Why you can not solve a bad diet with exercise if you want to lose weight

"If I kill myself in the gym I can eat whatever I want" or "as long as I go running, I will have a controlled weight." Have you ever thought similar things to these? Do you think that monitoring your diet is secondary if you comply with the exercise?

We are sorry to tell you that you are wrong. If you want to lose weight, you will have to be aware of what you eat, even if you go to the gym practically every day. Unfortunately for everyone, when it comes to losing weight there are no shortcuts.

To lose weight you need a caloric deficit

To understand why exercising is not enough, we have to start by explaining the basics when it comes to losing weight: you need to get a caloric deficit.

Our body gets the energy it needs from the food it consumes, and when it consumes more energy than it consumes, it stores it as fatty tissue in anticipation of lean times, when it ingests less than it needs.

So if you want to lose weight, you must get your body to use these fat reserves, consuming fewer calories than you spend. All diets, both long-term and promoted as miracle diets, are based on this principle. The difference is how this caloric deficit is achieved and how easy it is to avoid the yo-yo effect (quickly recover everything lost).

Fast ingesting calories, slow burning them

Taking the above into account, you may think that you have enough to increase the amount of physical exercise you do. So you would burn more calories and you could get that caloric deficit that will make you lose weight, right?

Well in theory, but in practice this is really difficult to achieve for the following reason: after thousands of years of evolution, most of it with a shortage of caloric foods within our reach, our body has developed a true talent to when it comes to quickly detecting, enjoying, and processing high-calorie foods and slowly burning those same calories.

From a purely technical point of view, our body is in this sense an enormously efficient machine. The problem is that in a world in which calories are no longer in short supply, but are surplus, this effectiveness works against us, and it is difficult to maintain a healthy weight by only focusing on physical exercise and neglecting food.

What you would have to run to burn these calories

A year ago, the British Royal Society for Public Health published a table in which it collected how much exercise it takes to burn certain unhealthy foods. We collect it here, translated into Spanish, to give you an idea of ​​the imbalance between calories that come in when eating and those that come out when exercising.

Always keep in mind that there are more factors that influence the rate at which your body burns calories, such as the percentage of muscle mass or the physical state of each one. This is especially relevant in aerobic exercise, to which the body gets used to and each time you have to do more of the same exercise to burn the same calories.

Unhealthy food

Approximate number of calories

Time to burn them walking at a good pace

Time to burn them running at a leisurely trot

Sugary soft drink


26 minutes

13 minutes

Standard chocolate bar


42 minutes

22 minutes

Vending machine sandwich (bacon and cheese)


1 hour and 22 minutes

42 minutes

A family pizza room


1 hour and 23 minutes

43 minutes

A medium coffee-smoothie


53 minutes

28 minutes

Potato chips package or similar snack


31 minutes

16 minutes

50 grams of roasted and spiced peanuts


54 minutes

28 minutes

Sweetened industrial pastries


1 hour and 17 minutes

44 minutes

Bowl of breakfast cereals


31 minutes

16 minutes

Muffin pastries


48 minutes

25 minutes

What if you do other sports?

Maybe neither running nor walking is your thing. So how many calories do you spend doing your favorite sport? The Mayo Clinic published in October 2017 a compilation with this information, calculating the number of calories per sport putting as an average subject a woman of 76 kilos and a man of 88.


Woman (76 kg)

Man (88 kg)

Ballroom dancing

219 calories / hour

273 calories / hour

Slow cycling (16 km / h)

256 calories / hour

319 calories / hour


314 calories / hour

391 calories / hour

Jogging on the elliptical

365 calories / hour

455 calories / hour

Swimming (moderate intensity)

423 calories / hour

501 calories / hour

Swimming (high intensity)

715 calories / hour

892 calories / hour

Rowing machine

438 calories / hour

546 calories / hour


584 calories / hour

728 calories / hour


584 calories / hour

728 calories / hour


438 calories / hour

546 calories / hour

Climbing stairs

657 calories / hour

819 calories / hour


752 calories / hour

937 calories / hour

Jump rope

861 calories / hour

1,074 calories / hour

Exercise without diet, bad solution

If you take a look at both tables you will realize why trying to lose weight relying exclusively on exercise without paying any attention to diet is not a great idea: if you are a woman, you need more than an hour of elliptical to compensate for a quarter of pizza, and swimming more than an hour at moderate intensity to burn a bun, and if you're a man, the numbers are a little more on your side, but you're also more likely to have consumed larger servings.

In addition to being ineffective, this approach to physical exercise can end up taking away all the fun by turning it into a compensation mechanism, as a way of atone the blame for what we eat. Likewise, unhealthy food can be seen as a prize that we give ourselves after doing sports, paving the way for a possible eating disorder.

For effectiveness when it comes to losing weight and also as a way to enjoy the process much more, a combined approach of exercise and diet is much more convenient, understanding diet not as a restrictive menu that tells you what to eat at any time , but as a way to improve eating habits by reducing and eliminating ultra-processed foods, those with added sugars, those with a high salt content and those using poor quality flours and fats.

By reducing these foods, we will reduce the calories we eat, especially those that do not provide us with beneficial nutrients, and combining it with exercise produces that caloric deficit that we talked about at the beginning and that is, in fact, the only real method to burn fat.

Images | Unsplash

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