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Which is more important for weight loss - diet or exercise?

By Kellyn Jason

The prevalence of obesity across the nation continues to rise and create a major strain on the health care system in the United States, impacting both children and adults. As of 2015-2016, the crude prevalence of obesity in U.S. adults was 39.8% and for U.S. youth, 18.5% with a significantly increasing trend observed (Hales, Caroll, Fryar, & Ogden, 2017). As of 2020, according to the CDC’s Behavioral Risk Factor Surveillance System Survey, 31.9% of the US population fall into the obese BMI category and 35.2% into the overweight BMI category ((CDC), 2020). Health risks associated with obesity are serious, including increased likelihood of cardiovascular disease and diabetes among other negative adverse effects. With just over half of the nation either overweight or obese, efficient, and cost-effective weight reduction methods are necessary. Though there are many methods to weight reduction, diet and exercise remain important steps for obese individuals. There has been a lot of conversation surrounding the effectiveness of the two, questioning which is more effective – diet or exercise.

Nutritional intake is a key component of weight regulation in humans. It relates to the energy balance that we rely on, energy intake and energy expenditure. If an individual consumes more calories than they use, that energy needs to be stored. Adversely, if an individual reduces calories and increases energy output by about 500 kcal per day, generally, they should lose 1-2 pounds per week (Wadden & Bray, 2018). In a review of 36 trials of various diets, all were associated with significant weight loss at 12 months. This led the researchers to conclude that any of the dietary interventions studied, which included low carb high fat, macronutrient moderation and high fat low carb diets, were superior when compared to the usual diet in weight, BMI, and waist circumference loss (Jabbour, et al., 2022). Researchers can conclude that reducing energy intake can result in weight loss with relatively immediate results.

In a review of 48 randomized control trials, researchers observed that low carbohydrate diets and low-fat diets resulted in slightly higher weight loss than other diets (Johnston, et al., 2014). Though, in a study of 36 randomized control trials, all agreed that a reduction in total caloric intake was necessary for success, especially within the first 12 months of the diet, noting that after 12 months, either plateau or drop off is likely to occur (Jabbour, et al., 2022). Many clinicians recommend a multi-disciplinary model in which a low-calorie diet and change in eating habits, increased physical activity and exercise as well as behavior modifications take place. This has been shown to have slightly higher success long-term than just focusing on reducing energy intake or increasing energy expenditure alone. Ultimately, it seems that an increase in physical activity long term is the best weight loss maintenance assurance, though it is challenging to get individuals to adhere to this, and a reduction in energy intake is best for initial and relatively immediate weight loss results (Flore, et al., 2022).

When looking at physical activity alone as a means of weight loss, a large amount of time ad high intensity would be necessary to create a clinically significant change in weight (Swift, et al., 2018). Typically, and exercise bout only burns 200-300 calories. An obese individual has a higher amount of lean muscle mass than an average individual, which works in their favor, though as they lose, they will need to continuously increase their exercise intensity or time. . Additionally, many question the higher calorie expenditure hours after a bout of exercise, known as excess post-exercise oxygen consumption, though again, a high level of effort is necessary to get to a point where this expends a significant number of calories (Zelasko, 1995). Exercise is helpful in the metabolic health long term, and it is recommended to exercise most days (Burfoot, 2015). In a six-month randomized control trial, participants loss less weight than anticipated. This compensation was primarily a result of increased energy intake, and those who did compensate typically were more likely to meet the criteria for metabolic syndrome (Martin, et al., 2019). With this, it seems exercise is a key component of the long-term maintenance of weight loss but may not play as significant of a role initially in the weight loss journey as energy intake does.

The energy flux is a long-standing theory that takes into account the history of humans and how a sedentary lifestyle has only occurred in the recent past. Humans need exercise and to move a certain amount each day. If humans can get that exercise, the body will then find the right balance of energy intake and expenditure which has been observed as being more successful long term than diets. The failure rate of diets alone is a whopping 80-90%. The Framingham Heart Study, a study that observed participants over seventeen years, found that the energy consumption of individuals increased by only 10 calories, despite an increase in BMI, which supports the idea of focusing on the energy expenditure would result in weight loss (Burfoot, 2015). If making adjustments to exercise long term will even out the energy intake aspect, one can conclude that this method of weight loss would take longer to accomplish, though would ultimately be more successful longer term.

When looking at weight loss methods, one must consider the time frame of review – nutrition has been demonstrated to be successful in weight loss short term. Without the collaboration of exercise, though, diet is not successful in weight reduction as most regain the weight lost without consistent exercise. Ultimately, in order to deem successful, it’s important to look at the period that the individual is able to either continue losing or maintain the loss that occurred. Therefore, behavioral changes should occur in addition to diet and exercise interventions. Additionally, a program that an individual can stick to, is one that should be deemed successful, and a calorie reduction and more movement should be included. Higher end moderate intensity exercise is the most effective in relation to calorie expenditure, but for an overweight or obese individual, may deter the necessary frequency (Zelasko, 1995).

In a study that looked at contestants of an extreme weight loss show, the long-term habits of diet and exercise were analyzed. They performed DEXA scans and doubly labeled water for measure assessments. During the show, energy intake had a significant correlation to weight change at weeks six and thirty. At a six-year follow-up appointment, the significant correlation between energy intake and weight loss remained, but physical activity was also significantly correlated. The individuals that regained weight, did not have the same level of physical activity, though energy intake was consistent with the group that maintained weight loss. This highlights the benefits of using both diet and exercise as a means to weight loss and maintenance (Kerns, et al., 2017). It also highlights the fact that in order to lose weight and maintain the weight loss, both diet and exercise need to be considered, as this was the key difference between the participants that maintained their loss and the participants that gained back the weight initially lost. Further highlighting the fact that focusing on energy intake and expenditure together seem to be the most effective means of successful and long-term weight loss.

The obesity pandemic continues to surge and create a major strain on the healthcare system in the United States and the health risks associated with obesity are serious and life-threatening. Increased likelihood of diabetes, cardiovascular disease and ultimately all-cause mortality are associated with obesity. Efficient and cost-effective treatment options in weight reduction are necessary. According to the BRFFS as of 2020, 31.9% of the US population fall into the obese BMI category and 35.2% in the overweight category– with well over half of the nation either overweight or obese. Both nutritional habits and exercise are inexpensive and effective ways to reduce weight. Energy intake can promote quick weight loss progress, though adherence after 12 months can be an issue. Exercise has been shown to assist with the maintenance of weight loss long term, as well as promote positive metabolic change.

Therefore, both energy intake and energy expenditure are key components of weight loss and the maintenance of weight loss.

I believe the conversation around diet versus exercise should shift. Research demonstrates how both play an important role in weight loss and the maintenance of weight loss. Therefore, clinicians should continue to promote the two, looking to support patients with whatever progress they are able to maintain, and continue to build on that. It is evident that the issue with both physical and nutritional interventions is the adherence to them, so clinicians should focus on building onto progress that has already been made. Consistency should be addressed first and foremost. Then, with exercise, duration, intensity, and frequency can be built up further (Zelasko, 1995). When we look at our history, humans had a much higher non-exercise activity thermogenesis and only in the last couple of hundred years have we become as sedentary as we have. This is supported by the rising obesity prevalence despite interventions being introduced. Therefore, in order to truly make change, we need to continue to promote more movement and healthier food options. This will assist in the reduction of obesity throughout the nation.

Let's chat more about this article in your next session! There is lots of really great information in here that we can relate to your specific goals!


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Flore, G., Preti, A., Carta, M. G., Deledda, A., Fosci, M., Nardi, A. E., . . . Velluzzi, F. (2022). Weight Maintenance after Dietary Weight Loss: Systemic Review and Meta-Analysis on the Effectiveness of Behavioural Intensive Intervention. Nutrients, 1-17.

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Martin, C. K., Johnson, W. D., Myers, C. A., Apolzan, J. W., Earnest, C. P., Thomas, D. M., . . . Church, T. S. (2019). Effect of different doses of supervised exercise opn food intake, metabolism, and non-exercise physical activity: The E-MECHANIC randomized controlled trial. The American Journal of Clinical Nutrition, 583-592.

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Zelasko, C. J. (1995). Exercise for weight loss: What are the facts? Journal of the American Dietetic Association, 1414-1417.

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