Can You Have a "Slow Metabolism?"

Is it possible to have a “slow” metabolism?

I see it way too often. A woman comes to me who has been dieting on and off for years. Whether she followed weight watchers, calorie counting, or low carb, she has always been off and on some type of diet. Her first diet attempt she was able to lose 15-20lbs, but over the course of several months and years, the weight crept back on. 

Certain that what worked in the past will work again, so she puts in hours at the gym each week and “eats clean” but the weight just won’t seem to budge this time around. She thinks it is because she isn’t being disciplined enough and restricts further. She might lose a few pounds, but she feels like she is starving all the time and her energy sucks. When she isn’t seeing more results, she takes a “break” from her diet and binges on all the foods she had been restricting. 

If this woman was able to lose weight the first time she dieted, why can’t she lose it again following the same principles?

This is a phenomenon called metabolic adaptation or “adaptive thermogenesis.” 

I am going to dive into the science behind this all too common phenomenon that I see many women experience, so if you aren’t a science nerd like me, then you can skip to the bottom of this post to get the cliff notes version! But, if you want to know the details (which I think is important,) then keep reading! 

Disclaimer: I don’t claim to be an expert in metabolism, but I do my best to interpret what research says and my experience of working as a Registered Dietitian for over 6 years. I also want to iterate that I am not giving any medical advice and that it is your responsibility to work with a qualified healthcare professional on your unique case. 

Before we dive into all of the science behind metabolism, let me first describe common signs of a slow metabolism:

• Difficulty losing weight even with dieting.
• Difficulty building muscle.
• Poor energy, constant need for afternoon naps
• Sleep disturbances (even to use the bathroom!)
• Constipation, bloating
• Poor sex drive and/or irregular periods
• Brain fog
• Thinning hair or hair loss
• Constantly feeling cold

While some of these symptoms can have other root causes, these are common signs I see in women who need a "boost" in their metabolism.

Let’s dive in…

In the words of Gloria Gaynor, "I will survive!" 

The first very important thing to understand is that the human body’s main objective is survival. It is hard to remember that in our modernized world, but the human body was made with intricate chemical messengers (hormones and neurotransmitters) that regulate homeostasis. Homeostasis is a big word for “keeping things stable.” According to Britannica, homeostasis is “any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival.” (emphasis mine.) 

Basically the human body does not like its normal functions being disrupted, so it will respond to whatever stimulus it is given with an adaptation. The human body is very good at adapting. 

Now that we have that on the table, let’s talk about the concept of energy balance. 

Energy Balance Explained

Calories are what give our bodies fuel or energy. Think of calories like gas for a car. We cannot function without calories, just like a car can’t run without gas. Our body receives calories through food and stored calories in the form of muscle and fat. We expend or “burn” calories four unique ways:

1. Basal metabolic rate (BMR): the amount of calories our body uses for all psychological functions (heart pumping blood through the body, respiration, brain function, etc.) This makes up for ~60% of all of the calories we expend daily.Basal metabolic rate (BMR) is higher in individuals who have never or seldom dieted, have more muscle mass, and exercise regularly. A person’s BMR can lower 5-15% in response to dieting. By eating less over a prolonged period of time, the body naturally lowers the amount of calories that it requires. Basically, our body is conserving energy. More on this in a bit!
2. Exercise: this is pretty self explanatory, but includes any intentional form of exercise (lifting weights, running, sports, etc.) It is important to note that anaerobic exercise (strength training) actually increases calories burned for several hours following exercise. Aerobic exercise on the other hand (think cardio) burns calories while the exercise is being performed, but few calories afterward. 
3. Non-Exercise Activity Thermogenesis (NEAT): the calories used doing non-exercise movements such as chores, fidgeting, walking, standing etc. This accounts for a large majority of the calories we burn (or don’t burn) each day. 
4. Thermic Effect of Food: The calories our bodies use in order to digest food. Fiber and protein have a HIGHER thermic effect on the body, which means our body’s burn more calories digesting foods that are high in protein and fiber. This is one of the many reasons that increased protein is often recommended for individuals looking to lose weight.

According to science, if the calories we consume are less than the calories that we expend, then our body has to break down stored calories (in the form of fat or muscle) in order to make up those extra calories that we need for energy. Simply put:

Calories consumed < calories expended = breakdown stored energy for fuel or calories. 

In case you need a refresher, < means less than:)

And the opposite is true. 

Calories consumed > calories expended = excess calories are stored (as fat, muscle, or both depending upon different factors) 

This is called the Energy Balance Equation.

The problem with taking this equation at face value is that most people forget that there are variables that can change, with the biggest one being a person’s basal metabolic rate.

So this goes back to the question, can a person have a slow metabolism?

Research has shown that a person’s BMR can decrease from 5-15% when a person loses weight. What this means is that each time a person attempts to lose weight, their metabolism slows down as an adaptation. This means that ENERGY OUT in the energy balance equation is going down. Not to mention when a person attempts to lose weight, they might also have less energy, so their non-exercise activity movements (fidgeting, walking, chores, general movement) may go down. 

We also have to consider the TYPE of exercise a person is doing and the impact of that on metabolism. Is a person doing moderate exercise that includes strength training or moderate exercise that just includes cardio? The type of exercise will determine the amount of calories a person is burning at rest. A female with more muscle will have a more efficient metabolism than a woman with less muscle mass. 

The TYPE of food also has to be considered. Is the person eating 1800 calories of processed foods or 1800 calories of minimally processed whole foods? A nutrition facts label can be off by as much as 25%, which leaves a lot of room for inaccurate food tracking information. If a person is eating a minimally processed diet of lean meats, vegetables, complex carbs, and healthy fats, then their body uses more calories digesting and processing the foods compared to a diet composed of processed foods. 

You can see where this equation can get pretty convoluted. So while the calories in versus calories out concept for weight loss is TRUE, it is highly individualized!

So back to the original question -- can a person have a slow metabolism? 

Simply put, yes. But there are things that we can do in order to improve our metabolic function! Let's look at the cliff notes version and summary!

Cliff Notes Version

1. Dieting slows down your metabolism. Each time you diet, weight loss will become harder and harder unless you focus on reestablishing adequate intake between diets. I do not recommend dieting more than once a year. Maybe twice depending upon how much weight you have to lose and your dieting history. 
2. Slow and steady wins the race. Diets that promote weight loss of greater than 2lbs per week have a higher likelihood of having rebound weight gain, not to mention you are most likely burning muscle along with fat. A healthy and sustainable amount of fat loss should be between 0.5-1.5lbs of fat per week. The leaner a person already is, the less they should expect to lose per week.
3. If you have never dieted before, you can expect to have better fat loss results the first time you attempt to lose body fat. Your body has not metabolically adapted to receiving less calories compared to someone who has dieted before. 
4. Slowly increasing your caloric intake back up following a diet is the most important step to keeping the weight off! This allows your metabolism and hormones to slowly adapt to receiving more food over time. This is called a reverse diet and can take anywhere from 8-12 weeks depending upon the person. 
5. A diet composed of whole, minimally processed foods will promote a better fat loss outcome due to the higher thermic effect of those foods. Focusing on getting 20-25% of your calories from protein will help promote fullness and increased metabolism. 
6. Strength training versus cardio will be more effective for preserving and building muscle during a fat loss attempt. Lifting weights increases post exercise calorie burn for several hours, which has a positive metabolic. Not to mention, more muscle mass = higher BMR! 

 If you are interested in reading more on this topic, here are two great additional resources created by Precision Nutrition. 

1. https://www.precisionnutrition.com/metabolic-damage

2. https://www.precisionnutrition.com/the-biggest-loser-study

My top recommendations for improving your metabolism: 

1. Stop restricting. Just stop! 

2. Eat 1-2 palm sized portions of protein at every meal (lean meat, eggs, dairy, tofu/tempeh)

3. Incorporate strength training (not HIIT, not Orange Theory, not Crossfit, not bootcamp) into your workout regime 3-5x/week.

4. Get enough sleep - at least 7-9 hours per night!

5. Cut out the junk! Make at least 80% of your food choices come from whole, minimally processed foods. The closer it can get to the ground, the better! 

If you are interested in working with a professional 1 on 1, I would love to book a time to chat through your goals, your health history, what you have tried, and whether or not my approach would be a good fit for you! You can schedule complimentary 20 minute call here. 

References: 

Lam YY, Ravussin E. Analysis of energy metabolism in humans: A review of methodologies. Mol Metab. (2016)

Bosy-Westphal A, et al. Issues in characterizing resting energy expenditure in obesity and after weight loss. Front Physiol. (2013)

Schwartz A, Doucet E. Relative changes in resting energy expenditure during weight loss: a systematic review. Obes Rev. (2010)

Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. Int J Obes (Lond). (2010)