When you don’t eat, your metabolism slows down.
This “nutrition fact” says that when your caloric intake is too low, your metabolism actually slows down. It has been referred to as “starvation mode” and is the basis for the current trend of advising people that they should eat every couple of hours, never skip meals, and never cut your calories too low while dieting.
But is it true?
To examine this truth, I decided to look into what happens to a person’s metabolism when they fast for a short period of time (between one and three days).
The first study I reviewed had six healthy male volunteers fast for 3 days. During this fast, the researchers measured the changes in the subject’s metabolism at 12, 18, 24, 20, 42, 54, and 72 hours of fasting. What they found was that there was no significant change in energy expenditure during any of the 7 time points. So from this study we can say that a 3 day fast in men does not cause a decrease in metabolism.
Already this evidence goes against the idea that if we don’t eat every couple hours our metabolism will slow down.
The second study I reviewed had 8 men and 8 women fast every other day for 22 days straight. There was no significant change in the subject’s metabolism from the start to the end of the study. From this study, we can say that fasting every other day for a period of 22 days results in no significant changes to a person’s metabolism.
So we now know that even if we eat sporadically for 22 days, most likely our metabolism won’t be affected.
The third study I reviewed had 8 men fast for either 12 hours or 72 hours and then eat a meal. After the meal their metabolisms were measured for 12 hours. This study found that regardless of whether or not the men fasted for 12 hours or 72 hours, their metabolism for 12 hours after eating a meal was not significantly different. So this study shows us that a short term fast doesn’t affect your metabolism after you eat.
So even if we don’t eat for 3 days, there is absolutely no change in the way eating effects our metabolism.
So from the research I was able to review, it doesn’t seem like short periods of fasting cause any negative effects on our metabolism. Nor does it affect our metabolism once we start eating again.
Since having absolutely no calories for a short period of time does not effect our metabolism, I feel safe in saying that the idea that you need to eat every couple hours in order to keep your metabolism “revving” is actually a nutrition myth and not a fact at all. Also, the phenomena of a “starvation mode” does not happen until after at least 3 days of fasting, if it actually even exists.
BP
PS- For those of you who are interested, I will post my references in the comments section.
