Dear Doctor: Can you please explain the keto diet? A bunch of my friends are on it, but it seems like they’re all doing it a different way.

Dear Reader: Your friends are among the millions of Americans who have jumped onto the keto bandwagon, making it the most popular diet in the United States right now.

The basic idea is simple: You cut carbohydrates to about 10% of your total food intake, typically fewer than 50 grams per day, and sometimes as low as 20 grams per day. This changes the way your body obtains energy. Instead of burning glucose, also known as blood sugar, your body is forced into Plan B -- burning stored fat. This is a metabolic state called ketosis. The name comes from compounds produced by the liver, known as ketone bodies, which the body burns for energy when glucose, its favorite energy source, is not available.

Any eating plan that causes this shift from burning glucose to burning stored fat is a ketogenic diet. You can check whether you are in ketosis with special test strips, available at your local drugstore, which detect the presence of ketones in your urine.

The high-fat, low-protein, low-carbohydrate formula may be the most widely accepted version of a keto diet right now, but it’s not the only one of its kind. Depending on your age, some of you may remember the Stillman diet from the 1960s, which eliminated carbs completely and focused instead on animal proteins such as beef, chicken, fish, eggs and cottage cheese. Part of the secret to the rapid weight loss on that diet? Ketosis. Ditto for the Atkins diet, which uses ketosis in certain phases of its eating plan, as do the paleo and Zone diets, both of which restrict carbs.

Today’s keto diet, in which up to 90% of calories come from fat, dates back to the 1920s. Sometimes referred to as “classic keto,” it was originally developed to help manage epilepsy, but soon fell out of favor with the advent of effective anti-seizure drugs. Other versions of the keto diet vary the percentages of fat, protein and carbohydrates, the trio of macronutrients our bodies require.

In addition to rapid weight loss, people in ketosis report decreased appetite. This makes sticking to such a restrictive way of eating a bit easier. The diet is also associated with improved insulin metabolism. However, while many people show improvements in blood lipids levels, the diet can raise levels of LDL cholesterol -- the so-called “bad” cholesterol -- in some people. Other challenges include headache, fatigue and irritability, particularly at the start of the diet. Many keto adherents also report dealing with chronic constipation, as well as food boredom.

A ketogenic diet can be a good way to jump-start weight loss. That means a focus on high-quality whole foods, including olive oil, nuts, avocados and fatty fish. But since this diet eliminates entire food groups, it makes getting needed nutrients a challenge. We think it’s wise to check with a registered dietician, or with your family doctor, 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.)

Hello, dear readers, and (yes, it’s mid-February) happy 2020. We hope the new year is treating you well. You’ve filled our mailbox with some very interesting questions and quandaries, including how to follow through on New Year’s resolutions. We look forward to tackling that topic -- and many more of your questions -- in the coming months. Meanwhile, onward to your most recent thoughts, tips and suggestions.

-- A reader from central Florida, who just recently caught up with a column about the growing role of nurse practitioners (also referred to as NPs) and physician assistants (also known as PAs) in primary care, wanted to add to that conversation. “Where we live it’s pretty rural, and if we didn’t have nurse practitioners at our local clinic, we wouldn’t have health care,” she wrote. “They make a difference to my family and all the people in our community.”

-- A column about hemorrhoids continues to get a lot of response, both from older adults and new moms. A reader from Ohio says when her hemorrhoids flare up, she knows she’s been slacking off on getting enough salad and fruit into her diet. “I use a drugstore cream, and that helps, but I also start eating a lot more from the produce section,” she wrote. “It takes a couple of weeks, but the episodes always end.”

Another reader, writing from Indiana, had this succinct advice: “Blackstrap molasses, taken orally.” While this approach to hemorrhoid relief isn’t supported by scientific research, there’s no downside to trying it. Blackstrap molasses is rich in minerals such as iron, potassium and magnesium, as well as B vitamins. It’s a byproduct of sugar production, though, so take it in moderation. (And it has a powerful and slightly bitter flavor.) About a tablespoon or so can be mixed into hot water as a drink once or twice a day, and it can be used in cooking as a flavoring or a glaze.

-- A column about a study that linked depression to certain missing microbes in the gut continues to generate a lot of interest. Researchers found that people living with chronic depression lacked two types of microbes, known as Coprococcus and Dialister. Many of you have written to ask how to bolster these populations in the gut. Although increasing the numbers of specific bacteria in the gut is beyond our abilities at this time, you can boost the general health of your gut microbiome with a few simple habits. Eat plenty of fiber from a variety of sources, add fermented foods to your diet, cut back on sugar, cut out processed foods, avoid unnecessary antibiotics and get enough sleep and exercise. These steps may represent a significant dietary shift for some of you, but it’s worth it. We now know without a doubt that a diverse and robust gut microbiome is tied to overall good health and immune function.

Thank you to everyone who took the time to write. We love hearing from you and look forward to continuing this conversation with you next month.

(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: Is it really that important to walk around during a long flight? I always take a window seat when I fly, and I pretty much stay put because it’s so hard to move around in a plane these days.

Dear Reader: Experts suggest walking around during flights because of the risk of developing a blood clot in the legs, which can be life-threatening. While you’re seated, your legs are bent, and gravity is at work. Over time, your blood flow can become restricted enough to encourage the formation of a blood clot.

When a blood clot forms in the deep veins -- the vessels we can’t see through the skin -- in the lower leg or the thigh, it’s a condition known as deep vein thrombosis, or DVT. And although it’s commonly associated with air travel, deep vein thrombosis is a risk for anyone who stays seated in one position for hours at a time. That includes a flight of about four or more hours, a car trip, a bus ride or even a long session of sitting still at your desk.

Many people who experience deep vein thrombosis won’t even realize it occurred because the clot that formed will dissolve on its own. The risk arises when the clot, or a piece of it, breaks free and travels through the bloodstream. The clot can then become lodged in an artery in the lungs and block the flow of blood, a dangerous condition known as pulmonary embolism. Not only can this result in damage to the lungs, the reduction in oxygen levels can cause harm to organs and tissues throughout the body.

Symptoms of DVT include unusual warmth, swelling, cramping or pain in a thigh, calf, ankle or foot, often on only one side of the body. The pain associated with DVT sometimes may be felt only while moving or walking. There may also be a change in skin color, which can become unusually pale, or perhaps take on a blueish or reddish hue. These symptoms can appear days and even weeks after a clot has formed.

Symptoms of a pulmonary embolism include chest pain that increases while inhaling deeply or while coughing, rapid heart rate, dizziness, sweating, panting and blood in the sputum (saliva). If you have any of these symptoms, seek medical help. A physical exam and simple tests can determine whether a blood clot is the cause.

The good news is that you can take steps to avoid DVT while sitting for extended periods. First, stay hydrated. Drink lots of water, but no alcohol. Wear loose and comfy pants. Avoid crossing your legs at the knee. While sitting, do in-seat exercises, such as wiggling your feet, contracting your calf muscles, and lifting and stretching (as much as you can) your legs. Even better is to stroll up and down the aisle for a few minutes every hour, taking care to consciously stretch your legs and engage the large muscles. We understand that you prefer to stay seated, but DVT is a serious condition, and your health and well-being are at stake.

(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.)