Brad posted this on the TI Discussion Forum
I know this is an old topic but I was shocked when my Primary Care Physician said that swimming was not very good for weight loss. I’ve had increasing back problems over the past year or so and have gained a few lbs but never stopped working out. Sometimes, swimming is all I can do but I’ve discovered that posture is my primary problem and my back has been great lately.
Still, I want to lose a few lbs so I’m doing mainly interval-style swimming. I still do some of my old weight training, but I’m no longer dead lifting 300+ lbs, etc. Instead I do mostly body weight exercise like chinups, pushups, bridges, etc along with swimming. I’ll be 55 in a couple of months so I’m focusing more on the long term . I haven’t forgotten diet but that’s always the hardest part! Btw, I’m 6’3" and about 215 but I’d like to get back down to 200.

Brad
I’m sure you’re aware that body weight isn’t the most reliable predictor of whether you’re at a "healthy" weight. Years of power lifting probably resulted in a musculature at which 215 lbs may be "lean" at 6-3. Still, reducing your weight to 200 will probably be helpful – toward back health – by reducing spinal compression.In that case, losing body weight probably means losing muscle mass – mostly in the "prime mover" muscles that power-lifting targets.

The muscles that contribute the most to a healthy, pain-free, back are spinal stabilizers and abs. Swimming — at least with the balance, alignment and fluency that TI teaches — will always help keep those muscles in good working order.
So, it seems to me that your PCP is addressing the wrong question. Your expressed goal is a healthy back. Swimming is certainly helping you achieve that – aided by the chin-ups, bridges etc, which you could augment with yoga or pilates. If your current body weight remains higher than you’d like — because of "legacy musculature" from years of weight training — replacing such training with swimming would unquestionably also move you toward the goal.

The question of how swimming compares with running and other land activity for weight loss and fat reduction is a wholly different discussion. And on this your PCP’s opinion reflects a common misapprehension. Reputable research has shown that when people swim with equivalent intensity to how they exercise on land, calorie consumption is equal. Studies that suggested otherwise had compared swimming at far lower intensity levels than the running with which it was compared . . . because the subjects in the study lacked the skill to sustain swimming at equivalent intensity levels as their running — which is a nearly-universal situation.

The value in pursuing weight loss through swimming is in being able to exercise with reduced impact — and spinal compression. Better skill will allow any swimmer to continue exercising long enough to gain health benefits. In that case someone interested in weight loss should benefit by swimming more, not less — at least if that added time is spent increasing skill rather than "practicing struggle." And your preference for interval training is particularly sound because it will keep your HR, and thus metabolism, higher, and make it easier to practice/maintain a higher efficiency level, than longer – most likely slower — swims.