or severed. In those cases, the person will be asked to rest and limit activities that involve the affected shoulder.

Nonsteroidal anti-inflammatories (such as ibuprofen) may be used to manage pain and swelling. Stretching and strengthening exercises can be helpful, as can ultrasound therapy and physical therapy. In some cases, corticosteroid injections may be used to manage inflammation. In more serious injuries, the connective tissues become frayed or torn or can completely detach from the bone. Depending on the extent and severity of the damage, surgery may be necessary.

After a fall, and with the onset of your symptoms, it’s a good idea to have your shoulder evaluated by your health care provider. Treatment can improve a rotator cuff injury. But when ignored, it is easy for these types of injuries to worsen.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)