We all have questions about metabolism. Among our most burning… what is it, why some people’s seem faster than others and how we can speed up our own?
So I decided to interview a legend in the field, David Katz, MD, MPH. Dr. Katz is not only the author of Disease Proof, The Remarkable Truth About What Makes Us Well, he’s also the director of the Yale University Prevention Center. And he’s the editor in chief of the journal Childhood Obesity and the author of nearly 200 scientific articles and textbook chapters.
David Katz: Metabolism is a complex biochemical process in which your body combines the food and liquid you consume with oxygen and converts it into energy. Your body needs this energy for every function, including breathing, pumping your blood, growing and repairing cells, brain and nerve function, controlling body temperature, etc.
Dr. Steve: Another term we hear a lot is “basal metabolic rate.” What’s that?
Dr. Katz: Twenty-four hours a day, no matter what you’re doing, the body is burning calories in order to execute all the tasks I mentioned above. The amount of energy – or calories – your body needs to keep up with these functions is known as the basal metabolic rate, or BMR, and it accounts for about 60 to 75 percent of the calories you burn every day.
Dr Steve: What determines your BMR?
Dr. Katz: There are several factors. First and foremost, your body size and composition. When you’re bigger in general, you’re going to be burning more calories all the time. One of the cruelest twists of fate is that as you lose weight your metabolism slows down. That’s because you have less mass in general on your body so it takes fewer calories for the body to keep up.
Another factor that influences your BMR is your gender. In general, men have higher BMRs than women. That’s because naturally, men have more muscle than women. Not fair, but true.
Why does muscle matter? I call muscle your calorie-burning engine because muscle burns more calories to sustain itself than any other tissue in the body. In other words, the more muscle you have, the more calories you’re going to burn no matter what you’re doing. (Yes, even sitting on that couch doing nothing.)
Dr. Steve: Does your metabolism really slow down as you age?
Dr. Katz: Unfortunately, yes. That’s because as you get older the amount of muscle tends to decrease and fat begins to account for more of your weight.
Dr Steve: Is there anything you can do to raise your metabolism?
Dr. Katz: Absolutely. The most important thing anyone can do is exercise to build up muscle. As I said before, muscle tissue burns more calories all the time. So for every pound of muscle gained, you’ll burn roughly 50 more calories per day.
Dr Steve: Is walking enough?
Dr. Katz: For health, walking is certainly good for you. But you really want to build muscle in order to bump up your metabolism. With walking, you’ll build some muscle in your lower body, which is where the big muscles reside. And that’s good. But I’d also suggest muscle-building exercises with more impact, at least 20 minutes, three times a week. Those include steppers; free weights; circuit workouts using resistance machines; or resistance bands.
Keep in mind, when you build muscle you’ll have a leaner look. You always hear about how muscle weighs more than fat. That’s not true – a pound of muscle weighs the same as a pound of fat – one pound! But muscle is denser than fat. So it takes up less space on your body. So the more muscle you have, not only will you burn more calories 24/7, you’ll also look slimmer.
Dr. Steve: You said earlier that your BMR accounts for about 60 to 75 percent of the calories you burn every day. What about the other 35 to 40 percent?
The rest – about 10 percent – results from the heat produced during the metabolism of food – the thermic effect of food. Some people naturally generate more heat than others, and they find it easier to lose weight.
Dr Steve: Speaking of food, are there really any foods that raise your metabolism?
Dr. Katz: As I mentioned above, there’s a small thermogenic effect when you metabolize any food. In general, it’s higher for protein – or carbohydrate-containing foods, lowest for fats. Some specific foods – caffeinated coffee, green tea, hot peppers – have a thermogenic effect, but it’s quite modest in the scheme of things. Some nutrients that stimulate metabolism such as L-carnitine and raspberry ketones are now being concentrated into supplements, and some of these show promise. But again, the effects are relatively small compared to a focus on exercise to build and maintain muscle mass, and attention to eating well.
Dr. Steve: They say that when you diet, your metabolism slows down. Any truth to that?
Dr. Katz: Yes, if only because you are shrinking yourself, and smaller bodies need fewer calories for maintenance. But there are other effects that suggest bodies adapt to calorie deprivation and become more fuel efficient – which makes weight loss more challenging. In other words, if you eat too little, your body starts to burn what you’re taking in more efficiently. That’s why crash diets don’t work. Even when you’re dieting, you need to be taking in enough calories every day in order for your metabolism to stay humming. For most women, this is at least 1,200 calories per day; for most men, at least 1,500 calories per day.
My biggest takeaway from our discussion? I need to make sure to do my resistance exercises three times a week. Unfortunately, it’s just too easy to neglect. But since I’ve entered my fifties, it’s vitally important to keep my metabolism from slowing down.
And I simply love talking to folks in the industry who know things I don’t. I always learn a thing or two.
I’m planning to do this type of a Q&A on a regular basis. Is there anyone you’d like to me talk to? Any subjects in particular I can research for you? Comment below, or shoot me an email at firstname.lastname@example.org and I’ll do my best!
Steve Sisskind, M.D.
Hi, I'm Dr. Steve Sisskind, Chief Medical Officer & Founder at RealDose Nutrition.
As a young physician, I struggled because my patients came to me with serious health issues, but I didn't have the right tools to help them. Medical school taught me how to put "band aids" on their symptoms with drugs and surgery, but not how to address the root causes of their problems.
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