Conventional advice tells you to exercise if you want to lose weight. Repeated studies and real-life experience show this is often not the case, leading many disappointed exercisers to ask “Why can’t I lose weight even though I’m exercising?”
This is a complicated question because there are a lot of different moving pieces to weight loss.
First, it's helpful to identify how the body loses weight. For weight loss, it's necessary to have a calorie deficit that is sustained over time so that you are taking in fewer calories than you are burning. Exercise burns calories, which is one reason people believe it will help with weight loss.
The trouble is that in reality, people often compensate for the calories burned during exercise by moving less in daily life or eating more. When it comes to weight loss, what matters is Total Energy Expenditure, which is the sum of the following:
Basal Metabolic Rate (BMR) is the energy burned at rest when lying in bed all day.
Physical Activity Level (PAL) is the energy burned during exercise.
Thermic Effect of Food (TEF) is the energy used by the body to digest and assimilate food.
Non-Exercise Activity Thermogenesis (NEAT) is the energy burned during “spontaneous” activity, not including exercise.
Studies show that it’s not uncommon for people to decrease their NEAT calories when they start an exercise program, which lowers total energy expenditure and negates any calorie deficit. One survey found that physical activity has a weak influence on daily energy expenditure, but only among subjects on the lower half of the physical activity spectrum (1). People with moderate activity levels had higher daily energy expenditures - about 200 calories more - than the most sedentary people. However, people who did more than moderate activity had nothing to show for it in terms of increasing the amount of energy they expended.
In regards to eating, many people increase their food intake in response to exercise, either due to increased hunger or as a "reward" for their physical efforts. Dietary compensation may be more subtle than simply rewarding oneself with more food. When people exercise, their psychological restraint around food can erode and they give themselves the freedom to eat more, often choosing higher calorie, hyper palatable foods, making it easy to overshoot calorie intake.
This tendency is probably more common in people who are exercising with the express purpose of losing weight. Psychologically, they are thinking, “oh, I'm exercising more and burning calories and should be able to eat whatever I want.” Research appears to support this with studies showing that individuals who exercise for reasons other than weight loss, such as health benefits or performance, will eat less after exercise compared to those who exercise for weight loss.
The second factor to consider is adaptation. Our bodies adapt to the exercise we do regularly, getting more efficient and stronger. Energy expenditure goes down as adaptation sets in, meaning that if you do the same type and duration of exercise daily, even if it is significant, you aren't burning as many calories as when you started.
You'll often find with short-term exercise interventions in sedentary individuals (such as 1 to 3 months) there will be a significant amount of weight loss because the exercise is new and the body must adapt to the physiological disturbance. In addition to burning significant calories, there will be improvements in insulin sensitivity, blood sugar, and inflammation, all of which impact metabolic function and weight management.
Over time with longer term interventions, especially those that don't include a dietary component, weight loss often stalls and weight regain will occur because the body has adapted to the exercise dose and is not getting the same improvements.. In a situation like this, there is evidence that incorporating anaerobic exercise in the form of interval and weight training can be helpful because both allow you to overload the body and elicit further adaptations.
Ultimately, if weight loss is the goal, you have to address both nutrition and exercise, and continually make adjustments to ensure continued adaptations.
The first step is to address diet. Do a food journal that encompasses your "worst" eating days so that you can identify when calorie intake overshoots your goals. Often when people do food journals they will remove all of the less healthy foods or else eat really well for several days and pretend that is how they eat all the time. This is completely useless since what you really need to do is identify trouble spots that are related to your worst eating habits when you are under the most stress.
Once you get an honest picture of how you are eating over the course of a week, you can troubleshoot, whether the issue is that you need to plan ahead more, avoid snacking, eat on a schedule, reduce portions, increase high-fiber, low-calorie foods, increase protein, or reduce sweets and simple carbs.
Another thing to consider regarding diet is when you are eating. Recent research shows that many people are literally eating all day long over the course of 14 to 16 hours. This is a problem because it reduces your ability to identify hunger and fullness and it impairs the circadian function of metabolic organs like the liver. Time restricted eating is recommended in which you identify a 12-hour window and eat scheduled meals separated by about four hours during that time. This method incorporates 12 hours of fasting overnight that allows the digestive system a chance to rest.
Although exercise is not the magic ticket for reducing body weight over the long term, it is an important component because it supports metabolic rate, counters inflammation, and has numerous health benefits. If weight loss is the goal, exercise should be designed to continually overload the body through interval training and weight lifting. In the case of weight lifting, this means to progressively increase weights or do a greater volume with more sets and reps.
In the case of intervals, studies show great short-term results for weight loss from doing 20 to 30 minutes of interval training several days a week. For example, a study of women who did 20 minutes of sprint intervals on a bike lost about 5.5 pounds of body fat over 15 weeks (2). A second study of men using the same workout protocol showed similar benefits (3).
Final Words: Optimizing body composition with exercise requires continual adaptation. Oftentimes people will get into a routine and not even realize that they've adapted to it and are not progressing in the way they would like. That's when it’s time to mix things up. Changing exercises, going heavier, sprinting harder, or altering the cadence of the exercise are all strategies that will ensure continued overload and progress.
To learn more about programming workouts for body composition goals, consider taking our online Program Design course.
1. Pontzer, H., et al. Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans. Current Biology. 2016. 26(3): 410-417.
2. Trapp, E., et al. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity. 2008. 32, 684-691.
3. Heydari, M., et al. The effect of high-intensity intermittent exercise on body composition of overweight young males. Journal of Obesity. 2012, 480467.