How Much Weight Can You Lose in a Week?

Listen, I totally get why you’re searching this topic.

Maybe you have an reunion that snuck up on you, and the newly single ex you should have married in the first place will be there. Why wouldn’t you want to feel sleek and adorable in your sexiest dress? Or perhaps you’re heading on a beach holiday and think you’ll have more fun pretending to be Helena Christensen circa 1991 frolicking in the surf if you looked a little more like her. Sure.

And I will answer your question - I pinky swear.

But as someone who has beaten back an eating disorder, I gotta point out that thinking of weight loss as a week-to-week calculation can suck you in to unhealthy weight control practices.

“We’re not into double workouts, laxatives, counting and aggressively skipping kilojoules, skipping meals or anything that leaves you feeling poorly,” says dietitian Lauren Slayton. “I guess that needs to be said.”

But since people do crave a quick slim-down, is there a way to do it wisely? “A week of pre-event eating can be confidence boosting as long as it isn’t insane, extreme or punitive.”

Thanks for the reminder. So how much weight can I lose in a week?

The simple math goes like this: How much fat you lose over the course of a week has to do with how many more kilojoules you burn than you take in. Half a kilo of fat is accumulated when you eat 14,600kJ (3,500cal) more than you burn; likewise, if you eat 14,600kJ (3,500cal) a week less than you burn - all else being equal - you’ll lose around half a kilo. If you manage a deficit of 29,300kJ (7,000cal), you’ll lose two. Up to a kilo in a week is a safe amount to lose if you’re doing it gradually and steadily.

But is it possible to lose more in a week?

Slayton’s one-week plans can result in up to 2.5kgs off (less if you're a small person with not much to lose). That’s according to the number on the scale. “But you’re not losing more than a kilo of body fat per week so it’s a little fat a and a little fluid loss,” she says. that's if you cook mostly at home as opposed to eating out, and eat lots of vegetables and fish, and cut booze and sugar out entirely. “We don’t advise weeks like this more than once a season - it’s not how to eat day in and day out.”

That’s because even if you’re not at risk of an eating disorder, being too restrictive has a rebound effect, says weight management expert Dr Caroline Apovian. “People who try to lose weight in a week or a month are going to gain it back,” she says. Plus, gaining and losing weight in succession is bad for your health.

Besides, you lose muscle mass (in addition to fat) when you go for quick weight loss, and it’s muscle that helps you burn kilojoules; that means your metabolism will slow and it’ll be harder to keep weight off - even if you restrict kilojoule intake, says Dr Apovian.

So what should I do if I want to look thinner in a week?

Aside from any weight you might lose, add what Slayton calls “delicious de-bloaters:” avocado, asparagus, lemons, and parsley. “Are those helping you lose more than water? No. But do they make you feel a little less bloated and puffy? Sure.”

Then - after you and your ex have happily reunited or you’re back from your holiday - go back to your regularly scheduled healthy but not-too-strict eating. Of course, we all know that doing a quick one-off sprint to thinner means you won't be able to sustain all of it, says Slayton, and that's OK: You achieved your purpose, and as long as you don't go nuts making up for food not eaten, you may even be able to keep off some of the weight off, she says.

Bottom Line:

Upping your weight loss ante short term, as long as you do it healthfully, is an OK thing to do a few of times a year. “This is not the way I have clients eat 48 weeks of the year - one is marriage and the other is like a one night stand or weekend fling. No judgement, but they’re just totally different.”