Monday, February 20, 2012

Too much Exercise can Simulate Starvation


Everybody knows that exercise is good for you, but many of you might not know that there is such a thing as too much exercise. This leads some people to engage in hours of cardio every day in a desperate attempt to "burn" extra calories--all without adequate rest. While they get some good results initially, within a couple of months their progress comes to a complete halt and they start to feel tired all the time. These gung-ho and constantly exhausted individuals are suffering from the effects of too much exercise (a.k.a., chronic cardio).

Dangers of Excessive Exercise
The best example of the dangers of too much exercise comes from The Biggest Loser (a show I love to watch, by the way). These contestants often engage in 4-6 hours of seriously intense aerobic exercise five to six days a week in an effort to burn those extra calories stubbornly hiding in their fat stores. This usually results in a massive amount of weight loss (often an average of 4-10 pounds per week, depending on the contestant) over the competition's 6-month period. When the winners are announced, their massive weight loss makes it seem as if all you need to do to lose weight is simply get off your butt and burn some calories.

But something weird happens in the months and years following these competitions: Most of the contestants start to gain their weight back (some will actually gain back all of the weight they lost), even if they didn't change their diet.

So what happened? In my opinion, the excessive amounts of exercise experienced by these contestants during the show created such a huge calorie deficit that it simulated starvation. It doesn't take much of a calorie deficit to simulate starvation: A person only has to consistently lose more than 7500 calories per week (or a weight loss of more than 2 pounds of fat per week). It seems that if a person loses more than 2 pounds of body weight per week, then their body can switch into starvation mode.

Once the body tips into starvation mode, it reacts defensively to prevent too many consumed and stored calories from being burned by lowering its metabolism (essentially, a body in starvation mode is super efficient).

This protective reaction doesn't take long: Researchers found that within six weeks of starting the Biggest Loser, contestants' metabolisms dropped an average of 16%. By the end of the competition, the average drop in metabolism was a whopping 39%! Doing the math, by week 30 of the competition each contestant required one less 500-calorie meal per day to maintain their final weight than a healthy person at that same weight.

This sizable drop in metabolism, plus the increased hunger and appetite created by too much sustained weight loss, means that once these contestants stopped their excessive exercise and left the show's heavily-controlled environment they were primed to regain all their weight--even if they didn't return to their bad eating habits and continued to count calories.

What Happens when a Person Exercises too Much?
First, too much exercise causes chronic stress on muscles and joints, resulting in a chronic elevation of the stress hormone cortisol. Cortisol controls the inflammation caused by exercise, but in chronic excess it reduces energy, breaks down lean muscle mass, increases belly fat, suppresses wound healing, and muscle recovery

Next, the constant exercising can cause too much of a constant calorie deficit. In an attempt to keep from losing too many calories too quickly, the body drops its metabolism to become more efficient at burning calories.

Finally, as you continue to lose weight, hormones that control hunger and appetite adjust as your body tries to get back all of the calories it lost. 

Conclusion
You have to be very careful with how much exercise you engage in. If you do too little, you don't stress the body enough to produce cellular recycling (known as autophagy). If you do too much, you can simulate starvation. Once in starvation mode, your body will react defensively by increasing hunger and appetite and lowering metabolism. This means that any weigh loss you realize will be temporary.

How much exercise is just the right amount? That will be a topic I discuss later this week.

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