Calorie deficit: how it works and how to start

What is a calorie deficit?

Your body needs a certain number of calories each day just to function, this is often called your Total Daily Energy Expenditure, or TDEE. It covers your basic metabolism, digestion, and physical activity. A calorie deficit exists when you consistently eat fewer calories than your TDEE, prompting your body to draw on stored energy, mainly body fat, to make up the shortfall.

This is sometimes called energy balance: calories in versus calories out. When intake is lower than output over time, weight loss tends to follow. When they're roughly equal, weight stays stable. It's a simple concept in theory, though day-to-day life, appetite, and habits make it more nuanced in practice.

Creating a deficit: eat less, move more, or both

There are three broad ways to create a calorie deficit, and none is inherently superior, it depends on what fits your life and preferences.

• Eat less: Reducing portion sizes, choosing lower-calorie swaps, or cutting back on energy-dense extras like sugary drinks and fried snacks. Many people find a low-calorie approach to certain meals (like a lighter lunch) easier to sustain than cutting everything uniformly.
• Move more: Increasing daily activity, whether through structured exercise, more walking, or simply standing and moving more throughout the day, raises the calories side of the equation.
• Both together: Combining a modest reduction in intake with a modest increase in activity often allows for a smaller, more comfortable deficit from each side, which many people find easier to maintain than relying on one method alone.

Tracking your intake and estimated output with an app like Nutari can help you see roughly where you stand relative to your TDEE, rather than guessing.

How big should your deficit be?

Bigger isn't necessarily better. A very large deficit can lead to fatigue, irritability, muscle loss, and a higher chance of giving up altogether. A moderate deficit of roughly 300 to 500 calories a day is commonly recommended as a starting point for many adults, as it tends to support gradual, steady progress while remaining liveable long-term.

This generally translates to losing around 0.25 to 0.5kg per week, though individual results vary based on starting weight, sex, activity level, and other factors. If you have a significant amount of weight to lose, a lot of muscle mass, or specific health conditions, your needs may differ, and it's worth speaking with a doctor or registered dietitian for personalised guidance.

Staying satisfied: protein, fibre, and food volume

Hunger is often what derails a calorie deficit, so managing it matters as much as the number itself.

• Protein: A high-protein approach tends to be more filling per calorie than fat or carbohydrate, and helps preserve muscle mass while you're in a deficit. Including a source of protein at each meal, such as eggs, yoghurt, fish, poultry, tofu, or legumes, can help.
• Fibre: Vegetables, fruit, wholegrains, and pulses add bulk and slow digestion, supporting fullness for relatively few calories.
• Volume: Choosing foods with lower calorie density, meaning more food weight for fewer calories, such as vegetables, broths, and fruit, can help you feel satisfied on less energy overall.

Together, these strategies mean you're not simply eating less of everything, but shifting the balance of what you eat to feel fuller for longer.

Why sustainability beats aggression

Very restrictive diets often produce fast initial results but are hard to maintain, and much of the lost weight is commonly regained once normal eating resumes. A more moderate, flexible approach that still includes foods you enjoy is more likely to become a lasting habit rather than a short-term fix.

Sustainable habits, consistent tracking, and gradual change tend to outperform extreme short bursts of restriction over the months and years that actually matter for long-term health.

Understanding plateaus

It's common to lose weight steadily for a while and then hit a plateau, where the scale doesn't move despite doing everything the same. This usually happens because your TDEE decreases as you lose weight, smaller bodies generally need fewer calories to maintain themselves, so a deficit that worked initially may shrink over time.

Plateaus don't necessarily mean something has gone wrong. Reassessing your TDEE periodically, being honest about portion creep, and factoring in normal fluctuations from water retention, hormones, or stress can all help. If a plateau persists for several weeks despite consistent tracking, it may be a sign to recalculate your calorie needs or review your plan with a dietitian.