IF your goal is to lose weight or reduce body fat, you’ve probably heard the term ‘calorie deficit’. Simply put, a calorie deficit occurs when your body burns more energy (calories) than you consume through food and drinks. When this happens, your body taps into stored energy, which is primarily fat, to meet its needs, which over time leads to weight loss.

“While it sounds straightforward, a calorie deficit isn’t just about eating less,” explained Nutritionist Helen Buckley-James. “It’s about creating a balance between energy intake and expenditure in a way that supports overall health, maintains muscle mass, and is sustainable for the long-term.

Buckley-James explained that your body requires energy for everything you do, from breathing and circulating blood to walking, working out and digesting food. This total energy requirement is called total daily energy expenditure (TDEE), which is made up of the energy used at rest for vital functions like breathing and maintaining body temperature, calories burned through exercise and everyday movement, and energy spent digesting and processing the food you eat.

“When you consume fewer calories than your TDEE, your body begins to break down stored energy, mainly fat, to make up the difference,” said Buckley-James. “For example, if your TDEE is 2,200 calories per day but you eat 1,700 calories, you’re in a 500-calorie deficit. Over a week, this can result in about one pound (0.45 kg) of fat loss.”

She said there are many benefits to a controlled calorie deficit, the main one of which is fat loss while preserving muscle, especially when combined with sufficient protein intake and resistance training.

“There is also improved metabolic health which can support better blood sugar control, lower cholesterol, and improved insulin sensitivity,” she said. “Also, it leads to sustainable weight management, where gradual changes are easier to maintain than in extreme diets.”

This deficit also increases nutritional awareness, helping you to learn portion sizes and the caloric content of foods.

How do you create a healthy calorie deficit? Buckley-James gives these suggestions:

1) Moderation over extremes: A daily deficit of 300-500 calories is generally safe and sustainable, supporting gradual fat loss without risking muscle loss.

2) Prioritise nutrient-dense foods: Lean proteins, vegetables, whole grains, and healthy fats keep you full and support overall health.

3) Combine with exercise: Physical activity increases energy expenditure and helps maintain muscle mass, making fat loss more efficient.

4) Track progress wisely: Daily weight fluctuations are normal. Focus on trends over weeks rather than obsessing over each day’s number.

5) Listen to your body: Adequate sleep, hydration, and stress management all influence how effective and sustainable a calorie deficit can be.

She said common mistakes to avoid include cutting calories too drastically, which can slow metabolism and cause fatigue; ignoring protein intake and skipping strength training, risking muscle loss; underestimating hidden calories in drinks, sauces, or snacks; and expecting rapid results.

“Safe, sustainable weight loss is usually around one to two pounds per week,” Buckley-James said. “And note that calorie deficit works best when combined with balanced nutrition, regular exercise, and realistic expectations.”