Are you one of the millions who have tried the high-protein, low-carb Atkins plan to lose weight or gone paleo for more energy? Do you stick with foods labeled fat-free to lower cholesterol or buy only gluten-free products because your stomach is sensitive? Those widely publicized regimens seem so promising. But does science support the claims? Consumer Reports spoke with doctors and dietitians, and read the research. Here’s what you need to know before going high-protein, low-fat or gluten-free:

High-protein

The promise: Remember the Scarsdale diet and the Stillman diet? Those high-protein/low-carbohydrate plans may have gone out of fashion, but Atkins, first published in 1972, is still hot. Protein-packed products are flooding stores, and the list of popular protein-rich diets — paleo, Zone and more — continues to grow. All claim that you’ll lose pounds, feel peppier and reduce your risk of heart disease.

The truth: People lose weight on high-protein plans because they take in fewer calories, not because they focus on protein. “Diets only work by lowering calories,” says David Seres, director of medical nutrition at the Columbia University Medical Center in New York and a member of Consumer Reports’ medical advisory board. “Where the calories come from doesn’t matter.”

In addition to pushing protein, many of these plans recommend cutting back on — or completely eliminating — carbohydrates. If you get less than 50 grams of carbs per day (the amount in two apples) for three to four days in a row, your body will start tapping its own fat and muscle for fuel instead of its usual source: glucose derived from carbohydrates. “You’re altering your metabolism away from what’s normal and into a starved state,” Seres says, adding, “People in starved states experience problems with brain function.”

A high-protein diet also overworks the kidneys. That’s especially worrisome for people with kidney disease and can predispose those with healthy kidneys to kidney stones. Over an extended time, excessive protein intake leaches calcium from your bones, which can lead to osteoporosis.

(Timur Arbaev/iStock)

As for heart disease, the saturated-fat-laden red meat that’s part of many high-protein diets may actually boost your risk. According to a Harvard study of more than 120,000 people followed for more than 20 years, a meat-based low-carb diet increased the risk of dying from cardiovascular disease by 14 percent.

The bottom line: It’s probably best to steer clear of high-protein diets, according to Consumer Reports’ experts.

Low-fat or no-fat

The promise: Proponents say these plans can prevent or ease heart disease, lower cholesterol levels, control blood pressure, and help you lose weight and keep it off.

The truth: Without some dietary fat, you can become deficient in essential fatty acids and have trouble absorbing vitamins that are fat-soluble. And certain kinds of fat — unsaturated ones — help protect your heart, reduce Type 2 diabetes risks and have other benefits. For example, a 2012 review of studies by the independent Cochrane Collaboration found that replacing saturated fat (found in animal products such as butter and ground beef) with unsaturated fat (from plant oils, fatty fish, avocados and nuts) lowered the risk of heart attacks and strokes. And if weight loss is your goal, be aware that low- and no-fat foods aren’t always lower in calories.

The bottom line: Stay away from no- or very low-fat diets; they can ultimately be harmful.

Gluten-free

The promise: Those who espouse this way of eating say that it improves gut health, cures stomach problems, aids weight loss and is energizing.

The truth: For most people, there’s nothing unhealthful about gluten, proteins that are found in barley, rye and wheat. The only people who need to give up gluten are the estimated 1 percent of Americans who have celiac disease and the up to 6 percent with non-celiac gluten sensitivity.

In fact, some evidence suggests that gluten may help fight heart disease by lowering levels of tri­glycerides (fats that circulate in your blood with cholesterol). It may also help reduce high blood pressure.

As for weight loss, a gluten-free diet may backfire, according to a study published in the Journal of Medicinal Food. Many foods without gluten are higher in calories, fat and sugar than the wheat-based versions. For example, a regular three-ounce Thomas’ plain bagel has 270 calories, two grams of fat and seven grams of sugar. A four-ounce Glutino Original New York Style bagel has 340 calories, seven grams of fat and 14 grams of sugar.

And some gluten-free products contain small quantities of arsenic, a carcinogen often found in the rice frequently used to replace flours that contain gluten. In 2012, Consumer Reports tested more than 60 samples of rice and rice-containing packaged foods, including rice pasta, rice crackers and cookies. Almost all contained measurable levels of arsenic.

The bottom line: Don’t opt to go gluten-free unless you have been diagnosed with celiac disease or a gluten sensitivity.

Copyright 2015. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.