Current guidelines recommend 60 minutes of exercise a day for weight loss. But recent research suggests that, when it comes to aerobic activity, shorter periods of exercise may actually be better.
You’ve heard it before: as a society, we don’t exercise enough, and we eat too much. Experts generally agree that if we want to be healthy, we should aim for at least 30 minutes of moderate physical activity a day. And if we want to lose weight or maintain weight loss, we should bump our activity up to 60 minutes a day.
But new research suggests that less may actually be more when it comes to the amount of physical activity we need for weight loss.
Sound too good to be true? To learn more, read on.
Fitting in structured exercise can be tough. You have to carve out the time and make it a priority. Organizations like the American Council on Exercise recommend at least 60 minutes of moderate activity most days of the week for folks trying to lose weight(1).
Sixty minutes a day! Dutifully, you buckle down, loading your MP3 player with enough Rihanna and Eminmem songs to power you through your hour of cycling, running or using one of those mind-numbingly boring indoor cardio machines.
You eat a pretty good diet. You’re even lifting weights. So why aren’t you losing more weight? Did somebody change the rules here?
Of course some of the discrepancy between expected and actual weight loss lies in changes in body composition. While muscle doesn’t weigh more than fat, it is more dense than fat. So if you’re trading fat for muscle, your scale weight might stay the same even as you shrink. (One good reason not to be a slave to the scale.)
Still, when we’re working hard to lose weight, it’s reasonable to expect some changes on the scale. And changes in body composition don’t explain everything. What’s going on?
The energy balance equation
Losing weight, gaining weight, or maintaining our weight depends on how many calories we take in versus how many we use up – or at least that’s the theory.
Ah, yes. The good ol’ “energy balance equation.”
Seems pretty straightforward, right?
It takes a lot of energy just to keep the body alive with all systems working. This is our resting metabolic rate (RMR). If we cut calories without also increasing activity at the same time, our resting metabolic rate can actually go down. And that’s the last thing we need when we’re trying to lose weight – which is precisely why you’re bopping along on that treadmill, right?
In addition to using calories just to maintain our body’s basic functions, we also use some to digest the foods that we eat. This is what’s known as the thermic effect of food (TEF), and it varies a bit, depending on what we eat.
Protein, for example, is harder for our bodies to digest than simple carbs, so eating it increases the thermic effect. In other words, just by trading a portion of your processed carbs for some lean protein, you’ll end up burning more calories each day!
But the aspect of the energy balance equation that we can influence most powerfully with our own behavior is physical activity. This includes planned exercise (the kind you do on the track or in the weight room) as well as non-exercise activity thermogenesis (NEAT).
Okay – so you knew all this. But did you also know that NEAT can vary enormously from person to person and that it is really hard to measure? And that NEAT can also decrease when calories are restricted?
This equation may not be as simple as it appears.
Next you may ask: When it comes to maintaining resting metabolic rate, can exercise offset a decrease in NEAT in the same way it can offset calorie restriction?
Well, the answer to that is yes and no…
The human body is very “smart” and has a strong innate drive to keep us alive and to maintain the status quo. When we cut calories without exercising, our metabolism decreases, and proteins like leptin set off the drive to eat more.
Likewise, when we exercise at the same time as we cut calories, the metabolic efficiency of exercise often increases so that we burn fewer calories for the same amount of exercise.
Meanwhile, we also want to eat more – and, without even meaning to, we may reduce our non-exercise activity thermogenesis (NEAT).
For example, maybe after a long, tough workout you decide to go through the drive-thru instead of cooking. Even if you choose healthy food, it doesn’t take much energy to get it. Meanwhile, if you’re a 150 pound male, you could have burned roughly 136 calories by cooking for one hour (2). That may not sound like a lot, but if in addition to going to the drive-thru, you also let the kids walk the dog and the dishwasher wash the dishes, and then you drive to the corner for your mail instead of walking, the calorie-burn edge of your workout is completely lost.
As this example demonstrates, it’s tough to capture everything that goes into our energy balance equation and this presents a puzzle for researchers trying to understand the relationship between exercise and weight loss.
In fact, a study conducted several years ago with overweight menopausal women found that, contrary to common sense and all expectations, women who exercised more didn’t lose more weight. Researchers concluded that they must have compensated in some other areas (3). Perhaps if they exercised longer, they “rewarded” themselves with a 16-ounce latte instead of the 8-ounce. The answers just aren’t clear.
60 minutes of exercise for weight loss?
You may now be wondering whether there’s any real basis for the recommendation that we should exercise for 60 minutes a day to lose weight.
If so, your doubts are grounded. This recommendation wasn’t pulled out of thin air, but it’s based on an extrapolation of sorts, using data collected from subjects in the National Weight Control Registry (1).
Many of the studies informing the current guidelines show that exercising for 30 minutes or less produces some weight loss, but not much. These studies also show that successful losers often exercise a lot – or that under laboratory conditions, more exercise means more weight loss.
If that’s the case, then it might seem reasonable to assume that outside the lab environment, we could expect the same results. Exercise longer, lose more weight.
But strangely, this doesn’t always happen. There are sex differences as well as other unexplained discrepancies. Overall, this means there’s a lack of really strong conclusive evidence for the 60-minute guideline (1).
Given the shaky support for the 60-minute rule, maybe it’s time to re-examine it.
After all, the thought of exercising for 60 minutes a day can be daunting to a beginner who wants to lose weight. Especially if that person is prone to “black-and-white” thinking. If I can’t do 60 minutes I might as well do nothing, she might think. And if she doesn’t do any exercise, her health, as well as her weight, will inevitably suffer.
But if more exercise doesn’t necessarily result in more weight loss, maybe she doesn’t really need 60 minutes a day. Maybe – with a little knowledge and forethought – she can get by with exercising less – and still lose the weight she wants to lose.
Maybe it’s all about finding the right balance between exercise, non-exercise related activity, and calories consumed. That’s the focus of this week’s research question.
Do we “compensate” for increased exercise — and if so, how?
Do people who exercise more involuntarily offset the number of calories burned in exercise by eating more or doing less non-exercise related activity (NEAT) throughout the day?
What actually happens to body weight and composition when we increase aerobic exercise?
Rosenkilde, M., Auerbach, P.L., Reichkendler, M.H., Ploug, T., Stallknecht, B.M., & Sjodin, A. Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise – a randomized controlled trial in overweight sedentary males. . Am J Physiol Regu Integr Comp Physiol, 2012 Aug 1; doi: 10.1152
This study used a randomized controlled design with two experimental groups and a control group. Over a period of 13 weeks, the 43 subjects in the experimental groups completed either a moderate (MOD = 30 minutes, n= 21) or a high (HIGH = 60 minutes, n=22) dose of aerobic exercise. These subjects also made changes to their diets. Meanwhile, the control group (CON, n=18) maintained a continuous sedentary lifestyle.
The randomization took place over a little more than a year, between January 2010 and February 2011, in three blocks of identical group allocations. Participants received a fee if they successfully completed the study. Few studies are well enough funded to offer payment, but rewards certainly go a long way towards decreasing the dropout rate!
The subjects in this study were not athletes; nor did they engage in regular exercise. They were male, white, 20-40 years old, and they fell into what’s called the “healthy overweight” category. In other words, their blood pressure and blood glucose levels were normal, they weren’t taking medications, and they had no first degree relatives with type 2 diabetes. They were overweight, yet not quite obese: BMI 25-30 kg/m2 (normal is 18.5-24.9 kg, overweight is 25.0-29.9 kg) and they had high levels of body fat > 25% (healthy range for men age 20-40 is ~8-19% and overweight is ~19-25%) (4).
Researchers also put together a control group of 30 people who didn’t use any nutritional supplements, and were matched for age, gender, sports discipline, body mass index (BMI), and training volume.
All subjects underwent a series of tests before they were randomized to the 3 groups. The information gathered from these baseline tests allowed the researchers to give the subjects personalized exercise prescriptions based on their body weight, resting and max heart rates, and their VO2max. The subjects were required to wear heart rate monitors so that exercise intensity and duration could be recorded. In other words, the subjects couldn’t “cheat” on their workouts without the researchers knowing.
Data collected during the study included:
- Body weight and composition: Researchers measured subjects’ body weight and composition after an overnight fast. Dual-energy x-ray absorptiometry (DEXA) was used for measuring body composition. This is a very precise but expensive way to measure lean and fat mass. If you’ve have ever had a bone density test, it was most likely performed using this type of machine.
- Resting energy expenditure (REE): To measure resting energy expenditure, the researchers used a respiratory calorimetry system. In order to ensure the study’s reliabilty, they needed to have a pretty accurate idea of how many calories the subjects burned at rest, so they measured the air the subjects breathed in and out (oxygen in and carbon dioxide out). Then they used a specific equation (called the Wier) to calculate resting energy expenditure.There are several methods to measure air consumption at rest, each requiring longer times at the lab. In this study, the subjects rested for 25 minutes before the researchers started collecting data. This is a reasonable length of rest time, which should ensure accurate results.
- VO2max: This measurement represents the maximum amount of oxygen a person can use during intense exercise. It’s considered an indicator of a person’s level of cardiovascular fitness.To find out your VO2max, you get on a treadmill (or in this case a bicycle) and move as fast as possible while researchers crank up the intensity and speed at specific intervals. Oh, and did I mention that while this is going on, you’re also hooked up to a machine covering your nose and mouth, which measures air in and out?Sounds like fun right? I’ll bet you wish you could have signed on for this study.
- Total physical activity including NEAT: So how do you measure a person’s sum total of physical activity in a 24 hour period? You ask him to wear a really cool monitor that measures the movements he makes throughout the day.While devices like this attempt to capture calories burned by NEAT (non-exercise activity thermogenesis) including very small movements like fidgeting, this is admittedly something of a technical challenge and is subject to large variability.The device used in this study was an ActiGraph® (like a BodyBugg® but waay more expensive and precise).
- Habitual energy intake (EI): Can’t forget about diet either. To measure habitual intake researchers asked the subjects to weigh and measure everything they ate and drank for 3 days and this information was entered into professional diet assessment software. (Nice method – very precise.) Subjects recorded their habitual intake for 3 days in a row, twice during the study: at baseline and again at week 11.
After they’d collected all the body comp and exercise data, the researchers developed personalized exercise prescriptions for the two experimental groups.
Subjects could choose their activity (running, cycling, etc.) but they were assigned to either the MOD (30 minute) or HIGH (60 minute) exercise-dose group. Each week, the subjects had to work pretty hard (70% VO2Max) for 3 of the sessions. For the remaining sessions, they could choose their intensity.
Remember, all of their exercise data was collected during each bout so the research could calculate their training-induced energy expenditure (TrEE).
The researchers also wanted to find out if the macronutrient composition (percentage of carbs, protein and fat) of the subjects’ diets affected overall calorie expenditure, so they devised two different diets for the subjects.
All food items in each meal were interchangeable in the sense that they all contained the same macronutrients. The researchers didn’t elaborate on this, but it sounds similar to an exchange type of system. For example, let’s say they offered sandwiches and soup. Whether a subject chose one or the other, each choice would contain the same amount of protein, carbohydrates and fat.
The researchers didn’t want the participants in either group to know that they were trying to figure out if the different doses of exercise resulted in changes in appetite or if the macronutrient content of the meals led them to eat more or less. So they told them not to restrain themselves, but to eat until satisfied.
The subjects were served the following diets in randomized double-blind order (which simply means that neither the subjects nor the researchers knew who was getting what type of diet):
- High carbohydrate: 65% carbohydrate, 20% fat, 15% protein
- Low carbohydrate: 35% carbohydrate, 50% fat, 15% protein
They were served these diets for 8 days at baseline (4 days of each diet) and then again at week 13. Researchers collected and analyzed data at both points.
In order to answer their questions, researchers had to calculate accumulated energy balance. They did so by measuring the change in fat mass versus fat-free mass.
They also needed a way to measure the degree to which the subjects compensated for the energy used in exercise. They assumed that subjects who exercised for 60 minutes should theoretically lose more weight than those who exercised for 30 minutes.
Their formula calculated exercise energy expenditure based on training duration and the subjects’ resting energy expenditure. This gave them what they called “accumulated energy balance”. If the accumulated energy balance was positive that meant the subjects lost less weight than expected, and if it was negative, that meant the subjects lost more weight than was expected.
Throughout, researchers were trying to zero in on slight increases in the amount of food eaten and/or the number of non-exercise calories burned (the subjects’ NEAT as measured by their monitoring device).
Most subjects complied well with the study’s rules (remember they were being paid) and both experimental groups stuck pretty close to their exercise prescriptions. These factors make the results more reliable.
- Body weight and body composition: Compared to the control group, both the MOD (30 minute) and HIGH (60 minute) group lost body weight (MOD = 4% decrease, HIGH = 3% decrease) and a substantial amount of body fat (MOD = 14% decrease, HIGH =13% decrease).
- Resting energy expenditure: Resting energy expenditure increased more in the HIGH (60 minute) group compared to the MOD (30 minute) group (205 kcal/day). This was likely due to the fact that fat-free mass (FFM) increased more in the HIGH group. The takeaway here is that exercise protects against a drop in REE when calories are reduced.
- VO2max: The exercise training improved the cardiovascular fitness of both the MOD (30 minute) group (18%) and the HIGH (60 minute) group (17%) by a similar amount.
- Total physical activity including NEAT: As might be expected, the total amount of physical activity increased for both groups. When exercise was subtracted there was no apparent difference in non-exercise activity between groups.
- Habitual energy intake: There were no statistically significant differences in what the subjects normally ate or in the amount they ate when served the two different diets.
- Changes in accumulated energy balance: The average daily exercise energy expenditure (ExEE) was 300 kcal for those in the MOD (30 minute) group and 600 kcal for those in the HIGH (60 minute) group, corresponding to the study protocol. However, when changes in body comp were used to calculate accumulated energy balance, people in the MOD (30 minute) group showed an average deficit of -550 kcal compared to those in the HIGH (60 minute) group who showed an average deficit of -470 kcal. Huh.
This study aimed to find out whether and to what degree aerobic exercise triggers compensatory mechanisms. This is important because if exercise does trigger compensatory mechanisms, that could in turn help explain why we often lose less weight from exercising than we might expect.
What researchers discovered was that both moderate and high amounts of exercise led to weight loss and fat loss. But even though the subjects in the HIGH (60 minute) group worked out twice as long as those in the MOD (30 minute) group, they lost about the same amount of weight.
The HIGH exercise group accumulated a negative energy balance that was 20% lower than expected. Meanwhile, the MOD group’s negative energy balance was 80% greater than expected.
Theoretically, the men who exercised more should have lost more weight than they did. But they didn’t – and we don’t really know why.
Interesting results to say the least!
What they suggest is that increasing aerobic exercise past a certain threshold won’t necessarily lead to greater loss of weight or fat. Why this is so isn’t clear yet, but it could be related to slight changes in NEAT and in diet.
I am sure this is not the last we will hear on the subject.
Remember, this was one small study performed with overweight men. Because the study was 13 weeks long, researchers could capture changes in body composition. And that’s a good thing.
But NEAT is much harder to measure than body composition, and varies with age, gender, and the type of activities that subjects engage in.
Also, even when subjects are very cooperative, it’s difficult for them to capture all the food and drink they consume. In this study, the subjects only recorded their intake twice: at baseline and week 11.
Additionally, the diet intervention only took place for a total of 8 days – once, 4 days after baseline data was collected, and then again at week 13. So there were many, many days in between when diet data was not collected. Over a 13 week period, a few unrecorded calories here and there could definitely add up.
In other words, it is difficult to control for every variable, and that means we need more studies.
Finding that sweet spot. Cost benefit ratio. The right balance for you. That is what the findings of this study are all about.
Here are some tips and takeaways.
You don’t need to start cutting all your workouts in half. This study doesn’t show that 30 minutes was necessarily always better, only that 60 minutes wasn’t precisely twice as awesome.
But shorter workouts may be almost as effective as longer ones. Cool! For more on this, check out Two Experiments in Exercise Minimalism.
Pay attention to your non-exercise related activity (e.g. household chores, daily movement, etc.). It really adds up, and can make a significant difference. Plus, these are things you can do if you can’t do a full “workout”.
Pay attention to how much you’re really eating. Just like daily activity can add up, so can little bits and bites here and there.
If you’re trying to lose fat, don’t fool yourself into thinking that you can eat more after a workout. It’s pretty easy to kill a 400-calorie exercise deficit with a small muffin (400 calories) and medium latte (200 calories), and then you’ve just wasted an hour of treadmill hamstering, plus you’ve tacked on more food than you needed! (And if you opted for the drive-thru… well, you get the idea.)
The more mindful you become, the easier fat loss will be. Take an honest look at all your daily activity and food intake — small improvements can actually make a big difference!
To learn more about making important improvements to your nutrition and exercise program, check out the following 5-day video courses.
They’re probably better than 90% of the seminars we’ve ever attended on the subjects of exercise and nutrition (and probably better than a few we’ve given ourselves, too).
The best part? They’re totally free.To check out the free courses, just click one of the links below.