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Is Exercise Crucial for Weight Loss?

by Matt Durkin
MSc Nutrition Specialist

With almost a quarter of the UK’s population being classed as obese, there is significant interest in the best ways to lose weight (and keep it off long-term). One of the questions regularly aimed at nutritionists, dieticians and medical experts relates to the importance of exercise for weight loss. Is it really 80% diet, 20% exercise? Can we really “out-exercise” a bad diet? 

Despite the myriad of health benefits that exercise possesses, most of us in the UK are not meeting the government recommended levels of exercise. Lack of time is the most commonly cited barrier to regular exercise, so in this article, we are going to explore whether exercise is crucial for weight loss. We’ll also examine some of the strengths and limitations of exercise as part of a weight loss programme. 

Energy Balance 

For weight-loss to occur more calories have to be expended than consumed. There are numerous aspects that play a part in what scientists call energy balance. One side of the energy balance equation is energy intake, which is the sum of calories obtained from carbohydrates, fats and proteins and alcohol. Carbohydrates and protein provide 4 kilocalories (kcals) of energy for every gram, with alcohol providing 7 kcals and fat 9 kcals.

The energy expenditure side of the equation is more complicated. The biggest contributor to the number of calories we burn is the basal metabolic rate or BMR for short. This is the amount of calories our body requires at rest to perform basic bodily functions. For most people, this will represent around 60-70% of calories burnt per day. The next largest contributor is the energy burnt from physical activity, whether it be through exercise or something called NEAT (Non-Exercise Activity Thermogenesis) which can be anything from walking to gardening or even fidgeting. This will typically represent 15-20% of energy expenditure.

The smallest contributor to energy output is the thermic effect of feeding, also known as TEF. The body actually requires energy to breakdown the food we eat. Protein typically requires 20-35% of its calorie content to be digested, with carbohydrates having around 8-10% with fats 2-5%. Proteins high TEF is one of the reasons why a diet rich in protein is recommended for those aiming to lose weight. 

Weight Loss

As weight-loss requires a negative calorie balance, we have seen that this can be achieved either through limiting the energy we obtain from food or by altering our energy expenditure, or a mixture of the two. As BMR will never change significantly, and the thermic effect of feeding only increases modestly through a high protein diet, an increase in energy expenditure mostly occurs through increased physical activity. 

The size of the calorie deficit depends on how quickly you aim to lose weight. Typically, someone aiming to lose a pound per week will ensure a daily calorie deficit of 400-600kcals, whereas those looking to lose two pounds per week will aim for a 1000kcal deficit per day. Someone with very high levels of body fat is likely to do better on a more aggressive calorie deficit, whereas leaner people should lose weight slowly to prevent muscle loss. Muscle loss should be avoided at all costs, as losing this tissue decreases BMR, making weight loss all the more difficult. Unsurprisingly, the research is pretty clear that those who don’t exercise while on a weight loss programme lose more muscle mass than those that exercise. This is a big positive for exercising regularly.

Now that we understand the basics of energy balance, and we have decided how quickly we wish to lose weight, the next step is to decide how the calorie deficit is created. As we have seen, the body actually burns most of its calories at rest, so exercise is not crucial to lose weight and because of this, many people choose not to do it. Others choose to decrease calorie intake whilst simultaneously increasing exercise levels. There are very few people that increase exercise levels whilst not making any significant dietary changes. We will find out why in the next section. 

Pros and Cons of Exercise for Weight Loss

Exercise is well-known to burn calories, which is obviously beneficial for weight loss. However, things are not as simple as that. Most people would need to exercise pretty intensely for an hour to burn 500kcals, which is unrealistic for many to perform on a day-to-day basis. Conversely, cutting 500kcals per day through the diet is relatively easy and can be achieved by making some simple changes.

Simple examples of dietary changes might involve limiting the consumption of high-sugar foods and drinks, bulking up on non-starchy vegetables to create satiety while minimising calorie intake and considering the use of glucomannan. According to the European Food Safety Authority (EFSA) glucomannan “in the context of an energy-restricted diet contributes to weight loss” which is why it is included in our SimplyGo Slim+ drink mix.

One problem with exercise is that most overweight people have low levels of physical fitness. When fitness levels are low, the amount of time you can exercise before tiring is limited. Furthermore, having a low level of fitness means you actually burn few calories. As a result, many people lose faith when their efforts are not reflected when stepping on the scales.

On the other hand, as people get fitter the amount of oxygen they can use increases; something scientists call VO2 Max. When someone can utilise more oxygen, it means you can work harder for longer and subsequently burn more calories. The key thing is to persevere with exercise, as fitness levels increase quickly, which subsequently means that more calories can be burnt. 

Another issue is that after exercise many people over-compensate, being far less active than normal for the rest of the day. For example, if you go for a sixty-minute jog then the idea of spending a few hours gardening afterwards probably won’t sound very appealing. On the other hand, if you have been sat down for an extended period of time then getting outside for some gardening may be a far more attractive idea.  If you are performing exercise with the intention of losing weight, therefore, try to ensure that you stay active throughout the rest of the day to experience the maximum benefit. 

Lastly, some authorities claim that the calories burnt during exercise will simply be replaced at the next meal thanks to increased hunger. This theory, however, has for the most part been disproved. One study showed, for example, that an hour of treadmill running leads to a significant reduction in a hormone that promotes hunger, while simultaneously increasing levels of a hormone that makes us feel full. These hormonal changes then led to the study participants consuming almost 300 fewer calories at the next meal when compared to those that didn’t exercise. Consequently, exercise not only burns calories but can also lead to reduced food intake, creating a larger calorie deficit.

The Different Mode of Exercise and Their Benefits to Health

Aerobic exercises such as running, cycling or swimming are the most beneficial for weight loss as they burn more calories than intermittent or resistance training. That said, each method has its own benefits, and each would ideally have a place in a healthy lifestyle. 

Aside from its calorie-burning potential, aerobic exercise is fantastic for cardiovascular conditioning as it promotes a strong heart and healthy blood pressure and cholesterol levels for example. 

Intermittent exercises, such as repeated sprinting or team sports like football, are brilliant for improving VO2 Max, which means one can exercise harder and subsequently burn more calories. Although all modes of exercise are beneficial for managing blood sugar, intermittent exercise is particularly beneficial as it uses a lot of glucose for fuel and improves sensitivity to the insulin, the hormone regulates blood sugar.

Resistance training is crucial for building and maintaining strong muscles, which can be beneficial during weight loss.  Muscle-strengthening exercise also promotes bone health as it encourages calcium to be deposited onto the bones to support the enlarged muscles. Good examples of muscle strengthening exercises are squats, arm curls and shoulder presses. 

As cardiovascular disease, obesity, diabetes, and osteoporosis are some of the largest causes of morbidity and mortality in the UK, it is clear to see that a mix of exercise modes is ideal. Physical activity decreases the risk of over 25 different chronic diseases and can improve longevity, mental health and quality of life. If you cannot perform structured exercise for any reason, it, therefore, pays to ensure that you are physically active in general.


As we have seen, your diet is likely to be the most significant contributor to weight loss. For best results you should, therefore, maintain a calorie controlled diet. 

At the same time, although exercise is not crucial to lose weight, it can certainly be beneficial when implemented correctly. To ensure exercise is beneficial to your weight loss efforts it is important to be patient, as increases in fitness levels will accentuate the beneficial impacts of exercise over time. Similarly, it is important to understand that exercise is a tool to induce a calorie deficit for weight loss, so it is crucial to not reward yourself with food because of the exercise efforts. 

Finally, exercise has many benefits aside from weight loss, so performing it regularly throughout your life is fundamental for good health. The key is to find methods of exercise that you enjoy and can see yourself performing regularly for long-term success. A good way to do this is to exercise with friends or family to enjoy the social aspects whilst bettering your health and wellbeing. 


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