What Happens to Your Metabolism When You Under Fuel Your Body?

Whether you're under fueling your body due to dieting, an eating disorder, or even unintentionally (life is busy — we get it!), the consequences are serious. Not to mention that dieting is a slippery slope, as it’s the number one predictor of eating disorders. In fact, the National Eating Disorders Association (NEDA) found that 35 percent of dieting becomes obsessive and 20 to 25 percent of diets turn into eating disorders.

When you consistently under-eat — meaning you don’t consume enough calories for what your body needs every day — your body adapts by lowering your resting metabolic rate (RMR). It also breaks down more of your muscle mass than it should. In today’s blog post, let’s look at a case study and consider how we can correct this problem. 

This case study focuses on someone who, many months before making an appointment at The Kahm Clinic, wanted to lose some weight.

Note that this individual was 5 feet, 8 inches tall and weighed about 170 pounds. To do so, she began dieting and eating 1,800 calories per day. She hoped this deficit would be enough to spur some noticeable weight loss. However, when she didn’t see the results she wanted, she cut her intake down to 1,600 calories per day and then 1,400 calories per day. By the time she booked her first appointment, she was only consuming around 1,100 calories per day.

To start, we completed metabolic testing. Her RMR was at 1,378 calories per day; it should’ve been just above 1,700 calories per day – or even higher. This drop in her metabolism is considered significant. Also problematic, her protein metabolism (or breakdown of muscle mass) was higher than normal. That means her body was chipping away at existing muscle to get additional fuel, fuel that it’s not getting through daily food consumption. 

These results are proof that her metabolism was adapting to her intake. 

She consistently under fueled her body, and thus, it began to use less and less energy. It’s not going to keep burning more than it's being given! So it slowly brought down her RMR. 

In order to correct her slowed down metabolic rate, she needed to take in more calories. We pulled that daily number back up to 1,800 calories per day. We eventually pushed that number even higher to 2,300 calories per day so she was actually fueling her daily activities. 

It’s important to taper this increase, as it’s naturally difficult to eat that much more food. Plus, just as her metabolism slowly dropped from under-eating, it will slowly increase as she’s fueling her body more and more. Her body will understand that it no longer needs to compensate for her lacking intake.  

During this correction process, it’s natural for weight to plateau or even increase a bit.

It definitely won’t come down — and that’s okay! This happens because the body is attempting to repair some of the broken-down muscle mass. As it builds back muscle, there might be some weight gain. It’s important to understand that this step must happen first in order for her metabolism to correct itself. Once her RMR returned to a normal rate, we worked together to determine the best way for her to appropriately fuel her body and also reach her goals. 

Subscribe to our YouTube channel for video content. To talk to a professional about eating disorder treatment, please reach out to our staff or schedule an appointment at The Kahm Clinic today.