The Best (and Worst) Days to Start a Diet, According to Science

The day of the week you decide to start eating better can make a bigger difference than you realize.

Best: The day you feel ready

sakkmesterke/ShutterstockBeing prepped to make a life change—like knowing 15 ways to change eating habits in a day—will help you get started. But being confident that you know the exact day may be more of a gut feeling: Often the most successful dieters start because of a wakeup call, says Amy Stephens, MS, RD, a registered dietitian in New York City. Maybe you went to the doctor and he told you that you'd have to go on medication unless you did something to get your cholesterol down, or a family member has a heart-to-heart with you about your health, or a friend gets sick. "When these things happen you set a goal that's more emotional rather than weight-based, and that's often more successful," explains Stephens. "If things get rough along the way, you can remind yourself why you're on this journey," she says.

Best: After your birthday

BoxerX/ShutterstockExperts dub this "the fresh start effect." In a study from the University of Pennsylvania, researchers found that people were more likely to act on their health goals after landmark dates, including holidays and birthdays. When you're thinking about how to start a diet, this is an ideal time. They explain that after a milestone, you're less likely to dwell on past mistakes, making it easier to perform behaviors more in line with "the new you." It also helps you think in big-picture ways, which can drive you toward your goals. You've got this!

Best: Monday

Sergey-Fedulov/ShutterstockIt's a new start to the week and you're ready to take that "new beginnings" mindset to heart. You know how to break bad habits in 12 easy steps. (You do, don't you?) Any Monday is a great day to begin anew. People report seeing Monday as a "reset" button and greater motivation to tackle their goals at the start of the week, reports The Monday Campaigns. Besides, if you've been indulging all weekend, you're probably ready to embrace lighter, fresher food.

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Best: Any day in October

Alexey-Borodin/ShutterstockWith the abundance of pie, cookies, mulled wine, and holiday cheese platters around the months of November and December, it's no wonder that research in the New England Journal of Medicine has shown that it can take people as many as five months to lose the weight from too many pigs in a blanket. Though there are good ways to beat the holiday bulge if it does happen, the easier fix is to make that resolution in October, says study co-author Brian Wansink. The idea is that preventing pounds is much simpler than trying to shed them later.

Best: After a big life change

nd3000/ShutterstockLet's say you moved to a new home and are all settled in. Or you're in a line of work where you have the summer off. "A new lifestyle and routine is the perfect time to start with new good habits," says Stephens. That might mean you make small tweaks to start marching toward your larger goal, like starting the day with a healthy breakfast (now's the time to break out your avocado toast skills) or reducing the amount of sugar or cream you have in your coffee.

Worst: New Years

Kamil-Macniak/ShutterstockThe problem with New Years is that we pick lofty goals that are difficult to achieve—and weight loss (along with these 14 other goals) is one you shouldn't plan for. "You're simply setting yourself up for more failure. If it hasn't worked in the past, why would this New Years resolution be any different?" says Stephens. If you'd like to set a goal when the clock strikes midnight, plan one thing at a time, like vow to stop eating in front of the TV or eat dessert every other night instead of every night, she advises. Then, set your weight loss goal another time.

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Worst: When you have a big project due at work

gpointstudio/ShutterstockWhen life gets super busy and you're preoccupied by something—you had a baby, you're really busy at work, you're taking on caregiver responsibilities for a family member—today is not the day to vow to lose weight. Stressful, busy circumstances are not the time to test your resolve and stick-to-it-ness, and there are also practical limitations, like lack of time or sleep. For dieting to be successful, "all the stars need to be aligned," says Stephens. Now more than ever good health habits are important (eating energizing food, for instance), but tackle that weight loss goal once life calms down.

Worst: Friday

Yulia-Davidovich/ShutterstockThe weekend is coming up and you have brunch, pizza, and ice cream cones on the calendar. Cornell University research found that people's weights tend to be lowest on Friday or Saturday and highest on Sunday and Monday. But that's not a bad thing—you don't necessarily have to necessarily vow to be super strict on the weekends. They concluded that people who compensate during the week for extra calories consumed over the weekend actually lost the greatest amount of weight over time. "Long-term habits, it appears, make more of a difference than short-term splurges," the researchers conclude. All that to say: go ahead and treat yourself over the weekend—it can help you stay the course.

Worst: Saturday or Sunday

Yulia-Davidovich/ShutterstockAlong with occasional splurges being good for your psyche, the weekend is a bad time to start because you have too much free time, says Stephens. Your schedule is off, so it's harder to stick to the healthy habits you practice all week. For instance, you may not be sitting down to oatmeal in the morning but rather running out for coffee and a muffin. Rather than cooking a meal at home, you're going out to eat. Save it for when you have a normal routine or a more rigid schedule, like the workweek, which can help you stick to a diet. (But you can still fit in exercise with these weekend warrior tips.)

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Worst: Right after vacation

MilanMarkovic78/ShutterstockFor many people, this is when they let loose and eat to their heart's content. For others, they follow these rules for staying fit while away. But dieting right after might be even worse. In an older study from 2002 researchers examined the psychological impact of planning a diet for the future. They discovered that planning to go on a diet can cause some people to overeat. You may have heard of it as the "last supper effect." You think, what the heck, I'm going to come home and be super strict with myself, so might as well load up on as many cookies as I can now, but that can slide you into a worse place than you started.
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