What Is a Calorie Deficit — and Why Does It Matter on a GLP-1 Journey?

Every day your body burns a certain number of calories just to function — breathing, circulating blood, digesting food, and moving around. That total is often called your Total Daily Energy Expenditure (TDEE). When you consistently eat below that number, your body uses stored fat and (to a smaller degree) other tissue to make up the shortfall, which results in weight loss over time.

What size deficit is typically needed?

As a general educational reference, a deficit of roughly 500 calories a day is commonly associated with losing around 0.5 kg (1 lb) per week, because approximately 3,500 calories represents one pound of stored fat. Aiming for closer to 1,000 calories a day below maintenance is sometimes cited in relation to losing around 1 kg (2 lb) per week — but at that level, the approach needs to be carefully managed to ensure adequate nutrition, and it is not suitable for everyone.

These figures are general estimates, not personal targets. Individual metabolism, activity level, muscle mass, age, and health conditions all affect the real number for any given person. For guidance tailored to your situation, speak with your prescriber or a registered dietitian.

Why GLP-1 medicines interact with this

Medicines like Mounjaro (tirzepatide) and Wegovy (semaglutide) act on appetite-regulating pathways, and many people report a significant reduction in hunger and "food noise" — the constant mental preoccupation with food. This can make it easier to eat less without feeling deprived. However, eating too little can risk under-fuelling the body and missing out on key nutrients, especially protein, which helps preserve muscle during weight loss. The goal is a sustainable, moderate deficit — not the lowest possible intake.

For a closer look at how deficit size affects your results, see our guide on how much of a calorie deficit to lose weight, or explore specifics around losing one pound a week with a calorie deficit. The broader topic — including how to calculate and track your deficit — is covered in our complete calorie deficit guide.

Knowing your deficit in theory is one thing — actually tracking it day to day is where most people struggle, especially when appetite fluctuates on a GLP-1 medicine. GLP Trackr makes this significantly easier, starting with AI-powered food logging: point your camera at a meal and the app estimates calories, protein, and macros instantly, with no manual entry needed. A barcode scanner and text search are there for packaged foods and anything the photo scan needs a hand with.

Beyond logging individual meals, you can set daily calorie and protein targets inside the app so you can see at a glance whether you are on track, under-fuelling, or have room to eat more. Hitting a protein target alongside a calorie deficit is particularly important on a GLP-1 journey, since adequate protein helps preserve muscle while the scales move downward.

The app also includes GLP-1-friendly meal plans and a recipe library built around higher-protein, easier-to-digest options — useful when appetite is low and you want meals that tick nutritional boxes without a lot of effort.

If you want everything in one place — food, weight, energy, mood, and how your body is responding — GLP Trackr brings it together so you can spot what is actually working and have more informed conversations with your prescriber.

Always follow the guidance of your prescriber or doctor when it comes to nutrition goals — they know your full health picture, and what works as a general estimate may not be right for your individual circumstances.

Start tracking your deficit today — GLP Trackr is free to try for 7 days on the App Store and Google Play. Snap your meals, set your targets, and see your progress come together in one place.