Most of the research suggests that the constrained energy expenditure model is what occurs. For example, with weight loss, basal metabolic rate decreases, lean mass decreases, NEAT level decreases, and hormone changes such as leptin result in fewer calories being burned over a day.
IS EXERCISE FOR FAT LOSS THE BEST STRATEGY FOR WEIGHT LOSS SUMMARY
- Exercise for fat loss with diet is an ineffective weight loss strategy.
- Dieting results in a constrained model of energy expenditure where metabolic adaptations result in less calories burned than predicted.
- Most people tend to compensate by reducing NEAT and moving around less when exercising more
- It’s much easier to achieve a caloric restriction thru cutting calories than by trying to burn excess calories thru more exercise.
What Does Research Say About Exercise for Fat Loss?
Hunter gathers used physical activity to gather and hunt food, whereas today, most people exercise to maintain fitness and prevent obesity. It has long been thought that to lose weight, exercise more. If you remember from the metabolic chart for calories burned, exercise can contribute about 5% of the energy expenditure. You often hear people say, “He or she can eat whatever she wants because she exercises every day!”
Two systemic reviews found that exercise alone without caloric restriction had minimal effects on weight loss. (1, 2) It has been found that 1% of participants can achieve significant weight loss by exercise alone. (3) It takes a considerable amount of calories burned during exercise to achieve significant weight loss. In a study of overweight adults, those whose exercise expenditure was greater than 2500 calories per week had half the weight regain as those who performed exercise expenditure with less than 2500 calories. (4)
CAN AEROBICS HELP YOU LOSE WEIGHT
The biological need to eat is more impactful when a caloric deficit is induced than exercise-induced energy deficit. People have different responses to exercise; some people have a suppressed appetite after exercise, while others will have an increase in appetite. The response is highly variable. For many people, exercise will have an appetite suppressing effect.
For example, researchers assigned subjects to a complete fast for one day (i.e., 24-hour energy restriction) or an exercise condition in which they had to expend their day’s energy expenditure thru exercise. They had to burn off an entire day’s calories thru exercise! Whatever they ate had to be burned off thru exercise. The subjects had to cycle for four hours and 52 minutes at 70% of their aerobic capacity!!! The following day, they were allowed to eat at a buffet. The subjects who did not eat for a day (i.e., fasted for 24 hours) increased their energy intake (i.e., ate more food) more the following day despite the exercise and food restriction groups having a similar caloric deficit. (5)
Thus, a food deficit resulted in a large drive to eat than a similar deficit created by exercise. It can be suspected that despite the large amount of calories burned during exercise, the appetite suppressing effects of the long duration protocol resulted in less food intake.
APPETITE RESPONSES TO EXERCISE
There is variability in the appetite response to exercise depending on the type, intensity, and duration of exercise. Some people have an increase in appetite in response to exercise, whereas others will have a reduction. In a review of the literature, an increase in energy intake (i.e., increased calories) of >119 calories was found in 25 of 29 studies. Exercise duration ranged from 30 to 120 minutes at exercises intensities of 36-81% VO2 max (i.e., a measure of aerobic intensity), with trials ranging from 2 to 14 hours, and ad libitum test meals offered 0-2 hours post-exercise.
Despite variability among studies, results suggest that exercise effectively produces a short-term energy deficit and that individuals tend not to compensate for the energy expended during exercise in the immediate hours after exercise by altering food intake. (6)
EXERCISE HAS BENEFICIAL EFFECTS IN THE ABSENCE OF WEIGHT LOSS
Exercise has a synergist effect with caloric restriction and better lean mass preservation. It has been found that without exercise, ~25% of weight loss will be from lean mass, with the remaining 75% from fat mass. (7) Aerobic exercise and resistance exercise can burn calories, with aerobic exercise able to burn more calories during exercise. In contrast, resistance exercise has more favorable effects on increasing lean muscle mass and reducing body fat. Variability in the number of calories burned through resistance exercise is influenced by lean mass, gender, age, amount of muscle mass activated during the lift, total workout volume, rest periods between sets, and time under tension.
A synergistic effect can occur when combined, despite an absence of weight loss. For example, when overweight men and women were placed on a combination of resistance exercise and aerobic exercise with no dietary changes, they had improvements in insulin sensitivity, physical fitness, and increases in lean mass with reductions in fat mass, yet their body weight remained unchanged. (8) This suggests that exercise training provides several beneficial health outcomes despite an absence of weight loss.