In 2005, with the publication of my book, The Fat Burning Bible (John Wiley & sons), I called for at least 300 minutes of weekly exercise to reduce excess scale weight and body fat. That’s in spite of current recommendations, which states that exercise programs should exceed 225 weekly minutes to induce clinically significant weight loss.
Now, my recommendation has found merit with research –”Exercise for Weight Loss: Further Evaluating Energy Compensation with Exercise” – which appeared in the November 2020 issue of Medicine & Science in Sports & Exercise.
The University of Kentucky study authors suggest that it will take in excess of 300 minute per week of exercise to overcome the approximate 1000 calories per week compensatory response that accompanies exercise.
“The lack of weight loss success with exercise is due to compensatory responses counteracting the negative energy balance created by exercise to maintain homeostasis, thereby alleviating the energy deficit required for weight loss.”
Maintaining energy balance, note the researchers, “can be viewed, as an evolutionarily conserved mechanism in place to retain bodily energy stores and reproductive function, a useful survival strategy in times of famine.”
Several reasons for the post-exercise compensation effect include an increased food intake stimulated by a need to have calories in to exceed calories expended, and hormone regulators – acylated ghrelin, peptide YY, insulin, leptin (after eating or fasting) – that regulate hunger.
Of specific note, are ghrelin – the hunger hormone produced by cells of the gastrointestinal tract – specifically the stomach, which increases food intake (stomach growl) and leptin – a hormone secreted by fat cells and enterocytes in the small intestine that regulate energy balance and inhibits hunger.
It appears that obese individuals can experience leptin resistance – a situation that makes them non-responsive to the fullness effect or satiety after food consumption.
To back up their exercise duration recommendations, the study authors employed a three-arm, randomized, controlled trial among sedentary adults between the ages of 18 to 40 – with a body mass index of 25 (overweight) to 35 (obese) to assess how individuals compensate for energy expended during a 12-wk aerobic exercise intervention – explaining the potential mechanisms and the role exercise dose plays in the compensatory response.
The 44 final study participants (32 women) were assessed, after a medical history, physical, and diet and exercise history, along with other relevant tests – as to their rate of exercise energy expenditure, which was calculated from a graded exercise test averaged across five heart rate (HR) zones – zone 1, 50-59% of heart rate reserve (HRR), zone 2, 60-69%, zone 3, 70-79%, zone 4, 80-89% and zone 5, 90% or greater. The heart rate zones were calculated – based on the Karvonen formula, (220-age) – resting heart rate (RHR) x a high and low zone percent + resting heart rate.
The energy compensation effect was calculated, as the difference between expected weight loss (based on exercise energy expenditure) and changes in fat and fat-free mass (DXA Scan).
Resting energy expenditure (REE) was assessed via indirect calorimetry, while concentrations of acylated ghrelin, leptin, insulin, and glucagon-like peptide 1 (GLP-1) were assessed fasting and postprandial (six timepoints over 2 hours.)
The exercise program consisted of a control group, who were asked to stay sedentary, while being offered exercise intervention, after the 12-week post-testing period; a 2-day per week exercise group, who performed exercise sessions between 90 to 120 minutes at a self-selected intensity (at minimum in HR zone 1); and a 6-day per week group, who trained between 40 to 60 minutes per session – with the same intensity qualifications, as the 2-day group.
All participants used the Polar A-300 HR monitor and the Polar Flow software, allowing for monitoring and compliance – which had to be 90% to stay in the study over the 12-week intervention.
The study, “demonstrates individuals do not increase their energy compensation with greater doses of exercise. This lack of significant compensation was observed as neither CI (energy compensation proportional to energy expended) or total energy compensated differed between groups. Rather, the greater dose of the 6-day per week group was needed to produce appreciable fat loss with exercise.”
Additionally, “reductions in postprandial (after meal) leptin concentrations influence energy compensation, when controlling for all relevant exercise dose variables. This supports what has only recently been observed in rodents, that reducing leptin concentrations can restore leptin sensitivity in hypothalamic neurons and reduce food intake.”
It also appears that, “reductions in postprandial ghrelin concentrations are an important predictor of body fat loss, regardless of exercise dose.”
In short, more frequent exercise equaling 300 minute per week in HR zones 3 to 5 may account for a more favorable scale weight and fat loss in light of the exercise compensation effect.