Why Crash Diets Don’t Work

Your body is really not a fan of quick weight loss — or maybe it’s just the more primitive parts of your brain. In any case, a new study shows that you need a lot of will power to lose weight fast and keep it off, because even a year later, your body still remembers it used to be fatter. In its infinite wisdom, it will try to make you eat more, because it feels less secure in its ability to survive… in case you got stranded somewhere with no 7-Elevens. (Apparently this need to survive in unlikely scenarios trumps more likely concerns, like the ability to not get heart disease, the ability to be attractive, and the ability to go up stairs without wheezing and having people stare.) Metabolism was also down.

So that’s why people usually gain all the weight back, and then some. Which just reinforces what the fitness community’s been preaching for years: eat healthy, eat less calories and exercise — for the rest of your life. You’ll end up losing weight slowly (you also gained it slowly, since you probably didn’t gain 30 lbs in 3 months), and your body, like the frog in boiling water, will get used to being thinner and not raise alarms about it.

Details of the study? Sure: the (Australian) researchers put 50 fat people on a crash diet (550 calories/day, meaning a quarter of normal) for 2.5 months. They lost about 30lbs each, or 14% of their body weight; they also tested their blood for levels of hormones dealing with appetite and hunger, and they were in “eat more” mode. Then they went back a year later, and the people had gained back about 13 lbs each and were now down to 8% weight loss. They also measured their hormones again, and they were still telling people to eat more. For example, leptin, a hormone that suppresses appetite, was low; ghrelin, which says you’re hungry, was high.


Ghrelin is not the same thing as Gremlin


From The New England Journal of Medicine, via NPR


  1. You can work your ass off in the gym and still not see good results if your diet is bad.