Active Expert: Gale Bernhardt: Optimal Body Fat Numbers

A fellow I know posed the question below:

Q: Hello Gale, I was wondering if you would know how low a percentage of body fat someone could get down to without loosing power? I've got one of the scales that measure body fat and at 167 pounds it says I'm at 13% and wondering how low I should go. Thanks.

A: Good question. The chart below is one that is referenced often, from The American Council on Exercise:

	Women	Men
Essential fat	10-12%	2-4%
Athletes	14-20%	6-13%
Fitness	21-24%	14-17%
Acceptable	25-31%	18-25%
Obese	32% or more	26% or more

I did not see any ages associated with these numbers.

The book, "Exercise Physiology" by McArdle, Katch and Katch lists body fat percentages for different types of athletes and professional cyclists (roadies) run 11.6 percent and distance runners go 11.8 percent. For the gals, distance runners go about 17.2 and there are no numbers on the chart for cyclists.

So, back to your personal question - how low can you go without losing power? First, let's assume that your scale accurately measures body fat and you are indeed 13 percent. That puts you on the top end of the athletic scale - a pretty lean guy.

My gut feeling, based on experience and knowing you, is that any lower than 10 percent would cause problems (loss of power). The only real way to know would be to gently work your way down a little at a time and keep tabs on how you feel, speed and power.

1,344 Views Tags: body_fat, optimal_body_fat, body_fat_percentage

Mar 6, 2008 6:10 PM

Jeff Homan says:

As a young adult I was obese. I am 5’ 7” and I weighed 273lbs. I lost the weight and started racing bicycles as an adult at 165 lbs and about 12% bodyfat. Over the years I decided to drop weight and have found that I’m able to race my best at 145 lbs and a bodyfat of 4 – 5% (as measured by calipers and Tanita scale). I know I lost muscle in the process, but most of that was upper body mass which wasn’t particularly useful on the bike. Regarding power, when I was heavier I could put out more watts for short bursts, but I couldn’t climb well at all. I also found that I would cramp during long races. I think the cramping was partly due to adaptation, but also due to hauling my mass around for hours on end. As I lost weight my cramping has almost vanished and my sustained speed in the flats improved as did my climbing. As I’ve adapted to my smaller size and changed my focus from trying to get lighter and leaner to trying to get stronger at the same weight, I found my power to weight ratio has steadily improved.

My personal philosophy is to stay as lean as I can and still maintain my health and power. This philosophy is not without risk. If you plan to change your body composition, you should consult your doctor and if you get the go ahead, consult a dietitian for nutrition and a coach to help monitor performance. I would recommend not getting overly obsessed with your weight. Stay focused on your health and your performance. I hesitate to say this, but it is a real issue, keep in mind that another risk is developing and eating disorder. As Gale said, make changes gently and gradually. It took me almost 2 years to get from 273 to 165 and about a year to get from 165 to 145.

Getting and staying lean is a commitment in both time and mental energy but I’ve rewarded with better race results and sense of satisfaction. Besides, at age 41 I can see my abs. That’s better than chocolate cake any day.

Mar 6, 2008 8:06 PM

Jamie says:

Excellent! I just had someone ask me about this tonight. Now I can pass along this information. Thanks, Gale! By the by, my experience with the scales that measure body fat has not been good; we have one at my house, and last time I checked it said 30% (I'm actually just under 24%). I would advise seeking some kind of validation for the scale's measurement.

Mar 6, 2008 8:28 PM

Keep Running says in response to Jamie:

All great articles today. I was a sprinter in college and I think the lowest I got to with my body fat percentage was around 8%. I think if I got any lower than that my power would drop. RIght now though I'm trying my legs at distance running and I think I relate to the "starving athlete" article. I even have come to the point where I really have to watch my calories because otherwise I don't eat enough. Now I'm hoovering around 5-6% which seem really low, almost too low. Besides being a wimp in the cold all the time, has anyone else heard of down sides for a male to be at a low body fat for such a long period of time?

Mar 7, 2008 8:24 AM

Gale Bernhardt says in response to Jeff Homan:

Great post Jeff and congrats on the weight loss. It takes discipline to change comfortable habits.

Mar 7, 2008 8:25 AM

Gale Bernhardt says in response to Keep Running:

Jamie ~ Good question on the low body fat for males. I don't know of anything off the top of my head, I'll keep a watch.

Mar 17, 2008 3:15 PM

niemsco says:

I don't understand the comment on "lose of power". Of course you will lose power, but that doesn't mean you are losing speed, you need to measure Watts/kg to really understand where you are on the bike. I way less than 140, 5% body fat, have an FTP of 210, but I can go 22 miles per hour in a half iron man, probably more now. That's why they say be as lean and powerful as possible. You can check out "Training and Racing with Power Meter". There is a lot written about watts/kg now. Can't just measure power.

Mar 17, 2008 4:20 PM

Gale Bernhardt says in response to niemsco:

Niemsco ~

"Of course you will lose power" - not true. You can lose weight and not lose power.

You are correct, however, watts per kilogram (or pound) is the critical measure.