I just got a pop-up ad for weight loss. Specifically, “Join The Weight Loss Challenge”. What was the challenge? “How Much Weight Can YOU Lose In Three Days?”
This is a terrible idea. Here’s why:
First and foremost, how do you lose “as much as you can”? For most people, this usually means very little food, a whole lot of exercise, or some combination of the two. The approach you choose can have a significant impact on your three day (or long term) weight loss outcome. Regardless of your chosen food-intake-and-exercise combination, the science says short-term diets aren’t the way to achieve sustainable weight loss. Consider the following:
You’re not losing what you think you’re losing.
Your body is always burning fat (on a daily basis, more than half the energy your body uses comes from your fat stores). Changing your food intake or exercise volume over the course of a few days will not drastically alter fat burning.
You may still see a drop on the scales though: Lots of water weight can be lost in this time. Normal urine outputs can be anywhere between 800-2000ml per day (equating to 0.8-2kg, or 1.75-4.4 pounds), and additional water weight is lost through other body functions like sweat, bowel movements, and breathing. If your food or fluid intake is low, you’ll have less fluid to lose, but your total body volume will still decrease to a degree. (There’s a lot more to the processes of losing or retaining water weight, including different hormone levels, exercise levels, external factors like heat and humidity, and others.)
And, though three days is a short timeframe, you might also see some (very small) weight loss due to muscle breakdown and the use of stored carbohydrate, though this depends on what you’re eating and drinking, and what kind of exercise you’re doing over these three days. It’s very unlikely that you’ll lose enough muscle mass to have a noticeable impact on scale weight, but I bring this up because it can impact the next point…
You’ll likely gain it back.
By the end of three days you’re going to be hungry – especially if you’re eating little/exercising lots. Physical and mental aspects contribute to how we react to feeling hungry; the end result is that usually we eat – perhaps more than we need to in the long run. Our bodies have an inbuilt “survival drive” to rebuild the energy stores – the amount of fat, stored carbohydrate, and muscle mass – your body used for fuel during those three days. Hunger may lead to eating beyond what you need to rebuild those stores. We can eat a lot of calories very quickly, and the body takes some time to process food, replenish stores, and register that things are back to normal.
This sounds like three days of… unpleasantness.
You might be able to go for a day or three eating little and/or exercising a lot and feel ok physically and/mentally. Different people respond to dieting differently, though, and deprivation can have a negative impact on feelings of well-being, energy and fatigue levels, mental health states like anxiety or depression. And being hungry is not fun.
True weight loss or gain takes time. You can definitely lose weight in three days, but it’s not going to be the fat loss that you want, and it’s very unlikely to stay off. I’m a big fan of the “do it once, do it right” approach, and making the process enjoyable. It can be done!
For More Information:
Johnstone, A. (2007). Fasting ? the ultimate diet?. Obesity Reviews, 8(3), 211-222. doi: 10.1111/j.1467-789x.2006.00266.x
Melzer, K. (2011). Carbohydrate and fat utilization during rest and physical activity. E-SPEN, The European E-Journal Of Clinical Nutrition And Metabolism, 6(2), e45-e52. doi: 10.1016/j.eclnm.2011.01.005