Dear Doctor: I want to lose 15 pounds but have had no luck cutting calories or carbs, or even trying that crazy (IMHO) keto diet where you eat mostly fat. What about that new diet where you only eat during certain hours? How does it work?

Dear Reader: We think you're referring to time-restricted eating, which is also called "early time-restricted feeding" or "intermittent fasting." No matter the language, these approaches all boil down to the same basic concept. That is, all of your calorie intake, including meals, snacks and beverages, takes place within a limited period of time. Instead of reducing the calories you take in each day, or limiting the types of food you eat, it's the timeframe in which calories are consumed that is strictly defined.

Before we go any further, we'd like to point out that this isn't a weight-loss regimen per se. Initial studies looked into the potential health benefits of the practice, such as blood sugar control. However, in studies done, as well as in anecdotal evidence from everyday participants, it has emerged that weight loss often takes place.

Restricted eating is based on a growing body of evidence that humans do best when we live in sync with our circadian rhythms, which are guided by the built-in "body clock" that operates within us on a 24-hour cycle. We already know that circadian rhythms influence a number of behavioral and physiological processes. These range from the obvious, such as our sleep/wake cycles, to the unseen, like body temperature, hormone secretion, enzyme function and even the speed at which wounds will heal.

So it's not that surprising to discover that nutritional intake would also have a spot on the list. There's no doubt that we've come a long way from the days of our primitive ancestors, when the rigors of hunting, gathering and preparing food, to say nothing of the challenges of storage, strictly limited mealtimes. These days, however, the average American eats from early morning until well into the night.

One of the thoughts behind restricted eating is that, over time, this type of behavior wreaks havoc on our circadian cycles, which use hormones and enzymes to prep the body in myriad ways for nutritional intake in the morning and afternoon. Then, during the subsequent fast, these processes rest. By front-loading our food consumption, as our ancestors presumably did, we allow our inner clocks to sync up for optimal operation. In a study in which men with pre-diabetes limited caloric intake to a six-hour period for five weeks, researchers saw a drop in participants' blood pressure and lower insulin levels.

There's no single formula for restrictive eating. Some plans suggest an eight-hour window for eating, while others stretch that to 10 hours. The one constant is that during the fasting period, nothing caloric -- and this includes the milk in your morning coffee or that handful of nuts at night -- passes your lips. It also appears that reversing the size of meals -- large breakfast, moderate lunch, light dinner -- helps with hunger management. If you do decide to move forward with a restricted eating plan, please check in with your primary care physician for advice and guidance.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Can white button mushrooms help control my blood glucose? I saw some headlines about this a while back, but it sounds like a correlation to me -- not a clear cause and effect. Maybe it's just that people who eat more mushrooms also eat less junk food?

Dear Reader: Spoken in the true scientific spirit. You are indeed correct that how we view the results of a study depends, in part, on how it is structured. In this case, we're talking about a mouse study in which researchers from Penn State's College of Agricultural Sciences looked at whether a diet that included daily servings of white button mushrooms would affect the gut microbiomes of laboratory mice.

What edges the results of this particular study into the realm of cause and effect is the use of two different groups of mice. One group included typical laboratory mice with a normal gut microbiome. The second group, however, was made up of germ-free mice who did not have a gut microbiome. That allowed the scientists to observe exactly how the microbiota of the "normal" mice changed as compared to the control group.

What they found was that eating a daily serving of white button mushrooms caused subtle changes to the makeup of the gut microbiome in the normal mice. Specifically, adding the mushrooms to their diets resulted in a rise in the overall numbers of a specific bacterium. Known as Prevotella, it produces certain short-chain fatty acids that have a positive effect on genes that improve glucose management.

What's interesting is that the function of the mushrooms in this case was as a prebiotic. That is, they served as food for the community of tens of millions of bacteria that make up the microbiome. For reasons that are not yet fully understood, the mushrooms allowed the Prevotella to flourish, which translated to a measurable effect on blood glucose management in the liver.

The results of the study invite future research into strategies to prevent and manage diabetes, a chronic and progressive disease in which the body cannot properly metabolize glucose. That's important, considering that more than 30 million Americans -- close to 10 percent of the population -- are now living with diabetes, and an estimated 1.5 million new cases are diagnosed each year. Diabetes, which increases the risk of heart attack and stroke, was the seventh-leading cause of death in the United States in 2015.

Another intriguing aspect of this study is the new light it sheds on the effect our diet can have on the populations within the gut microbiome, and how those microbial communities affect the workings of our bodies.

As for whether eating white button mushrooms can help you with your own blood glucose management, it's too soon to say. This study was conducted in mice and for a definitive answer, a human study is needed. According to the researchers in this study, the portion size fed to the mice translates to about 3 ounces of mushrooms per day for us humans. There's no reason not to add a portion of white button mushrooms to your daily diet, barring an allergy, of course. Just don't saute them in a lot of butter.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My husband and I have two teenagers, and we also take care of my 80-year-old mother. The kids and my husband and I all got our regular flu shots, but I just read about a new flu shot that's for people who are over 65. Why do older people need a different flu vaccine? Does it really work?

Dear Reader: You're referring to Fluzone High-Dose, which, as you say, is licensed specifically for individuals who are 65 and older. Like all flu shots, it works by priming the immune system to defend itself against the specific flu strain that the vaccine is targeting. This happens because a flu shot contains antigens, which are the uniquely shaped proteins found on the surface of a flu virus. When you get a flu shot, your immune system responds to the presence of those antigens by generating antibodies, which are your body's first line of defense against infection. It takes about two weeks after you get your flu shot for the antibodies to develop. Once that happens, you have an additional layer of protection against the virus in the vaccine.

The Fluzone High-Dose vaccine contains about four times more of the flu antigen than does the standard dose vaccine that you, your husband and your children got. That means the high-dose vaccine will generate a more powerful immune response. The reason this is important for older individuals is the fact that as someone reaches his or her mid- to late 60s, their immune system becomes weaker. The immune system becomes less effective at protecting the body from infection, and it no longer responds in a robust way to vaccines. That means that not only are people in their mid-60s and older more susceptible to becoming infected by the flu virus, they are also less able to build up the needed antibodies in response to a flu shot.

In a study mandated by the Food and Drug Administration to assess the safety of the new high-dose vaccine and to gauge how well it works, it was found to be 24 percent more effective than the standard-dose vaccine at preventing the flu among people 65 and older. In addition, there appeared to be a measurable reduction in serious complications among those individuals who did contract the flu. Those complications, which are often life-threatening, include pneumonia, inflammation of the heart, a worsening of existing heart disease and COPD, or chronic obstructive pulmonary disease.

At this time, the high-dose flu vaccine is specifically approved for older patients. In our practices, we are giving the high-dose flu shot to all of our patients who are 65 and older. However, if a high-dose vaccine is not available, it's important not to delay getting a flu shot. An advisory from the Centers for Disease Control and Prevention states: "No preference is expressed for any one vaccine type. Vaccination should not be delayed if a specific product is not readily available."

Bottom line: Everyone 6 months of age and older should get a flu vaccine, this season and every season.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)