Nutrition 101

Behind the Headline: Can You Really Drop 21lbs in 9 Days?

September 26, 2018

by Doreen Garelick, Dietetic Intern

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TURBO KETO. Drop 21 LBS in 9 DAYS. This was the largest, most colorful headline on the cover of the September 24, 2018 issue of First for Women that caught my eyes on a local newsstand. If only it were even close to true.

Let’s start with a bit of math. The 2015-2020 Dietary Guidelines for Americans provide estimated calorie needs per day, based on age, sex and physical activity level. A good, average number to work with is that a woman should eat about 2,000 calories each day. So, in the 9 days it would supposedly take to lose 21lbs, a woman should consume about 18,000 calories.

On the other side of the weight loss equation, the common rule is that losing one pound requires a 3,500-calorie deficit between calories burned and calories consumed. Using this logic, a woman would have to burn 73,500 calories in total to loss 21lbs, and to achieve that in 9 days would require an 8,167-calorie deficit each day!  To lose 21 pounds in 9 days, a woman would not only have to stop eating, but would also have to find some way to burn off 8,167 calories on each of those 9 days. To put that number in perspective, walking at a brisk pace for one hour burns about 240 calories.

Even if you could walk 24 hours a day for 9 days, and didn’t consume any calories, it would be impossible, and severely damaging to your health and vitality, to burn enough calories to lose 21lbs so quickly. And this doesn't even consider other factors that can make it hard to lose weight even in a calorie deficit.

So how can the publication get away with such an exaggerated headline?  You may have dieted before and lost more weight than you thought was possible in the first week or two of the diet. When you begin almost any eating plan that can result in weight loss, especially a plan that restricts carbohydrates, your body will soon begin to burn its glycogen (stored carbohydrates), which holds a lot of water within it. This can result in an initial drop in weight that comes from a loss of body fluid. So while you may initially lose more when starting a diet, a more steady rate of losing 1 to 2 pounds a week is a healthier, more sustainable approach than plans that promise more rapid weight loss. The Academy of Nutrition and Dietetics reminds us that, “If a diet or product sounds too good to be true, it probably is.” Try to remember that the next time a headline about weight loss catches your eye.

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