Dear Doctor: Does eating for one's blood type really work? For my own blood type, I am supposed to avoid foods like avocados, bananas, strawberries and many other foods that I would consider healthy choices. I certainly don't want to feel guilty for eating foods that this plan suggests avoiding. What is your take on this?

Dear Reader: You're referring to an eating plan that was popularized by a diet book published in the mid-1990s. The author's premise was that what you eat, as well as the way in which you exercise, should be based on your own particular blood type. For instance, individuals with Type A blood are advised to become vegetarians, substituting plant-based proteins for meat, which the diet refers to as "toxic." The plan also recommends they seek out gentle and calming exercise, such as yoga and tai chi. For those with Type O blood, by contrast, the dietary emphasis is on meats, with advice to limit grains and dairy. Type O individuals are urged to take up vigorous exercise like running, contact sports and martial arts. Those with Types B and AB blood also have personalized diet and exercise guidelines. Each of the eating plans, which also includes vitamins and supplements, is quite specific and even restrictive. The outcome of following the diet, according to claims made by the author, is improved health and a lower risk of disease.

The argument for this dietary approach hinges in part on the differences in blood group antigens, which are markers that are present on the membranes of red blood cells. These antigens will set off an immune response when they encounter foreign antigens. For example, someone with Type A blood cannot receive a transfusion of Type B blood because the antigens in the Type B blood will set off alarms and cause the immune system to go on the attack. Someone with Type AB blood can receive either Type A or B blood but, due to the blood antigens, can safely donate only to someone else with Type AB.

It's true that blood can reveal a lot about a person's overall health. Physicians rely on blood tests to learn a patient's glucose and cholesterol levels, hormone levels, how well the liver, kidneys and vascular system are functioning, whether the body is fighting some type of infection, and whether the signs of certain cancers are present. In addition, it is now generally accepted that specific blood types are associated with a higher risk of certain diseases and conditions, including pancreatic cancer, deep vein blood clots and heart attack associated with coronary artery disease. But whether blood antigens dictate food choices and exercise methods in the ways that this diet lays out remains up for debate. At this time, rigorous studies in peer-reviewed journals are lacking.

Diet is a highly personal choice, and as we all know from the ever-shifting content (and lately, the shape) of the so-called food pyramid, it's not an exact science. In our opinion, as long as you're eating a healthful and balanced diet, you have nothing to feel guilty about.

(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: We're often told we can consume alcohol, sweets, or burgers and fries "in moderation." My sister and I had a conversation about that sort of recommendation just the other day. What does moderation actually mean? Is it one beer a day? One burger a month? Ten french fries once a week?

Dear Reader: You're right -- moderation is a term that makes a lot of sense in theory but turns out to be somewhat slippery when it comes to actual practice. That's because moderation is relative and varies from person to person. What amounts to a moderate amount of a certain food or beverage for one person may actually be a binge for someone else. And moderation isn't only about the amount or the type of food or beverage -- it's linked to an individual's patterns of consumption as well.

Let's look at alcohol, for example. The current guidelines, put forth by the National Institute of Alcohol Abuse and Alcoholism, define low-risk drinking for women as no more than seven drinks per week, with no more than three drinks on any single day. For men, that number is no more than 14 drinks per week, and no more than four on any one day. (One drink is further defined as 5 ounces of wine, one 12-ounce bottle or can of beer, and 1 ounce of hard liquor.) A man who abstains from drinking during the week, but then downs four drinks per night over the weekend, is technically within the safe drinking guidelines. However, that pattern, which goes from zero to the edge of a binge, doesn't exactly say moderation.

When it comes to sweets, snacks and splurge foods like the burger and fries you mention in your letter, things get a bit murkier. For patients in our practices, we start with the advice to set a baseline with a healthful, balanced diet. In our opinion, that's lean proteins and fish, whole grains and legumes, and a wide variety of fresh fruits and vegetables. When it comes to sweets and treats, whether it's a foray into the potato chip aisle of the grocery store, a visit to the ice cream shop or dinner at your favorite burger joint, make them a fraction of your weekly -- or monthly -- calories. For our patients who are in ideal health, we advise a split of 80 percent being good about diet, and 20 percent "cheat." For those with diabetes, hypertension or any cardiac issues, the ratio changes to 90 percent good and 10 percent cheat.

One of the best guides to figuring out moderation is how the cheat or binge made you feel after it was over. A hangover after a few cocktails or a headache the morning after a chocolate spree, and your body may be asking you to please take a step back and reconsider. That doesn't mean you have to give up on splurges. Indulge in your pleasures, but in quantities and at a frequency that don't require the word "guilty."

(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: What is considered a normal blood pressure for a person in their late 70s? My doctor said it should be in area of 120/80. But I have read that older persons' pressure may be higher -- closer to 140/90 -- and that pressure would not be dangerous. Am I the only one confused by the new blood pressure guidelines?

Dear Reader: No, you are not alone in struggling to understand the revised blood pressure guidelines. They were issued in November 2017, and we have been receiving mail about them ever since. The questions aren't limited to the lay public, either. Due to several issues, which we'll address in a moment, these more stringent guidelines are also an ongoing topic of discussion among health care providers. But let's start with your main question.

You're correct that in the past, blood pressure goals for elderly adults were looser. They allowed for a slightly higher range for normal blood pressure compared to younger adults. However, the newest guidelines do not make the same allowances. As your doctor explained, the American College of Cardiology and the American Heart Association now define normal blood pressure for adults as readings less than 120/80. If the top number falls between 120 and 129, even with a lower number of 80 or less, this is considered to be elevated blood pressure. Readings of 130/80 and higher are the threshold for several escalating stages of high blood pressure. At this time, these guidelines apply to all healthy adults, regardless of their age.

By some estimates, the updated guidelines have moved close to half of all adults into the hypertension category, basically overnight. Part of the thinking behind the update was that flagging potential hypertension earlier would encourage patients and their doctors to discuss appropriate lifestyle changes. However, the rigor of the new goals has caused quite a bit of discussion, and even discord.

The updated guidelines are based on results from a study known as the Systolic Blood Pressure Intervention Trial, or SPRINT. In the study, participants rested quietly for five minutes before their blood pressure readings, which were taken with an automated device. Three consecutive readings were then averaged together to arrive at a final number. This is different enough from the way in which blood pressure is typically measured in a doctor's office that many health care professionals have made the argument that the methodology had a statistically significant impact on results. In addition, they address your question, saying it's unreasonable to expect someone in their later years to have the same blood pressure as someone in their 30s.

None of this changes the fact that hypertension is dangerous. Blood pressure that is uncontrolled raises your risk of grave health problems, which include blood clots, stroke, kidney disease, heart disease and heart attack. Not only that, the higher the numbers, the higher the risks. Our advice is to discuss the issue with your primary care physician, who is familiar with your general health, your medical history and any specific risks that you face. He or she will help you set the blood pressure goals that are right for you.

(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.)