Health trends come and go — some helpful, some not so helpful, and some downright dangerous. CBS News asked medical experts about some of the popular trends they recommend ditching in 2017.

Trend: Cooking with coconut oil

“People seem to be eating it and drinking it with everything — adding it to coffee, cooking their vegetables with it — and it’s giving them large quantities of fat. I wish this trend would go away,” said Dr. Andrew Freeman, a cardiologist and director of Cardiovascular Prevention and Wellness at National Jewish Health in Denver, Colorado.

The latest guidelines from the American College of Cardiology recommend against tropical oils, he said. Freeman is the chair of the American College of Cardiology’s nutrition and lifestyle working group.

Coconut oil, a tropical oil, is not recommended because it’s likely to be artery clogging.

“Years ago, it was fed to lab animals to induce atherosclerosis,” said Freeman.

“It’s not a recommended oil by any of the guidelines that I know of. In general, it can contribute to cardiovascular disease risk because of its very high saturated fat content. The standard American diet most people already eat is already high-fat and full of a lot of processed meats and cheese, and now everyone’s adding coconut oil and we’re going in the wrong direction,” he said.

People who already have cardiovascular risk factors should definitely avoid it, he advised.

“Coconut oil is not a ‘superfood.’ Coconut meat by itself is probably not a bad thing to eat, but it’s when you start extracting the oil out of a plant — that’s when you get into trouble. I’m not entirely sure why it’s caught on the way it has,” Freeman said.

Trend: Smartphone apps to diagnose melanoma

Don’t use an app to diagnose skin cancer, said Dr. Abigail Waldman, a dermatologist at Brigham and Women’s Hospital in Boston and an instructor at Harvard Medical School.

She’s had lots of patients ask about the apps, which require users to upload a photo of the mole or skin area in question, then run the image through an algorithm that is supposed to tell you whether or not it’s potentially cancerous.

“Essentially, a large number of melanomas are not going to be picked up by these apps,” Waldman told CBS News.

They’re only about 60 percent sensitive, research suggests, so a lot of cases would slip through the cracks. On the other hand, she noted, when the apps do identify one, they’re about 99 percent accurate.

“If you’re worried about a spot enough to use an app to diagnose it, you should get it checked by a doctor,” she said.

A dermatologist is best, but if that’s not an option, make an appointment with your primary care physician.

Trend: Guzzling water all day long

Carrying a water bottle around and chugging H20 all day long won’t bolster health, said Dr. Stanley Goldfarb, a professor at Perelman School of Medicine at the University of Pennsylvania.

The human body is an efficient water-regulating machine, said Goldfarb, who studies kidney function.

“Thirst is designed to make sure we get water in when we need it. The kidneys excrete it rapidly when it’s not needed and you also lose some water through the skin,” he said.

Pushing ourselves to drink more water than we need, he said, “doesn’t make a lot of sense from the way the kidney works or from an evolutionary standpoint.”

Drinking more than eight 8-ounce glasses of water a day isn’t required for most people, unless you’re an athlete or a soldier stationed in desert climes, or have other special hydration needs. Kids, for example, can sometimes get too little water. In Philadelphia, where he works, some schools don’t have functioning water fountains due to lead pipe issues, or some don’t have water fountains near where they’re playing sports, so kids in those situations should have access to bottled water.

Goldfarb said other water-related myths include the notion that gulping lots of it flushes toxins from the body, but there’s no research supporting that claim. It won’t improve your complexion, either, unless you’re very dehydrated.

“When you drink a glass of water, it’s not targeted to the skin in your face. The percentage of cells in your face compared to the rest of your body is about the same as a 6-foot-tall man standing by the Eifel Tower. The amount of water that actually gets to the face is a thimbleful and that includes the scalp,” Goldfarb said.

“It’s not that we don’t need water — 60 to 70 percent of body weight is water — but you have a system that is very carefully designed to be sure you have the proper amount of water,” Goldfarb said.

Eight glasses a day should be plenty to do the job.

Trend: Bone broth for nutrition

Bone broth has become popular with nutrition-conscious consumers but it’s not the magical brew it’s touted to be, said Linda Antinoro, a registered dietitian at Brigham and Women’s Hospital.

Typically made from roasted bones, sometimes with meat attached, it’s cooked for 24 hours and strained, then seasoned.

“It sounds so trendy but it’s just a cross between a stock or broth,” Antinoro said.  Bone broths can be much pricier, though.

Antinoro said bone broth has been promoted as a digestive aid, an immunity booster, and a wound healer; it supposedly helps detox the liver and reduce arthritis and inflammation, but none of this is proven.

“We don’t want someone using this as a nutritional supplement. It’s been linked to many nutritional claims but nothing’s been substantiated with research,” she said.

The packaged versions vary widely in nutritional content, she said, and if ordered from a food truck or restaurant, there’s no guarantee what the ingredients are or what its nutritional value might be.

A 2013 study also suggested that meat bones may contain heavy metals and a bone broth may carry a risk of lead contamination.

Trend: Bottled fruit smoothies

Bottled fruit smoothies are packed with sugar, said Antinoro.

“Eat fresh fruit or make your own, versus the sugar-laden bottled ones. Not to bash any brands, but a 15-ounce bottle can have 40 to 50 grams of sugar. That is about 10 to 12 teaspoons of sugar,” Antinoro said.

The American Heart Association recommends limiting added sugars. For most American women, that means eating no more than 100 calories from sugar per day, or about 6 teaspoons of sugar. For men, it’s 150 calories per day, or about 9 teaspoons.

“If drinking fruit smoothies from a bottle is your only way of getting fruit, it’s better than nothing, but eating fresh fruit or making your own version with a vegetable blend is better,” Antinoro said.

Whole fruit gives you more intact fiber, she explained. And it takes more time to eat a whole apple than to gulp down a smoothie.

When making homemade smoothies, Antinoro suggested, “Add a teaspoon of chia seeds or flax to give them a fiber boost and omega 3s and other nutrients, using any fruits you enjoy. Pop in leafy greens, like spinach, kale, and broccoli, and carrots.”

Trend: High-tech medical tests

With medical technology booming, it’s tempting for some people to undergo tests “just to be sure.” But it may be risky.

Dr. Eliot Nierman, a general internist and associate professor of clinical medicine at the University of Pennsylvania, said people can overdo it on medical tests these days. He said it’s time to scale back and question the necessity of undergoing tests that aren’t recommended, based on the evidence, before they’re performed.

“People always think a test is the answer — there’s a belief in technology — but in some sense they are dangerous if you develop a lot of false positives. They an end up doing things to patients that may actually cause them problems down the road,” said Nierman.

He recalls a patient who wanted a routine stress test even though he did not have any heart problems at all. But the test came up with a false positive, so the patient went for a catheterization test. It turned into a real medical horror story.

“The catheterization broke off cholesterol in his heart and it caused complications and he lost both of his legs,” said Nierman.

He said a classmate of his had a PSA test for prostate cancer — a test whose widespread use has been the subject of ongoing medical debate — and it led to a false positive which required a biopsy.

“That procedure ended up causing an infection in one of his heart valves and he ended up getting open heart surgery,” said Nierman.

While it’s rare that such complications occur, the risks are not to be taken lightly, he said.

“If you start to do tests in people were it isn’t indicated, you tend to pick up a lot of noise. Occasionally we do help someone pick up a cancer that would have been missed, but most tests as a screen are not valuable,” he explained.

Doing too little is risky, too, he warned.

Tests that are of value include cholesterol, breast cancer, colon cancer, cervical cancer screenings and blood sugar tests, Freeman said. Patients should discuss with their doctors recommended health screenings and other questions they have about medical tests.

Trend: “I’m not a person who needs a lot of sleep”

“There are some people who claim they don’t need sleep,” said Penn’s Nierman, but it’s not true for most.

Most people need seven hours a night, and some even more, he said. 

“Younger people in particular often need more and often don’t get it. That has a lot of deleterious effects on mental health, memory.”

Poor sleep habits, over time, can increase your risk of obesity, diabetes, and cardiovascular disease.

Lack of sleep may also take a toll on your immune system. “Studies show that people who don’t get quality sleep or enough sleep are more likely to get sick after being exposed to a virus, such as a common cold virus. Lack of sleep can also affect how fast you recover if you do get sick,” according to the Mayo Clinic.

Trend: Setting a weight-loss pound goal

“Setting a goal of losing like 30 or 50 pounds isn’t recommended,” said Elisabetta Politi, nutrition director of the Duke Diet and Fitness Center at Duke University.

It sets people up for frustration over time. Weight loss is a long, steady process, she said, and it may help to approach it with smaller, more reachable goals.

“There’s a reason gyms are packed in January and February and then in March start emptying out. Try goals that are more relevant to you, more reachable,” said Politi.

“Instead of signing up for the gym, try saying, ‘I’m going do more physical activity. I’m going to take a walk, 15 minutes, twice a day.’ Make very specific goals,” she said.

She said shows like “The Biggest Loser” can give a false impression that losing a lot of weight fast is doable for the average person.

The people on those shows have a whole team of trainers, nutritionists and chefs assisting them.

“It really doesn’t really help regular people who have jobs and can’t dedicate themselves completely to weight control,” she said.

Politi also recommends people try being more mindful about meal planning if they want to lose weight — in other words, pay attention to what foods give you energy and which ones make you feel uncomfortably full or sleepy or zapped of energy afterward.

“If you feel better, it will help you lead a long, productive healthy life,” she said.

Trend: Hot yoga and hot fitness classes

More than 36 million U.S. adults practice yoga, according to a 2016 Yoga Alliance report, and while its many benefits are well known — it improves strength and flexibility, and can help lower stress, among other health perks — there’s one type of yoga that some experts recommend crossing off your list in 2017.

“Hot yoga and hot fitness classes are a surefire way to increase your chance of overheating,” said Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City and a spokesperson for the American College of Emergency Physicians.

Hot yoga is practiced indoors in a room cranked up to between 105 to 110 degrees Fahrenheit and set at about 40 percent humidity. The typical hot yoga class runs 90 minutes.

It’s a trend that’s been around for a few years and has expanded more recently beyond yoga studios to include hot Pilates and hot cycling, for example. But some ER doctors like Glatter say working out in high-heat environments can lead to serious health risks.

“It puts you at risk for developing heat cramps and heat exhaustion which can lead to heat stroke, a potentially lethal condition. In a nutshell, your body loses the ability to cool itself, leading to dangerously high temperatures which may place you at risk for seizures, muscle breakdown known as rhabdomyolysis, and can even lead to coma,” said Glatter.

Trend: No snacking after dinner

Snacking in the evening a couple of hours after dinner isn’t necessarily the big diet-buster it’s cracked up to be. It can actually be good for you if it’s healthy and light, said Dr. Michelle Terry, a clinical professor at the University of Washington and an attending physician at Seattle Children’s Hospital.

“Eating after 8 p.m. will not necessarily make you gain weight, unless you are eating low-nutrient foods in large quantities,” Terry told CBS News.

That means staying away from salty, high-calorie, high-fat, carbohydrate-packed chips and cookies. Instead, choose one of these healthier options: a small apple with peanut butter or a half-cup of cottage cheese, a half-cup of plain Greek yogurt, a cup of fat-free or low-fat milk, a small serving of raw vegetables and low-fat dip, or a handful of unsalted nuts.

If you have diabetes, eating a small snack in the evening  — about 150 calories and 15 grams of carbohydrates — that contains some protein can be a healthy choice.

“Before bed, it helps control blood sugar levels. And if you feel hungry before bed, having a small snack may help you sleep better too,” said Terry.

© 2017 CBS Interactive Inc. All Rights Reserved.