Exercise vs Diet for Long-Term Weight Loss Success
“Eat less, move more.”
This is the advice typically given to those seeking the simplest method to lose weight and achieve a base level of health and wellness. For decades, researchers, fitness professionals, and casual gym goers have long known that both diet and exercise play a role in maintaining healthy body weight.
But recently, the focus has shifted more to learning which is more important, diet or exercise?
Related - The Best Workout for Weight Loss
It’s commonly believed that diet is the primary driver of weight loss, and that exercise plays a “supporting role.” Essentially, exercise is the Goose to diet’s Maverick.
Goose watches Maverick’s six and helps target the bogey, but in the end, it’s Maverick pulling the trigger and saving the day.
The main reason cited for why diet is the driving force behind weight loss is that calorie expenditure through exercise is relatively small in the grand scheme of things.
And, since we all have a limited amount of resources (time, money, energy, motivation, etc.) to dedicate to achieving our goals (which in this case is weight loss), it would make sense to focus the majority of our efforts on the factor that has the biggest impact on our energy balance, which for all but the elite athlete, is diet.
However, a new study finds that while diet may be the key factor for initially losing the weight, it is exercise that is the key to maintaining weight loss in the long run.
Researchers from the University of Colorado Anschutz Health and Wellness Center (AHWC) at the CU Anschutz Medical Campus recruited participants through campus-wide flyers and email announcement between October 2009 and August 2012. 
Individuals were excluded from the study if they had any physical or medical condition that limited their ability to perform regular physical activity, including:
- Cardiovascular disease
- Significant neurological, psychological, or musculoskeletal disorders
An individual could also be excluded from the study if they had weight loss surgery or were currently taking any medications for weight loss. Additionally, if they were not “weight stable”, meaning they had a fluctuation in body weight greater than 10 pounds in the preceding six months before enlisting in the study, they were not allowed to participate.
Finally, if an individual was a smoker, pregnant, lactating, or on any medications that affect their metabolism or appetite, they were excluded.
Once an individual was deemed a good fit for the study, they were divided into one of three groups:
- Weight-loss maintainers (BMI 24.1 ± 2.3 kg/m2 ; maintaining ~30 pounds weight loss for over 1 year)
- Normal weight control group (BMI 23 ± 2.0 kg/m2)
- Overweight or obese control (BMI 34.3 ± 4.8 kg/m2)
The reason for the two different control groups is that researchers were comparing energy expenditure between the weight-loss maintainers and those having a BMI similar to their pre and post weight loss.
To track total daily energy expenditure, researchers used the “gold standard” method of DLW -- doubly labeled water. Unlike other trackers which provide a close approximation of TDEE, doubly labeled water measures an individual's energy expenditure via urine sample collection over a period of 1-2 weeks after the individual has consumed a dose of doubly labeled water.
What is Doubly Labeled Water?
Basically, doubly labeled water is water that has its hydrogen and oxygen atoms replaced with two isotopes in 2H2 (deuterium) and 18O. 
These two isotopes equilibrate with an individual’s total body water and then they are eliminated differentially from the body.
Deuterium is excreted as water while the 18O isotope leaves as water and carbon dioxide leaves the body as water, while 18O leaves as water (H2O) and carbon dioxide (CO2). As a result, carbon dioxide production can be calculated by researchers and from that they can obtain an accurate measurement of both energy expenditure and energy intake.
This is important as previous studies measuring energy intake in weight-loss maintainers relied of self-reported food journals or questionnaires, which are well-known to be inaccurate measures of an individual's’ food intake in most cases as people tend to overestimate their energy expenditure and underestimate their food intake.
Researchers noted that weight-loss maintainers burned more calories each day (~300 more calories/day) in the form of physical activity energy expenditure than either control group. On average, weight-loss maintainers burned ~812 calories per day through physical activity, while normal weight control subjects burned an average of 621 and overweight/obese individuals expended an average of 637 calories through daily exercise.
As you would expect, weight-loss maintainers also had a greater total daily energy expenditure than individuals of normal body weight. However, there was not a significant difference in total daily energy expenditure between the weight-loss maintainers (2,495 ± 366 kcal/d) and the overweight/obese ones (2,573 ± 391 kcal/d).
This last point is especially noteworthy, as one would expect the overweight/obese subjects to have a significantly higher total daily energy expenditure than the weight-loss maintainers on account of the increased amount of energy it takes to move a larger body mass throughout the day as well as the fact that the weight loss maintainers consumed roughly the same number of calories per day as the overweight/obese control group. 
However, the fact that the weight-loss maintainers had a non-significantly different total daily energy expenditure from the overweight/obese group indicates they moved more throughout the day than the overweight/obese group, indicating a greater level of energy expended through physical activity.
And, when researchers checked the step counts of each group, their thought process was confirmed. Weight-loss maintainers took significantly more steps per day on average than either of the control groups. In a typical day, weight-loss maintainers took ~12,000 steps, while normal weight control members averaged 9,000 steps and overweight/obese individuals took 6,500 steps.
FYI, physical activity was tracked via activPAL activity monitor.
These findings are supported by a host of previous studies which found that high levels of physical activity are a hallmark characteristic in individuals who successfully maintain weight loss. [2,3,4,5,7,8]
Based on the findings of this stuff (and several others), it would appear that the key to successfully maintaining a significant amount of weight loss for the long-term ultimately depends on an individual’s ability to exercise regularly.
The reason for this is that while calorie restriction is needed to lose weight initially, most people cannot last for years on end eating a severely restricted calorie intake. Therefore, if you want to “have your cake and eat it too” (maintain weight loss and not survive on a paltry amount of calories), then you will need to exercise more.
One interesting point brought up in a commentary by Church and Martin published as a follow-up to the recent study noted:
“These findings beg the question, who are these individuals who can achieve large amounts of exercise on a consistent basis and what drives this behavior? Is their psychology or physiology different, or both? Does the energy flux or high amount of energy in and energy out affect their bodies in unique ways?
Achieving the activity level observed in the weight loss maintainers is a significant time commitment; therefore, it is logical to conclude that this group of people may have tremendous discipline or willpower (e.g., type A exercisers), or they are driven to exercise for reasons other than weight management and weight loss maintenance is essentially a by‐product of exercise.” 
Valid questions indeed, and hopefully future studies will investigate more into the psychology of the “type A exercisers.”
For now, realize that when it comes to weight loss, it’s not an either-or proposition. Both diet and exercise are needed to lose weight and keep it off in the long term.
What do you think of the study’s findings?
Do you feel that exercise is vital to maintaining weight loss over multiple years? If so, how much exercise is needed, and is it more critical to weight-loss maintenance than diet?
Leave a comment down below with your thoughts.
1) Ostendorf, D. M., Caldwell, A. E., Creasy, S. A., Pan, Z., Lyden, K., Bergouignan, A., Catenacci, V. A. (2019). Physical Activity Energy Expenditure and Total Daily Energy Expenditure in Successful Weight Loss Maintainers. Obesity (Silver Spring, Md.), 27(3), 496–504. https://doi.org/10.1002/oby.22373
2) Schoeller DA, Shay K, Kushner RF. How much physical activity is needed to minimize weight gain in previously obese women? Am J Clin Nutr 1997;66: 551-556.
3) Weinsier RL, Hunter GR, Desmond RA, Byrne NM, Zuckerman PA, Darnell BE. Free-living activity energy expenditure in women successful and unsuccessful at maintaining a normal body weight. Am J Clin Nutr 2002;75:499-504.
4) Jakicic JM, Winters C, Lang W, Wing RR. Effects of intermittent exercise and use of home exercise equipment on adherence, weight loss, and fitness in overweight women: a randomized trial. JAMA 1999;282:1554-1560.
5) Borg P, Kukkonen-Harjula K, Fogelholm M, Pasanen M. Effects of walking or resistance training on weight loss maintenance in obese, middle-aged men: a randomized trial. Int J Obes Relat Metab Disord 2002;26:676-683
6) Institute of Medicine (US) Committee on Military Nutrition Research; Carlson-Newberry SJ, Costello RB, editors. Emerging Technologies for Nutrition Research: Potential for Assessing Military Performance Capability. Washington (DC): National Academies Press (US); 1997. 12, Doubly Labeled Water for Energy Expenditure.Available from: https://www.ncbi.nlm.nih.gov/books/NBK233774/
7) Fogelholm M, Kukkonen-Harjula K. Does physical activity prevent weight gain–a systematic review. Obes Rev 2000;1:95-111.
8) Jakicic JM, Marcus BH, Gallagher KI, Napolitano M, Lang W. Effect of exercise duration and intensity on weight loss in overweight, sedentary women: a randomized trial. JAMA 2003;290:1323-1330.
9) Church, T. S. and Martin, C. K. (2019), Exercise is the Key to Keeping Weight Off, but What is the Key to Consistently Exercising?. Obesity, 27: 361-361. doi:10.1002/oby.22429