It is a common misconception that if you're trying to lose weight, you should start with aerobic workouts and lose the fat first before adding weight training.
Obviously, weight training is the chief element in developing strength and muscle mass. We already know that. What few people realize is that weight training can also increase fat loss dramatically, although it occurs through an "indirect effect." Weight training is anaerobic and therefore burns carbohydrates (sugar). Cardiovascular exercises such as jogging, cycling, step classes, or stairclimbing are aerobic and therefore burn fat. So it seems logical to focus on aerobic training for fat loss. However, something interesting happens "beneath the surface" when you lift weights. Weight training increases your lean body mass - aerobic training does not. Low calorie dieting and aerobic training without weight lifting can make you lose muscle - in fact, it can actually make you fatter!
If you lose lean body mass, your metabolism slows down, and this makes it easier to gain fat. If you increase your lean body mass, you increase your metabolic rate. And the faster your metabolism is, the more fat you'll burn all day long - even while you're sleeping! This explains why bodybuilders, who have extremely high muscle to fat ratios, can stay lean year round without doing much aerobic work.
Losing body fat as quickly and efficiently as possible requires a three-pronged approach. You must pay equal attention to nutrition, aerobic training and weight training. All three ingredients are essential. If you neglect any one of these components, it will prevent you from reaching your goals, or at the very least it will compromise your results.
The most amazing thing about this fusion of weights, cardio and nutrition is that the effects of the three parts brought together are not linear, they are exponential! The synergy between them complements each other and magnifies the results. The result is an efficient metabolism and a lean, muscular body. Your metabolism is enhanced through the thermic effects of nutrition, it is elevated for several hours after every cardio session and it is also increased with every ounce of lean body mass you add.
In "The Seven Habits of Highly Effective People" Author Steven Covey wrote, "Synergy means that 1 + 1 may equal 8, 16, or even 1600. Synergy is everywhere in nature. If you plant two plants close together the roots commingle and improve the quality of the soil so that both plants will grow better than if they were separated. If you put two pieces of wood together they will hold much more than the total of the weight held by each separately. The whole is greater than the sum of its parts."
The best you can hope for from diet and aerobics alone is to become a "skinny fat person." You may lose weight from diet and aerobics, but much of it will be muscle, your fat to muscle ratio will plummet and you will take on a "soft" appearance. It is not uncommon for a woman 5 feet 4 inches tall to weigh 125 pounds and yet have 25-30% body fat. According to the Metropolitan Life height and weight tables, 125 pounds is ideal for a medium-framed 5' 4" female, but 25-30% body fat is extremely poor for anyone!
Without the weight training, you will never optimize your muscle to fat ratio and you will always struggle to keep fat off permanently. If you have extremely limited time, and your main priority is to lose fat, then you should do a brief weight training program and spend the majority of your time concentrating on cardiovascular exercise. But never neglect the weights completely - always do both, and if possible, devote an equal amount of time to each.
Last, but not least, don't forget that weight training, not cardiovascular training, is what shapes and sculpts your muscles. Simply put, lifting weights makes you look better! If you want a lean, hard, fat-free body, then get out of the aerobics studio, get off that bike or treadmill, and pick up some barbells and dumbbells! Lifting weights isn't just for "muscle-heads" anymore.