The formula for losing weight is simple: Eat fewer calories than you burn. But the methods of doing this can vary. In truth, there is no one "best" way to lose weight — what works for you might not work for someone else. To get the lowdown on the latest science on weight loss, Live Science conducted a months-long search for the best information. We contacted nearly a dozen experts who have researched weight loss, and looked at the most well-regarded studies of weight loss done to date.
We wanted to know what these studies found and, most importantly, when all the science and evidence were boiled down, what experts recommend for people who would like to shed pounds in a safe, healthy manner. All of the experts emphasized one thing: A person's approach to weight loss should be one that is enjoyable and can be maintained over the long term. Weight loss shouldn't be about deprivation, because diets that deprive people of their favorite foods tend to be short-lived, said Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School and general internist at Cambridge Health Alliance.
"If you make this commitment to lifestyle changes, then maybe five years from now, you're 10 pounds [4.5 kilograms] lighter," Cohen said. "If you're doing crash diets, you would probably be 10 pounds more."
People should focus on making lifestyle changes — sometimes even small ones, like cutting down on the sugar in coffee — to reduce their overall calorie intake. While these changes might not lead to drastic amounts of weight loss in short periods, they can produce healthy, gradual weight loss that will counter the natural tendency for people to gain weight as they age, Cohen said.
As we'll describe in detail below, a successful weight loss program usually involves cutting back on your calories, increasing your physical activity and making behavioral changes to help you stick with a diet and exercise regimen over the long term. [How to Get Started on a Weight Loss Program]
Who should lose weight?
Obesity is a growing problem in the United States. Over the past 15 years, the nation's obesity rate rose by 24 percent (7.2 percentage points) among adults, from 30.5 percent in the years 1999-2000 to 37.7 percent in 2013-2014, according to a report from the Centers for Disease Control and Prevention published in November 2015. The adult obesity rate in 2013-2014 was the highest ever for the nation, and equates to more than 78 million people.
The extra pounds come with baggage; they increase the likelihood of many health conditions, including the following:
- heart disease
- high blood pressure
- Type 2 diabetes
- high cholesterol levels
- sleep apnea
Though science has yet to establish a surefire link between obesity and each health risk, the extra fat tissue seems to be the biggest culprit. More fat in the neck has been tied to sleep apnea, while compounds released by fat cells may increase the chances of developing type 2 diabetes. In addition, the more body fat a person carries, the more blood is needed to provide the tissue with oxygen and nutrients, resulting in higher blood pressure. (On the other hand, losing weight can relieve such burdens on the body, leading to health benefits, including reduced blood pressure, cholesterol and blood sugar.)
That's why one of the most widely used gauges of whether a person needs to shed pounds is body mass index (BMI) — an indicator of body fatness developed by Belgian statistician Adolphe Quetelet in 1832 that's based on the ratio of height to weight. For example, a person who is 5 feet 7 inches (1.7 meters) and weighs 172 lbs. (78 kg) would have a BMI of 27. [BMI Calculator: What's My BMI]
The goal with BMI is to be what the National Institutes of Health considers "normal." The lowest risk for health conditions related to weight has been tied to a BMI between 18.5 and 24.9 (labeled "normal weight"). Risks go up as a person climbs this BMI ladder, with numbers between 25 and 29.9 considered overweight, and BMIs of 30 or greater considered obese, according to the NIH.
Although BMI is easy to calculate, it is not a perfect measure of body fatness. For example, people with a high amount of muscle mass can have a high BMI without being overweight or obese.
If your BMI places you in the obese category, it's time to lose weight, according to the most recent (2013) weight management guidelines from the American Heart Association and other professional organizations. Weight loss is also recommended if you're overweight and have other risk factors for heart disease, such as diabetes, high blood pressure, high cholesterol levels, or a waist circumference greater than 35 inches (88 centimeters) for women and 40 inches (102 centimeters) for men.
The 2013 guidelines were put together by an expert panel from the American Heart Association, the American College of Cardiology, and the Obesity Society, and were reviewed by the National Heart, Lung, and Blood Institute. The guidelines are based on a rigorous review of recent scientific studies.
People who are normal weight, or overweight and do not have any additional risk factors for heart disease, should focus on avoiding weight gain, rather than losing weight, the guidelines say, because there is no strong evidence that weight loss provides health benefits for these people. However, additional weight gain could lead to problems, experts said.
"It's common to gain weight with age, and weight maintenance is much easier than weight loss, so the best plan for these patients is to maintain their weight, eat healthier and exercise more — but not to focus on weight loss," Cohen said.
How much weight should you aim to lose?
Obese people who lose as little as 3 to 5 percent of their body weight improve their health. Research suggests that losing 5 percent of body weight results in a 3-mmHg drop in systolic blood pressure (the top number in a blood pressure reading, which is a measure of the pressure in the arteries when the heart beats) and a 2-mmHg drop in diastolic blood pressure (the bottom number in a blood pressure reading, which is a measure of the pressure in the arteries between heartbeats), according to the 2013 guidelines. Losing even more weight is associated with greater health benefits, so the guidelines recommend that people start out with a goal of losing 5 to 10 percent of their body weight over six months.
To accomplish this weight loss, most experts interviewed by Live Science recommended that you shed 0.5 to 2 lbs. (0.23 to 0.9 kg) every week. This usually means cutting 250 to 1,000 calories out of your daily diet. (If you cut 500 daily calories, you'll lose about a pound per week.)
For women, that means consuming about 1,200 to 1,500 calories a day. For men, it means a daily intake of about 1,500 to 1,800 calories. However, the number of calories you should consume can vary depending on your current weight and activity level.
To figure out how many calories to consume, you may want to use a calculator, such as the National Institutes of Health Body Weight Planner, which takes into account your current weight and activity level to determine how many calories a day are needed to maintain your current weight and how many are needed to achieve your desired weight loss.
You'll lose more weight if you cut even more calories. However, trimming too many calories will likely backfire and can even kill you.
Experts warn that severely restrictive diets — which cut more than 1,000 calories per day — tend to be unsustainable. You might see a rapid weight loss at first, but you'll likely regain much of the weight. For example, Oprah Winfrey famously lost 67 lbs. (30 kg) on a diet that allowed her to consume just 420 calories a day, only to later regain the weight.
Over the long term, severely restrictive diets tend to result in about the same amount of weight loss as diets that are less restrictive, said Robert Jeffery, director of the University of Minnesota Obesity Prevention Center.
For example, researchers reviewed data from six trials of very-low-calorie diets (fewer than 800 calories a day) and found that, after about 26 weeks, participants lost 16 percent of their initial body weight, whereas participants on a typical low-calorie diet (1,000 to 1,800 calories a day) lost about 10 percent of their body weight. But after about two years, both groups retained about the same amount of weight loss — around 5 to 6 percent of their initial body weight, according to the 2012 study.
The study is notable because it looked at data from clinical trials that directly compared very-low-calorie diets with typical low-calorie diets, which is a better method than looking at studies that do not involve a comparison, and instead include only a single diet.
Even the weight you lose on these restrictive diets may not be the right kind of weight, as cutting too many calories can cause you to lose muscle instead of fat, said Dr. Louis Aronne, director of the Comprehensive Weight Control Center at Weill-Cornell Medical College in New York.
"If you lose weight very rapidly, on a diet like a cleanse, then you're going to lose excess muscle," Aronne said. Muscle loss can be detrimental, because muscle tissue burns more calories than fat tissue; therefore, keeping muscle tissue can help with weight loss and maintenance, said Aronne, who is the author of the upcoming book "The Change Your Biology Diet" (Houghton Mifflin Harcourt, 2016).
Finally, any adult diet that allows fewer than 800 calories per day can be harmful and should only be undertaken under the supervision of a medical professional, according to the 2013 guidelines. People who follow such a diet may experience dehydration, irregular periods (for women), kidney infections and even sudden death, among other health problems, according to the Michigan Department of Health and Human Services. Such diets also increase the risk of developing gallstones.
It's important to have realistic expectations for weight loss with a reduced-calorie diet over the long term. Studies suggest that people can lose about 9 to 26 lbs. (4 to 12 kg) after six months of a typical reduced-calorie diet. Afterward, people usually gain back some of that weight, so they end up with a total of 9 to 22 lbs. (4 to 10 kg) of weight loss after one year, and 6 to 9 lbs. (3 to 4 kg) of weight loss after two years, according to the 2013 guidelines. [2016 Best Bathroom Scales]
Is there a "best" diet for weight loss?
People can lose weight on a number of different diets, as long as they consume fewer calories than they burn. "There's no one diet that's superior to other diets for long-term weight loss and maintenance," said Kathy McManus, director of the Department of Nutrition at Brigham and Women's Hospital in Boston.
A successful plan for weight loss is often one that is tailored to an individual's lifestyle and other personal factors. McManus and her colleagues found that the breakdown of calories from protein, fat and carbohydrates doesn't matter for weight loss. They followed 800 people assigned to different calorie amounts from these food categories. After two years, the participants had dropped about 9 lbs. (4 kg), on average. Few diet studies have followed such a diverse group — the McManus study involved people ages 30 to 70 with a wide range of incomes, from cities in the northern and southern United States — for more than a year.
Often, even small changes in your diet can help you lose weight. For instance, just replacing an unhealthy snack every day with fruits and vegetables, or eliminating an evening snack, can result in weight loss, said Katherine Tallmadge, a registered dietitian and an op-ed contributor to Live Science. "If people make minor changes that they can live with, it's more likely that they can lose the weight and keep it off," Tallmadge said. [ 4 Calorie-Cutting Tips That Won't Leave You Hungry]
Moreover, nothing magical happens when you cut fat — it doesn't result in extra weight loss, studies have shown. A recent study, published in October 2015, found that people on a low-fat diet lost about the same amount of weight as people on diets with more of their calories from fat.
But what if you're the type of person who "cheats" because you feel hungry? That's where the type of calories and a few other tricks come in.
Though not foolproof, a low-glycemic diet that's chock-full of protein, fiber and healthy oils, and low in starches and other sugars, may help combat feelings of hunger. Researchers think that nutrients like protein and fiber help to create the "I'm full" feeling, while sugars and refined carbohydrates cause spikes in blood sugar that may increase hunger later, Aronne said. In that way, people on a low-glycemic diet may feel more satisfied while cutting back on overall calories and thus may be more likely to stick with the diet.
Liz Applegate, director of sports nutrition at the University of California, Davis, said she recommends a diet that is about 20 percent protein (about 60 to 70 grams, or 2 to 2.5 ounces, per day), spread across all three meals. This recommendation agrees with findings from a study of people in the National Weight Control Registry who have lost at least 30 lbs. (13.6 kg) and kept it off for at least a year. An analysis of 900 people in this registry showed that about 18 to 20 percent of their daily calories came from protein. This would be the equivalent of eating 6 ounces of Greek yogurt at breakfast (17 grams of protein), 3 ounces of salmon for lunch (21 grams of protein) 1 ounce of nuts for a snack (7 grams of protein) and 3 ounces of chicken for dinner (19 grams of protein).
Applegate also encourages people not to skip meals, because that deprivation often causes people to overeat later in the day. In particular, studies show that people who skip breakfast tend to weigh more than people who eat a healthy morning meal, according to the NIH.
According to a 2015 report from the Dietary Guidelines Advisory Committee, which advises on the nation's diet recommendations, people tend to have a healthy body weight if they eat a diet high in fruits, vegetables and whole grains; moderate in dairy products; and low in meats and sugar-sweetened foods and beverages.
In addition, since alcoholic drinks are essentially "empty" calories — they don't contribute towards you're daily nutrition — cutting back on alcohol may be one way to help you lose weight, experts said.
As an alternative to eating a reduced-calorie diet every day, some people try to do "intermittent fasting." This means they significantly cut their calories on a few days per week and eat normally the other days. This diet is generally not recommended, but early research suggests that some people may find it easier to follow this diet than a traditional one, Tallmadge said. A review study published in April 2015 found that people on intermittent-fasting diets lost about 9 percent of their body weight over six months, and about 80 percent of the participants were able to stick with the diet.
Still, studies on this type of dieting are limited, and more research is needed to confirm the findings, the researchers said.
As for commercial weight loss programs, the most effective programs are in-person ones, where people regularly meet with a trained health professional, according to the 2013 guidelines. People should look for a program that lets them meet with a registered dietitian, psychologist, exercise specialist or health counselor at least 14 times over a six-month period, the guidelines say. If you can't attend an in-person program, some studies show that programs that use telephone calls, email or text messages to provide feedback on your progress can also help with weight loss.
How much exercise do you need?
You've worked on the calorie intake part of the equation. Now what about the "calories out?" Studies show that people who exercise while dieting lose more weight, and are better able to keep it off, than people who diet and do not exercise, said Wayne Miller, programs director at West Virginia School of Osteopathic Medicine's Center for Rural and Community Health.
Miller and his colleagues reviewed 25 years' worth of weight loss research and found that, during a typical 15-week weight loss program, people lost, on average, 23 lbs. (10.4 kg) by only dieting and 24 lbs. (10.9 kg) by dieting and exercising, they reported in 1997. That difference may seem small, but after one year, the people who only dieted kept off 14 lbs. (6.4 kg), on average, whereas those who dieted and exercised kept off 19 lbs. (8.6 kg). [2016 Best Heart Rate Monitor Watches]
As for how strenuous the exercise has to be, experts recommend that people who want to lose weight meet the government's guidelines of at least 150 minutes of moderate physical activity (such as brisk walking) every week, or about 30 minutes a day for five days a week.
But those who want to maintain weight loss over the long term may need to do more exercise. A 2008 study of the National Weight Control Registry involving 3,600 people who lost at least 30 lbs. (13.6 kg) and kept it off for a year or longer found that they reported at least 60 minutes of moderate physical activity per day. [Best GPS Watches]
The National Institutes of Health also recommends resistance training to strengthen muscles at least twice a week. These activities include lifting weights and doing push-ups and crunches, which can help build muscle. Resistance training exercises are important for weight loss maintenance because muscle tissue requires more calories to maintain itself, meaning you will burn more calories just by having more muscle. [ 4 Easy Ways to Get More Exercise]
Do diet pills and supplements work?
If weight loss sounds like a lot of physical and mental work, that's because it is. And there's no magic pill: Dietary supplements that claim to help people lose weight have not been proven to work, and they have the potential to be dangerous, Cohen said. Many nutritionists and researchers agree that such supplements can do more harm than good. Supplements can contain drugs that are not listed on the label, and may have harmful side effects. In 2014, the Food and Drug Administration identified more than 30 weight loss supplements that contained hidden drugs, but only seven of these were recalled by their manufacturers.
Weight loss supplements send more than 4,600 people to the emergency room every year, often due to heart symptoms, such as chest pain and a rapid heart rate, according to an estimate by a study published in October 2015.
The bottom line, many experts told Live Science, is that there is often no scientific evidence supporting a supplement's claims. The makers of diet supplements do not need to prove that their supplements actually help people lose weight in order to sell them in stores.
In contrast, makers of prescription and over-the-counter weight loss drugs, such as orlistat (brand names: Alli and Xenical) and lorcaserin (brand name: Belviq), must conduct studies showing that the drugs can lead to weight loss before the pills are approved by the FDA for use in obese individuals and those considered overweight (BMI of 27 or greater) who also have obesity-related risk factors.
Generally, people who take weight loss drugs — which often work by decreasing appetite and increasing feelings of satiety — can lose an average of 5 to 10 percent of their body weight in a year, according to the Mayo Clinic. However, these drugs still need to be used along with diet and exercise for people to achieve this level of weight loss. (Studies of these drugs involve people who have also made changes to their diet and activity level.)
According to the 2013 guidelines, the drugs might be helpful for people who aren't able to lose weight with diet and exercise alone, but people should consider discontinuing the drugs if they don't lose at least 5 percent of their body weight within 12 weeks of starting them.
However, Cohen cautioned that the long-term safety of weight loss drugs hasn't been studied. Most of the studies look at these drugs' safety after just one year, he said, and some earlier drugs that were approved by the FDA were later taken off the market because of their side effects. For example, in 2010, the weight loss drug sibutramine (sold under the brand name Meridia) was removed from the market — even though it had originally been approved — because it was later linked with an increased risk of heart attack and stroke.
In any case, weight loss drugs may not be a long-term method for keeping weight off, because people may regain the weight when they stop taking the drugs, Cohen said.
Can a lack of sleep cause weight gain?
Here's a bit of advice that may make a dieter smile, or yawn: Get more sleep. A growing body of evidence suggests that getting insufficient sleep increases the risk of obesity. However, most of these studies have been conducted at a single point in time, which makes it hard to determine whether a small amount of sleep was a cause or an effect of weight gain.
The longest-running study on the link between short sleep and weight gain followed about 68,000 women for 16 years. It found that women who slept 5 hours or less per night gained about 2.5 lbs. (1.1 kg) more, on average, than those who slept at least 7 hours per night, over 16 years. In addition, those who got 5 hours or less were 15 percent more likely to become obese during the study period than those who got at least 7 hours of sleep.
Getting too little sleep, which most experts define as less than 7 hours of shut-eye per night, may increase levels of an appetite-stimulating hormone called ghrelin, and decrease levels of the hormone leptin, which makes you feel full, according to the NIH. This may lead to an increase in hunger. In addition, people who sleep less could have more time to eat. In a small study of 11 people who stayed in a sleep lab, participants ate more snacks when they slept for just 5.5 hours than when they slept for 8.5 hours. This increase in snacking occurred mostly during the late-night hours.
Still, it's not clear if getting more sleep actually helps people lose weight. However, studies are now being conducted to answer that question. In one study, researchers from the National Institute of Diabetes and Digestive and Kidney Diseases will look at whether obese people who usually sleep less than 6.5 hours a night see changes in their weight if they increase their sleep by an hour per night. [Best Fitness Trackers]
Should you consider bariatric surgery?
Bariatric surgery, an operation on the stomach and intestine used to treat obesity, may be an option for people who are still severely obese after attempting to lose weight through other methods, such as diet and exercise. People with a BMI of 40 or greater, or those with a BMI of 35 or greater who also have obesity-related health conditions (such as type 2 diabetes), are candidates for this invasive surgery, according to the NIH.
People who have bariatric surgery will still need to make lifestyle changes, including following a healthy diet and engaging in regular exercise, to lose weight and keep it off.
A 2009 study that reviewed outcomes for more than 11,000 bariatric surgery patients found that patients typically lost about 56 percent of their excess body weight, or nearly 85 lbs. (38.5 kg), and maintained it for at least two years. Scientists who reviewed 89 studies on weight loss after bariatric surgery found that patients with a BMI of 40 or higher benefited most from the surgery, losing 44 to 66 lbs. (20 to 30 kg), on average, and maintained that weight loss for up to 10 years, they reported in 2005 in the Annals of Internal Medicine.
The operation has the following side effects:
- The surgery alters the gut's ability to absorb nutrients, so you may need to take vitamins and minerals, to prevent malnutrition.
- You will not be able to eat large meals.
- You will need to eat liquid or pureed foods for several weeks following the surgery, according to the Mayo Clinic.
How can you keep weight off?
It's typically harder to keep weight off than it is to lose it, the experts agreed. Many studies show that people usually experience their maximum weight loss after about six months of a diet-and-exercise program. After that, the pounds come creeping back, although most people don't regain all of the weight. For example, a 2007 review of 80 diet studies involving more than 26,000 people found that dieters lost about 11 to 19 lbs. (5 to 8.5 kg) after six months, but then their weight loss plateaued, and after four years, they maintained about 6.5 to 13 lbs. (3 to 6 kg) of weight loss.
Participating in a program that focuses on maintaining weight loss — one that meets at least once per month for a year or more — can increase the chances that you'll keep the weight off. A 2008 study of more than 1,000 people who lost about 19 lbs. found that people who participated in a weight loss maintenance program that met in-person once a month kept off about 3 lbs. (1.4 kg) more over a 2.5-year period than people who didn't participate in the program.
To assist any weight loss effort, weigh yourself twice a week, continue the lower-calorie approach indefinitely and exercise at least 200 minutes per week, according to the 2013 guidelines. The Centers for Disease Control and Prevention recommends that you make a plan for how to keep up your healthy eating pattern, even on weekends, vacations and special occasions. [2016 Best Pedometers]
Eating breakfast may also stave off hunger later in the day. In a 2002 National Weight Control Registry study of nearly 3,000 people who kept off 30 lbs. (13.6 kg) for at least a year, researchers concluded that one habit that stood out was eating a morning meal: 78 percent of the participants ate breakfast every day.
Once you've lost weight, keeping it off can seem like a never-ending battle. But it's a battle worth fighting, even if you slip sometimes. Trying, even if you don't always succeed, is better than not doing so, scientists say. There's no clear evidence that "yo-yo dieting" — or weight cycling, as researchers call it — is linked with an increased risk of early death or disease, compared with remaining obese, McManus noted. And very few studies report harmful effects of yo-yo dieting.
"Weight loss intervention should not be discouraged because of a person's tendency to be a weight cycler," McManus said.
In a nutshell, the bulk of the evidence says that maintaining your weight loss is achievable if you do the following: keep up your healthy diet, continue to exercise and monitor your weight so you notice when your regimen needs adjusting.
This article is part of a Live Science Special Report on the Science of Weight Loss. It will be updated whenever significant new research warrants. Note that any significant change in diet should be undertaken only after consultation with a physician.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.