Does a High-Fat Diet Increase DCS Risk?

In decompression sickness (DCS) research, the effect of a diver's diet hasn't been studied much. A group of Polish researchers at the Medical University of Gdansk decided to see if a high fat diet plays a role.

They consider obesity a significant risk factor in DCS, because more inert gas is stored in fat tissue and the solubility of nitrogen in fat is 5.3 times higher than in hydrated tissue. Another predisposing factor, they say, is the poor circulation in fat tissues, which slows down the elimination of inert gas. However, some in the scientific community dispute those assertions.

The researchers believe that, due to the long duration of fat metabolism, a diet that is rich in fats will raise the level of lipids in the blood, which increases the amount of dissolved nitrogen, and thus the probability of DCS. So the researchers set out to see whether lipid level could be used to assess a diver's risk of DCS.

They gathered 56 men, ages 20 to 48, who were either sport or professional divers, and had them fill out questionnaires about their diet and work habits, which were used to calculate the approximate consumption and percentage of fat in their daily food intake. They tested each man's blood for lipid levels, then took them on two simulated dives in a recompression chamber -- one to a 100-foot dive, then a 200-foot dive after a 24-hour break -- and ran Doppler tests to determine whether any bubbles had formed.

Following the 100-foot dive, there were no symptoms of DCS, but after the 200-foot dive, symptoms were found in 29 of the 56 men. The group with no symptoms had an average daily fat intake that was four percent below the norm, while the group with stress averaged a daily fat intake 54 percent above the norm. Men without decompression stress also had lower cholesterol levels, averaging 188 milligrams per deciliter of blood (mg/dL) while the group with stress averaged 211 mg/dL. And when it came to body mass index (BMI), the no-stress men averaged 24.9, while men with stress averaged 26.3. There was no significant difference between groups in relation to age.

"A statistically significant correlation was observed between the occurrence of decompression stress and daily fat intake, cholesterol and triglyceride levels and BMI values," the researchers reported in their study, published by the journal Underwater and Hyperbaric Medicine. "Despite a statistically significant correlation, decompression stress occurred both in the groups with normal body weight and in those who were overweight, but not among all the overweight individuals. It may suggest that BMI is an overrated risk factor and could indicate new, additional risk factors such as the diver's diet, overall cholesterol and triglyceride levels."

An excess of fat in the diet leads to disturbances in the lipid balance, the researchers summarized, and higher consumption of animal fats, with a lack of vegetable and fish fat, leads to increased cholesterol and triglyceride levels. The time required to metabolize excess fat will result in consistently higher post-meal lipid levels. "No one dives on an empty stomach," the researchers wrote. "Dives should be performed approximately two hours after a meal, when nutrients have been absorbed into the bloodstream, and fats in the diet have a direct impact on the increasing volume of inert gases that are dissolved in the blood serum during a hyperbaric exposure . . . in the case of someone who has eaten a fatty meal, normal decompression time consistent with the dive tables may prove to be insufficient for complete desaturation . . . From our experience, such a situation will result in at least a greater severity of decompression stress."

Some dive medicine experts question their results, one of whom is Nico Schellart, a professor of biomedical engineering at the University of Amsterdam. He has also studied whether body fat affects divers, and in a controlled study found that neither body fat nor BMI enhanced bubble formations; the correlations were "highly non-significant." However, age and, especially, maximal oxygen consumption (VO2 max) determined bubble development.

Schellart wrote to Underwater and Hyperbaric Medicine¸ disputing the validity of the Polish study, stating, "It seems likely that [daily fat intake, and triglyceride and cholesterol levels] are indicators for bubble stress, but with the present study design and statistical analysis, the question cannot be answered whether they are stressors. To date, BMI is an indicator, poorer than body fat; according to new insights, [those two factors] have lost their status as stressors."

The researchers replied, "For years, the research on the impact of age, body weight, fat mass, maximal oxygen uptake went on, but no one paid attention to the factor as obvious as nutrition . . . Many times it has been proven that a high-fat diet with a predominance of animal products causes an increase in cholesterol and triglyceride levels in the blood. It should also be stressed [that] in the mechanism of fat digestion and absorption, [there is] a long half-life in the blood, from a few hours to a few days . . . the results indicate a strong causal relationship between the studied parameters. Just highlighting the effects of diet was the aim of our research . . . there is a high probability that a high-fat diet increases the maximal oxygen uptake, not the mass of [body fat]."

We contacted Petar DeNoble, research director at Divers Alert Network, who knows the study well, and is skeptical about its results. "First, the 'decompression stress' was estimated by monitoring venous gas embolism [VGE] using Doppler detector, but quantitative measures [i.e., bubble grades] were not presented . . . The dive to 100 feet for 30 minutes did not cause VGE in any diver, which is quite unexpected. The dive to 200 meters caused VGE in 29 out of 56 divers despite 180 minute of decompression. It is likely that the VGE grade was very low. One thing is sure: Nobody among exposed subjects developed symptoms of DCS.

"Although the high-fat intake was the variable of interest, the subjects were divided in two groups not based on their fat intake but rather on the response to decompression. Results would probably be very similar in either way, but the chosen approach raises suspicion of possible research bias."

In short, don't panic, DeNoble says. "The dive exposures used in this study are not representative of recreational diving. DCS in recreational diving is a very rare outcome, and so far there is no evidence that diet or obesity measurably increases risk of DCS in real life. However, obesity increases risks of other diving injuries, and obese divers should be aware of it. Divers -- and non-divers -- should balance their diet and maintain physical fitness to mitigate their risk of chronic diseases."

We'll also add that there are plenty of other reasons to eat a diet low in animal fat, so why gorge yourself on a second plate of ribs at that resort or liveaboard barbecue just because you've already paid for it?

"The influence of high-fat diets on the occurrence of decompression stress after air dives," by D. Kaczerska, P. Siermontowski, R. Olszanski, K. Krefft, S. Malgorzewicz and K. Van Damme-Ostapowicz, Underwater and Hyperbaric Medicine, Vol. 40, No. 6, pgs 487-497