Why do Calorie Deficits Help You Lose Weight?

Posted on June 17, 2024 by Sally-Anne Turner

Losing weight can be a challenging journey, and many individuals struggle to achieve their desired results despite their best efforts. The weight loss industry is saturated with conflicting advice, miracle solutions, and quick-fix promises that rarely deliver lasting results. However, one crucial aspect of weight loss that is now being highlighted by medical professionals and nutritionists alike is creating a calorie deficit, which means consuming fewer calories than your body needs to maintain its current weight. This fundamental principle of energy balance is the cornerstone of all successful weight loss programmes, regardless of the specific dietary approach or method used.

At Bodyline, our established and fully supported medical weight loss programmes combine medical treatments and personalised plans to create a calorie deficit that can be sustained longer than fad diets to ensure successful weight loss. With over 18 years of experience supporting more than 100,000 patients across the UK, we have developed a comprehensive understanding of what works for sustainable weight loss and what doesn't. Our clinics in Birkenhead, Liverpool, Manchester, St Helens, Stockport, Stoke-on-Trent, and Warrington, along with our nationwide online consultation service, provide accessible support to individuals throughout their weight loss journey.

That's why we'd like to help you understand the science behind calorie deficits and how they contribute to effective weight loss. Understanding the biological mechanisms that drive weight loss empowers you to make informed decisions about your health and helps you recognise why certain approaches work whilst others fail. This knowledge is particularly important in an era where misinformation about weight loss is widespread, and many people have become frustrated after years of unsuccessful dieting attempts.

Understanding Calorie Deficits

Calories are a unit used to measure the energy content in food and beverages. The term "calorie" is actually a shortened version of kilocalorie, which represents the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. Every food and drink we consume contains calories, which our bodies convert into energy to fuel all of our physiological processes, from breathing and circulation to movement and brain function.

When we consume more calories than our body needs, the excess energy is stored as fat, leading to weight gain. This is an evolutionary mechanism that served our ancestors well during times of food scarcity, allowing them to survive periods of famine by storing energy when food was abundant. However, in our modern environment where high-calorie foods are readily available and physical activity levels have decreased, this survival mechanism often works against us, contributing to the obesity epidemic we see today.

On the other hand, when we consume fewer calories than our body requires, it creates an energy imbalance, making the body tap into its fat stores for additional energy. This is known as a calorie deficit and is the key to weight loss. Your body requires a certain number of calories each day to maintain basic physiological functions such as breathing, circulation, digestion, and cell repair. This baseline requirement is called your Basal Metabolic Rate (BMR). On top of this, you burn additional calories through daily activities and exercise. The total amount of energy you expend in a day is called your Total Daily Energy Expenditure (TDEE).

When you consume fewer calories than your TDEE, your body must find the energy elsewhere to meet its needs. Initially, it may break down glycogen stores in your liver and muscles, but these stores are limited and typically depleted within 24-48 hours of calorie restriction. After this point, your body increasingly turns to fat stores as its primary energy source. This process of breaking down stored fat for energy is called lipolysis, and it's the fundamental mechanism by which we lose body fat and reduce our overall weight.

It's important to understand that not all calories are created equal in terms of how they affect your body. The source of your calories matters significantly for overall health, satiety, and metabolic function. For example, 200 calories from a doughnut will have a very different effect on your blood sugar, hunger hormones, and energy levels compared to 200 calories from lean protein and vegetables. This is why quality matters alongside quantity when creating a sustainable calorie deficit.

The Science Behind Weight Loss

To comprehend why calorie deficits are essential for weight loss, we need to understand the science behind it. When you consistently maintain a calorie deficit, your body starts utilising stored fat as an energy source. As the body uses the stored fat for energy, the fat stores reduce, which leads to a reduction in body weight and body fat percentage. This process is governed by the fundamental laws of thermodynamics, specifically the principle of energy conservation, which states that energy cannot be created or destroyed, only transformed from one form to another.

The process of fat loss involves complex biochemical pathways. When your body needs energy and insufficient calories are coming from food, it releases hormones such as glucagon and adrenaline that signal fat cells to release stored triglycerides. These triglycerides are then broken down into fatty acids and glycerol, which enter the bloodstream and are transported to cells throughout your body where they can be used for energy. The fatty acids undergo a process called beta-oxidation in the mitochondria of cells, where they are converted into ATP (adenosine triphosphate), the energy currency of cells.

Essentially every fad diet ever created is a new way to attempt a calorie deficit, whether you're cutting out carbohydrates, intermittent fasting, or only eating eggs and nuts! The Atkins diet, the ketogenic diet, the cabbage soup diet, juice cleanses, and countless other trending approaches all achieve weight loss through the same fundamental mechanism: creating a calorie deficit. The specific rules and restrictions of each diet are simply different strategies for helping people consume fewer calories than they burn.

The issue is most of these fad diets are very difficult to sustain for long periods of time, so when results aren't manifesting quickly enough, people give up, end up bingeing, and undo all the progress they made. Restrictive diets that eliminate entire food groups or require complicated meal preparation often fail because they don't fit into people's real lives. They may work temporarily whilst motivation is high, but once the initial enthusiasm wanes or life circumstances change, adherence becomes impossible. This creates a frustrating cycle of starting a diet with high hopes, experiencing some initial success, then gradually falling back into old habits and regaining the weight.

No wonder data has shown that Brits are likely to try 126 fad diets in their lifetime, as none of them work long enough to produce good weight loss results! This statistic highlights the enormous frustration and financial cost that people experience in their search for an effective weight loss solution. Each failed diet attempt can also take a psychological toll, damaging self-confidence and creating a sense of hopelessness about the possibility of ever achieving lasting weight loss.

The science behind successful weight loss is sustainable calorie deficits, so the secret to weight loss is to find a calorie deficit that you can maintain long-term! This is precisely why Bodyline's medical weight loss programmes focus on creating individualised plans that fit into your lifestyle rather than requiring you to completely overhaul your life. Our approach combines medical treatments that make it easier to maintain a calorie deficit with practical nutritional guidance and ongoing support from our specialist weight loss nurses.

Research has consistently shown that the most successful weight loss programmes are those that create a moderate calorie deficit that can be sustained over time, rather than aggressive restrictions that lead to rapid initial weight loss followed by regain. A sustainable approach typically involves reducing your daily calorie intake by 500-750 calories below your TDEE, which should result in a steady weight loss of approximately one to two pounds per week. This rate of weight loss is considered optimal because it maximises fat loss whilst minimising muscle loss and metabolic adaptation.

Benefits of Calorie Deficits

Creating a calorie deficit offers several benefits for weight loss beyond simply reducing the number on the scales. Understanding these additional benefits can help motivate you to maintain your calorie deficit even when progress seems slow or when you encounter challenges along the way.

Fat Utilization

When you maintain a calorie deficit, your body starts using stored fat as its primary energy source. This leads to a reduction in body fat percentage, resulting in weight loss and improved body composition. However, it's important to understand that fat loss doesn't happen uniformly across your body. Your genetics largely determine where you lose fat first and where it tends to be most stubborn. Many people find that they lose fat from their face, arms, and legs before seeing significant changes in their abdomen or hips, which can be frustrating but is completely normal.

The process of fat utilisation also has important implications for your health beyond aesthetics. Visceral fat, which is stored around your internal organs, is particularly harmful to health and is associated with increased risk of cardiovascular disease, type 2 diabetes, and certain cancers. Fortunately, visceral fat is often among the first types of fat to be mobilised when you create a calorie deficit, meaning that even before you see dramatic changes in your appearance, you may be experiencing significant improvements in your metabolic health.

At Bodyline, we use comprehensive measurements including weight, BMI, body measurements, and where appropriate, body composition analysis to track your progress. This helps ensure that you're losing fat rather than muscle mass, which is crucial for maintaining your metabolic rate and achieving a healthy, sustainable outcome. Our weight loss treatments are specifically designed to preserve lean muscle mass whilst promoting fat loss.

Improved Insulin Sensitivity

Calorie deficits can improve insulin sensitivity, which is crucial for effective weight loss. When your body becomes more insulin-sensitive, it can better regulate blood sugar levels and prevent excessive fat storage. Insulin is a hormone produced by your pancreas that helps cells absorb glucose from your bloodstream. When you're insulin resistant, your cells don't respond effectively to insulin, causing your pancreas to produce more and more insulin to achieve the same effect. High insulin levels promote fat storage and make it very difficult to lose weight.

Improving insulin sensitivity through calorie restriction and weight loss creates a positive feedback loop. As you lose weight, your insulin sensitivity improves, which makes it easier to lose more weight and keep it off. Better insulin sensitivity also reduces your risk of developing type 2 diabetes and can help manage existing diabetes more effectively. Many of our patients at Bodyline who have type 2 diabetes find that as they lose weight, their blood sugar control improves significantly, and some are even able to reduce or eliminate their diabetes medications under their doctor's supervision.

The improvement in insulin sensitivity occurs relatively quickly after starting a calorie deficit, often before significant weight loss has occurred. This is one reason why even modest weight loss of 5-10% of body weight can have profound health benefits. For individuals with metabolic syndrome or prediabetes, improving insulin sensitivity through weight loss can potentially reverse these conditions and significantly reduce the risk of progression to type 2 diabetes.

Increased Metabolism

Consistently maintaining a calorie deficit can increase your metabolism over time. When your body senses an energy deficit, it adapts by increasing energy expenditure to compensate. This can lead to a higher metabolic rate, allowing you to burn more calories even at rest. However, this statement requires some nuance and explanation, as the relationship between calorie deficits and metabolism is more complex than it might initially appear.

In the short term, aggressive calorie restriction can actually slow your metabolism as your body attempts to conserve energy. This is called metabolic adaptation or adaptive thermogenesis. Your body becomes more efficient at using energy, which means you burn fewer calories performing the same activities. This is one reason why very low-calorie diets often lead to plateaus and make long-term weight loss difficult to maintain.

However, when you create a moderate calorie deficit and lose weight gradually whilst maintaining physical activity and adequate protein intake, you can minimise metabolic adaptation. Additionally, as you lose weight and become more active, you may build muscle mass through exercise, which increases your resting metabolic rate since muscle tissue burns more calories than fat tissue even at rest. This is why our programmes at Bodyline emphasise not just calorie reduction but also appropriate physical activity and protein intake to preserve and build lean muscle mass.

Furthermore, the weight loss itself can improve your metabolic health in ways that make your body more efficient at burning fat for fuel. As insulin sensitivity improves and inflammation decreases, your cells become better at accessing and utilising stored fat for energy. This metabolic flexibility is a key marker of metabolic health and makes weight maintenance easier in the long term.

Supported Medical Weight Loss Treatment Programmes

Sticking to a calorie deficit can be challenging, especially when you haven't been able to stick to one before. The biological and psychological factors that make weight loss difficult are real and significant. Hunger is a powerful drive that is regulated by complex hormonal systems, and willpower alone is often insufficient to overcome these biological signals, particularly over the long term. This is not a personal failing; it's simply how our bodies are designed to function.

However, diet and exercise alone are not necessarily enough to help some people lose weight. Obesity itself can significantly impact the ability to stick to a calorie deficit, as the hormones are impacted and dysregulated. People with obesity often have elevated levels of ghrelin (the hunger hormone) and reduced levels of leptin sensitivity (leptin is the hormone that signals fullness). This means they feel hungrier more often and don't feel as satisfied after eating, making it extremely difficult to maintain a calorie deficit through willpower alone.

At Bodyline, we use the latest in obesity treatments to help those struggling to lose weight stick to a calorie deficit with the help of appetite suppressing and hormone mimicking medications. These include oral treatments like Phentermine and Diethylpropion, and injectable therapies like WeGovy and Mounjaro. These medications work by various mechanisms to reduce appetite, increase feelings of fullness, and help regulate the hormonal imbalances that make weight loss difficult.

Phentermine, for example, is a centrally-acting appetite suppressant that works in the appetite centre of the brain to reduce hunger levels and control cravings. It has been used safely and effectively for weight loss for decades and remains one of our most prescribed treatments. WeGovy and Mounjaro are GLP-1 receptor agonists that mimic the action of natural gut hormones to reduce appetite, slow stomach emptying, and improve blood sugar control. These newer injectable medications have shown remarkable results in clinical trials, with average weight losses significantly greater than what most people can achieve through diet and exercise alone.

We can assess your specific needs, medical history, and lifestyle, and provide personalised prescriptions and recommendations to help you create a sustainable calorie deficit and reach your wellness and weight loss goals. Our experienced team of doctors and nurse prescribers conduct thorough consultations to ensure that any medication prescribed is safe and appropriate for you. We also provide ongoing monitoring and support throughout your treatment, with regular appointments to track your progress, adjust your treatment plan as needed, and provide nutritional and lifestyle guidance.

Book a consultation at Bodyline Clinic to discuss which medical weight loss treatment might be suitable for your individual circumstances and goals.

How to Create a Calorie Deficit

Katie Illingsworth, one of our nurse prescribers and a trained nutritional therapist believes the importance of finding out what a personal calorie deficit is for you is fundamental to weight loss. With years of experience supporting patients through their weight loss journeys, Katie has seen firsthand how crucial it is to individualise the approach rather than applying generic calorie targets that may be inappropriate for a person's specific circumstances.

Weight loss cannot be a one size fits all approach; it has to fit around your life. Your calorie needs depend on numerous factors including your age, sex, height, current weight, body composition, activity level, metabolic health, and even your genetics. Two people of the same weight and height may have very different calorie requirements based on these other factors. This is why copying someone else's diet plan or following generic advice from social media rarely leads to success.

"There is a common misconception that when you're significantly overweight you should go into a dramatic calorie deficit. Now yes, you will lose weight short term and you'll think it's working. But hormonally, you are physiologically causing harm, because your body isn't designed to do that. It will think it's gone into starvation mode, or in hibernation. This will mean it starts to store the fat and instead burn your muscle, causing them to feel weak, and tired, and make you more likely to binge.

"When people go through our weight loss programme, they need to work out how many calories they burn, which is called your Total Daily Energy Expenditure (TDEE). That's available online. It is based on your height, weight, age, gender, and activity levels. Let us say it might be 2,500 calories – if you want to lose a pound a week, you will take off 500 calories, which will mean that the calorie deficit for you would be 2,000 calories. Even though it may not sound like it, that is the calorie deficit for some body types, and it is what helps weight loss become sustainable."

This approach challenges the common assumption that everyone needs to eat 1,200 or 1,500 calories per day to lose weight. In reality, many people, particularly those who are taller, heavier, or more active, can lose weight effectively whilst eating significantly more than this. Eating too few calories can backfire by slowing your metabolism, causing muscle loss, depleting your energy levels, and making the diet impossible to sustain. It can also lead to nutritional deficiencies that impact your health and wellbeing.

Here are the tips that can help find your calorie deficit, stick to it, and help you lose weight sustainably. These strategies are based on evidence from nutritional science and our extensive clinical experience supporting thousands of patients through successful weight loss.

Track Your Caloric Intake

To create a calorie deficit, you need to have a clear understanding of your daily caloric intake. Track the number of calories you consume from food and beverages using a food diary or a mobile app. This will help you identify areas where you can adjust to create a deficit. Many people significantly underestimate how many calories they consume each day, which is why tracking is such a valuable tool, particularly in the initial stages of your weight loss journey.

There are numerous free apps available such as MyFitnessPal, Lose It!, or Cronometer that make calorie tracking straightforward. These apps have extensive food databases that include most common foods and restaurant meals, and many allow you to scan barcodes for quick entry. The key is to track everything you eat and drink, including cooking oils, condiments, and beverages, as these "small" items can add up to hundreds of calories per day.

Tracking your intake also increases your awareness of your eating patterns and habits. You may discover that you're consuming most of your calories in the evening, or that weekend eating is significantly different from weekday eating, or that certain situations or emotions trigger overeating. This awareness is the first step toward making sustainable changes. At Bodyline, we provide guidance on effective tracking methods and help you interpret your food diary to identify opportunities for improvement without requiring you to track calories forever.

Work Your Calorie Deficit

Depending on your weight, height, gender, and physical activity, calorie deficits can vary from person to person. Use online calculators like this one to work out what your personal calorie deficit should be, and ensure you stick to that number or below. When using these calculators, be honest about your activity level. Many people overestimate how active they are, which leads to an inflated TDEE calculation and a calorie target that is too high for weight loss.

As a general guideline, a deficit of 500-750 calories per day below your TDEE should result in weight loss of approximately one to two pounds per week. This is considered a safe and sustainable rate of weight loss for most people. Larger deficits may lead to faster initial weight loss but are often difficult to maintain and may result in muscle loss, nutritional deficiencies, and metabolic adaptation that makes further weight loss more difficult.

It's also important to recalculate your calorie needs periodically as you lose weight. As your body weight decreases, your calorie requirements decrease as well, since there is less body mass to maintain. This is why weight loss often slows down over time, and it's why your calorie target may need to be adjusted every few months to continue making progress. Our team at Bodyline monitors this for you and adjusts your plan accordingly to ensure continued success.

Reduce Portion Sizes

Portion control plays a crucial role in creating a calorie deficit. Be mindful of serving sizes and aim to reduce them gradually. Opt for smaller plates to visually trick your mind into feeling satisfied with less food. This simple psychological trick has been validated by research and can help you consume fewer calories without feeling deprived. Using a smaller plate makes a standard portion look larger, which can increase satisfaction and reduce the tendency to serve yourself additional helpings.

Learning appropriate portion sizes is a valuable skill that will serve you well beyond your active weight loss phase. Many people have become accustomed to restaurant-sized portions that are two to three times larger than what is nutritionally appropriate. Retraining your perception of normal portions takes time but is essential for long-term weight management. Simple strategies like using your hand as a portion guide (palm-sized serving of protein, fist-sized serving of vegetables, cupped hand for carbohydrates) can help you estimate appropriate portions when you're not able to measure precisely.

Another effective strategy is to pre-portion snacks and treats rather than eating directly from large packages. When you eat from a family-sized bag of crisps or a large tub of ice cream, it's easy to consume far more than you intended. Taking the time to portion out a single serving and putting the rest away removes the temptation to mindlessly overeat. At Bodyline, we provide practical guidance on portion control strategies that fit into your lifestyle and don't require you to weigh and measure everything you eat indefinitely.

Increase Physical Activity

Physical activity is another key component of creating a calorie deficit. Incorporate regular exercise into your routine to burn additional calories and boost your metabolism. Aim for a combination of cardiovascular exercises and strength training for optimal results. Cardiovascular exercise such as walking, cycling, swimming, or dancing burns calories during the activity itself and can improve your cardiovascular health, whilst strength training builds muscle mass that increases your resting metabolic rate and helps you burn more calories even when you're not exercising.

However, it's important to have realistic expectations about how much exercise contributes to weight loss. Whilst exercise is crucial for health and helps create a calorie deficit, it's difficult to out-exercise a poor diet. Many people overestimate how many calories they burn through exercise and then compensate by eating more, which can negate the calorie deficit they've created. Exercise should be viewed as one component of your weight loss strategy rather than the primary method.

For many people starting a weight loss journey, particularly those with significant weight to lose or mobility limitations, increasing general daily activity through lifestyle changes can be more sustainable than structured exercise programmes. Simple changes like taking the stairs instead of the lift, parking further away from your destination, standing while talking on the phone, or going for a short walk during your lunch break can add up to significant calorie expenditure over time. As you lose weight and your fitness improves, you can gradually increase the intensity and duration of your physical activity.

Our team at Bodyline provides personalised exercise recommendations based on your current fitness level, any physical limitations or health conditions, and your personal preferences. We understand that not everyone enjoys going to the gym, and we work with you to find forms of physical activity that you'll actually stick with long-term. The best exercise is the one you'll do consistently, not necessarily the one that burns the most calories per session.

The Importance of Sustainability

While calorie deficits are essential for weight loss, it is crucial to approach them with sustainability in mind. Drastic and unsustainable calorie restrictions can lead to nutrient deficiencies, muscle loss, and metabolic slowdown. It is important to focus on creating a moderate calorie deficit that allows for gradual and healthy weight loss. The goal is not just to lose weight quickly but to lose weight in a way that you can maintain for life.

Sustainability means different things for different people, but generally it involves finding an approach to eating and activity that you can maintain long-term without feeling deprived, exhausted, or socially isolated. If your weight loss plan requires you to avoid all social events, never eat your favourite foods, or spend hours each day preparing special meals and exercising, it's probably not sustainable. The most successful weight loss approaches are those that involve moderate changes that gradually become new habits rather than requiring constant willpower and sacrifice.

This is why Bodyline's approach focuses on creating individualised plans that fit into your real life rather than requiring you to completely overhaul your lifestyle. We help you identify the changes that will have the biggest impact on your calorie balance whilst being realistic about what you can actually maintain. This might mean finding lower-calorie versions of foods you enjoy, identifying trigger situations where you tend to overeat and developing strategies to manage them, or finding forms of physical activity that fit into your schedule and that you genuinely enjoy.

Sustainability also means being prepared for the fact that weight loss is rarely linear. You will likely experience weeks where you don't lose weight despite your best efforts, or even weeks where you gain weight due to water retention or other factors. You may face challenges like holidays, stressful periods, or social events where sticking to your plan is difficult. Having realistic expectations about these challenges and having strategies to manage them is crucial for long-term success. Our ongoing support at Bodyline helps you navigate these challenges without giving up on your goals entirely.

If you're struggling to create a calorie deficit or need support on your weight loss journey, speak to us here at Bodyline. Our experienced clinicians specialise in medical weight loss and can provide the guidance and support you need to achieve your weight loss goals safely and effectively. With clinics throughout the Northwest of England and online consultations available UK-wide, we make it convenient to access expert support wherever you are.

We understand that weight loss is about more than just calories in versus calories out. It involves addressing the hormonal, psychological, and lifestyle factors that have contributed to weight gain and that make weight loss difficult. Our comprehensive approach combines medical treatments when appropriate, personalised nutritional guidance, support with physical activity, and ongoing monitoring and encouragement from our specialist team. We celebrate your successes, help you learn from setbacks, and adjust your plan as needed to ensure you continue making progress toward your goals.

Book a consultation at Bodyline Clinic to discuss how we can support you in creating a sustainable calorie deficit and achieving lasting weight loss. Call us on 0800 995 6036 today or complete an on-line enquiry form for a call back. Take the first step toward a healthier future with the support of the UK's leading medical weight loss specialists.