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.
WHY EXERCISING MORE MAY NOT BE THE ANSWER TO MORE FAT LOSS
Current guidelines for individuals seeking to lose weight or prevent weight regain are recommended to increase exercise duration thru aerobic exercise to 200–300 min/week. This roughly equates to 2000 kcal/week or an average of over 400 kcal per exercise session. This roughly translates to about 60 minutes at 3.5 mph on a treadmill or a leisurely bike ride, depending on your body weight.
Now the scary part is that to compensate for that hour of exercise, one Chewy Trail Mix Granola Bar contains 415 calories. You have eaten more than you burned in 60 minutes in 5 bites! It’s easy to see how hard it is to lose weight just by exercise. A large-scale study of over 38,204 college students found that most students reported more exercise is the best way to lose weight rather than a diet. (9) This is not true despite the widely held belief that just exercising more is better for fat loss.
Most studies show that exercise without diet results in minor or no changes in weight loss. (2, 10, 11) It is possible to lose weight thru increasing exercise, but the exercise duration is substantially longer than what is recommended. For example, one study found an 8% reduction in body weight thru aerobic exercise alone, but they had to burn ~700 calories per session. (12) They had to walk at 70% of their max aerobic capacity for an hour, which is not an easy task. For most people, losing weight thru an exercise-only approach is unrealistic for the general population, although it is possible.
CONSTRAINED VS. ADDITIVE ENERGY MODELS
The typical advice for weight loss is just to eat less and exercise more to lose weight. This will initially work in the early phases of dieting, but body weight and fat loss seem to plateau, as is well known. If you exercise two people for an hour and they both burn 300 calories, you would expect an increase in energy expenditure to tip the balance for greater daily expenditure to be similar for all people, but unfortunately, it’s not.
There are two energy models that represent thus tipping the favor for greater weight loss, but this varies dramatically among individuals. The calories burned during exercise over a day are divided into two groups: Constrained Energy Expenditure and Additive Energy Expenditure.
Constrained compensation is the concept that not all the energy spent when activity levels increase translates to additional energy spent that day. Additive energy expenditure suggests that the calories burned during exercise increase total energy expenditure.
The additive energy expenditure model suggests a dose-dependent response between exercise and energy expenditure (i.e., more exercise results in greater calories burned). As much as we would like to think that more exercise results in more calories burned simply does not reflect the true science.
HUNTER GATHERS SOCIETIES ENERGY EXPENDITURE
In a fascinating study by Pontzer et al., he examined the energy expenditure of the Hadza hunter-gatherer. The Hadza lifestyle is similar in critical ways to our natural ancestors. They hunt and gather on foot with handmade weapons; they have no modern tools or equipment (e.g., no vehicles). They walk extensively, and they have no modern-day technology. With all the walking they do, one would expect their total energy expenditure to be thru the roof with all the walking they do.
Their physical activity levels were 2.26, categorized as vigorously active, compared to Western men, which is 1.81, which is moderately active. Shocking, their total energy expenditure was the same as Western men! (13) The Hadza men had a greater physical activity level because they walked everywhere. Still, they compensated in NEAT levels by sitting more, less fidgeting, or doing less chores outside of hunting. This suggests once a certain threshold of physical activity occurs, the body will compensate by reducing energy expenditure in other areas, such as resting more and less movement.
WHY EXERCISING MORE DOES NOT ALWAYS RESULT IN GREATER WEIGHT LOSS
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. In a large-scale study of 332 participants from five populations across North America and Africa, low physical activity increases total energy expenditure but the relationship between total energy expenditure and high physical activity levels plateaued. (14)
Those with the highest physical activity levels compensated by reducing physical activity in other areas of their life, resulting in less calories burned across the day. They also found that the more energy burned during physical activity, the more BMR decreased. The researchers found that for every 100 calories burned during activity-related energy expenditure, there was a decrease in BMR of approximately 28 kcal. This was further demonstrated in a recent study in which subjects were assigned to either burn 8 kcals/kg of body weight or 20 kcals/kg/bw per week. The group that performed the high energy expenditure aerobic exercise (20 kcals/kg/wk.) lost a significant amount of weight. Still, it was only half of what was predicted based on metabolic calculation. (15)
ULTRA DURANCE STUDIES
Another study investigated participants who participated in the extreme endurance event Race Across America, in which participants ran a marathon a day six days a week for 20 weeks. The participant’s energy compensation for the running energy expenditure for the marathon was nearly 3,000 kcal per day, but they compensated by reducing NEAT-related activity by an average of 600 kcal/d.(16) Another interesting finding was that these athletes were eating massive amounts of food to compensate for their daily energy burned thru running.
Despite the massive energy expenditure of exercise, there was no decrease in BMR. These studies suggest that exercise burns more calories, but it’s not a dose-dependent response. When people exercise more, they compensate by resting more and reducing energy expended in other activities such as sitting around more and moving less.
DIETING RESULTED IN A CONSTRAINED MODEL
This suggests a negative feedback loop to the brain to move around less to conserve energy with decreasing body fat levels. In another study, researchers examined the relationship between a constrained and additive model of energy expenditure in a calorie surplus, maintenance, and deficit. When in a neutral or slight calorie surplus, the total energy expenditure and physical activity were consistent with an additive model, meaning that calories burned during exercise were additive. However, when dieting or in a negative calorie balance, the subjects followed a constrained model meaning that fewer calories were burned over the day. (17)
This makes sense, as most people often comment on how weight and fat loss seem to slow down on a diet as the caloric deficit is increased. Our genes have not changed from evolutionary times. The body tried to keep metabolic energy expenditure within a narrow range. Losing all your body fat in a short period is not helpful for the survival of a species. Whether people compensate by increasing calories by eating more food or becoming less active is highly individualized.
Exercise alone for fat loss is not really a great strategy. This may explain why one person can lose weight and keep it off, whereas others would have difficulty with weight loss and rebound weight gain. This suggests a diminishing return with excess exercise, leading to a plateau in energy expenditure and reduced weight loss. The constrained energy model is not unique to just humans, but other animals demonstrate similar characteristics. For example, mice gradually forced to increase exercise duration substantially reduced NEAT. (18)
KEY POINTS OF EXERCISE FOR FAT LOSS
- 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 mor
- It’s much easier to achieve a caloric restriction thru cutting calories than by trying to burn excess calories thru more exercise.
REFERENCES
3. Wing RR, Phelan S. Long-term weight loss maintenance. Am J Clin Nutr. 2005;82(1 Suppl):222S-5S.
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