If we consider the calorie theory of weight loss for a moment (i.e. calories in vs. calories out) it postulates that all that is necessary for weight loss is a calorie deficit. Basically it doesn’t matter what food you eat, so long as you’re in a calorie deficit, you will lose weight. Acutely this often works, however what we see is that long-term weight loss, via calorie deficit, is not sustainable with rebound weight gain almost always being the inevitable conclusion of this type of diet. This suggests that the calorie theory of weight loss is an insufficient explanation for the complexities of weight gain/weight loss and that a calorie is not a calorie and weight gain/weight loss is far more complex than a simple energy balancing equation. This is why I am inclined to think the hormonal theory of weight loss is a more accurate representation of this complex issue. This theory espouses that it us our neuroendocrine system responsible for weight gain and weight loss (which seems logical as it this system that controls our appetite and energy balance) and that we should focus on eating foods that have a positive effect on this system. This is not to say that calories don’t matter but that it is far more important to consider where these calories are coming from.
So why does this matter?
So we know calorie restriction doesn’t work. 30+ years of research on this type of diet has conclusively demonstrated this with some of the largest studies failing to show calorie restriction has any long-term benefit . Research aside, our steadily climbing obesity rates clearly confirms the failure of low calorie diets. Then there’s also this issue – the World Health Organisation (WHO) released a document in 2009 showing physical inactivity as the 4th greatest risk global health risk.  People, who are designed to be physically active, are becoming increasingly sedentary. This is a real concern. Now anyone who knows me, knows I am the first to say there are many complex issues surrounding weight loss BUT diet and exercise are strongly linked and are modifiable i.e. we can do something them (unlike things like age, gender, genetics etc.) So when I hear people saying, out of context, that exercise is not needed for weight loss, I get very concerned.
Dr Jason Fung describes this concept in one of his blogs where his point is that exercise is not needed for weight loss from the view of creating a calorie deficit. However, the message has become somewhat warped with people thinking this gives them a free pass on exercise. So here’s the deal, exercise IS actually needed for weight loss and here’s why. When we look at the habits of slim people, healthy people and those that have successfully lost weight and kept it off, most of these people undertook regular physical activity and/or exercise [3, 4]. There are many things about exercise that make it essential for weight loss and it is not about creating a calorie deficit.
So how does exercise promote weight loss?
Well first of all, I’ll start by saying every single system of the body benefits from exercise. Exercise quite literally improves the function of every system in our body but let me outline how each system benefits, from a fat loss perspective.
Anyone who knows anything about weight loss, knows that the maintenance of muscle mass is integral in the attempt to prevent rebound weight gain. In fact, so important is muscle tissue, undertaking a resistance-training program is a key recommendation by just about every health professional. The reason behind this is pretty simple; muscle mass influences our basal metabolic rate (BMR). Essentially our metabolism is driven by mass (more mass = higher metabolism) so as we lose mass, our metabolism is reduced. Weight training, via increasing muscle mass, helps offset this metabolic reduction . Ultimately, if our metabolism is sufficiently suppressed, then there is high chance that weight regain will follow. This means that exercise and weight training is a key component to successful, long-term weight loss.
Exercise improves the function of this system significantly. Exercise has been shown to improve the sensitivity of a number of key hormones involved in weight loss, particularly insulin, leptin, and growth hormone. Exercise has repeatedly been shown to reverse insulin [6, 7] and leptin resistance , which is not only essential in losing weight but also in reversing chronic illness. Exercise also simulates the production of growth hormone, which is essential for body growth and maintenance and a healthy metabolism . Exercise also lowers triglycerides and inflammation in addition to promoting the building of new hormone receptors, further improving function. This means normal appetite function returns, constant hunger abates and the body is able to utilise stored fat as an energy source.
Exercise has a profoundly positive impact on the cardiovascular system. In particular, exercise that promotes fitness is especially significant. As we exercise, our body adapts to the stress placed on our body by making it more efficient at the exercise you’re doing. Exercise improves enzyme activity, increases lipolysis (the breakdown of fat into a useable form of energy), improves oxygen utilisation and delivery, improves mitochondrial function and essentially enables us to utilise stored fat more efficiently.
Exercise improves our moods and mental health , which means from a food perspective, we are more likely to make better food choices. People who are depressed or anxious are less likely to make good food choices and are more likely to use food as a coping strategy. So when we exercise, our mood improves, meaning we are less likely to use food as a means of improving how we feel about our situation or ourselves. Furthermore, low-grade inflammation is associated with adverse mental health outcomes, so the anti-inflammatory benefits of exercise will assist in this manner also. 
Every day we are learning new things about the importance of gut health. Our gut health is closely linked to our psychological well-being so when we care for our gut, we care for our mind. What’s exciting about exercise is that it improves gut health (via reducing inflammation) and gut function (increased motility and absorption). People who suffer from gastrointestinal disorders all show improvements in their condition with regular, physical activity. What’s also exciting, from a weight loss perspective, is the role in gut health and obesity. There is an emerging body of evidence that demonstrate gut inflammation and microbiota play a role in diet-induced obesity. [12, 13] Exercise positively affects gut microbiota  and reduces inflammation  so once again it is a crucial part of any weight loss plan.
So what type of exercise should I do?
Hopefully by now I have convinced you that exercise is necessary, not only for weight loss, but for good health. So then the question that remains is what type of exercise should we do? Everyone has an opinion on what the best type of exercise is and can back it up with countless numbers of studies but there is one thing they all have in common; fitness. This is because there is a degree of intensity that must be undertaken to achieve physical fitness and it is the intensity that stimulates all the protective features of fitness. This means getting fit offers the greatest health and weight loss benefits. However, when it comes to how you get fit, I am pragmatic. I want to see people improve all areas of fitness (cardiorespiratory, muscular, flexibility, agility, balance etc.) but I don’t mind how this is achieved. I am happy for people to do it in anyway they enjoy. Some people love high intensity interval training (HIIT), some love the gym, others love playing sport. I think you need to find something that you enjoy, as you will stick with it. I personally love HIIT due to its potent effects [16, 17] and speedy results [18, 19] but I also combine this with other types of training. I would suggest you do a combination of high intensity and low intensity exercise and do a few high intensity sessions every week. If you are worried about doing high intensity exercise on your own, I would recommend finding an exercise physiologist or personal trainer and work with them. Alternatively you could join a group training class or if you have a look on my website, you could try our free 30 day fitness challenge.
What it boils down to is this; exercise is one of the most powerful health habits you can employ. It improves every system of the body (especially those involved with weight loss) and, as an added bonus; it makes us feel so damn good! Whether or not you are making a lifestyle change for weight loss purposes or just to get healthy, exercise is a key component to any successful lifestyle intervention.
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