How Much Exercise is Enough? An Interview with Dr. Bryan Bergman


Believe it or not, our bodies were made to move.  We all need exercise. Dr. Bryan Bergman, Assistant Professor in the Division of Endocrinology at the University of Colorado Denver Anschutz Medical Campus, explains just how much exercise we need for cardiovascular health, increasing insulin sensitivity, and weight loss.


How much, or should I say, how little should one exercise to see a benefit?

First of all, you need to decide what you want to accomplish. If your goal is cardiovascular disease prevention we have a lot of epidemiological data demonstrating the minimum amount of exercise necessary. These are classic studies and what they show is what you hear all the time from doctors. ‘Exercise 2 – 3 times per week, 20 – 30 minutes per session.’ It’s been drilled into people’s heads.

So that’s for cardio. What heart rate should we be going for?

Basically you want to achieve a moderate level of exercise for that period. If you are on a fancy machine in the gym, it would be the ‘cardio zone’ on the built in monitor.

Can people lose weight exercising at this moderate level?

The trouble is that many physicians then translate that into the perfect formula for weight loss. But, it is not nearly enough for weight loss. We have a lot of very good data from people who have lost a lot of weight and kept it off long term and that’s the data that I’ll quote you. It’s part of the National Weight Control Registry. These people have kept an average of over 60 pounds of weight loss for over 6 years. So they are doing something right. Now, there is no similarity among them as to how they lost the weight, however, the amount of exercise they are doing is very similar.

These people self report and the data shows that people generally over report by about 25%. Anyway, they self report an hour of vigorous activity every single day of the week. So if we consider that they are probably over reporting they are still exercising 45 minutes a day – every day. It takes almost an hour of exercise every day to maintain the weight loss.

For losing weight, people are going to have a much easier time restricting calories rather than adding exercise. For example, if they work out on a treadmill as hard as they can for an hour – so hard that they crash on the couch for the rest of the day, they might burn 500 calories. If you think about that typical person who is exercising at a lower intensity because it is going to be more tolerable, more fun, they might be burning 200 calories. So it’s much easier to lose weight by restricting calories but exercise is necessary to keep the weight off….and if they don’t they’re out of luck. That’s the bottom line.

Is it that they don’t have the mental power to keep the weight off?

I don’t know if it’s mental power that is the answer. I think it’s more of an energy buffer issue. Your body actually conspires against you to regain the weight. Enzyme levels change. Your metabolic rate changes. Your body is trying to defend the weight it was at. I think that without the exercise component, the body always wins.

How does exercise fit in with diabetes prevention?

Let’s start with insulin resistance. Exercising every other day appears to be the minimum necessary to maintain sensitivity. For example, when we look at people exercising, we find that if someone exercises on Monday, afterwards, their insulin sensitivity (the opposite of insulin resistance) is better. On Tuesday, assuming no exercise that day, their insulin sensitivity is still better than it was Monday before they exercised. By Wednesday they are back to where they were before they exercised.

What do you think is going on?

It probably has something to do with glycogen replenishment. Glycogen is made up of long chains of glucose and so this is where glucose is stored. When you exercise you deplete these glycogen stores and this provides empty space which can then be taken up by glucose entering the cells. Once it fills back up, insulin sensitivity is gone.

Now I know you have an idea about old fat versus new fat (to read about this in more detail click here).

That’s true, I do think it contributes but we don’t have a lot of data on it yet. it’s more of a work in progress.

So how intense does this workout need to be?

This will not surprise you. The more intense the workout, the greater the gain will be in insulin sensitivity. Harder and longer is better. In terms of a minimal dose, at least that I have data to support; it seems that 15 minutes is the minimal time necessary to get a measureable increase in insulin sensitivity. Now there is a caveat to the intensity issue. There was this great study done in South Carolina by a fellow named Joe Houmard and I quote his dataset a lot. The wild thing about his data set was that in his study exercise intensity turned out not to be so important. What was important was the duration of the exercise. He had 3 groups: high intensity short duration, moderate intensity moderate duration, and low intensity long duration. Things were set up so that each group did the same amount of work. What they were expecting to see was that the high intensity group would reap the greatest benefits but this is not what they saw at all. That group did not do as well as the long duration group. So it was the time people were moving in that study group that seemed to be the most important factor.

So this is really interesting. What you are saying is that if someone is walking vigorously around the mall window shopping over their lunch break that could work?

Yes, that could be effective. Now that could be effective for helping to maintain or facilitate weight loss. It will be effective for increasing insulin sensitivity. It will not be effective for improving cardiovascular disease prevention. The data says that for cardiovascular disease prevention you need a sustained bout of exercise.

So to sum up: 20 – 30 min a day 2 – 3 times per week will improve cardiovascular health and will contribute to helping keep insulin sensitivity up, but will not do much for either weight loss or maintaining weight loss. To really focus on weight loss, you need both diet and exercise with diet being the main component for losing the weight and about 45 min to an hour every day to maintain the weight loss. For combating insulin resistance: the more the better. Increased intensity is good but long duration at even modest intensity is good.

That’s the schema.

Dr. Bryan Bergman is an Assistant Professor in the Division of Endocrinology at the University of Colorado Denver School of Medicine.

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[…] to Dr. Bryan Bergman, exercising every other day appears to be the minimum  amount of exercise necessary to maintain […]

13 years ago

Thank you for including this informative interview regarding physical activity.  It’s what we should all strive for (if physically able), diabetes or not. 

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