The Role of Aerobic Exercise and Diet in Weight Loss

A new study reviewed the research to find the best ways to lose weight and keep it off.

When it comes to losing weight, there is often a difference between what clients expect and what a trainer wants them to do. Many clients believe you need more exercise, whereas coaches often believe diet yields the greatest improvements. In a recent study published in PLoS ONE, researchers reviewed the literature to find the truth.

What the research says:

  • Aerobic exercise alone caused significant weight loss.
  • A combination of diet and exercise had best results for weight loss and related health factors.

Study Design

The research team examined past literature on the effects of diet and exercise on long-term weight loss. The studies they looked at had to be peer-reviewed. The research was also required to cover either an active weight-loss period of six months (although many were a year long) or a shorter weight-loss period with a longer follow up (most lasting two years in total).

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There were twenty studies total that fit the requirements noted above. Here’s a summary of some of the important findings:

  • Exercise and Weight Loss: The researchers found that clinically significant weight loss can be achieved through aerobic exercise alone. However, there was a greater amount of weight lost in the programs that used diet alone. Not surprisingly, diet and exercise together were the best option.

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  • Health Factors: One of the reviewed studies compared diet to exercise in terms of disease risk factors, and there were no apparent differences between the two plans. Similar to the weight-loss results, there was a greater magnitude of good health outcomes, such as better cholesterol scores and blood pressure, when diet and exercise were combined.
  • Weight Maintenance: None of the plans resulted in great maintenance of the new bodyweight once the weight-loss period was over. When the participants stopped dieting, they couldn’t keep the weight off.


The advice from this study is to promote diet over exercise for weight loss and to do both together for optimal results. As the researchers noted, the combination of diet and exercise has more benefit, both for weight loss and other related health effects:

The present systematic review found limited evidence to suggest better long-term weight loss and more favorable long-term changes in body composition and chronic disease risk factors when diet is combined with aerobic exercise compared with either diet or aerobic exercise alone.

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The researchers also emphasized that there are variations for each individual. For example, if you already eat well and want to reduce fat just a little, it might actually be that more exercise, rather than fewer calories, is the way to go. If you struggle with weight maintenance, the only answer is consistency. Weight regain is a fact of life if you don’t stick to your plan.

The research team called for further studies to investigate the role of additional factors such as resistance training and supervised exercise programs.


1. Richard Washburn, et. al., “Does the Method of Weight Loss Effect Long-Term Changes in Weight, Body Composition or Chronic Disease Risk Factors in Overweight or Obese Adults? A Systematic Review,” PLoS ONE 2014, 9:10

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