Weight Loss Strategies: Eat fewer calories or burn more?

Do you, like most people, assume you’d lose weight equally well by burning more calories or eating fewer? Research on weight loss says otherwise. It’s clear that to lose weight, you’ve got to somehow burn more calories than you consume.  In this video interview, Dr. Steven Heymsfield explains that the two strategies to accomplish this tend to produce different weight loss results.

In earlier portions of my interview with Steven Heymsfield, MD, executive director of the Pennington Biomedical Research Center, he explained why the commonly-heard “rule” that each 3500 calories cut equals a pound of weight loss is obsolete, and how we have to adjust eating and activity habits for weight management once we reach middle age.  In this portion of our conversation, Dr. Heymsfield, recognized internationally for his research, explains that burning more calories in exercise does not bring the same weight loss as eating or drinking fewer calories.

Following the video, read on for some thoughts on how to put this message in context for good health and a healthy weight.

Isn’t Physical Activity a Key Part of Weight Management?

Long-term studies of people who successfully lose weight and keep it off nearly always identify regular physical activity as a key lifestyle change.  But in the short-term, most people find they don’t lose as much weight as they expect when they start exercising.

Why Exercise Brings Less Weight Loss than Expected

Dr. Heymsfield was part of a team of researchers who addressed this question by analyzing the results of 15 intervention trials of physical activity, looking at how exercise affected the balance of calories consumed versus burned.

In this review paper, they looked at several previous hypotheses that have attempted to explain the common experience of less-than-expected weight loss:

♦ Are people adding exercise but moving less the rest of the day?  Even people who get recommended physical activity are likely to be spending too much time sitting these days.  It’s important to recognize that whether for weight management or overall health, even if you exercise, sitting too much is not healthy.  However, research does not seem to support the hypothesis that slow weight loss from activity might stem from people sitting more – either intentionally or unintentionally – when they boost exercise.

 ♦ Is metabolism slowing down (causing them to burn fewer calories all day long) when they add activity? Dr. Heymsfield mentioned this as one possibility in our video interview, yet the conclusion of this research review was that this is not likely the explanation for less-than-expected weight loss in most cases. This might be more of a problem if people attempt intensive physical activity programs or add lots of exercise while making drastic reductions in caloric intake.  Those were not the circumstances in the studies these researchers examined, nor is it likely the case among those adults who start taking a walk a few times a week and hope that will produce weight loss.

♦ Are people gaining muscle weight? How many times have you heard people frustrated with lack of weight loss remind one another, “Muscle weighs more than fat”? Certainly, when people gain muscle that offsets part of how loss of body fat shows up in total weight change. However, especially with aerobic exercise like walking and swimming, if there’s not an increase in calorie consumption, studies show that while it may help prevent loss of muscle, gain of muscle weight is unlikely.

This team of researchers concluded that studies on aerobic exercise did not provide much support for the above hypotheses as explanations for lack of weight loss with exercise. They identified two other hypotheses as more likely to be true:

♦ Do we counteract weight loss effect of exercise by eating more? For some people, this may be true. This is an active area of research right now, and as noted in a previous video interview with researcher Barry Braun, PhD, answers are not clear. In cases where someone does increase calorie consumption as they add exercise, this could occur for different reasons.

• In some cases an increase in calorie consumption can stem from some sort of physiological drive producing increased hunger.  Some research suggests this is more likely to occur in people who are thin or have limited lean muscle mass, meaning it could be a protective mechanism to keep the body from losing important lean tissue.
• In some cases, inappropriately fueling themselves for exercise — eating too little or too much — might lead to a net increase in calories consumed.
• In some cases, people reward themselves with food for their exercise efforts. People often overestimate the number of calories they are burning by taking a walk.  Treadmills and other gym equipment also often overestimate calories expended.  And it’s all too easy to forget how quickly calories add up from healthy foods in excessive portions and even small portions of “treat” foods concentrated in sugar or fat.

♦ Are physical activity choices “low dose” exercise? People differ in how many calories they burn when taking a walk or adding any activity.  For example, heavier people burn more calories going the same distance for the same amount of time than people who weigh less.  Still, the choice of activity type, speed, intensity and total time dramatically alter how many calories are burned. A 30-minute walk going a very brisk 4 miles per hour can burn about 50 percent more calories than the same walk at a moderate 3 miles per hour.  Perhaps the effort in making a behavior change makes it seem  such a gargantuan task we must surely be burning lots of calories, but in actuality, we are choosing “low dose” versions that simply take a long time to add up to significant weight loss.

A typical strategy to promote weight loss is to search for cuts in calorie consumption that add up to 500 calories a day.  In comparison, a typical adult taking a 30-minute walk each day burns 100 to 200 extra calories, depending on pace and the terrain they cover.  What’s more, the impact on weight is the additional calories burned compared to those you’d burn sitting at home. You might burn 100 to 200 calories on that walk, but the actual difference it makes is closer to 50 to 150 calories.  Therefore, to achieve a comparable 500 calorie “deficit” without any change in eating habits would require that person to walk at a moderate-to-brisk pace 1.5 to 5 hours a day.

Interval training (with brief pockets of more intense activity inserted into moderate-paced exercise), and  “high intensity” exercise for people fit and healthy enough, can burn calories more quickly. But for the average adult picking up a walking program, it’s easy to see that the calorie-burning from that alone are small compared to what can be accomplished by diet.

And based on Dr. Heymsfield’s research that he noted in our interview, because of other factors, the “calorie deficit” achieved from activity may not produce as much weight loss as the same deficit achieved through moderate decreases in calorie consumption.

The Take-Home Message

Being physically active is an essential component of a healthy lifestyle. You may not see the impact on your weight for months. Don’t lose sight of the goal, however: each day that you walk or get some moderate physical activity you have immediate effects promoting healthy levels of insulin, which ripples out into multiple health benefits. It doesn’t take long after beginning regular physical activity to see improvements in blood pressure and heart health. Besides, if the stress relief of exercise leads to less emotion-based non-hunger eating, you may indirectly have dramatic effects on weight outside of the calories you burn.

Resources

This table from the  federal ChooseMyPlate website shows how many calories a 154-pound man might typically burn in various activities.

The American Council on Exercise (ACE) provides a calculator of calories burned in a variety of activities based on your weight.

These tools can be a helpful reminder of why physical activity doesn’t lead to weight loss as quickly as we often expect.

However, I stand by the comment I made in the conversation with Dr. Heymsfield: Let’s move our thinking about physical activity away from a weight-focus, and instead think of the many health benefits we can get from something that can be such fun.

References

Thomas, DM et al. Why do individuals not lose more weight from an exercise intervention at a defined dose? An energy balance analysis.  Obes Rev. 2012 Oct;13(10):835-47.

Braun, B. Active Voice: Understanding Physical Activity Guidelines and Weight Loss. Sports Medicine Bulletin. Amer College of Sports Medicine.