The Fitness Zone

Cracking the Code of Weight Loss: The Science of Metabolism, Hormones and Calorie Balance

May 15, 2023 | by Brodie Hicks

Obesity is at an all-time high, with roughly one-third of the world’s population classed as overweight or obese, a figure that has more than doubled since 1980 [1]. While this is a worrying statistic, the sharp rise in rates of overweight and obesity has led to a significant amount of research being conducted. Each component, from metabolism to hormones and calorie balance, is critical in reaching the ultimate goal: successful weight loss [2]. Join us as we go deep into these aspects, exposing weight management secrets and solutions for attaining your weight loss objectives.

Metabolism and Weight Loss

Consider the body to be a well-oiled engine that is continually running, even when we are sleeping. How is this even possible? The answer: metabolism! Our metabolism is the process that converts food and drink into the energy our body requires to function 24 hours a day, seven days a week [2]. Behind the scenes, our metabolism is the engine that keeps our breathing, circulation, growth, and cell repair ticking along like a beautifully tuned engine. The energy we burn at rest is known as our Basal Metabolic Rate (BMR), and it accounts for the majority of our daily energy consumption [2]. Did you know that our organs, such as our brain, liver, kidneys, and heart, utilise about half of the energy we burn at rest, while our digestive system and muscles consume the other half?

The speed of a person’s metabolism is not fully under their control, as it is influenced by a variety of factors. Some of these uncontrollable elements include age, gender, and genetics [3]. Our metabolism naturally slows down as we age due to hormonal changes and muscle mass loss. When it comes to gender, men have a higher metabolism than women since they have more muscle mass and testosterone. Finally, genetic variations can influence how our bodies process and store energy, ultimately impacting our metabolic rate.

While the above may be true, taking control of our metabolism is not just about genetics or age. We have the power to boost our metabolic rate with the following factors:

  • Body Composition: The amount of muscle and fat we have can have a significant impact on our metabolism. Did you know that at rest, muscle tissue burns more calories than fat tissue? So, if we have greater lean muscle mass, our metabolic rate will be higher than if we have less muscle.
  • Diet: Protein-rich foods require more energy to digest and metabolise than carbohydrates and fats, so consuming a higher-protein diet can increase our metabolic rate [4].
  • Exercise: In the long run, exercise will  do wonders for our metabolism. By increasing our muscle mass we increase our metabolic rate. In addition, high-intensity interval training (HIIT) has been shown to increase metabolic rate for up to 24 hours after exercise [5].
  • Stress: Stress can affect our metabolism in both good and bad ways. In the short term, stress hormones like cortisol and adrenaline can actually raise our metabolic rate by increasing our heart rate and blood pressure. Chronic stress, on the other hand, has been found to have a detrimental impact on metabolism and lead to weight gain [6].

Understanding our client’s metabolic rate and what influences it can help us create an effective weight loss strategy. We should be well on our way to changing our clients overall body composition if we focus on increasing muscle mass, eating a protein-rich diet, and reducing chronic stress.

Understanding Hormones and their Role in Weight Loss:

Hormones are the unsung weight-regulating heroes, influencing hunger, satiety (the feeling of being full), and metabolism [7]. Weight gain and trouble reducing weight typically occur when our hormones are out of balance. Some hormones, such as insulin and leptin, are essential for fat storage and breakdown. While insulin regulates blood sugar levels and encourages glucose (carbohydrate) storage, chronically high levels can result in insulin resistance and increased fat storage. The satiety hormone, leptin, sends a signal to the brain when the body has enough energy stored as fat [8]. Leptin levels can rise in overweight or obese people, leading to resistance to its effects as well as increased appetite and hunger.

Ghrelin, cortisol, and thyroid hormones are other hormones that play a role in weight management. Ghrelin is regarded as the hunger hormone because it stimulates appetite, while cortisol is a stress hormone that can enhance abdominal fat accumulation. Both of these hormones when unregulated can lead to an increase in fat tissue storage. In addition, thyroid hormones, which regulate metabolism, can become imbalanced in hypothyroid patients, resulting in a slowed metabolism and weight gain.

So, what can we do to ensure that our hormones work in our favour when losing weight? A healthy diet that balances macronutrients and eliminates processed and sugary meals that might boost insulin levels is one strategy. Consuming fibre-rich meals can also aid in the regulation of insulin and blood sugar levels.

Another key aspect in hormone regulation and weight management is regular exercise. Exercise can improve insulin sensitivity, which improves the body’s capacity to use glucose for energy and reduces insulin resistance. High-intensity interval training (HIIT) has also been demonstrated to improve hormonal balance and promote fat burning [9].

Finally, stress management can help enhance hormonal balance and lower cortisol levels. Yoga, meditation, and deep breathing techniques can all assist to reduce stress and enhance general well-being.

Calorie Balance and Weight Loss:

There’s no getting around the fact that calorie balance is essential for weight loss. To lose weight, we must have a calorie deficit, which means consuming less calories than we burn via everyday activities and exercise [10]. This is the foundation of every successful weight loss program, as without it, we’re unlikely to get the desired outcomes. However, it is not only about reducing calories. The quality of our diet is also important, as certain meals can help us feel full and content while still lowering our overall calorie intake. A diet high in protein, fibre, and healthy fats, for example, has been demonstrated to be particularly effective for weight loss.

Protein is especially helpful for weight loss because it is more satiating than carbohydrates or lipids. This means that eating protein-rich meals can help reduce hunger and cravings, making it simpler to follow a low-calorie diet [11]. Protein is also crucial for maintaining muscular mass, which is necessary for a healthy metabolism [11].

Fibre is another important component of a weight loss-friendly diet since it slows digestion and keeps us feeling full for extended periods of time [12]. Fruits, vegetables, and whole grains, which are high in fibre, are also lower in calories than other types of foods, making them an excellent choice for weight loss.

Finally, healthy fats like those found in nuts, seeds, avocados, and fatty fish can help with weight loss. While eating fat while trying to lose weight may seem paradoxical, good fats are actually quite satiating, meaning they can help keep you feeling full and content while also supplying key nutrients for general health.

Exercise and its Impact on Metabolism and Hormones:

Now that we have a greater understanding of the role metabolism and hormones play in weight loss, we can look into how exercise can favourably influence these mechanisms. Exercise is one of the most potent strategies for helping our clients achieve their weight loss goals. We’ve already examined the role of exercise in improving metabolism, namely the growth of lean tissue (muscle mass). This is significant because muscle tissue burns more calories at rest than fat tissue, so having more muscle means burning more calories throughout the day.

However, the benefits of exercise for weight loss go beyond simply improving metabolism. Exercise can also have a beneficial impact on hormones like insulin and cortisol, which can aid in the reduction of fat around the abdomen. As previously stated, insulin is a hormone that regulates blood sugar levels and, when levels are excessively high, can contribute to fat storage. Exercise can improve insulin sensitivity, allowing our bodies to use glucose more effectively for energy and decrease the amount of glucose deposited as fat [13]. Cortisol, on the other hand, is a stress hormone that can lead to increased abdominal fat storage. Exercise has been demonstrated to lower cortisol levels and improve stress management.

When it comes to exercise, we should incorporate both aerobic and strength training in ours and our client’s routine. Cardiovascular exercise like running or cycling, for example, can help burn calories and enhance cardiovascular health. As we know, outside of metabolism and hormones, calorie balancing is another important aspect of weight management, and cardiovascular exercise is one of the most effective strategies to increase the number of calories burned that day. Strength training, on the other hand, can aid in the development of lean muscle mass and thus an increase in metabolism. A combination of both types of exercise can help our clients lose weight and improve their overall health.

While listing the “best” sorts of exercise for weight loss is important, it is also crucial to choose types of exercise that our clients enjoy and are sustainable for them in the long run. This can help them stay motivated and consistent with their fitness plan – the best program in the world is meaningless if they don’t stick to it! Having a support system can also help us and our clients stay consistent to our exercise plan and reach our weight loss objectives, whether it’s joining a fitness class or finding a workout companion. Remember that losing weight is a gradual process that demands patience and perseverance.


Achieving weight loss can be a challenging process due to the various factors that influence it. Metabolism, hormones, and calorie balance are some of the primary aspects that influence losing weight, making it critical to build a personalised plan that takes the specific needs of our clients into account. As research into the science of weight reduction progresses, we should expect to see more successful ways for supporting long-term weight loss emerge. With this increased knowledge we can continue to create more focused and personalised interventions that support sustained weight loss and improved health outcomes!


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Brodie Hicks

Brodie Hicks

With his background in Strength and Conditioning, Brodie Hicks has coached multiple semi-professional & professional athletes in Australia over the last 7+ years, whilst also working to improve training and vocational outcomes within the fitness industry in his role as General Manager of Training at the Australian Institute of Fitness (AIF). Brodie brings a raft of knowledge and experience to the health and fitness industry, holding a Bachelor’s Degree in Exercise and Movement Science, as well as a Masters Degree in High Performance Sport. Brodie is also a Level 2 ASCA Strength and Conditioning Coach with the Australian Strength and Conditioning Association. In addition to his work at the AIF, Brodie also manages a coaching business, Performance Evolved Australia, and is Master Coach and Program Director of an interstate boutique group training studio, bringing his extensive strength and conditioning knowledge to the group training world.

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