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Understanding Metabolism: How Undereating Hinders Results

Fast metabolism, slow metabolism, broken metabolism, increased metabolism. These are all buzz phrases in the fitness and nutrition industry. But what is your metabolism, why does it change so much from person to person and how does the amount you eat impact how many calories you burn each day?

Your metabolism is the combination of all the processes going on in your body all the time. The foods you eat (and therefore, the calories you consume) are going to fuel the buildup and breakdown of nutrients in your body that are necessary for optimal health. Ultimately, your body needs adequate energy intake to stay active, support day-to-day activity, maintain (or grow!) muscle and keep you from experiencing fat gain or weight plateaus.

There are five main components that make up your metabolism and each can be affected if you don’t get enough calories through your day.


1. Basal metabolic rate (BMR):
This includes the very minimum energy needed to keep vital bodily functions fueled. Think heartbeat and breathing! This accounts for about 70% of the total energy you expend each day.

2. Resting metabolic rate (RMR): This is pretty similar to your BMR in that it is still measuring minimal functioning in your body. RMR extends to respiration, circulation, synthesis of organic compounds (like building muscle!) and basic cellular functioning. There is usually about a 10% difference between your BMR and your RMR.

How undereating affects BMR and RMR — BMR and RMR are affected by age, body composition, body size, climate, gender and hormone status. People with more lean body mass (aka more muscle!) have an RMR that is about 5% higher than non-athletic individuals. If you’re not eating enough to support healthy muscles, your RMR will be lower and you will burn fewer calories at rest. Undereating can also cause hormone imbalances, which can cause water retention and unwanted fat storage.

3. Thermic effect of food (TEF): This is the energy expended in the digestion, breakdown, and absorption of the foods you eat.

How undereating affects TEF — Eating food takes energy. Chewing, swallowing, digesting, creating the enzymes that break down your food — these things all cost you calories. Protein especially has a high-thermic effect, which means it takes your body extra energy to digest, process and store protein. Fat has the slowest thermic effect out of the three macronutrients. When we undereat, we are decreasing this overall calorie output. This is also why eating sufficient protein is so important.

4. Exercise activity (EA): I bet you can guess what this includes! Your exercise activity includes deliberate exercise like going for a run or hitting a CrossFit class. EA can vary drastically from one person to another, accounting for anywhere between 10% (or less) to 30% (or more) of total daily energy expenditure.

How undereating affects EA — Have you ever had a day in the gym when your energy was through the roof and you felt like you could go forever? Have you ever had a day when you were dragging and headed home feeling like you didn’t accomplish much because you didn’t have enough energy? Getting adequate calories allows you to push hard in the gym, build and maintain muscle and get stronger. Sufficient nutrients also support quick recovery so you can hit it hard again tomorrow!

5. Non-exercise activity thermogenesis (NEAT): This is the most variable part of energy expenditure from person to person. It includes all energy expended for the activities you do that aren’t eating, sleeping, breathing or exercising. NEAT includes things like walking your dog, doing yard work, standing instead of sitting at work, fidgeting, walking around the grocery store, meal prepping, etc. In extreme cases. people’s NEATs can differ by 2,000 calories a day!

How undereating affects NEAT — When you are under-fueled, your body will automatically start down-regulating your NEAT to conserve as much energy as possible. This means you will naturally stop moving around, you’ll opt for the closest parking spot, you’ll avoid taking your dog for a walk, you’ll sit instead of stand at your desk, etc.

If you want to make some drastic changes in fat loss without feeling like you need to live in the gym, focus on your NEAT. Here are some quick ideas to help you increase your NEAT:

  • Make it measurable. Wear a watch and set a movement or step goal.
  • No more princess parking — pick a spot farther away from the door.
  • Put yourself on a clock, set a timer and make sure you get up every 20-30 minutes to walk, stretch or knock out some air squats.
  • Stand — at work, in the coffee shop, while you’re chatting at a get-together — any chance you get! If you’re stuck at a desk all day, check out these Stretches You Can Do at Your Desk to keep yourself moving and mobile.
  • Take the stairs or the long way to your office instead of jumping on the elevator.

We get it — the idea of “eating more to lose weight” can seem a bit counterintuitive and it definitely takes a bit of experimentation to get to know what nutrient levels support your body composition and performance goals. Thankfully, our coaches at WAG can help you learn what will keep you moving, keep your metabolism going and keep you tracking toward your goals!

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