Adding a new spin to the battle of the sexes, researchers say severely obese women outperform their male counterparts when it comes to both physical fitness and their ability to properly digest carbohydrates.
"We found that the women were better able to handle the obesity than the men," says study co-author Dr. Emile F.L. Dubois, from the department of pulmonary diseases at the Hospital Reinier de Graaf Groep in Delft-Voorburg, the Netherlands.
Dubois and his colleagues focused on 56 severely obese Dutch patients—22 men and 34 women, all white. None was known to have a history of heart disease or diabetes.
With an average age of 42, all the patients were scheduled to undergo a form of bariatric surgery intended to help them lose weight by having their stomachs wrapped with a restraining band. The procedure, known as "gastric banding," is usually recommended for patients who have a body mass index (BMI) of over 40.
All of the patients took part in a weight-management program to prepare for surgery, involving access to a dietician as well as nutritional information, an exercise program and, in some cases, medication.
Blood samples were taken, and all patients were assessed for evidence of carbohydrate intolerance and diabetes. Hormone levels and body fat composition were also calculated, and all the men and women completed a bicycle exercise test to observe respiratory health, muscle strength and fatigue.
Researchers say that men generally failed to meet expectations on the cycle test while women exceeded the anticipated results. The women demonstrated better lung capacity and endurance during exercise.
In addition, 59% of the men were found to be either carbohydrate-intolerant or diabetic, compared with just 35% of the women. A person who is carbohydrate-intolerant is unable to utilize carbs as a high-energy fuel source, and instead stores unprocessed, excess carbohydrates as body fat.
These results suggest that severely obese men face a higher risk than similarly overweight women for developing "metabolic syndrome," a precursor to diabetes and heart disease, say the researchers.
The researchers and other experts are speculating on the reason for these results. One possibility is that women are naturally more efficient at energy storage due to the role they play as a food source for newborns. Another theory is that men could be more negatively affected by the hormones produced by fat tissue—including estrogen.
But the most promising explanation might be linked to the distribution of fat around the body. Men, he notes, tend to store fat in the upper parts of their bodies and directly inside muscle tissue, whereas women store fat in the lower part of the body. This may lead to a reduced lung capacity among men, because abdominal muscles are compressed under the weight of stored fat.
Dr. Ken Fujioka, an expert in nutrition and metabolism at the Scripps Clinic in San Diego, agrees that fat distribution may indeed account for the fitness gap.
"We've known for years that women tolerate obesity better than men, and our guess is that it's hormone-mediated," he says. "It's mainly because men store fat centrally around the organs and in the abdominal area, while women store it in their hips and thighs. And, essentially, when you increase the fat in the abdominal area, insulin levels have to rise, and you increase pressure on the abdominal cavity. So I'd have to say they're right. It is harder to take in oxygen and breathe."
Alice H. Lichtenstein, director of the Cardiovascular Nutrition Lab at the USDA Human Nutrition Research Center at Tufts University in Boston also thinks this line of reasoning might have merit.
"It's true that there is a difference between men and women in body fat distribution," she says "And men tend to have more central obesity, so that could be the issue influencing what (the study researchers observed. But more research is needed."
"We had the idea that severely obese men and women would both have muscle and endurance capacities above normal, because they're carrying a lot of weight around all day," says Dubois. "But this was only true among women. The men really underperformed."