Weight loss is supposedly simple math; if you expend more energy than you consume, you’ll lose weight. The equation doesn’t care much if you burn more, consume less, or combine both approaches. Unfortunately, the body doesn’t always perform as a simple equation, but rather a complex system which reacts in ways [sometimes] counter to your own goals. Numerous studies have looked into the results of weight loss without exercise and have come to interesting conclusions.
Weight Loss: Creating a calorie deficit
A calorie deficit is the magic behind weight loss. When you burn more than you consume, you create a deficit of energy. This calorie deficit forces the body to use fat stores for energy resulting in weight loss.
Conventional wisdom tells us one pound of body weight equates to a deficit of 3,500 calories spread over a period of time. In other words, if you create a deficit of 3,500 calories per week, you should lose one pound per week. The problem is the body does not like calorie deficits. Reducing energy consumption causes a decrease to energy expenditure in order to conserve energy.
As diets continue, one pound of body weight begins to “cost” way more than 3,500 calories leading to a slowing or complete stop to weight loss. A diet only approach to weight loss seems to exacerbaute this problem.
Study 1: This article was a meta-analysis which looked at 18 studies to compare the effects of diet-only vs. diet plus exercise strategies for weight loss. Of the 18 studies reviewed, 16 showed more weight loss when participants combined a diet and exercise strategy. This meta-analysis provides an overwhelming amount of data supporting the conclusion that a weight loss strategy of diet and exercise leads to more weight loss than diet alone1.
Study 2: This study examined the effects of three weight loss strategies (diet-only, exercise-only, and combination – both diet and exercise) of 127 men and women who were at least 31 pounds overweight. After one year, the diet-only group lost 15 pounds, the exercise-only group lost 6.4 pounds, and the combination group lost 20 pounds2.
During the second year, the diet-only group regained all of the weight they lost plus two pounds (gained a total of two pounds through the entire study). The exercise-only group regained 5.9 pounds (lost a total of 0.44 pounds). The combination group regained 4.9 pounds (with a total weight loss of 15.1 pounds)2.
Though the diet-only group lost a large amount of weight initially, they ended up gaining weight over the entire period while the other two groups saw a decrease. The exercise-only group’s decrease was small compared to the combination group’s total weight loss.
Study 3: This study looked at the effects of a weight loss strategy with and without exercise in a group of 35 overweight men. The participants were split into a diet-only group, a diet group that performed only aerobic exercise, and a diet group that performed aerobic exercise and strength training. After 12 weeks, the diet-only group lost 21 pounds, the diet and aerobic exercise group lost 20 pounds, and the diet and aerobic/strength group lost 22 pounds3.
Though the total weight lost was similar across the three groups, the type of weight lost was different. Of the 21 pounds the diet-only group lost, 69% was fat. Of the 20 pounds the diet and aerobic group lost, 78% was fat. Of the 22 pounds the diet and aerobic/strength group lost, 97% was fat. The diet-only group lost a significant amount of muscle mass over the course of the study3.
Does research show diet-only weight loss doesn’t work?
The research shows that while diet-only weight loss is feasibile, it is not efficient and the results are not desirable. Studies 2 and 3 showed that significant weight loss is possible with diet-only strategies. However, the results were less than optimal. In one of the studies, the diet-only group regained all of the weight (plus extra) and in the other study, the diet-only group lost a significant amount of muscle mass.
The Bottom Line
If you’re only losing weight to see the number on the scale go down (temporarily), research shows you may be able to achieve this through diet alone. If you’re losing weight in order to build a permanent, healthier lifestyle, improve physical appearance, and increase performance, a diet-only approach is ineffective. Besides the many health benefits exercise provides, a diet-only approach leads to temporary and less desirable results when compared to an approach combining diet, aerobic exercise, and strength training. Unfortunately, quality weight loss is not possible through diet alone.
1. Wu, T., & Gao, X. (2009). Long-term effectiveness of diet-plus-exercise interventions vs. diet-only interventions for weight loss: a meta-analysis [Abstract]. Obesity Reviews, 10(3), 313-323. doi:10.1111/j.1467-789x.2008.00547.x. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1467-789X.2008.00547.x/full
2. Skender, M. L., & Goodrick, G. (1996). Comparison of 2-Year Weight Loss Trends in Behavioral Treatments of Obesity. Journal of the American Dietetic Association, 96(4), 342-346. doi:10.1016/s0002-8223(96)00096-x. Retrieved from http://jandonline.org/article/S0002-8223(96)00096-X/fulltext
3. Kraemer, W. J., & Volek, J. S. (1999). Influence of exercise training on physiological and performance changes with weight loss in men [Abstract]. Medicine & Science in Sports & Exercise, 31(9), 1320-1329. doi:10.1097/00005768-199909000-00014. Retrieved from http://europepmc.org/abstract/med/10487375