It's estimated that $4 billion is spent a year in the pursuit of weight loss, yet the epidemic is continuing to grow. Americans are consuming more calories than ever before, but certainly aren't compensating with increased physical activity.

The prevalence of fast food outlets, vending machines, the huge increase in portion sizes at restaurants and the many hours spent in front of a computer and watching television are all contributing to the obesity epidemic.

Genetics
At the turn of the 20th century, an estimated 10 percent of the population was overweight. By 1960, about 24 percent of the adult population was overweight. Today more than 33 percent of adults are overweight. It is, therefore, unlikely that genetics cause obesity.

Genetics are theorized to predispose certain individuals to weight gain when challenged by a positive energy balance. However, genetics don't cause weight gain or prevent weight loss. A positive or negative energy balance is the ultimate cause of weight gain or loss.

The importance of exercise in fat loss and especially in weight maintenance cannot be stressed enough. Sedentary individuals may burn only a few hundred calories over their resting energy expenditure. For the average Joe, this may be about 2,000 calories a day. On the other hand, top athletes like ultra endurance cyclist Lance Armstrong, may burn up to 8,000 calories on an average training day.

Diet or Exercise... or Diet AND Exercise?
Inactivity is one of the major causes of weight gain. With no exercise, individuals are destined to lose muscle and gain fat with age. When looking at subjects who just engage in cardio without dieting, they can expect to lose fat but have little to no effect on muscle.

Those who only strength train with no dietary changes have little effect on their scale weight, but increase lean muscle. Those who just diet without exercising can expect to lose fat and lose muscle. The good news is that those who diet and exercise can expect to lose fat and gain muscle. At one year follow-ups, diet plus exercise groups tended to be the superior program for sustained weight maintenance.

Low-fat to moderate-fat eating is of importance if exercise is to have an optimal impact on fat stores. Cardio helps promote a negative caloric balance. Strength training can benefit dieters by preserving lean mass and a high metabolic rate, creating a negative caloric balance.

Aerobic exercise does not preserve metabolic rate when combined with a very low calorie diet. Strength training results in preservation of muscle and weight loss when combined with a very low calorie diet.

Overall, the results of available studies suggest a weight loss/fat loss benefit of combining diet and exercise. Resistance exercise is encouraged as it generally increases or at least prevents loss of fat-free mass, which it is a major determinant of metabolic rate.

There are no short cuts to weight loss. Muscle gain, fat loss and weight maintenance are all possible through a combination of strength, cardio and diet. There is no magic ratio of carbs, protein and fat for optimal weight loss. Recent evidence suggests that the traditional recommendation of a high carbohydrate low fat diet may not be the best choice for everyone.

Proper food choices, serving sizes and a long-term commitment to incorporating exercise and healthy eating into your lifestyle are still the best guidelines to follow. Falling prey to the newest fad diet book and weight loss supplement claim -- or using prescription drugs for weight loss instead of choosing exercise and a healthy diet -- will potentially increase your risk of disease, cause frustrating and potentially harmful fluctuations in weight and postpone your journey to optimal health.