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The Plate: Q&A, The Science of Metabolism

Welcome to The Plate, where food meets science at your table. 

In each episode, founder and CEO Sherry Zhang, Ph.D., asks subject experts questions in nutrition, biology, and health that are relevant to our approach to eating and living healthfully in our time. We visit complex topics such as how the science of metabolism influences our healthy body compositions, why it’s important to understand and practice personalized weight loss/gain, and how food affects us as individuals. 

We invite you on an intellectual tour of current scientific ways to envision and approach solutions to many of our questions and problems revolving around food in modern-day living. We may not know all the answers, but we will always be one more step closer to the truth by asking scientifically fueled questions. 

So, come join us! 

In this The Plate episode, Kristin Ricklefs-Johnson, Ph.D., M.S., R.D.N., and Kelly Van Gorden, M.S., R.D.N., C.D., join Sherry in a dynamic discussion on the science of metabolism, and its daily effects on each of us. 

Why should you care about the science of metabolism? If you could peek inside any cell of your body, you would find that there is constant activity occurring, like a 24-hour factory line. Whether you are sleeping, sitting on the couch, working on your computer, or going for a walk, your cells are transforming energy to power the chemical reactions that keep you alive. 

Sherry: When we talk about metabolism, it could feel like a big, vague word, right? People mention it from time to time when they talk about healthy eating, smart exercising, or anything to do with nutrition and health, but what exactly is metabolism? Why is it so important? Why do experts in nutrition and medicine hope people become more knowledgeable about it? Because once a person understands the fundamentals about how his or her metabolism works, we can start helping that person apply that knowledge and take actions with purpose in life. To help our audience to relate to their own experiences, I would like to share my struggle with metabolism, as I turned 40 recently. 

In the past, I could eat plenty of all kinds of food that I loved. I'm a kind of foodie [chuckles]. I'm genuinely attracted to a variety of cuisines and the idea of trying different food. Ever since I moved into my late 30s, though, it feels as if there's an off switch in my molecular reactions, and I just can't burn the same quantities and qualities of foods that come into my body that I used to. As a result, I either feel sluggish at the end of the day, or I gain some fat mass that I don’t want to. 

As a scientist, I understand what's going on with my metabolism, which is helpful in understanding the struggle. It helped me with my frustration with it and, eventually, my regaining control of the situation. Because I heard over and over again, people have had the same kind of stories when they also struggle with physiological responses to their biological interactions with internal factors—such as aging and hormones, and external factors—such as food and living environment. People struggle, usually, because people don’t understand it. So, I think it is time for us to talk about the science of metabolism. Welcome, and thank you for joining me on this topic, Kristin and Kelly. 

What is Metabolism?

Kristin: Sherry, with your experience in molecular biology, how would you describe what metabolism is, and why is it essential in our everyday lives?

Sherry: If I can use an analogy to our everyday life, I see metabolism as the process where we're building a house—and that house is you. Let’s imagine your dream house for a second. You must want it to be strong, beautiful, and capable of doing all the jobs you need to be done. Your metabolism is the process that does exactly that for your body. [Your metabolism] never stops working for it and is on an autopilot mode. 

When you are small and fast growing, your metabolism follows the instructions in your genomic DNA code, like an architect and construction team that follow their floor plan and construction blueprint to make sure your body is built according to the life path that was lived and tested by your ancestors in their evolving living conditions. 

As you can imagine, this process is not set in stone. Even though your genomic DNA is a very powerful force in dictating the dimensions of your “building,” the materials you use to build it depend on your supplies and what’s available. Do you use sturdy building materials such as wood, metal, or marble, or do you use wood chips that may crumble easily over time? You get the idea? 

The amazing feature about your metabolism is that it is an ongoing and dynamic process. It is on 24 hours and every day of your entire life. It mediates the interaction between your genomic DNA blueprint that you are born with and today’s living environment that you are in. You can help it do you good by understanding how it works and providing it with the right supplies (such as food), and work with it on its effects and outcomes on your overall body and health by moving your body in the right way at the right time. 

Your metabolism is also unique to you. There are thousands of short to long chains of metabolic reactions that are happening right now in you to keep you going, right? When you run, lots of biochemical reactions will be elevated to a level to keep your performance up. When you sit down, rest, and eat, you know, other molecular reactions will turn on and off. All of these are the work of metabolism. 

The Origin of Metabolism

You may ask, where did our metabolism come from?

The origin of metabolism is quite interesting. Our biological system is intelligent and adaptable, such that it has evolved over millions of years and actively taken in important signals from our environment, and makes decisions on whether or not to adapt to [the environment] by making changes in our genomic code, for example, so we will have a better chance of survival. 

Genes are selfish. Their only job is to help the body succeed. That turned out to be a fabulously effective mechanism. That drives every molecular decision, cellular decision, tissue, organ, and system decision to make as efficient a body as possible. 

When genes, over hundreds to thousands of generations, know you changed your living habitat from an iron-rich to an iron-deprived region, they eventually decide to make a change in the iron metabolism pathway so that your tribe (thus, gene pool) will be able to pump in several times more iron from the same food than people from other genetic tribes. When my ancestors lived without cattle farming culture in the far east, my gene pool didn’t change to the version that can digest lactose—the sugar in milk—as Northern Europeans’ or Eastern Africans’ [gene pools] did. 

As you probably can imagine, all biological creatures—bacteria, fungi, plants, and mammals—all developed their unique ways of “talking” to their specific environment and worked out their metabolism to generate and manage energy for them. They used millions to billions of years to tweak their metabolic system so it works best for their species, at least for the time being. 

Overall, the science of metabolism is naturally developed in all biological systems—including us—to make compounds so the body does not have to rely on all the external sources for generating the energy and the building blocks to maintain the body. Over a long time, this process becomes extremely complex and efficient. 

All vertebrates—including us—lost the ability to make vitamin C, and yet we require a large amount of it to stay functional and healthy.1 Now, after our discussion, you must know why we have lost it. That’s the beauty of crosstalk between metabolism and the changing environment. 

So, Kristin, Kelly—that’s the science of metabolism. You know, there’s so much more to this that we can apply to our everyday lives. Can we talk about that? 

What influences the science of metabolism?

metabolism and nutrition

Kelly: Absolutely! Kristin, do you want to tell us about some of the nuances that go into the science of metabolism? What are these different parts of our metabolism? What makes us different beyond a cellular level? I'd love to hear your insights on that.

Kristin: I think, Sherry, you did a great job of really highlighting that metabolism is more than just weight and that it has so many different components to it. But I think a lot of us still think in terms of calories in versus calories out. Because at the end of the day, what we eat powers our metabolism. I find it really interesting to understand what controls the science of metabolism or a metabolic rate. 

If we look at the science of metabolism, in its most basic form, there are really three different areas that impact or influence our metabolic rate.

Basal Metabolic Rate (BMR)

The first one is called basal metabolic rate, or BMR. This is what's going on in your body when you are just sleeping and when you first wake up. It is the bare minimum [amount of] calories that you have to burn in order to keep yourself alive. Sometimes, you will see it called resting metabolic rate—for example, [if you’re] just sitting quietly when you're watching TV or reading a book, you don't have a lot of activity. That one might be a little bit more realistic to use versus BMR for most of us due to some amount of movement we engage in during the day. 

Basal metabolic rate accounts for anywhere from 50 percent all the way up to 80 percent of the calories that we burn, or how we use our food for fuel. And this can be because we are building new tissue; it powers making hormones and protein turnover. So that is the biggest component of what our body is doing to burn calories.

Thermic Effect of Food

Another component of what controls our metabolic rate is actually just processing the food we eat. So, the technical term for it is called the thermic effect of food. And this is our body digesting, absorbing, and assimilating all the different foods for fat, carbohydrates, and protein. This counts for about ten percent of the calories we burn. 

Physical Activity

The last one is physical activity. Physical activity can be going for a run; it can be gardening—it can be any type of intentional physical activity, with the caveat that there is another type of physical activity that is called non-exercise activity thermogenesis (NEAT) and this is fidgeting. It is for those people who you see fidgeting, standing, or do other movements they are unaware of. 

There are other factors that can influence the science of metabolism behind your metabolic rate. One is lean body mass. So, your muscle and anything that is not fat tissue can be considered lean body mass. The other one is fat tissue. Fat is now considered an endocrine organ, and it can produce different hormones—including adiponectin, which can also play a role in your metabolism.


So, with lean tissue and adipose tissue body, size can then affect your metabolic rate. Just because somebody is a larger person, it doesn't mean, necessarily, that they have a slower metabolic rate. They might have a really high level of lean body mass. Football players are a really great example—they might have a high BMI, which may be above the range recommended for most people, but they have so much muscle that they're burning so many more calories compared to somebody that is half their size. 

Sherry: Yeah, they are off the chart of BMI but normally metabolically healthy! 

Kristin: Right! There is also physical activity, but as we already talked about, aerobic exercise is not going to burn near as many calories as just your resting metabolic rate during the day. However, exercise, especially resistance training, can increase your lean mass, leading to an increase in your metabolic rate.

Genes and Aging

We know that genes play a role in your metabolism, as well as your age. If you are a baby and you're growing, you will have a really high metabolic rate. Babies eat all day long, they're constantly processing those calories. Your metabolism tends to be higher as you go through your teenage years since you're still growing until you get to the age of around 20. Then, our metabolism starts to level off, and then drop off. 

As Sherry mentioned, when we get into our late 30s, we see an even steeper decline. We often associate weight gain with age. There are some different things that are happening with our bodies as we age. If you're a female, your estrogen levels go down. If you're a male, you lose testosterone. Both of which can affect the science of metabolism. 

There can also be dysregulation of other hormones—including hunger-signaling hormones leptin and ghrelin. Leptin functions to tell your body that you have enough energy and helps prevent overeating. Ghrelin is the hunger hormone and tells your body that you need to eat.

In addition to hormones, physical changes such as loss of taste, decreased physical activity, problems with chewing, nutrient deficiencies, and so on [affect metabolism]. Most of the weight that we associate with aging isn't so much hormones but decreased movement. The science of metabolism can also be affected by genetics, diseases, medications, weight, and diet history. 

A lot of people find the thermic effect of food pretty fascinating. Fat is our preferred way to store energy. So, we're really good at getting it and keeping it in our bodies if we need to. So that only might bump up your, you know, the thermic effect of food by maybe five all the way up to 15 percent, depending on if, you know, you're somebody who has a harder time processing carbohydrates—our body's really good at processing those. 

Protein, though, is where that really bumps up the thermic effect of food that can go all the way from 20–35 percent of that calorie bump. That doesn't mean to go out and just eat nothing but protein—that's terrible for your kidneys. But it's just showing how different meal compositions can impact how you are processing calories just by consuming food.

Sherry: There are individual differences in processing each too, right?


Kristin: Absolutely. So again, going back to those hormones, going back to lean, body mass—those are all different things. That can impact [individual processing]. 

And then I think we've all heard it, or at least have read about it—that there are these foods that have this thermic effect, like cayenne peppers. Spicy foods are thought to help us raise our metabolism. And there is evidence to show that they can maybe raise it a little bit. But this is usually right after you get done eating them. And it's not long term. So, the actual impact that it has on your overall calorie burn isn't really significant to put you into some weight loss mode. 

So, that was a really long list. And we can probably go into any one of those subjects for hours. But for the sake of time, I think we should probably move on to the next one and go from Kelly's perspective in the clinical sense, but also in real life.


Even though we just confirmed that metabolism is more than regulating how much you can eat, there is a pretty strong link between the science of metabolism and weight. Kelly, could you explain this relationship further?

The Science of Metabolism and Weight

Kelly: We started this conversation talking about how it is common for people to think about their weight when they think about the science of metabolism. And that's for a reason—our weight does have a big influence on our metabolism, especially when it comes to our weight history. 

You may have heard about how someone who yo-yo diets or does crash diets is more likely to gain weight back. Unfortunately, because of yo-yo dieting, metabolism can slow when our calorie intake is insecure. Your body may be responding, “What's going on here? I don't feel like my sources of calories are going to be known. I'm going to hold on to every ounce of energy that I have because I want to make sure that my body is supported and I can keep doing my basic functions.”


If you have a goal of weight loss, slow and steady truly is the right way to go for keeping your metabolism healthy, so you're not scaring your body into thinking about survival mode to hold on to those calories. If you see any diet or fads or magazine articles about quick weight loss, be cautious. I always try to remind others that the faster that we lose weight, the more likely we are to put it back on. You might have seen some of those popular weight loss TV shows where fast, dramatic weight loss is encouraged. Unfortunately, many contestants have a really hard time maintaining their drastic weight loss, or they may gain the weight back. 

Another thing that I always think about when it comes to weight and the science of metabolism is that we are all so unique. I like to use myself and my husband as an example. We just went for a run yesterday morning together, and we love tracking our runs on our GPS watches. When we compare our statistics after our runs, my husband will burn hundreds more calories than I do. He is taller than me, and he has more muscle mass. 

That’s something that I think is important for all of us to learn and accept. We cannot compare ourselves to who we live with, or our family members or friends. And so if my husband and I enjoy a meal together, I know that I shouldn't plate our meals to look the same. Even though we're doing the exact same amount of activity, my husband is going to need to eat more than I am in order to be healthy and maintain his weight and feel good. And if I were to eat as much as him, I might feel sluggish and full. If he ate the same amount as I did, he might feel hungry soon after from not eating enough. We are all different in our weight, our muscle mass, our different genetics, our different bodies. 

Sherry: Your metabolic rates and your husband’s are highly distinctive. That's a great example, Kelly. So, is there a way we can calculate those parameters? I would want to know my daily calories based on my age and gender and my lifestyle—you know, with more nuanced configurations. I feel that I will be able to navigate my days with more direction. Is there a way to do that?


Kelly: Yes, there are predictive equations. They are scientific equations that can calculate estimated needs. They take into consideration if you are male or female, your age, activity level, your height, and your weight. There is also a machine called a metabolic cart that can provide a more accurate number by analyzing how much oxygen you consume and how much carbon dioxide you produce. Most of us do not have access to that technology. So a great place to start is using those predictive equations. 

But, as Kristin mentioned earlier, many of us have those little different nuances that do not come up in equations. Like, are you a fidgeter? You might be more active, or you might be in a stage in your life where you are not as active. I know when I was in college, I had a busy semester, and I wasn't working out as much because I was sitting and studying. At that time in my life, I didn’t need to eat as much. But if it’s summer and I'm outside and moving a lot, my metabolism may be higher, and I may need to eat more. 

Ultimately, it's important to take note on how you feel and track your weight trends. Asking yourself questions can help to keep you on track. Am I moving more or less? Am I feeling energized or sluggish? How are my portions? What do I need to adjust in my diet?

Common Myths About the Science of Metabolism

Sherry: There are so many misconceptions and contradicting information regarding the science of metabolism. We could probably talk for the entire afternoon about them! Could we focus on two or three top misconceptions and discuss the evidence that supports debunking them? 

Metabolism-Boosting Foods

Kristin: So, I already mentioned spicy foods and the misconception that you can eat certain foods to boost your metabolism significantly to help you melt the pounds or burn fat. Again, there is evidence to support that they can give you a slight metabolic boost, but it's probably not going to be significant to the point where it can really help you lose weight since the effect is very short term. 

Similarly to spicy foods helping to control weight, another misconception is negative-calorie foods. This used to be a really big trend. An example is eating celery, which was supposed to burn more calories than it contained. Again, foods do give you a slight boost just by eating and processing them, but there's no true negative-calorie food.

Eating Late at Night

I consider one of the biggest misconceptions to be eating late at night. The myth is that if you eat late at night, you automatically will put on weight. In fact, it really is about total calories throughout the day—what you're eating versus what you're burning. Where that myth probably originated is from a number of individuals who have less control over their eating later in the day and at night. We tend to exert less self-control towards our eating habits as we get tired. 

Many of us also have a tendency to be unaware of what foods and quantities we are truly consuming, and we also may want to reward ourselves for our accomplishments—or even self-control from earlier in the day. So, it's not necessarily the timing as much as it is we're not really paying attention to what we're eating. 

That being said, there is some research on this. The subject matter is called chronobiology. There is evidence that supports that it is really the timing of your meals and how you distribute your meals throughout the day. 

Chronobiology research indicates that it's not necessarily eating late at night that causes an issue, but the time you stop eating before you go to bed. The goal is to create a three-hour window of time between the last meal you eat and when you go to bed. This may result in better weight control, as well as other health outcomes. It doesn't matter if you go to bed at nine, 12 or six am in the morning, as long as you stop eating three hours before you go to bed, that is really what that sweet spot is to help your metabolism. 

That being said, there are a couple health conditions that eating closer to when you go to bed actually might be good for your metabolism—for example, people with poor blood sugar control or type 2 diabetes. 

In the morning, naturally, to help us wake up, we have elevated levels of a hormone called cortisol, which I think most of us are familiar with because it's known as the stress hormone. This hormone also helps us wake up in the morning. Cortisol has the opposite effect of insulin, meaning it blocks insulin from doing its job of getting glucose into the cells. For some individuals, this causes very high blood sugar levels. Eating a small healthy snack with protein [before bed]—100 to 150 calories in total, about a serving of Greek yogurt—can help blunt that cortisol response in the morning so blood sugar levels are more stable. 

Sherry: What about you, Kelly? What are your top two or three things to debunk?

Smaller Meals Throughout the Day

Kelly: Kristin, those are great examples. One that I hear a lot about is eating smaller, more frequent meals as a way to keep metabolism high. There may be some truth behind that, as eating more frequently can make sure that we don't get too hungry (and over-consume later) or let our blood sugar levels drop. 

Where there may be a problem is when those small meals are actually not as small as they should be, and overall calorie intake actually increases. So, make sure that they are truly half of a meal, or when you are having a snack, make sure that it’s going to fill you up with fiber or some protein to truly keep you satisfied.

Slim Figure

I have one more myth to debunk. And this is that if you see somebody who appears to be very slim. We might think, wow, they have a really fast metabolism. This may not be the case if they don’t have a lot of muscle mass. They may just eat less. How somebody looks on the outside might not tell their whole story, which is why it's hard to compare apples to apples. So, those are just some of my myths that come to mind.

Science of Metabolism Takeaways

Kelly: We have gone through a lot of fun material here! If you were to summarize, what would you say are the biggest takeaways when it comes to the science of metabolism?

Sherry: I learned that the basal metabolic rate is an important metric for understanding the basic level of a person’s metabolism and that it’s tightly linked with a person's lean mass, not so much fat mass. I also learned in order to keep your basal metabolic rate at the levels you want it to be, the types of exercise regimen you select makes a difference. What have you learned, Kristin? Kelly? 

Kristin: Yeah, I think you bring up a good point—maintaining your muscle mass is definitely important. And I, I hope that down the road we have an exercise physiologist come onto this program so we can really dive into the different types of exercise to incorporate into your life—especially as you age—and what the benefits are. But definitely resistance training, cardiovascular, or aerobic exercise is great. It does help us burn calories, and is really good for our heart, our circulation, [etc.], depending on the type. 

I used to be a runner (not so much anymore), but as we age, how it can impact our joints … resistance training and building that lean muscle mass and preserving it is really where your metabolic rate is going to thrive and what's going to help it. 

And then also, Kelly mentioned this before, but not drastically cutting your calories—so, going on crash diets or fad diets. Short term, your body, when it is undergoing what it considers starvation, can drastically lower your metabolic rate. But long term, even if you are on a healthy diet, as we lose body mass, as any of us diet, we're going to lose fat. But we're also going to lose lean muscle. That is just how our bodies physiologically are going to react. 

So, two people can be 150 pounds. But the person who dieted, most likely, is going to have a slower metabolic rate because of the weight loss than the person who had never dieted in their life. So, really understanding what you eat, and how that can impact it. And actually, next month, we're going to talk about a subject called reverse dieting to try to minimize the impact of dieting on your metabolism. So, we'll dive more into that later on. 

And then, last for me (this is something I have to work on every single day)—hydration. So, your metabolic process can't happen unless you are hydrated. And the better you're hydrated, the better it is for your body—not only for your metabolism but just general health. So, those are the things that I would consider some of the major takeaways. But what about you?

Kelly: Well, you've both inspired me. Tomorrow morning, I'm gonna do some resistance training.

Sherry: There we go!

Kelly: To build off what you were saying, Kristin, a big takeaway for me is to avoid the temptation of yo-yo dieting, and to be kind to yourself. And I mean that more than just physically. Be kind by fueling your body with foods that are going to make you feel good, physically and mentally. Know that we are all different, we all process nutrients differently, and we are all going to look different. We can just do the best that we can by fueling ourselves with healthy foods that are going to make us feel good now and in the long term. Those are my big takeaways.


Sherry: This is awesome. Be kind! I love it. Be kind to yourself and think about your body as your dream house. Invest in building it and maintaining it. From time to time, renovate it and be intelligent about it. 

With our science, you are very fortunate having your genome as your blueprint. Your body is really smart. 

You own a great number of smart molecules that serve as your architects, project managers, and construction workers that are available for building your house at all times. You just need to know about their existence and treat them well. Eat the right foods and do the right exercise for your unique body needs. I loved it. 

Thank you both so much. I enjoyed this. I hope GenoPalate's network of friends and family also enjoyed the talk as [much as] I did! Let’s meet again soon for other topics people can benefit from. 

Kelly: Thank you so much, Sherry. I love talking about the science of metabolism with you too.

Kristin: Until next time! I hope everyone has a great and healthy day! 


1. Drouin G, Godin J-R, Page B. The Genetics of Vitamin C Loss in Vertebrates. Current Genomics. 2011;12(5):371-378. doi:10.2174/138920211796429736.


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