Calorie deficit diet: How does it actually work?

If you've ever tried to lose weight, you've probably come across the term ‘ calorie deficit’ .

Put simply, a calorie deficit happens when you consume fewer calories than your body uses. Over time, this encourages your body to use stored energy, which can contribute to weight loss .

But it isn't simply about eating as little as possible. The most sustainable approach is one that supports your body with the nutrients it needs while helping you work towards your goals.

Because when it comes to long-term results, consistency beats extremes - every time.

So, how does a calorie deficit diet work?

A calorie deficit doesn't need to be complicated.

At its simplest, weight maintenance happens when the calories you consume match the calories your body uses. A calorie deficit creates a gap between the two.

As a general guide, women typically require around 2,000 calories per day to maintain their weight, while men typically require around 2,500 calories. Individual needs will vary depending on factors such as age, activity levels, height and body composition.

The science behind calorie deficits.

When you eat, your body converts food into energy. Any excess energy that isn’t immediately used is stored, primarily as glycogen.

Think of glycogen as your body’s readily available fuel reserve. The more calories you eat, particularly from carbohydrates, the more glycogen your body stores.

When you reduce your calorie intake and create a deficit, your body begins using these stored energy reserves to make up the shortfall.

Typically, the body will use glycogen stores first before turning to stored body fat for energy. Once glycogen levels begin to drop, your body becomes more likely to access and burn fat stores.

“Calorie restricted diets are a great way to burn fat and help you lose weight. Calorie deficits work best when matched with exercise routines, but it’s always best to check with a nutritionist or healthcare professional to make sure it’s right for you.” - Dr Dave Reilly - Senior Scientist at Absolute Collagen

Calculating your deficit

To create a calorie deficit for weight loss, reducing your intake by around roughly 300 - 500 calories per day can support gradual, sustainable weight loss .

So, the average deficit would look like this:

• Women: around 1,500 calories per day
• Men: around 2,000 calories per day

Remember, these are only ballpark figures. Your individual calorie needs will depend on factors such as height, weight, age, and whether you regularly exercise. Two people of the same age and sex may still have very different calorie requirements.

Online calorie calculators can help provide an estimate, but these should be treated as guidance rather than exact numbers.

If you’re unsure how large your calorie deficit should be, speak with a doctor or registered nutritionist to help you find a more personalised approach.

Why is my calorie deficit not working?

One of the biggest challenges with a calorie deficit is expecting results too quickly.

Weight loss isn't always linear. Factors such as hydration, hormones, digestion and muscle gain can all influence what you see on the scales from week-to-week.

That's why it's helpful to look beyond weight alone. Changes in how your clothes fit, your energy levels and your overall wellbeing can be just as important.

If you've recently increased your exercise, you may be building muscle while losing body fat. The number on the scales might stay similar, even though your body composition is changing.

Consistency matters too. Hidden calories from drinks, sauces and snacks can quickly add up, making it harder to maintain a deficit than you realise.

What’s a ‘good’ calorie deficit?

A good calorie deficit is one you can maintain without feeling deprived.

Rather than cutting out entire food groups, focus on building balanced meals that include:

• Protein
• Fibre
• Healthy fats
• Carbohydrates
• Plenty of fruit and vegetables

Protein is particularly important when dieting because it helps support muscle maintenance and can help you feel fuller for longer.

“High quality proteins such as Greek yoghurt, eggs, oily fish and beans and pulses are nutrient-dense foods which can support blood sugar balance, weight loss and skin health. ” - Jenna Hope - Nutritionist at Absolute Collagen.

Many nutrition professionals also recommend planned periods at maintenance calories during longer dieting phases. These breaks can make a calorie deficit feel more manageable and support long-term consistency.

What are the negative effects of a calorie deficit?

A calorie deficit can be effective for weight loss, but reducing calories too aggressively may make it harder to get the nutrients your body needs.

Here are some signs your approach may need adjusting:

1. You feel fatigued.

A lower calorie intake can sometimes leave you feeling tired or lacking energy, particularly if meals aren't balanced. Prioritising protein, fibre and complex carbohydrates can help support energy levels throughout the day.

2. Your gut health is disrupted.

Eating less food overall may affect digestive regularity for some people. Ensuring you're consuming enough fibre, taking probiotics and staying hydrated can help support normal digestion.

3. You experience hair loss.

If your body is in a nutritional deficit, it’ll prioritise key organs first. Making your hair bottom of the list. Eating extra omega-3 rich foods like oily-fishes or chia seeds as a vegan alternative can help maintain your body’s natural levels via diet.

4. Your skin feels looser.

Drops in elastin and protein reduce your skin's firmness and bounce, when you lose weight at rapid pace, the fibres can’t react quick enough. This is the main cause of loose skin . Making sure your diet is high in collagen and protein should help maintain elastin levels

How can Absolute Collagen help your calorie deficit?

A calorie deficit is about more than simply eating less. It's about making sure your body continues to get the support it needs while you work towards your goals.

That's why many people look for ways to support areas such as hydration, digestion, energy and skin health throughout their journey.

Sculpt Pro has been developed by leading experts to support you on your weight loss journey, providing the benefits of 17 supplements in just 1 formula:

• 8,000mg collagen & vitamin C  to boost skin elasticity and hair growth
• Hyaluronic acid & electrolytes  to maintain hydration and glow
• Probiotics & fibre  to support gut function and digestion
• Creatine & BCAAs  to improve muscle tone and energy levels
• Magnesium & vitamin D3  to aid relaxation, quality sleep, and bone health
• B vitamins  to boost energy, mood and vision health

When taken twice a day, the targeted nutrients may help prevent all the harder side effects of a calorie deficit like hair loss, loose skin, weak nails and fatigue to name a few.

Sculpt Pro isn’t a replacement for food, and it’s not intended to do the heavy lifting on its own. Instead, it’s designed to  support  your diet, helping you stay consistent, nourished, and supported as your body adapts.

Curious to learn more about how weight loss injections can affect appetite, muscle, skin and hair? Explore  our blog  for expert insight, practical guidance, and  real-life stories  to help you feel informed, supported and confident - every step of the way.