How a Calorie Deficit Works — and Why It Matters on GLP-1
Your body has a daily energy requirement — sometimes called your Total Daily Energy Expenditure (TDEE) — that accounts for your metabolism at rest plus the calories you burn through movement and activity. When you consistently eat less than this figure, your body draws on stored energy, which is the basis of gradual, sustained weight loss.
Estimating your numbers
Working out your calorie deficit starts with estimating your maintenance calories. Common approaches use factors like your height, weight, age, and activity level. The resulting figure is an estimate rather than a precise measurement, and it shifts over time as your body composition changes — so treat it as a useful starting point, not a fixed rule.
A commonly referenced moderate deficit is roughly 500 calories below your maintenance level per day, which many people find manageable without feeling deprived. Larger deficits can sometimes lead to muscle loss or fatigue, which is worth being aware of on a GLP-1 journey where protein intake already needs attention. For specific targets that suit your health situation, your prescriber or doctor is the right person to advise you.
Protein and the deficit
One of the most important considerations when eating in a deficit on GLP-1 medicines is protecting protein intake. Because appetite is often lower, it is easy to eat less overall — including less protein — which the body needs to preserve muscle. Many people find it helpful to prioritise protein-rich foods first at each meal, even when portions are small.
For a closer look at the practical steps involved, see our guide to how to work out your calorie deficit, or explore the broader topic in our calorie deficit hub.
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How GLP Trackr Helps You Stay in Your Deficit
Tracking a calorie deficit manually — especially when appetite is unpredictable — is where many people lose momentum. GLP Trackr's AI food-scanning feature makes logging meals as simple as pointing your phone camera at your plate: the app estimates calories, protein, and macros instantly, without manual searching or guesswork.
Once your food is logged, GLP Trackr compares it against your daily calorie and protein targets so you can see at a glance whether you are on track. The app also logs your weight over time, turning individual days into a trend line that shows how your deficit is playing out in practice — far more informative than a single weigh-in.
If you want to go deeper into your numbers, our page on working out a calorie deficit step by step walks through the calculation in detail.
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A note on targets: general educational ranges are a helpful guide, but personalised calorie or nutrition goals should always be discussed with your prescriber or doctor, who knows your full health history. GLP Trackr helps you record and visualise your intake — it is not a substitute for professional dietary or medical advice.
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Frequently asked questions.
Working out your calorie deficit means calculating the gap between the calories your body burns each day and the calories you eat. When you consume less than you burn, your body uses stored energy. The size of that gap influences the pace of weight change over time.
Many people find that reduced appetite on a GLP-1 medicine naturally leads to eating less, which can create a deficit. However, the size of that deficit varies between individuals, and tracking food intake helps you understand whether your actual calorie intake aligns with your goals.
A moderate deficit of around 500 calories below your estimated daily needs is commonly referenced as a manageable starting point. Larger deficits can increase the risk of muscle loss or fatigue. Your prescriber or doctor is best placed to advise on a target that suits your individual health situation.
When eating less overall, it is easy to under-eat protein, which the body needs to maintain muscle. On GLP-1 medicines, where appetite is often reduced, many people benefit from prioritising protein-rich foods at each meal to help preserve muscle while in a calorie deficit.
Apps like GLP Trackr let you log meals via an AI photo scan or barcode scanner, automatically calculating calories and protein. Setting a daily calorie target and reviewing your intake against it gives you a clear, ongoing picture of whether you are hitting your deficit goals.