Exercise won’t fix bad diet (see Myths), but it can certainly enhance good diet. I have a lot of practical experience with some forms of exercise; running, cycling, and Jazzercise, not to be confused with Prancercise. Except for when I started Jazzercise I didn’t do those activities to lose weight or stay in shape, I do them for their own sakes. That said, I originally started running to lose weight in graduate school. I found out it was the first athletic activity I was any good at, then got interested in the running for its own sake. Since then I’ve done a variety of road and trail runs, up to 100 miles on a couple of occasions. I started cycling shortly after turning 50 when my running had deteriorated and my knees were hurting. The cycling helped heal up the knees; the running is still too slow, but more fun without sore knees. Actually, lately I’ve pretty much given up on actual running, just fast walking when I don’t use a bike. I’ve done a lot of road and mountain bike rides, up to a distance of 125 miles for the Death Ride (http://www.deathride.com). I started the Jazzercise in 2011 when a friend invited me to a class. I got 1/3 of the way through the class, and thought “this is silly, I can’t follow the moves.” Then at the end of class, I could touch my toes for the first time in awhile and had the best hour’s workout I could remember. I’ve since learned to follow the moves, more or less. So these days, I’m a slow but persistent and competent runner/walker, cyclist, and a persistent Jazzerciser. There’s a theme there.
Strenuous exercise trains your muscles, whether it’s resistance (weights, etc.) or endurance. Training changes the muscles, making them better at storing and processing energy sources sources, typically fats and glucose. Cross sectional area of the muscle can increase. More mitochondria, the intracellular energy factories, are created. Mitochondria are tiny “organelles” within the cells of your body. We think mitochondria are bacteria that started living inside larger single-celled organisms many millions of years ago. The bacteria and their hosts worked out a deal where the bacteria could stay if they did something useful. They decided to make ATP.
Energy from breaking down glucose and fats is used to make Adenosine Triphosphate (ATP) out of Adenosine Diphosphate (ADP). A little bit of ATP can be made in the muscle cell cytoplasm; glycolysis splits glucose into two pyruvate molecules and 2 ATPs. However, the big money ATP production is in the mitochondria. The pyruvate molecules go through the Krebs Cycle (also called the Citric Acid Cycle). That makes 28 to 36 more ATP depending on how it’s counted. Your muscles use ATP to contract, dropping it back to an ADP. See also Endurance Training in How To.
Where it gets interesting is that the Krebs Cycle can use fats as well as glucose. Even if you’re not ketone (fat) adapted, you may still be using mostly fat molecules for most of the energy of forward motion. Carbohydrate eating endurance athletes still train endurance by doing exercise bouts that teach their muscles to store and use more fat. Many years ago, I attended a lecture by a famous exercise physiologist, Dave Costill. Dr. Costill said that biopsies of the muscle cells of trained endurance athletes showed fat globules actually stored in the cells.
Exercise changes your body so you process sugars and fats better. Even at rest, trained muscles use more fuel than untrained muscles. However, if you eat a diet very high in carbs/sugars, especially if they digest quickly and elevate insulin, you may find that you just eat more and gain more weight. If you shift to a diet without sugars or easily digested carbohydrates, you’ll get more benefit from the exercise.
The most striking effects will occur if you shift to a low carb high fat diet combined with good exercise. In their book, the “Art and Science of Low Carbohydrate Performance” (See Sources), Jeff Volek and Steve Phinney, describe small scale studies they did combining diet with exercise. The subjects who ate the low carb high fat diets and exercised vigorously got the best results.
That matches what we’ve seen with the Tucson Trail Runners, who start out in good physical shape. TTR members who have shifted to low carb high fat diets lose some amount of body fat, 40 pounds in one case. I’ve dropped maybe 10 pounds. Why don’t you join our experimental group?