Why Exercise Alone Won’t Help You Lose Weight

An expert dietitian explains why you can't "out exercise" your diet

Have you ever pushed yourself to spend an extra 30 minutes at the gym in order to “make up” for eating a few extra cookies the night before, or so you could indulge in a few more drinks at happy hour later on?

On the surface, this line of thought seems like it should make sense, but the unfortunate truth is that weight loss doesn’t really work this way, at least not in the long-term anyway.

“A combination of diet and exercise is the most powerful for managing our weight and achieving our fitness goals,” explains Alexandra Miller, RDN, LDN, corporate dietitian at Medifast, Inc. “When it comes to weight loss, our diet has a much stronger effect than exercise; that's because to lose weight, you need to consume less calories than you burn.”

When I asked Miller what she thinks is the number one mistake people make when it comes to losing weight, she said its relying on either exercise or diet alone.

“It takes 60 minutes on the stair master to burn about 500 calories and ten minutes to slurp down a milkshake that’s over 600 calories,” she said. “Even if you are committed to making healthier choices, an hour on the elliptical can easily be undone with a few peanut butter crackers. Exercise alone is simply not as effective for weight loss as is our diet.”

However, when it comes to maintaining a healthy weight, Miller says that exercise actually plays a stronger role than diet.

“Sixty minutes of exercise most days of the week is recommended to prevent weight regain,” she explained. “Exercise also offers a whole slew of benefits aside from weight management. So in order to live a healthy and happy life, you really need a combination of both.”

But why exactly is diet so important for the process of losing weight?  

“Simply put, you can't out exercise a bad diet,” Miller said. “In order to lose weight, you need to eat less calories then what your body burns in a day and the best way to do that is to reduce portion sizes and eat a well-balanced diet.”

Plus, she explained, our diets are what fuel our bodies for exercise, so successfully achieving our goals in the gym is much more likely if we’re nourishing our bodies with nutrients that will help aid muscle repair and replenish energy stores.

“A well-balanced diet, rich in fruits and vegetables, lean proteins, low-fat dairy, healthy fats, and whole grains, will help improve performance during exercise by providing the body with the nutrients it needs,” Miller said.

At the end of the day, if you’re not paying attention to your diet, exercising more won’t lead to losing more weight.

“This may be for several reasons,” Miller explained. “First, when we increase our exercise our body recognizes a need for more energy—calories. This often causes us to feel hungrier, experience more cravings and eat more. Secondly, as mentioned earlier, it takes a lot of time and effort to burn calories, but not necessarily to eat them. You can go for a long run then go out to eat and undo the work you’ve done quite easily.”

She also mentioned that because we’re typically tired after a long workout, we’re more likely to remain sedentary throughout the remainder of the day, which means you’ll burn less calories from simple everyday activities.

“That’s why exercise and lifestyle activity (standing more often, taking the stairs, etc.) are both important,” she said. “Plus, while exercise does burn calories, it is important to respect our bodies and not overdo it. You can put yourself at risk for injury.”

So, it’s clear that diet is an important factor when it comes to weight loss, but what are some things you can do to make sure yours isn’t holding you back from reaching your goals?

A few suggestions from Miller:

  • It is easy to miscount calories from the foods we eat, even the healthy ones. A 20-ounce Vitamin water has 120 calories and 31 grams of sugar; that’s 30 minutes of canoeing. 1/2 cup of trail mix has about 350 calories; that’s about an hour on the elliptical. A pack of peanut butter crackers has 190 calories; that’s one hour and 15 minutes of walking at 3.5 MPH. To prevent miscounting your calories, keep a food journal. Track every morsel and drop for two to three days per week. That way you’ll know whether or not your diet may be hindering your weight loss goals.
  • Remember, while it is important to reduce your calories in order to lose weight, you still need to eat. Avoid skipping meals in an effort to reduce your calories; it may impact your performance during exercise (meaning you won’t get as much out of your workouts). You may also miss out on key nutrients and slow down your metabolism.  

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