Obesity and Diving

Our Dive Doc has the skinny on overweight divers.
-By Sam Shelanski, M.D.

Question:
Can a fairly overweight person pursue certification in diving? I'd like to know for a couple of reasons.

First, I need to become certified in order to continue my current study of rays. The problem is, I'm embarrassed about my weight unless at least one other person around me is overweight.

Secondly, it seems to me that diving would be a good form of exercise, but is it a safe activity for me?

C.H.
Rochester, N.Y.

Answer:
Before answering your questions, it's important to define what we mean when we say a person is overweight or obese. Obesity is best defined as excess fat - adipose - tissue that leads to increased health risks. Being obese increases a person's risk of hypertension, diabetes, arthritis and heart disease.

The Risks to Overweight Divers | Giant Stride Into Weight Loss

Determining Your Ideal Weight

The Risks to Overweight Divers

It's not uncommon to see obese divers; they are a reflection of the general lack of fitness among Americans. However, obesity doesn't preclude a person from diving. Some of the most experienced and skillful divers I have known were significantly overweight. But obesity in a diver does lead to an increased risk of complications and health problems when diving. In fact, anyone who is 20 percent or more above their ideal body weight is disqualified from commercial, military or scientific diving in the United States.

Risk #1 - Improperly Fitting Gear.

The obese diver's problems often begin when trying to purchase gear. Off-the-rack wetsuits are generally cut for an average body build, and trying to squeeze into a too- small suit can lead to constriction of the chest, inability to breathe properly and carbon dioxide buildup.

Obese divers may also have difficulty finding BCs that fit properly. If constricting, a poorly fitting BC can cause problems that are similar to the ones caused by a too-small wetsuit.

It's also difficult for many large divers to find an appropriately sized weight belt. On several occasions I have watched overweight divers link two belts together. This is clearly a safety concern. During my certification dives, I saw one of my fellow students lose a jury-rigged weight belt at a depth of 20 feet and rocket to the surface - twice.

Porcupines of the sea, urchin spines are like hypodermic needles that break off once deep inside you, injecting their venom. The venom from stonefish spines is delivered deep into the wound and produces excruciating pain that may last several days. Stingrays use one or more large spines or stings on their tails as defensive weapons. When you step on one, the ray thrusts its tail forward and upward, lacerating or puncturing your foot, ankle or leg.

Risk #2 - Poor Buoyancy Control.

The increased buoyancy of adipose tissue means that obese divers must carry more weight in order to descend. I have seen divers in colder water load as much as 40 pounds on a weight belt when wearing a 6 mm two-piece wetsuit. If this weight is not well distributed, it can cause problems with buoyancy and balance at depth, as well as significant back and hip discomfort.

Also, the problems caused by a too-tight BC can be compounded when it must be inflated to compensate for the increased amount of lead and loss of buoyancy at depth.

Risk #3 - Increased Air Consumption.

Obese divers also tend to consume more air than other divers because of the greater effort required to move through the water. This is particularly true if there is a current. Currents can lead to even faster air consumption, a dangerous situation for overweight divers. Being out of shape is a factor in increased air consumption, too.

Risk #4 - Increased Risk of Heart Attack.

Because overweight people are generally less physically fit than those who fall within the ideal weight-for-height range, they may be less prepared to deal with the increased exertion that a current or long surface swim demands. It has already been noted that obesity predisposes one to hypertension and heart disease, which I discussed in a previous column (August '96). Obese people are at an increased risk of heart attack and subsequent drowning while diving.

Risk #5 - Increased Risk of DCS.

Lack of physical fitness also contributes to an obese diver's risk of decompression sickness (DCS). However, fitness is probably less of a factor than the obesity itself. Nitrogen, the gas most responsible for causing DCS, is five times more soluble in fat than in muscle tissue. This means that an overweight diver will absorb more nitrogen than a leaner diver for any given time and depth. This increased absorption of nitrogen translates into an increased risk of DCS. It's important to remember that dive tables were originally devised using data on Navy divers: young, fit, males. Overweight divers must therefore dive more conservatively to minimize their risk of getting bent.

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Giant Stride into Weight Loss

So, does all of this mean that overweight people should be discouraged from diving? The answer is no, but two caveats apply:

• Diving is a sport, and while it may appear less rigorous than jogging or cycling, it can put significant strain on a body.
• Like any diver, an overweight person must see a physician prior to commencing diving. However, medical clearance to dive should not be seen as a final goal, but rather as a motivation to lose weight and become more physically fit. 20 to 35 percent of all scuba fatalities result from heart and other circulatory problems. Physical fitness will make your life not only more enjoyable, but also a lot safer.

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Determining Your Ideal Weight

There are several ways that people determine what constitutes an ideal weight for a given height. The most commonly used tables are those derived by insurance companies from actuarial data on life expectancy. That is, they define an ideal weight-for-height as that which correlates to the longest life span. The original tables were derived in 1959. When they were revised in 1983, it was necessary to increase the average weight for each given height by anywhere from five to 13 percent to account for the increasing tendency of Americans to be overweight.

Many in the medical community use a measurement called the Body-Mass Index (BMI). This is a person's weight in kilograms divided by his height in meters. For adults who are 20 to 29 years old, the 85th percentile for BMI is 27.8 for males and 27.3 for females. A BMI above the 85th percentile is considered equivalent to a weight greater than 20 percent above ideal.

The easiest way to calculate the ideal weight for a given height is to use a simple rule of thumb. For women, allow 100 pounds for the first 5 feet, and 5 pounds for every additional inch. This means that the ideal weight for a woman who is 5 feet, 5 inches is 125 pounds. Add and subtract 10 percent from this number to get the normal range of weights for a given height. For men, start with 106 pounds for the first 5 feet, and add 6 pounds for each additional inch.

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Questions for Dr. Shelanski should be addressed to RSD, Dive Medicine, 6600 Abercorn St., Suite 208, Savannah, GA 31405; e-mail: RSDmgzn@aol.com.