Question: I was just curious; When I was in my mid-twenties, I was an ultra-strict dieter, and my body fat was at a regular 4.2-4.7 percent. However, I seemed to catch a cold once a month. Now, I'm about 10 percent, but almost never sick. What's a good safety gauge to go in body fat (as in, how low can I go) while retaining my health?

Answer: I think you already found your safety gauge for healthy body fat levels: As soon as you start getting sick repeatedly, you're probably trying to maintain your body fat too low for too long a period of time. That being said, I'd always prefer to err on the side of being too lean rather than too fat: According to the American Obesity Association, scientific evidence has established a strong relationship between obesity and at least 15 medical conditions including diabetes, heart disease, cancer, high blood pressure, osteoarthritis, stroke, gout and low back pain.

It might not be the low body fat that made you sick – it might be what you did to yourself in the process of getting there: Super-strict dieting and training such as bodybuilding contest prep, is a stress to the body. When you remove entire food groups from your diet and reduce your calories drastically, you are more likely to develop nutrient deficiencies that can lead to colds, flus, etc. The overtraining that is often necessary to reach extremely low body fats can also lower your immune function.

I know several guys who maintain 3-5% body fat all year round, and they are as healthy as can be. However, they are the very skinny, hyperactive, fast metabolism types (ectomorphs) so they are naturally lean anyway – they don’t have to stress themselves to get to that lean – its natural for them.

You will find that you have a certain "setpoint" towards which you will naturally gravitate unless you are making a concerted effort to lower your body fat. For example, if you’re not dieting strictly, you might naturally creep up to 10% or so. At that point you’ll tend to stabilize and you won’t fluctuate much either way unless your diet or activity level changes. That's your "set point" - that’s the level your body is "comfortable" at.

If you try to drop your body fat too far below your set point and hold it there too long, your body may not "like it." It's hard to put a specific number on how low is too low, but personally I think it's perfectly healthy for men to go down to 6-9% and women to 13-15% and hold it there indefinitely. For women to drop into single digits or men to low single digits and keep it there is not really natural for the body (unless you are an ectomorph). Your body may react by suppressing your immune system.

Personally, my set point is about 9-10%. Unless I work hard constantly, I will always creep back up to 9-10% - my body seems to like it there. However, I don't like how I look at 10%. I prefer to hold it around 7% (that's "ready for the beach", but nowhere near contest condition). For contests, I drop down to 3-4% but that’s a temporary peak condition. The key word is temporary: To maintain my health, I only try to stay that low for a few weeks, and my absolute best peak condition is maintained for perhaps only a few days.

Remember, any condition you can maintain all year round is not a peak condition and a true peak condition is not something you should even try to hold all year round. To be healthy, there must be balance. For every peak, there must be a valley.

To give you a benchmark for your body fat, here are some typical fat % levels:

Men:
Contest bodybuilder: 3-5%
Extremely lean: 6-9%
Lean: 10-15%
Average Male: 16-20%
Poor: 20-25%
Very Poor: 25%+

Women:
Fitness model/bodybuilder: 8-11%
Extremely lean: 12-15%
Lean: 16-19%
Average female: 20-25%
Poor: 25-29%
Very Poor: 30%+

Try to find a happy medium where you are satisfied with how you look, but where your diet is not stressing your body’s immune system to the point of causing sickness. You’re going to have to determine that level for yourself. The best advice I can give you is to listen to your body!