I have clients that are dieters, and I have clients that are exercisers. The exercisers far outnumber the dieters. This group of clients (and people, in general) tend to rely heavily on long exercise sessions to make up for an imperfect nutrition.  Looking at the numbers alone, this is a bad strategy.
According to The Observer magazine;
“More and more research in both the UK and the US is emerging to show that exercise has a negligible impact on weight loss. That tri-weekly commitment to aerobics class? Almost worthless, as far as fitting into your bikini is concerned. The Mayo Clinic, a not-for-profit medical research establishment in the US, reports that, in general, studies “have demonstrated no or modest weight loss with exercise alone” and that “an exercise regimen… is unlikely to result in short-term weight loss beyond what is achieved with dietary change.”
Why is this so?
First and foremost, losing weight is about putting yourself in a calorie deficit below what it takes to maintain your body. This means, if it takes 2100 calories to maintain your current body weight, then you won’t realize any weight loss unless you eat less than 2100.
Performing physical activity will raise this maintenance number, modestly. For example, running at 5 MPH for 30 minutes will burn 288 calories (for a 150 pound woman).
That means your new maintenance number would be 2388.
When planning on weight loss, you have to keep in mind that it takes a 3500 calorie deficit per week to lose ONE pound of bodyfat. That’s 500 calories per day. So, with the running giving you 2388 maintenance calories, you still have to be at about 1900 calories per day to lose ONE POUND per week.
Conversely, 288 calories can be consumed in much less than 30 minutes with far less work. One BIG MAC hamburger is 560 calories, one small donut is 300 calories. Even healthy foods, like an avocado, pack a punch at 270 calories.
It takes time and effort to burn of a negligible amount of calories through exercise, and it takes SECONDS to blow a whole session of cardio on a snack.
This is in NO WAY saying that cardiovascular work should be avoided when losing weight. Studies have shown that people who lose substantial amounts of weight keep it off by performing a structured cardio routine, and the benefits of exercise and cardio go WELL beyond calorie burning.
The point is, if your intention is to lose weight, understand the role that exercise will play in directly impacting the number on the scale. It’s small. It should be part of your program, but the main contributor to your weight loss will be your diet. Exercise because it brings so many other health benefits.
When trying to lose weight, never try to out exercise your diet, the diet will win every time.
Matt Pirtle MA CSCS
Emerge Fitness Training