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If you’re trying to lose weight, you’re probably suffering from advice overload. Should you shed pounds slowly? Guzzle water? Stock up on nuts? Eat frequently? Fast for most of the day? Here’s the lowdown.
Slowly but surely
Claim: “People who lose weight gradually and steadily (about 1 to 2 pounds per week) are more successful at keeping weight off,” says the Centers for Disease Control and Prevention.
Evidence: The best study may upend that widely held belief.
“We randomized 200 volunteers with obesity, about 100 to a slow weight-loss group and 100 to a rapid weight-loss group,” explains Joseph Proietto, emeritus professor of medicine at the University of Melbourne in Australia.1
The “slow” group was told to cut their usual intake by about 500 calories a day, with a goal of losing about one pound a week. The “rapid” group consumed only 450 to 800 calories a day, all from meal-replacement drinks.
“The slow group had nine months to lose 15 percent of their body weight,” says Proietto. “The rapid group had to do that in three months.”
By the end of each group’s weight-loss period, “78 percent of the rapid group had achieved their target weight, compared to just 50 percent of the slow group,” says Proietto.
What’s more, 18 people in the “slow” group—but only three in the “rapid” group—had dropped out. Losing weight quickly might motivate people to stick with a program, Proietto points out.
The researchers then tracked those in both groups who had lost at least 12.5 percent of their starting weight. After three years, both had regained, on average, 75 percent of the weight they had lost.
“There were no differences in the amount or the rate of weight regain between the two groups,” notes Proietto.
Bottom Line: It’s hard to keep weight off. But you’re no more likely to regain lost pounds if you’ve lost them quickly. And don’t try to slash calories to 450 to 800 a day without a doctor’s supervision.
A water appetizer?
Claim: “Drinking a lot of water has long been a staple of weight-loss programs, in part because doing so makes you feel fuller,” wrote the Washington Post in January.
Evidence: “We have done a couple of studies where we gave folks two cups of water before a meal, presented them with a large tray of food, and asked them to eat as much as they’d like,” explains Brenda Davy, professor of human nutrition, foods, and exercise at Virginia Tech.
“After drinking water, middle-aged and older adults ate about 60 to 75 calories less than when they didn’t drink water before their meal.” 2,3 (Water had no impact on how much younger adults ate at their next meal.)
“So the question was, if you drank water before a meal repeatedly over a period of time, could it promote weight loss?” Davy wondered.
To find out, “we prescribed a structured weight-loss diet of 1,200 to 1,500 calories per day to 48 middle-aged and older adults with overweight or obesity.”
“One group was not given any instructions about water intake, while the other group was told to drink two cups of water prior to each main meal. And we provided the water group with bottled water.”
After 12 weeks, “the water group had lost about 15 pounds and the control group had lost around 10 pounds,” says Davy.4 (That study, as well as one of the single-meal studies, was funded by a nonprofit organization that received money from the water-filter maker Brita.)
How does water help people shed pounds? “We have some evidence that people feel more full before eating a meal if they drink water first,” says Davy. “Another possibility is that folks may drink water instead of calorie-containing beverages.”
But Davy is cautious. “We have preliminary evidence supporting the effectiveness of pre-meal water to help people lose weight, but those findings need to be confirmed with a larger study,” she says.
What’s more, “we’ve only seen a benefit in middle-aged and older adults. Whether this works in younger folks is a big question mark.”
Bottom Line: Drinking water before a meal may help you eat less. Just don’t expect the pounds to melt away.
Graze or gorge?
Claim: “Try to stick to small, frequent meals throughout the day,” a dietitian told the Eat This, Not That website in September. “I think that’s very important to speed up the metabolism to make sure you’re not feeling overly hungry.”
Evidence: “Early observational studies showed that people who were grazers—meaning they ate small meals throughout the day—tended to be thinner than those who were eating larger meals,” says Brad Schoenfeld, associate professor of exercise science at Lehman College in New York City.5
“But, of course,” he adds, “correlation is not causation.”
Why would grazing keep you trim? “The general hypothesis is that if you eat more frequently, it will stoke your metabolic furnace, helping you burn more calories,” says Schoenfeld.
“But that idea is unfounded,” he notes. In one study, 15 young adults ate the same number of calories—divvied up into either three or six meals—on two separate days. The volunteers burned the same amount of fat and calories on the day they ate six meals as on the day they ate three.6
Grazing doesn’t help people lose weight over the long term, either.
For example, researchers told 51 adults with overweight or obesity to eat 1,200 to 1,500 calories a day, either as three meals or as mini-meals (with at least 100 calories each) every few hours. After six months, the grazers had lost no more weight than the three-meals-a-day eaters.7
And when Schoenfeld analyzed the data on weight from 15 trials that lasted two weeks to a year, “there was no difference if people ate, say, one meal or five.”8
“It really doesn’t matter.”
Bottom Line: When it comes to how often you eat, “do whatever fits your lifestyle best,” says Schoenfeld. “It comes down to calories in, calories out.”
Go nuts?
Claim: “Just a handful of nuts may help keep us from packing on the pounds as we age,” reported National Public Radio in 2019.
Evidence: NPR’s piece was triggered by a study in which researchers (some partly funded by the nut industry) followed nearly 145,000 people for 20 to 24 years.9 Compared to those who didn’t eat nuts, those who ate at least half an ounce of nuts a day (the equivalent of about 12 almonds) had a 23 percent lower risk of gaining roughly 10 pounds over any given four-year period.
Why look at nuts and weight?
“People think nuts are fattening because they’re high in fat,” explains Marion Nestle, the Paulette Goddard professor emerita of nutrition, food studies, and public health at New York University. That may lead people to avoid them.
Enter the nut industry.
“In general, nut-industry groups fund studies to demonstrate that their nuts have health benefits, which can increase the market share of the type of nut they grow,” says Nestle.
The key question: What happens in studies that randomly assign people to either eat or not eat nuts?
In most—they’re typically funded by the nut industry—the nut eaters don’t gain weight, likely because they compensate by eating less of something else.10
And nearly every study that randomly assigns dieters to eat or not eat nuts as part of a low-calorie diet finds little or no difference in weight lost between the groups.11
For example, in a study funded by the American Pistachio Growers, 96 adults with overweight or obesity were instructed to eat a low-calorie diet that included 1½ oz. of pistachios (about 75 nuts) every day or a nut-free diet with the same number of calories. After four months, each group had lost about 10 pounds.12
But that didn’t stop the pistachio growers trade association from declaring on its website, “Study shows pistachios may be helpful in a weight loss plan.”
“This is an instance of interpretation bias, a common problem in industry-funded research,” Nestle explains.
“Though the study found no difference in weight loss between the groups that did or did not eat nuts, the results are interpreted as favorable to nuts.”
Bottom Line: Nuts are unlikely to have much impact on your weight. Just keep your serving sizes in check.
Watch the clock?
Claim: “Somehow during lockdown I managed to lose weight instead of gain it,” wrote freelance journalist Dana McMahan on Today.com in September.
“How on earth did that happen? I stumbled into intermittent fasting.”
Evidence: “Intermittent fasting is an umbrella term for three different types of diets,” explains Krista Varady, professor of nutrition at the University of Illinois at Chicago.
■ Alternate-day fasting. “People restrict their intake, often to about 500 calories a day, and they alternate those days with ‘feast’ days on which they can eat whatever they want.”
■ 5:2 diet. “This is a spinoff of alternate-day fasting where you have two ‘fast’ days and five ‘feast’ days per week.”
■ Time-restricted eating. People limit themselves to eating only between certain hours, with nothing but calorie-free drinks at other times.
“You can apply that window to any part of the day,” says Varady. “A popular version is the 16:8 diet, where people fast for 16 hours and eat during an 8-hour window.”
Most studies show that people lose no more weight when they try alternate-day fasting or the 5:2 diet than when they simply eat fewer calories every day.13
In other words, while fasting may be a simple strategy, it isn’t magic.
“The reason people lose weight is because they’re eating fewer calories,” explains Varady.
In her studies on alternate-day fasting, “you’d think that people would go crazy on their ‘feast’ days, but they don’t. They eat about 10 percent more calories than they normally would. So the net result is that they have an average calorie deficit of about 600 to 700 calories per day.”
But for many, eating so little food is a struggle. “A lot of people drop out of the studies because it’s really hard to adjust to,” Varady notes.
Instead, she is now looking at time-restricted eating, which “short-term findings suggest is a lot easier to stick to.”
In a recent study, researchers randomly assigned 116 adults with overweight or obesity to eat three meals at any time of day or to eat only between noon and 8 p.m. After 12 weeks, the time-restricted eaters had lost no more weight than the control group. (Each lost, on average, about two pounds.)
And in a subgroup of the time-restricted eaters whose body composition was measured, 65 percent of the weight they lost was muscle.14
Those results give Varady pause. “The researchers didn’t collect diet records,” she notes. Without knowing what people ate, it’s hard to explain why the time-restricted volunteers lost so much more muscle than fat.
In a new study, Varady tested whether a shorter eating window would boost weight loss.
She randomly assigned 58 people with obesity to one of three daily eating patterns: eat their usual diet; eat only between 1 p.m. and 7 p.m.; or eat only between 3 p.m. and 7 p.m.
(Why those time frames? “People really don’t want to skip dinner,” says Varady.)
After eight weeks, only people in the two time-restricted groups had lost weight—about seven pounds each.15
“You don’t have to torture yourself and eat within a small, four-hour window when a six-hour window produces the same weight loss,” says Varady.
But the research on time-restricted eating for weight loss is limited, she adds. “It’s so popular, but there are only a handful of studies.”
Varady is hoping to run a year-long study comparing time-restricted eating to daily calorie cutting. Stay tuned.
Bottom Line: “If you want to lose weight, find something that works for you long term,” says Varady. “I’m not pushing intermittent fasting, but it’s simple and it probably works better than cutting calories for some people.”
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2Obesity 15: 93, 2007.
3J. Am. Diet. Assoc. 108: 1236, 2008.
4Obesity 18: 300, 2010.
5Am. J. Clin. Nutr. 30: 712, 1977.
6Obesity 21: 336, 2013.
7Obesity 20: 985, 2012.
8Nutr. Rev. 73: 69, 2015.
9BMJ Nutr. Prev. Health 2: 90, 2019.
10Adv. Nutr. 2020. doi:10.1093/advances/nmaa113.
11Am. J. Clin. Nutr. 96: 249, 2012.
12Nutrients 12: 2155, 2020.
13Nutrients 11: 2442, 2019.
14JAMA Intern. Med. 2020. doi:10.1001/ jamainternmed.2020.4153.
15Cell Metab. 32: 366, 2020.