"Cardio kills," says Jim Karas in his new book, "The Cardio-Free Diet."
"Cardiovascular exercise kills a weight-loss plan, your internal organs, your immune system, your time and your motivation. If your true goal is to lose weight, interval strength training is the only way to go," says Karas, an ABC News correspondent, celebrity trainer and fitness expert.
When he first tried to lose weight as a 21-year-old, Karas found that he would work up an enormous appetite after running several miles. So while his cardiovascular health improved he still wasn't losing weight.
He grew more interested in strength training and started exercising with weights. In a short period of time he noticed changes in his body's composition. Gradually, experimenting on himself, he started doing more strength exercise and less cardio -- and his weight went down.
His experiment resulted in a cardio-free exercise program that includes two routines with 10 exercises. Every two weeks, after beginning with Phase 1, you add two exercises as you progress to the next phase, ultimately getting to Phase 4.
Most of the exercises require you to use many muscles at the same time, increasing the number of calories burned and maximizing the creation of new muscle tissue.
According to Karas, with his program you still get all three elements -- strength training, cardio and flexibility. He says people who engage in his program see an increase in their heart rate.
"It's really a three-for-one solution, when you look at exercise," says Karas.
Critics Call Karas' Program 'Dangerous'
Exercise physiologist Richard Weil is not convinced. "I'm flabbergasted, I'm astonished at what I'm reading. I genuinely believe he's deluding people and he's leading them to believe information that is really not factual. I believe that the book is dangerous."
Weil, director of the weight-loss program at the New York Obesity Research Center at St. Luke's-Roosevelt Hospital Center, says it's untrue to suggest that aerobic exercise is not effective or helpful.
"That it kills your weight-loss plan is just completely contradictory to the evidence. The evidence shows that people who keep their weight off are doing 30 minutes of walking or whatever it might be. Some are doing strength training, but the majority are not," says Weil.
"There's data to show that exercise improves joint strength. And people with arthritis have fewer symptoms and things like that. Your internal organs? Which internal organ is upset by exercising?" Weil asks.
"Your immune system -- moderate intensity -- you know, he uses the case and this is classic, the immune system, yes. Marathon runners and so forth have higher rates of respiratory infections. This is well known. That's their decision. In moderate intensity exercise, it is just the opposite. You see an increase in lymphocytes, an increase in T-cells, an increase in natural killer cells, which are implicated in cancer," Weil adds.
"All the public health officials have spent decades attempting to facilitate behavior change in people" and Karas will confuse them, says Weil.
Cardio-Obsessed, Obese Nation
But engaging in cardiovascular exercise is difficult for many overweight people, and if their goal is to lose weight, they often don't see results, says Karas.
"If you look at running, it's a 1970 solution to our 21st century problem. We are an obese country. Running has been the operative way in cardio that people have tried to lose weight. But the numbers show us, it's just not working," says Karas.
By doing his interval strength training program, he says, you are getting the cardiovascular benefit. "And any time we exercise," he says, "the No. 1 goal should be to maintain and increase your body's lean muscle."
Dr. Jennifer Mieres, a cardiologist and American Heart Association spokesperson, agrees. She thinks people should build and strengthen their muscles, especially women who face the possibility of developing osteoporosis.
"But the evidence is overwhelming," she says. "You need to do some cardio workout to change your cardiac profile to make it better, to prevent death from heart disease and stroke."
The idea of eliminating cardio exercise from your weekly regimen frightens Mieres. Although she does agree that Karas raises an interesting point when he says that we're a cardio-obsessed nation.
"Treadmills have skyrocketed in sales," she says, "yet we're still an obese nation. We have focused on cardio fitness and pretty much ignored strength training. This could be a wake-up call."
Still, she says, we need to do cardio fitness to prevent heart disease, the leading cause of death in the United States, according to the Center for Disease Control and Prevention.
"So before you can say cardio kills, or forget about the cardio, let's get the evidence," says Mieres. "Let's get some more clinical trials. Let's really do some research to investigate his technique before we can say it's available for the entire public."