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I want to lose weight. Is diet or exercise more important?

I’m a healthy eater, but I’ve always been sedentary. Last month, I started exercising to help me lose 15 pounds over the next three months. So far, I’ve lost only two, which is frustrating. Is my goal unreasonable?


A mix of diet and exercise is best

Assuming that you do, in fact, have 15 excess pounds of body fat to lose, then, yes, your goal to shed them over three months is quite reasonable. But, given your approach, it’s probably not realistic.

If you want to lose weight – and keep it off for good – here’s what you need to know about diet versus exercise.

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How to lose weight: A mix of diet and exercise

A mix of diet and exercise is the best approach to weight loss.

First, resistance training can help prevent muscle loss associated with dieting only. Regular exercise also helps reduce stress, which otherwise could lead to overeating. And it builds self-esteem, something that’s important for motivation and success.

But to take off excess weight, you also need to pay attention to your diet.

To lose one pound a week, for example, a 185-pound person would need to run for 40 minutes, power walk for 70 minutes or do one hour of vigorous weightlifting every day. If you weigh less, you’d have to exercise longer to burn the same number of calories.

It’s easier for most people to consume 500 fewer calories each day than it is to sweat them off at the gym seven days a week. That goes for healthy eaters, too.

Relying on exercise alone to lose weight isn’t sustainable. A busier-than-usual work schedule, an injury or boredom at the gym can disrupt a consistent workout schedule.

Plus, eating one indulgent meal can wipe out a day’s calorie burn from exercise.

In addition, healthy eating doesn’t always equate to fewer calories. Eating a larger-than-needed portion of salmon, an extra handful of nuts or too many salad toppings can stall weight loss.

How to maintain weight loss

Weight-loss success means keeping lost pounds off for the long term. But physiologic changes that occur while losing weight, and persist afterward, make that difficult to do.

Weight loss is associated with an increase in hunger hormones, which makes it harder to stick to a lower-calorie diet.

After losing weight, the body also burns fewer calories at rest and during physical activity than it did before. That’s not unexpected since a lighter body requires less energy to function than a heavier one.

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It’s hypothesized that the more weight you lose and the faster you lose it, the greater these unfavourable metabolic effects will be.

Research conducted among 14 contestants of The Biggest Loser, a reality-TV weight-loss competition, found that, six years after the show, participants’ resting metabolic rates were lower than expected based on their body-composition changes.

The Biggest Loser participants lost a dramatic amount of weight in a short time through extreme dieting and exercise. The findings may not translate to more modest weight-loss methods.

Is exercise the secret weapon for weight loss?

According to a study published in March 2019 in the journal Obesity, successful weight-loss maintainers (people who had kept off at least 30 pounds for an average of nine years) rely on exercise to keep the pounds from piling back on.

The University of Colorado researchers measured daily calorie expenditure, resting metabolic rate and physical-activity levels in weight loss maintainers and two control groups: normal-weight people and overweight individuals.

The amount of calories burned for physical activity (800) by weight-loss maintainers was significantly higher compared with the two other groups.

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Successful weight-loss maintainers also achieved more than 12,000 steps a day – compared with 6,500 for the overweight group and 9,000 for the normal-weight group.

The findings also suggested that weight-loss maintainers ate a similar amount of calories as the overweight participants. In other words, these people avoided regaining their lost weight by being physically active, not restricting their calorie intake.

Unlike the Biggest Loser study, the researchers didn’t find that successful weight-loss maintainers had a lower-than-expected resting metabolic rate.

Bottom line: Diet matters more than exercise

Your diet plays a bigger role than exercise when it comes to losing weight. Include physical activity, though, to help maintain muscle and motivation.

To keep lost pounds from returning, consistent evidence suggests that physical activity is key. That doesn’t mean that diet isn’t important, it is.

But changing your daily habits to achieve more steps and to include a fitness class can allow you to ease up a little on restricting calories.

9 tips for weight loss

Here are nine additional tips and resources from Leslie Beck to help you lose weight:

  1. Trying to lose weight? Here’s why slow and steady is the best approach
  2. The Mediterranean diet promotes weight loss. What to know about the healthy eating plan
  3. Adding resistance training can help prevent muscle loss associated with dieting only
  4. To gain muscle while losing weight, eat more protein and add resistance exercise
  5. A detox cannot ‘cleanse’ the body. What to know if you are considering a detox dietw
  6. Gut health influences our metabolism, weight and more. Five foods to eat for a healthy microbiota
  7. Does intermittent fasting work for weight loss? What the research says
  8. How many calories should you consume to maintain a weight loss?
  9. Experiencing a weight-loss plateau? Five tips to break through

Leslie Beck is a registered dietitian.

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