In the real world – even if you do everything right – weight loss never happens in a straight line. Weight loss tends to start out quick and then get progressively slower over time, making the last 5 pounds much more challenging to lose than the first 5 pounds.
In many respects, our bodies are no different than they were 2,000 years ago. They aren’t designed to make fat loss easy, they are designed to ensure we continue to live when food is scarce. We are created that way.
During a fat-loss diet, your body doesn’t realize that you’re restricting your food to lose fat. Your body believes that food is scarce, so it enacts mechanisms to ensure survival. Hunger levels increase to stimulate the search for food, and your body decreases the number of calories it burns, extending how long you can live without adequate food. In other words, our metabolic rate slows down.
Typically, we call this phenomenon a “slowing metabolism.” However, the term “slowing metabolism” is a little misleading because several factors cause your body to burn fewer calories when dieting to lose weight.
The major factors that can contribute to a “slowing metabolism”
So why does your metabolism slow down as you lose weight? Why does fat loss/weight loss slow down the more and more you lose?
Non-Exercise Activity Thermogenesis (NEAT)
By far the biggest factor that can contribute to a “slowing metabolism” is a reduction in non-exercise activity thermogenesis (NEAT). NEAT is a fancy scientific term for the calories we burn from subconscious activities such as fidgeting, walking, and even texting our friends. You might not guess it, but subconscious activity can cause you to burn up to 1,000 calories a day. Weight-loss diets naturally make us more sedentary to help slow fat loss, reducing the number of calories burned from the subconscious activity. Depending on the person, a weight-loss diet can naturally cause you to decrease subconscious activity by 100 to 350 calories per day.
The second biggest factor that can contribute to a “slowing metabolism” is metabolic adaptation. During a weight loss diet, your organs and tissues will become more efficient and burn fewer calories than normal, called metabolic adaptation. In effect, metabolic adaptation is a natural safeguard to help extend the time you can live without adequate food. During a typical weight loss diet, metabolic adaptation should only slow your metabolism by about 50 to 125 calories a day. In most cases, metabolic adaptation isn’t permanent. Once you stop dieting and return to eating at maintenance, your metabolism should return to normal.
For the first few days, while your metabolism is still running at normal, the restriction in calories works and you lose weight. Weight loss is always greatest for the first few weeks. After a while, as your body adjusts to lower calorie intake, metabolism gradually slows down. Now the calories you consume are balanced with the calories you burn. Weight loss stops. You hit a plateau.
In order to lose more weight, you must cut your calorie intake even further. If you do, you will lose a few more pounds until your body adapts and your metabolism again slows down.
The Less You Weigh, the Fewer Calories You Burn
Another factor that can slow fat loss is a reduction in your body’s fat and muscle mass. At rest, a pound of fat burns about 2 calories per day, and a pound of muscle burns about 6 calories per day. So, if you lose a considerable amount of fat or muscle, your body will need fewer calories to sustain itself. A smaller body also means that you have to move less weight during physical activity so the same activity – whether it’s formal exercise or walking to work – will burn fewer calories. If two people run for the same length of time and at the same intensity, the heavier person will burn far more calories than the lighter person.
Eating more protein can reduce the drop in metabolism often associated with losing fat. This is because protein helps prevent muscle loss, which is a common side effect of dieting. As you know, more muscles mean more burned calories even when muscles are at rest. Eating more protein can boost your metabolism so that you burn more calories.
Closing thoughts: We are not doomed to fail entirely
Now you know for sure why fat loss gets harder over time while dieting. However, you shouldn’t worry that these factors (i.e., a “slowing metabolism”) will prevent you from losing weight entirely. What will happen is that weight loss will slow over time because your body will burn fewer calories. For instance, you may start out eating 500 fewer calories than your body burns and losing about a pound a week. But, over time you’ll experience a decrease in subconscious activity, metabolic adaptation, and fat loss, which will decrease how many calories your body burns. After 3 to 6 weeks of dieting, you may only be eating 250 fewer calories than your body burns, which will slow fat loss. To continue losing weight, you’ll need to make small reductions in how many calories you eat or increase exercise. Another strategy that can help to prevent the effects of a “slowing metabolism” is taking diet breaks.