Diet and Exercise vs. Dieting Alone

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Diet and Exercise vs. Dieting Along

Conventional wisdom is typically that excessive food intake is the primary cause of obesity. Due to this commonly accepted notion, most people believe that the only way to reduce unwanted body fat is caloric restriction through dieting. However, the best approach is a combination of diet and exercise. Learn Why.

While it is true that caloric restriction generates short-term weight loss, typically one- to two-thirds of lost weight returns within 1 year, and almost all lost weight returns with 5 years!1-3 More often than not, all your hard work and sacrifice go for naught, and you actually end up worse off for the effort.

Why the discouraging but highly typical failures of long-term weight control through caloric restriction alone?

Caloric restriction, especially severe caloric restriction, decreases resting metabolism.4,5 Pursuing caloric restriction without exercise causes a loss in lean body mass (muscle mass) as well as fat. Typically, larger caloric restriction produces greater loss in muscle mass.

Weight Loss Equation

The amount of lean body mass is directly related to resting metabolism – a decrease in lean body mass results in a decrease in resting metabolism. Therefore, dieting reduces metabolism causing the diet to become progressively less effective. This produces a frustrating weight loss plateau. Further weight loss occurs at a slower pace than predicted by the mathematics of the restricted energy intake.

Dieting + Exercise: The Ideal Combination

As discussed above, the greatest threat to long-term weight loss success comes from loss of lean body mass and the resulting decrease in resting metabolism. So, the next question is how can you preserve your lean body mass while dieting?

Both aerobic exercise and resistance exercise protect against the loss of lean body mass that occurs with weight loss by diet alone (resistance exercise more so than aerobic exercise). Resistance exercise during weight loss induced by caloric restriction typically results in better maintenance of lean body mass than aerobic exercise. Therefore, resistance exercise is preferable for maintaining lean body mass. However, aerobic exercise typically burns more calories during exercise, which makes achieving a caloric deficit easier. Additionally, aerobic exercise improves many cardiovascular risk factors better than resistance exercise. Therefore, the ideal exercise regimen during any period of restricted caloric intake should incorporate both aerobic and resistance exercise.

Although severe caloric restriction may still cause a loss in lean body mass, the loss will be significantly decreased if exercise is regularly incorporated. By conserving lean body mass with exercise training, your resting metabolism will stay higher than it would with dieting alone. Maintaining a high resting metabolism also counteracts the age-related increase in adiposity.6,7

The Conclusion: Any successful long-term weight loss solution should incorporate both caloric restriction and regular exercise with both aerobic and resistance training. 

The following sections provide more detail on beginning an exercise regimen. For more information on dieting guidelines, check out Dieting Guidelines: An Introduction.

1. Jeffery RW, Drewnowski A, Epstein LH, et al. Long-term maintenance of weight loss: current status. Health Psychol. Jan 2000; 19 (1 Suppl): 5-16.
2. Miller WC. How effective are traditional dietary and exercise interventions for weight loss? Med Sci Sports Exerc. Aug 1999; 31 (8): 1129-1134.
3. Long-term pharmacotherapy on the management of obesity. JAMA. 1996; 276: 1907.
4. Molé PA, Stern JS, Schultz CL, Bernauer EM, Holcomb BJ. Exercise reverses depressed metabolic rate produced by severe caloric restriction. Med Sci Sports Exerc. Feb 1989; 21 (1): 29-33.
5. Weyer C, Walford RL, Harper IT, et al. Energy metabolism after 2 y of energy restriction: the biosphere 2 experiment. Am J Clin Nutr. Oct 2000; 72 (4): 946-953.
6. Despres J-P. Physical activity and adipose tissue. In: Bouchard C, ed. Physical activity, fitness, and health. Champaign, IL: Human Kinetics; 1994.
7. Dolezal BA, Potteiger JA. Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals. J Appl Physiol. Aug 1998; 85 (2): 695-700.