Physical activity is key to keep the weight off after a fat loss process (the hard part is not losing weight, but keeping it off). In fact, physical activity and exercise can be the determining factors in keeping the weight off (even more than diet), because they help to maintain an adequate energy balance, which is practically impossible with diet alone at a certain point. And failure to lose weight in the long term is not so much due to metabolic adaptations (which is also the case) but to not maintaining high levels of physical activity. High energy flow is synonymous with success, but low energy flow is synonymous with failure.
A study from the University of Colorado shows that physical activity is more effective in maintaining weight loss than dieting. Study shows that those who SUCCESSFULLY maintain weight after a period of fat loss (over a year) rely on physical activity to keep them in energy balance (rather than chronic restriction in dietary intake).
The total calories “burned” (and consumed) each day by those who maintained their lost weight were significantly higher (300 kcal/day) than those who regained weight. Despite the higher energy cost of moving a larger body mass as occurs in overweight/obese people, those who maintained the lost weight were burning more energy due to elevated physical activity.
This group demonstrated significantly higher levels of steps per day (12,000 steps/day) compared to participants with normal body weight (9,000 steps/day) and overweight/obese participants (6,500 steps/day).
Textually from the authors, “Our findings suggested that the group that maintained weight loss was consuming a similar amount of calories as people with obesity , but avoided weight regain by compensating for this through high levels of physical activity.”
It’s absurd to see whether diet or exercise matters more (both are 100%), but keeping physical activity elevated is key to not regaining lost weight.