Weight loss myths: Obesity doctor on GLP-1s, supplements, diet, fasting, and more

Neither is healthy weight loss swiftly attained; the Centers for Disease Control and Prevention (CDC) recommends losing no more than 2 pounds per week for those who plan to keep off what they shed. Meaning, even if you started your weight loss journey today, you could be months or years away from reaching your goal.

So it’s no surprise that weight loss myths and get-thin-quick gimmicks are rampant. Dr. Nisha Patel, medical director of the Obesity Medicine and Metabolic Health Program within the transplant department at California Pacific Medical Center in San Francisco, recently took to social media to dispel five such falsities that “need to die.” She breaks down each with Fortune.

Myth No. 1: Calorie deficit doesn’t matter for weight loss

If you’ve ever tried to lose weight through dieting, you know you must create a calorie deficit by burning more than you consume. Easier said than done, especially when that discrepancy is filled by food cravings and hunger pangs. Patel acknowledges these factors contribute to the difficulty of long-term deficit maintenance but says they don’t make it any less critical.

“Calorie deficit is the driver of weight loss, and it still matters what you eat,” says Patel, who is also a certified culinary medicine specialist. “If you’re eating foods that are higher in fiber, higher in lean protein, they’re going to be more satiating. They’re also in line with health-promoting dietary guidelines, and it’s going to be easier to create a calorie deficit with those types of foods versus [ultra-processed foods].”

In theory, Patel jokes, you could consume nothing but Oreos and lose weight, as long as you log a calorie deficit. However, that’s neither a nutritious nor a sustainable diet. Plus, she says, trying to create a calorie deficit on ultra-processed foods alone may be harder than you think; their calculated blend of fat, salt, and sugar makes you more likely to overeat.

“We really want to focus on the fruits, the vegetables, the lean proteins, whole grains, lentils, beans, those types of foods, to really help us with creating that calorie deficit,” Patel tells Fortune. “You’re going to feel fuller because of the fiber and the protein, you’re going to meet your nutrient needs, and you’re going to reduce your consumption of ultra-processed foods.”

Myth No. 2: Fasting is magical for weight loss

Perhaps you’ve tried limiting when you eat via intermittent fasting. The method takes many forms, from complete fasting for 24 hours once a week, to eating only between 10 a.m. and 6 p.m. daily. While some people fasting intermittently may lose weight, that the practice better promotes weight loss than traditional approaches is a misconception, Patel says.

“Fasting can be a tool to help individuals reduce their calorie intake because, at the end of the day, it is reducing calorie intake that actually drives weight loss,” Patel tells Fortune. “What we eat during that eight-hour eating window does matter. It’s not just a free-for-all; you can still eat more calories than you intend to in a span of eight hours, so they still need to focus on their diet quality.”

A person’s intent behind intermittent fasting is also important, she says. If fasting for 16 hours a day and eating for eight is conducive to their lifestyle and they’re still able to eat a balanced diet, great. In Patel’s experience, however, people who find themselves fasting unintentionally, such as those with busy mornings who skip breakfast, tend to eat more later in the day and into the evening.

“That is going to be counterproductive for weight loss,” she says.

A study published this spring in the Annals of Internal Medicine supports Patel’s clinical experience. In a randomized controlled trial of adults with obesity and prediabetes, researchers at the Johns Hopkins University School of Medicine found that people who ate regularly and those who were restricted to a 10-hour eating window had similar weight loss outcomes—suggesting that the amount of calories consumed has a greater bearing on weight loss than when they’re consumed.

Myth No. 3: Keto is best for weight loss

The goal of a ketogenic or “keto” diet is to put your body into a metabolic state called ketosis. In ketosis, instead of primarily burning carbohydrates, your body uses fat for fuel. That said, the keto diet is high in fat and low in carbs, with a moderate protein intake.

Benefits of the keto diet can include weight loss, lower blood pressure, lower blood sugar, reduced inflammation, and increased focus and energy. Side effects, however, range from dehydration to kidney stones to “keto flu,” a group of symptoms such as fatigue and upset stomach.

Low-carb diets like keto aren’t necessarily bad, Patel says, but their often extreme restrictions make them challenging to maintain long term. Plus, people tend to regain weight.

“People often forget that it’s not carbohydrates that are the problem per se, because we do have many health-promoting sources of carbohydrates, like fruits, vegetables, whole grains [that] people can’t incorporate on a keto diet,” she says. “The other problem with the keto diet is that the way certain individuals do it, they start incorporating more saturated fat into their day-to-day eating. So there is a risk of developing high cholesterol, and that could raise your risk of heart disease.”

Patel is adamant that the most powerful component of the keto diet is—you guessed it—calorie deficit.

“Within the first six to 12 months, people may experience maybe a little bit more weight loss with the keto diet compared to other forms of calorie restriction,” Patel tells Fortune. “But it’s not, again, sustainable in the long term. I would say that that difference in weight loss is pretty insignificant.”

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Myth No. 4: Over-the-counter weight loss supplements are FDA-approved

Countless over-the-counter weight loss supplements exist, and it’s easy to remember which ones are approved by the Food and Drug Administration (FDA): none. The agency regulates dietary supplements as foods, not drugs, and typically does so after they’re on the market.

“A lot of the onus falls on the supplement manufacturer to prove its safety and ‘efficacy,’ and there’s just so many supplements out there that the regulatory bodies can’t keep up with trying to police all of them,” Patel says.

Little scientific evidence suggests that over-the-counter weight loss supplements work, according to the Office of Dietary Supplements, part of the National Institutes of Health. What’s more, they may be dangerous. The FDA maintains a list of tainted weight loss products that contain active drug ingredients not listed on product labels—potentially interacting with medications or supplements you’re already taking.

“[Supplements] don’t undergo the same testing and regulation as medications that have to go through clinical trials and prove safety and efficacy before they’re FDA-approved,” Patel tells Fortune. “It can be scary. As consumers, it’s important for us to understand the risks versus benefits of certain supplements.”

Before taking a dietary supplement of any kind, Patel recommends discussing it with your doctor, who can help ensure your supplement comes from a legitimate source and has been third-party tested.

Myth No. 5: Taking weight-loss medications is the easy way out

Social media may have given you the impression that GLP-1 drugs such as Wegovy (FDA-approved for chronic weight management) and Ozempic (FDA-approved for the treatment of Type 2 diabetes) are miraculous medications abused by celebrities looking to slim down. Or maybe you’ve heard that people who take such glucagon-like peptide 1 agonist drugs are “cheating” their way to weight loss. Not so, Patel says.

“People forget that there are some strong neurohormonal factors at play that make it difficult to not only lose weight, but to keep that weight off in the long term,” Patel says. “Medications have really helped level the playing field. It can help interrupt some of that disruptive signaling.”

Neither should people associate weight management drugs with vanity; obesity is a serious, chronic disease, not to mention a global epidemic, according to the World Health Organization. In the U.S., the CDC estimates one in five children and two in five adults have obesity. GLP-1 drugs can help people lose weight by decreasing appetite and increasing feelings of fullness. Plus, Patel points out, such medication is meant to be paired with reduced calorie intake and regular exercise.

“It’s not the easy way out,” she says. “People [are] still having to practice healthy lifestyle habits.”

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