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How Much Should I Exercise To Lose Weight And Fat Mass?

December 9, 2020


The CDC estimates that 2 out of every 3 American adults are either overweight or obese. These added pounds carry significant health risks to the individual including higher rates of disease, including COVID, and early death. The main strategy for weight loss involves creating a caloric or energy deficit each day through increased exercise and/or decreased caloric intake. Unfortunately, maintaining this deficit is challenging and our bodies resist changes to our current weight or set point.

One of the main strategies our bodies use to resist weight loss from exercise is called energy compensation. In short, our body reduces energy expenditures outside of exercise or lowers our metabolic rate, as well as, increases caloric intake to compensate for the caloric burn of a new exercise. This evolutionary mechanism helps maintain our body’s set point or weight. Energy compensation can be up to 50% of the calories burned during a bout of exercise. For example, a walk that produces a 300 calorie burn may cause the body to adjust its metabolic rate so half of this deficit is actually realized. In part, this explains the added benefits of combining an exercise program with less calories for long term weight loss success. A recent well designed research article details how much exercise may be needed to work around our body’s compensatory energy strategies.

Flack and colleagues in the journal Medicine and Science in Sports and Exercise reported on the effects of different exercise durations each week on weight loss (2020). Authors randomized 52 adults into one of three groups over 12 weeks including

  • Sedentary or control group

  • Two days a week of aerobic exercise for 90-120 minutes in zone 1

  • Six days a week of aerobic exercise for 40-60 minutes in zone 1

Researchers collected pre and post study data on fat free mass and metabolic blood markers, as well as, weekly estimated caloric expenditure. As expected, the 6 day a week group burned more calories (2754 vs. 1491) and exercised for more minutes per week (321 vs. 1889) than the 2 day a week group. Interestingly, the two exercise groups did not differ on their body’s energy compensatory strategy thus the longer duration group obtained a greater caloric deficit each week. This deficit created greater decreases in fat mass and weight compared to the twice a week group. Authors concluded approximately 300 minutes per week are needed to overcome the body’s compensatory strategies and create significant fat loss.

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