WEIGHT MANAGEMENT ∙ 5 minutes read

What’s more important: diet or exercise?

By Kirsty Mason | Medically reviewed by Dr Luke Pratsides

The importance of diet and exercise has been drilled into the psyche of every weight loss expert - and for good reason. There’s endless evidence to support the role that diet and exercise play in weight management. But sticking to a good routine packed with exercise and healthy eating isn’t easy. For the inevitable ‘off’ days where you feel that you can’t do both, could one trump the other?

There’s a mountain of evidence to support the roles that both diet and exercise play in the management of weight. Yet restricting food and increasing exercise may not promote weight loss in equal measures. To add another layer of complexity, the extent to which you shed pounds when following a healthy routine depends on an elaborate set of events.

Our bodies all metabolise food, store fat and grow muscle in different ways. And good news for men - there’s anecdotal evidence to suggest that men lose weight quicker than women. That’s why sticking to a particular routine might work for one person, but not the next.

Despite individual differences, it’s agreed that weight loss occurs when calorie expenditure is greater than calorie consumption. This is known as a calorie deficit. It’s vital to consume a healthy amount of calories for energy and nutrition, but if you consistently consume more calories than you burn, your body will store extra fat and this will translate to weight gain.

Time and time again, a combination of diet and exercise has been shown to be an effective method of sustained weight loss. Let’s take a look at why they’re the two major players when it comes to losing weight…

Why does exercise help you to lose weight?

To achieve a calorie deficit you must burn more calories than you consume. For a man who burns 2500 calories in a day, he should consume around 2000 calories a day to see gradual healthy weight loss. 

Burning 2500 calories in a single day seems like a daunting prospect when considering the effort required to burn just 500 calories (depending on your weight, you’d probably have to cycle for around an hour to achieve this goal). But our bodies function in a mesmerising way and we actually burn calories throughout the day, simply by existing.

Our total energy expenditure (the number of calories we burn throughout the day) consists of three components:

  • Energy expenditure for maintenance: This encompasses the energy we need for basic functions such as breathing, blood circulation, maintenance of body temperature, cell repair, and cardiac function. This is how we burn the majority of calories throughout the day.
  • Diet-induced energy expenditure: Also known as the thermic effect of food, this refers to the energy used in response to food intake. Energy is needed for the digestion, absorption and distribution of nutrients.
  • Physical activity: Physical activity includes high-intensity activities such as sports, gym sessions and running, but it also includes walking, fidgeting and blinking - any movement that requires our body to exert energy.

So, even without doing a high-intensity physical activity, you still tend to burn a lot of calories throughout the day, depending on various individual characteristics. But, of course, physical activity greatly increases the number of calories that are burned and provides several other health benefits as well.

A systematic review looking at the weight loss benefits of aerobic exercise found that long-term participation in the activity resulted in reduced weight and body circumference. The benefits of exercise for weight loss were also reflected in a 12-week clinical weight loss program that compared the effects of diet combined with exercise and diet without exercise. Although all groups showed a decline in body weight, fat mass and waist circumference, the results were pronounced in the groups that exercised.

Knowing the weight loss benefits of exercise might inspire you to hit the gym, but how many calories are you actually burning?

Understanding how many calories you burn in response to exercise

The number of calories you burn during exercise depends on the intensity of the exercise as well as your individual characteristics. This includes your gender, fitness, weight, and muscle mass. As your fitness increases, you burn fewer calories. This is because your body requires less energy to perform the same activity.

People tend to overestimate the number of calories they burn in a single fitness session. To achieve your weight loss goals, it’s important to bear this in mind (unfortunately, the croissant you grab on your way back from the gym is probably not only levelling out the calories you’ve just burned, but surpassing the total calorie reduction you had achieved).

To burn 500 calories, you probably need to participate in moderate physical activity for over an hour (depending on your weight and the exertion of exercise). So, if you’re aiming for a deficit of 500 calories a day, you’re unlikely to achieve this with exercise alone. That brings us to why diet is so critical when it comes to weight loss…

Why does diet help you to lose weight?

A healthy diet that promotes a calorie deficit is absolutely essential if you want to lose weight but it’s important not to restrict your diet in extreme measures. Not only is this an unsustainable method of weight loss (after rapid loss of weight, people tend to quickly regain weight), but it will also lead to nutrient deficiencies. Very low-calorie diets can also lead to a lack of energy, dizziness, and hair thinning.

To lose weight, it’s important to select the right foods, regardless of calorie intake. Unfortunately, that means if you’re aiming for 1500 calories a day, chomping down on three chocolate-stuffed 500 cal doughnuts isn’t going to see you packing off the pounds. For healthy weight loss, it’s critical to eat a balanced diet rich in nutrients. The easy way to ensure that your diet is full of a good variety of nutrients is to eat several different coloured vegetables in your meals. This is because different colours have different health benefits.

Even if it’s low in calories, reaching for a sugary treat is a common mistake. The calories in sugar are known as ‘empty calories’ as they provide no nutritional value. This means that you won’t be provided with the energy that you need and you’re likely to find yourself hungry again after a short while. It can also lead to leptin resistance which is a hormone that influences appetite regulation and fat storage. As well as this, the effects of sugar are cognitive with evidence to indicate that a diet high in fructose interferes with the appetite control functions of the brain.

For healthy, sustainable weight loss, you should eat a diet that’s high in fibre (which is found in vegetables, legumes and whole grains) and protein (which is found in lean meat, fish and eggs). Fibre and protein are extremely efficient in making you feel fuller for longer by slowing the digestion process and keeping your sugar levels in check. Try following our 7-day high cholesterol diet plan if you’re not sure where to start.

So, it’s clear that diet and exercise are both beneficial for weight loss. But does one help you pile off more pounds than the other? Let’s take a look at what the science says.

Diet vs. exercise: which is more important?

As a general rule of thumb, it’s far easier to slice back your total calorie count by cutting down on food intake rather than increasing exercise. That’s because the amount of time it takes for you to burn 500 calories is significant whereas cutting down your food intake by 500 calories per day is much more straightforward.

It’s easy to understand why there’s such a disparity between the two when you look at how long it takes to burn 500 calories compared to how little you need to eat to consume 500 calories. For most people, you’ll need to exercise for around an hour to burn 500 calories whereas you can consume 500 calories in one single hearty slice of chocolate cake. People tend to overestimate the number of calories burned during exercise and underestimate the number of calories they’re consuming. It’s also common for a person to ‘reward’ themselves with a treat after exercise, counteracting the progress that they just made.

Exercise alone tends to have less of an impact on weight loss compared to diet alone. But before you put your feet up and chuck away the gym clothes, there are a plethora of reasons why exercise is a critical part of a healthy weight loss routine.

Firstly, just because exercise alone doesn’t lead to such dramatic weight loss, doesn’t mean that it doesn’t lead to weight loss at all. In a study on obese men, exercise led to substantial weight loss. They also wanted to measure the effects of exercise without weight loss and found that exercise led to a reduction in abdominal fat and prevented further weight gain.

This points to a critical benefit of exercise: fat burn. When you lose weight through diet, you’ll lose bone density, muscle and tissue as well. Exercise helps you to target the right areas by burning fat while strengthing bones and muscles.

Other benefits of exercise include cardiovascular health, reduced risk of diabetes, fitness, longevity, and the regulation of hunger hormones.

In general, studies have shown that the most effective and sustainable method of weight loss is to follow a routine that combines both diet and exercise. A combination of the two is the best predictor of weight maintenance.

So, remember that the best way to lose weight is to incorporate both diet and exercise but if you have a day where you really must decide between couch potato and actual potato, pick the couch.

The bottom line

Studies show that diet is a critical factor for losing weight, but this doesn’t discredit the importance of exercise. Exercise helps you to lose fat rather than muscle and bone, as well as promoting cardiovascular health and fitness benefits.

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