The harmful effects of obesity on the heart can't be undone by exercise, and it's not possible to be "fat but healthy," Spanish researchers warn.

"Exercise does not seem to compensate for the negative effects of excess weight," said study author Alejandro Lucia, a professor of exercise physiology at European University in Madrid.

The study findings "refute the notion that a physically active lifestyle can completely negate the deleterious effects of overweight and obesity," he said.

Lucia and his colleagues analyzed data from nearly 528,000 working adults in Spain. The participants' average age was 42 and close to 7 out of 10 were men.

About 42% of these adults were normal weight; 41% were overweight, and 18% were obese. Most were inactive (63.5%); 12.3% got some but not enough exercise, and 24.2% were regularly active.

About 30% of participants had high cholesterol, 15% had high blood pressure, and 3% had diabetes.

No matter how active they were, however, overweight and obese people had a higher risk of heart disease than those whose weight was normal, according to the study, published Jan. 22 in the European Journal of Preventive Cardiology.

Compared to active people of normal weight, active obese people were about twice as likely to have high cholesterol, four times more likely to have diabetes, and five times more likely to have high blood pressure.

"One cannot be 'fat but healthy,'" Lucia warned in a journal news release.

But the researchers did not disregard the importance of exercise. In all weight categories, any physical activity was associated with a lower risk of diabetes, high blood pressure or high cholesterol, according to the findings. And the risk of diabetes and high blood pressure fell as physical activity rose.

"This tells us that everyone, irrespective of their body weight, should be physically active to safeguard their health," Lucia said.

"More activity is better, so walking 30 minutes per day is better than walking 15 minutes a day," he noted.

Lucia said it's equally important to fight obesity and inactivity. "Weight loss should remain a primary target for health policies together with promoting active lifestyles," he concluded.