How to Lose Weight With 45 Minutes of Cardio

A gym membership might seem exactly what you need when you want to lose weight. While exercise has a place in a weight-loss regimen, rarely does exercise alone promote or sustain weight loss. Forty-five minutes of exercise per day is a good start, but you'll also need to amend your eating habits and lifestyle to make significant body changes.

A group of people in a spin class. (Image: jean-marie guyon/iStock/Getty Images)

Mechanisms of Weight Loss

The process of losing weight is whittled down to the simple equation of consuming fewer calories than you burn. In theory, a weekly deficit of 3,500 calories yields a pound of weight loss; so in theory if you burn 500 calories in each of your 45-minute exercise sessions, you should lose about 4 pounds per month. This doesn't always manifest in reality, however. In a 2011 issue of the "Journal of Obesity," Stephen A. Boutcher, who resides on the faculty of medicine at the University of New South Wales, points out that steady-state aerobic exercise has a negligible effect on body composition.

The Dilemma

To burn 3,500 calories to lose a pound a week, you must engage in high-intensity activity for 45 minutes every day -- Sunday through Saturday. For example, a person who weighs 155 pounds can burn around 500 calories during a 45-minute vigorous step aerobics class, a 5.2-mph run or a 15-mph bike ride. Beginners, though, may not be able to work hard enough in a session to burn the 500 calories due to their fitness level. And, if you keep up this intensity seven days per week, weeks on end -- you'll eventually burn out or get injured. Even if you could keep up this intensity every day, you still have to keep your calorie intake in check. Burning 500 calories per day does you no good if you're eating an extra 500 calories, because you are negating the calorie deficit. Exercise increases your appetite, so you may not even realize you're sneaking in the extra food.

Realistic Goals

Instead of overdoing it day in and day out to burn these calories, plan on more moderate intensity workouts. They may burn fewer calories and result in a weight loss of slightly less than a pound per week -- or about 2 to 3 pounds per month -- but they'll be more sustainable for the long term. Aim for a weekly routine that combines cardio and strength training. The cardio helps you burn calories relatively quickly and the strength training builds lean muscle mass, which may help enhance your metabolic rate, meaning you burn slightly more calories all day long.

A Plan

A total-body routine that addresses all the major muscles of the body -- the hips, back, legs, chest, arms, shoulders and abs -- takes just 20 to 30 minutes when you do only one set of eight to 12 repetitions with weight that feels heavy. Add another set or two of each exercise and you'll fill up the whole 45 minutes. You should allow at least 48 hours between strength-training sessions for recovery, so do only two to three of these per week to burn about 168 calories per workout.

On days you don't do strength training, your most effective cardio activity for weight loss involves high-intensity intervals, maintains Boutcher. This approach, which involves all-out efforts lasting 6 seconds to 4 minutes with equal amounts of recovery, significantly lowers insulin resistance and makes your body more efficient at burning fat calories. You can burn between 300 and 500 calories for each of these sessions, depending on your intensity, number of intervals and size. Allow yourself a day of rest from intense exercise weekly so you don't burn out or become injured. Larger people do burn more calories and may find the weight comes off more quickly at first.

Lifestyle Amendments

Consider lifestyle changes that make exercise and weight loss easier. These changes will also help you maintain your new weight. Sleep seven to nine hours per night so you have energy to hit the gym. Inadequate sleep also causes your body to release hunger-stimulating hormones so you have a harder time controlling your appetite. Keep stress to a minimum so you are less tempted to eat for comfort and produce the hormone cortisol, which encourages weight gain.